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Electrical installation handbook
Volum e 2
1SD C 010001D 0202
ABB SACE
Electrical devices
ABB SACE S.p.A.
An ABB Group Company
L.V. Breakers
Via Baioni, 35
24123 Bergamo - Italy
Tel.: +39 035.395.111 - Telefax: +39 035.395.306-433
http://www.abb.com
D ue to possible developm ents of standards as w ell as of
m aterials, the characteristics and dim ensions specified in
this docum ent m ay only be considered binding after
confirm ation by AB B SAC E. 1
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2
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Volume 2
Electrical installation handbook
Electrical devices
2
nd
edition
February 2004
First edition 2003
Second edition 2004
Published by ABB SACE
via Baioni, 35 - 24123 Bergamo (Italy)
All rights reserved
1 ABB SACE - Electrical devices
Index
Introduction .............................................................................................. 2
1 Standards
1.1 General aspects .............................................................................. 3
1.2 IEC Standards for electrical installation .......................................... 15
2 Protection of feeders
2.1 Introduction................................................................................... 22
2.2 Installation and dimensioning of cables ......................................... 25
2.2.1 Current carrying capacity and methods of installation .......... 25
Installation not buried in the ground ..................................... 31
Installation in ground............................................................ 44
2.2.2 Voltage drop ........................................................................ 56
2.2.3 Joule-effect losses ............................................................... 66
2.3 Protection against overload ........................................................... 67
2.4 Protection against short-circuit ...................................................... 70
2.5 Neutral and protective conductors ................................................ 78
2.6 Busbar trunking systems............................................................... 86
3 Protection of electrical equipment
3.1 Protection and switching of lighting circuits ................................. 101
3.2 Protection and switching of generators ....................................... 110
3.3 Protection and switching of motors ............................................. 115
3.4 Protection and switching of transformers .................................... 131
4 Power factor correction
4.1 General aspects .......................................................................... 146
4.2 Power factor correction method .................................................. 152
4.3 Circuit-breakers for the protection and
swiching of capacitor banks ........................................................ 159
5 Protection of human beings
5.1 General aspects: effects of current on human beings .................. 162
5.2 Distribution systems .................................................................... 165
5.3 Protection against both direct and indirect contact ...................... 168
5.4 TT system................................................................................... 171
5.5 TN system .................................................................................. 174
5.6 IT system .................................................................................... 177
5.7 Residual current devices ............................................................. 179
5.8 Maximum protected length for the protection of human beings ... 182
Annex A: Calculation tools
A.1 Slide rules ............................................................................. 200
A.2 DOCWin ............................................................................... 205
Annex B: Calculation of load current I
b
.............................................. 209
Annex C: Calculation of short-circuit current ................................... 213
Annex D: Calculation of the coefficient k for the cables .................. 227
Annex E: Main physical quantities and
electrotechnical formulas ................................................... 230
1.1 General aspects
In each technical field, and in particular in the electrical sector, a condition
sufficient (even if not necessary) for the realization of plants according to the
“status of the art” and a requirement essential to properly meet the demands
of customers and of the community, is the respect of all the relevant laws and
technical standards.
Therefore, a precise knowledge of the standards is the fundamental premise
for a correct approach to the problems of the electrical plants which shall be
designed in order to guarantee that “acceptable safety level” which is never
absolute.
Juridical Standards
These are all the standards from which derive rules of behavior for the juridical
persons who are under the sovereignty of that State.
Technical Standards
These standards are the whole of the prescriptions on the basis of which
machines, apparatus, materials and the installations should be designed,
manufactured and tested so that efficiency and function safety are ensured.
The technical standards, published by national and international bodies, are
circumstantially drawn up and can have legal force when this is attributed by a
legislative measure.
Application fields
Electrotechnics and Mechanics, Ergonomics
Electronics
Telecommunications
and Safety
International Body IEC ITU ISO
European Body CENELEC ETSI CEN
This technical collection takes into consideration only the bodies dealing with electrical and electronic
technologies.
IEC International Electrotechnical Commission
The International Electrotechnical Commission (IEC) was officially founded in
1906, with the aim of securing the international co-operation as regards
standardization and certification in electrical and electronic technologies. This
association is formed by the International Committees of over 40 countries all
over the world.
The IEC publishes international standards, technical guides and reports which
are the bases or, in any case, a reference of utmost importance for any national
and European standardization activity.
IEC Standards are generally issued in two languages: English and French.
In 1991 the IEC has ratified co-operation agreements with CENELEC (European
standardization body), for a common planning of new standardization activities
and for parallel voting on standard drafts.
1 Standards
3 ABB SACE - Electrical devices 2 ABB SACE - Electrical devices
Introduction
Scope and objectives
The scope of this electrical installation handbook is to provide the designer and
user of electrical plants with a quick reference, immediate-use working tool.
This is not intended to be a theoretical document, nor a technical catalogue,
but, in addition to the latter, aims to be of help in the correct definition of
equipment, in numerous practical installation situations.
The dimensioning of an electrical plant requires knowledge of different factors
relating to, for example, installation utilities, the electrical conductors and other
components; this knowledge leads the design engineer to consult numerous
documents and technical catalogues. This electrical installation handbook,
however, aims to supply, in a single document, tables for the quick definition of
the main parameters of the components of an electrical plant and for the selection
of the protection devices for a wide range of installations. Some application
examples are included to aid comprehension of the selection tables.
Electrical installation handbook users
The electrical installation handbook is a tool which is suitable for all those who
are interested in electrical plants: useful for installers and maintenance technicians
through brief yet important electrotechnical references, and for sales engineers
through quick reference selection tables.
Validity of the electrical installation handbook
Some tables show approximate values due to the generalization of the selection
process, for example those regarding the constructional characteristics of
electrical machinery. In every case, where possible, correction factors are given
for actual conditions which may differ from the assumed ones. The tables are
always drawn up conservatively, in favour of safety; for more accurate
calculations, the use of DOCWin software is recommended for the dimensioning
of electrical installations.
5 ABB SACE - Electrical devices
1.1 General aspects
1 Standards
4 ABB SACE - Electrical devices
1.1 General aspects
1 Standards
“Low Voltage” Directive 73/23/CEE – 93/68/CEE
The Low Voltage Directive refers to any electrical equipment designed for use
at a rated voltage from 50 to 1000 V for alternating current and from 75 to 1500 V for
direct current.
In particular, it is applicable to any apparatus used for production, conversion,
transmission, distribution and use of electrical power, such as machines,
transformers, devices, measuring instruments, protection devices and wiring
materials.
The following categories are outside the scope of this Directive:
• electrical equipment for use in an explosive atmosphere;
• electrical equipment for radiology and medical purposes;
• electrical parts for goods and passenger lifts;
• electrical energy meters;
• plugs and socket outlets for domestic use;
• electric fence controllers;
• radio-electrical interference;
• specialized electrical equipment, for use on ships, aircraft or railways, which
complies with the safety provisions drawn up by international bodies in which
the Member States participate.
Directive EMC 89/336/EEC (“Electromagnetic Compatibility”)
The Directive on electromagnetic compatibility regards all the electrical and
electronic apparatus as well as systems and installations containing electrical
and/or electronic components. In particular, the apparatus covered by this
Directive are divided into the following categories according to their
characteristics:
• domestic radio and TV receivers;
• industrial manufacturing equipment;
• mobile radio equipment;
• mobile radio and commercial radio telephone equipment;
• medical and scientific apparatus;
• information technology equipment (ITE);
• domestic appliances and household electronic equipment;
• aeronautical and marine radio apparatus;
• educational electronic equipment;
• telecommunications networks and apparatus;
• radio and television broadcast transmitters;
• lights and fluorescent lamps.
The apparatus shall be so constructed that:
a) the electromagnetic disturbance it generates does not exceed a level allowing
radio and telecommunications equipment and other apparatus to operate
as intended;
b) the apparatus has an adequate level of intrinsic immunity to electromagnetic
disturbance to enable it to operate as intended.
An apparatus is declared in conformity to the provisions at points a) and b)
when the apparatus complies with the harmonized standards relevant to its
product family or, in case there aren’t any, with the general standards.
CENELEC European Committee for Electrotechnical Standardization
The European Committee for Electrotechnical Standardization (CENELEC) was
set up in 1973. Presently it comprises 27 countries (Austria, Belgium, Czech
Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary,
Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway,
Portugal, Poland, Slovakia, Slovenia, Spain, Sweden, Switzerland, United
Kingdom) and cooperates with 8 affiliates (Albania, Bosnia and Herzegovina,
Bulgaria, Croatia, Cyprus, Romania, Turkey, Ukraine) which have first maintained
the national documents side by side with the CENELEC ones and then replaced
them with the Harmonized Documents (HD). CENELEC hopes and expects
Cyprus to become the 28
th
members before May 2004.
There is a difference between EN Standards and Harmonization Documents
(HD): while the first ones have to be accepted at any level and without additions
or modifications in the different countries, the second ones can be amended to
meet particular national requirements.
EN Standards are generally issued in three languages: English, French and
German.
From 1991 CENELEC cooperates with the IEC to accelerate the standards
preparation process of International Standards.
CENELEC deals with specific subjects, for which standardization is urgently
required.
When the study of a specific subject has already been started by the IEC, the
European standardization body (CENELEC) can decide to accept or, whenever
necessary, to amend the works already approved by the International
standardization body.
EC DIRECTIVES FOR ELECTRICAL EQUIPMENT
Among its institutional roles, the European Community has the task of
promulgating directives which must be adopted by the different member states
and then transposed into national law.
Once adopted, these directives come into juridical force and become a reference
for manufacturers, installers, and dealers who must fulfill the duties prescribed
by law.
Directives are based on the following principles:
• harmonization is limited to essential requirements;
• only the products which comply with the essential requirements specified by
the directives can be marketed and put into service;
• the harmonized standards, whose reference numbers are published in the
Official Journal of the European Communities and which are transposed into
the national standards, are considered in compliance with the essential
requirements;
• the applicability of the harmonized standards or of other technical specifications
is facultative and manufacturers are free to choose other technical solutions
which ensure compliance with the essential requirements;
• a manufacturer can choose among the different conformity evaluation proce-
dure provided by the applicable directive.
The scope of each directive is to make manufacturers take all the necessary
steps and measures so that the product does not affect the safety and health
of persons, animals and property.
7 ABB SACE - Electrical devices
1.1 General aspects
1 Standards
6 ABB SACE - Electrical devices
1.1 General aspects
1 Standards
ABB SACE circuit-breakers (Isomax-Tmax-Emax) are approved by the following
shipping registers:
• RINA Registro Italiano Navale Italian shipping register
• DNV Det Norske Veritas Norwegian shipping register
• BV Bureau Veritas French shipping register
• GL Germanischer Lloyd German shipping register
• LRs Lloyd’s Register of Shipping British shipping register
• ABS American Bureau of Shipping American shipping register
It is always advisable to ask ABB SACE as regards the typologies and the
performances of the certified circuit-breakers or to consult the section certificates
in the website http://bol.it.abb.com.
Marks of conformity to the relevant national and
international Standards
The international and national marks of conformity are reported in the following
table, for information only:
COUNTRY Symbol Mark designation Applicability/Organization
EUROPE
AUSTRALIA
AUSTRALIA
AUSTRIA
–
AS Mark
S.A.A. Mark
Austrian Test Mark
Mark of compliance with the
harmonized European standards
listed in the ENEC Agreement.
Electrical and non-electrical
products.
It guarantees compliance with
SAA (Standard Association of
Australia).
Standards Association of
Australia (S.A.A.).
The Electricity Authority of New
South Wales Sydney Australia
Installation equipment and
materials
OVE
When the CE marking is affixed on a product, it represents a declaration of the
manufacturer or of his authorized representative that the product in question
conforms to all the applicable provisions including the conformity assessment
procedures. This prevents the Member States from limiting the marketing and
putting into service of products bearing the CE marking, unless this measure is
justified by the proved non-conformity of the product.
Flow diagram for the conformity assessment procedures established by the Directive
73/23/EEC on electrical equipment designed for use within particular voltage range:
Manufacturer
Technical file
The manufacturer
draw up the technical
documentation
covering the design,
manufacture and
operation of the
product
EC declaration of
conformity
The manufacturer
guarantees and declares
that his products are in
conformity to the technical
documentation and to the
directive requirements
A
S
D
C
0
0
8
0
4
5
F
0
2
0
1
Naval type approval
The environmental conditions which characterize the use of circuit breakers for
on-board installations can be different from the service conditions in standard
industrial environments; as a matter of fact, marine applications can require
installation under particular conditions, such as:
- environments characterized by high temperature and humidity, including salt-
mist atmosphere (damp-heat, salt-mist environment);
- on board environments (engine room) where the apparatus operate in the
presence of vibrations characterized by considerable amplitude and duration.
In order to ensure the proper function in such environments, the shipping
registers require that the apparatus has to be tested according to specific type
approval tests, the most significant of which are vibration, dynamic inclination,
humidity and dry-heat tests.
CE conformity marking
The CE conformity marking shall indicate conformity to all the obligations
imposed on the manufacturer, as regards his products, by virtue of the European
Community directives providing for the affixing of the CE marking.
9 ABB SACE - Electrical devices
1.1 General aspects
1 Standards
8 ABB SACE - Electrical devices
1.1 General aspects
1 Standards
COUNTRY Symbol Mark designation Applicability/Organization
CROATIA
DENMARK
FINLAND
FRANCE
FRANCE
FRANCE
FRANCE
FRANCE
KONKAR
DEMKO
Approval Mark
Safety Mark
of the Elektriska
Inspektoratet
ESC Mark
NF Mark
NF Identification
Thread
NF Mark
NF Mark
Electrical Engineering Institute
Low voltage materials.
This mark guarantees the
compliance of the product with
the requirements (safety) of the
“Heavy Current Regulations”
Low voltage material.
This mark guarantees the
compliance of the product with
the requirements (safety) of the
“Heavy Current Regulations”
Household appliances
Conductors and cables –
Conduits and ducting –
Installation materials
Cables
Portable motor-operated tools
Household appliances
COUNTRY Symbol Mark designation Applicability/Organization
AUSTRIA
BELGIUM
BELGIUM
BELGIUM
CANADA
CHINA
Czech Republic
Slovakia
Republic
ÖVE Identification
Thread
CEBEC Mark
CEBEC Mark
Certification of
Conformity
CSA Mark
CCEE Mark
EZU’ Mark
EVPU’ Mark
Cables
Installation materials and electrical
appliances
Conduits and ducts, conductors
and flexible cords
Installation material and electrical
appliances (in case there are no
equivalent national standards or
criteria)
Electrical and non-electrical
products.
This mark guarantees compliance
with CSA (Canadian Standard
Association)
Great Wall Mark Commission for
Certification of Electrical
Equipment
Electrotechnical Testing Institute
Electrotechnical Research and
Design Institute
11 ABB SACE - Electrical devices
1.1 General aspects
1 Standards
10 ABB SACE - Electrical devices
1.1 General aspects
1 Standards
COUNTRY Symbol Mark designation Applicability/Organization
ITALY
NORWAY
NETHERLANDS
POLAND
IMQ Mark
Norwegian Approval
Mark
KEMA-KEUR
KWE
Mark to be affixed on electrical
material for non-skilled users; it
certifies compliance with the
European Standard(s).
Mandatory safety approval for low
voltage material and equipment
General for all equipment
Electrical products
KEUR
B
A
P
P
R
O
V
E
D
T
O
SINGAPO
R
E
S
T
A
N
D
A
R
D
M
A
R
C
A
D
E
C
O
N
F
O
RMIDAD
A
N
O
R
M
A
S
U
N
E
SINGAPORE
SLOVENIA
SPAIN
SISIR
SIQ
AEE
Electrical and non-electrical
products
Slovenian Institute of Quality and
Metrology
Electrical products.
The mark is under the control of
the Asociación Electrotécnica
Española(Spanish Electrotechnical
Association)
RUSSIA
Certification of
Conformity
Electrical and non-electrical
products. It guarantees
compliance with national standard
(Gosstandard of Russia)
COUNTRY Symbol Mark designation Applicability/Organization
GERMANY
GERMANY
GERMANY
GERMANY
HUNGARY
JAPAN
IRELAND
IRELAND
VDE Mark
VDE
Identification Thread
VDE Cable Mark
VDE-GS Mark
for technical
equipment
MEEI
JIS Mark
IIRS Mark
IIRS Mark
For appliances and technical
equipment, installation accessories
such as plugs, sockets, fuses,
wires and cables, as well as other
components (capacitors, earthing
systems, lamp holders and
electronic devices)
Cables and cords
For cables, insulated cords,
installation conduits and ducts
Safety mark for technical equipment
to be affixed after the product has
been tested and certified by the VDE
Test Laboratory in Offenbach; the
conformity mark is the mark VDE,
which is granted both to be used
alone as well as in combination with
the mark GS
Hungarian Institute for Testing and
Certification of Electrical Equipment
Mark which guarantees
compliance with the relevant
Japanese Industrial Standard(s).
Electrical equipment
Electrical equipment
geprüfte
Sicherheit
M
A
R
K
O
F C O N
F
O
R
M
I
T
Y
I.I.R . S.
13 ABB SACE - Electrical devices
1.1 General aspects
1 Standards
12 ABB SACE - Electrical devices
1.1 General aspects
1 Standards
COUNTRY Symbol Mark designation Applicability/Organization
UNITED
KINGDOM
UNITED
KINGDOM
U.S.A.
U.S.A.
U.S.A.
CEN
CENELEC
BSI
Safety Mark
BEAB
Kitemark
UNDERWRITERS
LABORATORIES
Mark
UNDERWRITERS
LABORATORIES
Mark
UL Recognition
CEN Mark
Mark
Compliance with the “British
Standards”
Compliance with the relevant
“British Standards” regarding
safety and performances
Electrical and non-electrical
products
Electrical and non-electrical
products
Electrical and non-electrical
products
Mark issued by the European
Committee for Standardization
(CEN): it guarantees compliance
with the European Standards.
Cables
A
P
P
R
O
V
E
D
T
O
BRITIS
H
S
T
A
N
D
A
R
D
A
N
IN
D
EPENDENT LABORATO
R
Y
T
E
S
TI N
G FOR PUBLIC SA
F
E
T
Y
L I S T E D
(Product Name)
(Control Number)
UNITED
KINGDOM
BEAB
Safety Mark
Compliance with the “British
Standards” for household
appliances
COUNTRY Symbol Mark designation Applicability/Organization
SWEDEN
SWITZERLAND
SWITZERLAND
SWITZERLAND
UNITED
KINGDOM
UNITED
KINGDOM
UNITED
KINGDOM
SEMKO
Mark
Safety Mark
–
SEV Safety Mark
ASTA Mark
BASEC Mark
BASEC
Identification Thread
Mandatory safety approval for low
voltage material and equipment.
Swiss low voltage material subject
to mandatory approval (safety).
Cables subject to mandatory
approval
Low voltage material subject to
mandatory approval
Mark which guarantees
compliance with the relevant
“British Standards”
Mark which guarantees
compliance with the “British
Standards” for conductors, cables
and ancillary products.
Cables
C
E
R
T
IF
IC
A
T
IO
N T
R
A
D
E
M
A
R
K
SPAIN AENOR Asociación Española de
Normalización y Certificación.
(Spanish Standarization and
Certification Association)
15 ABB SACE - Electrical devices
1 Standards
14 ABB SACE - Electrical devices
1 Standards
IEC 60027-1 1992 Letter symbols to be used in electrical
technology - Part 1: General
IEC 60034-1 1999 Rotating electrical machines - Part 1:
Rating and performance
IEC 60617-DB-12M 2001 Graphical symbols for diagrams - 12-
month subscription to online database
comprising parts 2 to 11 of IEC 60617
IEC 61082-1 1991 Preparation of documents used in
electrotechnology - Part 1: General
requirements
IEC 61082-2 1993 Preparation of documents used in
electrotechnology - Part 2: Function-
oriented diagrams
IEC 61082-3 1993 Preparation of documents used in
electrotechnology - Part 3: Connection
diagrams, tables and lists
IEC 61082-4 1996 Preparation of documents used in
electrotechnology - Part 4: Location and
installation documents
IEC 60038 1983 IEC standard voltages
IEC 60664-1 2000 Insulation coordination for equipment
within low-voltage systems - Part 1:
Principles, requirements and tests
IEC 60909-0 2001 Short-circuit currents in three-phase a.c.
systems - Part 0: Calculation of currents
IEC 60865-1 1993 Short-circuit currents - Calculation of
effects - Part 1: Definitions and
calculation methods
IEC 60781 1989 Application guide for calculation of short-
circuit currents in low-voltage radial
systems
IEC 60076-1 2000 Power transformers - Part 1: General
IEC 60076-2 1993 Power transformers - Part 2: Temperature
rise
IEC 60076-3 2000 Power transformers - Part 3: Insulation
levels, dielectric tests and external
clearances in air
IEC 60076-5 2000 Power transformers - Part 5: Ability to
withstand short circuit
IEC/TR 60616 1978 Terminal and tapping markings for power
transformers
IEC 60726 1982 Dry-type power transformers
IEC 60445 1999 Basic and safety principles for man-
machine interface, marking and
identification - Identification of
equipment terminals and of terminations
of certain designated conductors,
including general rules for an
alphanumeric system
1.2 IEC Standards for electrical
installation
STANDARD YEAR TITLE
COUNTRY Symbol Mark designation Applicability/Organization
EC
CEEel
EC - Declaration of Conformity
The EC Declaration of Conformity is the statement of the manufacturer, who
declares under his own responsibility that all the equipment, procedures or
services refer and comply with specific standards (directives) or other normative
documents.
The EC Declaration of Conformity should contain the following information:
• name and address of the manufacturer or by its European representative;
• description of the product;
• reference to the harmonized standards and directives involved;
• any reference to the technical specifications of conformity;
• the two last digits of the year of affixing of the CE marking;
• identification of the signer.
A copy of the EC Declaration of Conformity shall be kept by the manufacturer
or by his representative together with the technical documentation.
Ex EUROPEA Mark
CEEel Mark
Mark assuring the compliance
with the relevant European
Standards of the products to be
used in environments with
explosion hazards
Mark which is applicable to some
household appliances (shavers,
electric clocks, etc).
1.1 General aspects
CENELEC
Harmonization Mark
Certification mark providing
assurance that the harmonized
cable complies with the relevant
harmonized CENELEC Standards
– identification thread
17
1.2 IEC standards for electrical installation
1 Standards
ABB SACE - Electrical devices
1.2 IEC standards for electrical installation
1 Standards
16 ABB SACE - Electrical devices
IEC 60947-5-6 1999 Low-voltage switchgear and controlgear -
Part 5-6: Control circuit devices and
switching elements – DC interface for
proximity sensors and switching
amplifiers (NAMUR)
IEC 60947-6-1 1998 Low-voltage switchgear and controlgear -
Part 6-1: Multiple function equipment –
Automatic transfer switching equipment
IEC 60947-6-2 1999 Low-voltage switchgear and controlgear -
Part 6-2: Multiple function equipment -
Control and protective switching devices
(or equipment) (CPS)
IEC 60947-7-1 1999 Low-voltage switchgear and controlgear -
Part 7: Ancillary equipment - Section 1:
Terminal blocks
IEC 60947-7-2 1995 Low-voltage switchgear and controlgear -
Part 7: Ancillary equipment - Section 2:
Protective conductor terminal blocks for
copper conductors
IEC 60439-1 1999 Low-voltage switchgear and controlgear
assemblies - Part 1: Type-tested and
partially type-tested assemblies
IEC 60439-2 2000 Low-voltage switchgear and controlgear
assemblies - Part 2: Particular
requirements for busbar trunking systems
(busways)
IEC 60439-3 2001 Low-voltage switchgear and controlgear
assemblies - Part 3: Particular
requirements for low-voltage switchgear
and controlgear assemblies intended to
be installed in places where unskilled
persons have access for their use -
Distribution boards
IEC 60439-4 1999 Low-voltage switchgear and controlgear
assemblies - Part 4: Particular
requirements for assemblies for
construction sites (ACS)
IEC 60439-5 1999 Low-voltage switchgear and controlgear
assemblies - Part 5: Particular
requirements for assemblies intended to
be installed outdoors in public places -
Cable distribution cabinets (CDCs) for
power distribution in networks
IEC 61095 2000 Electromechanical contactors for
household and similar purposes
STANDARD YEAR TITLE
IEC 60073 1996 Basic and safety principles for man-
machine interface, marking and
identification – Coding for indication
devices and actuators
IEC 60446 1999 Basic and safety principles for man-
machine interface, marking and
identification - Identification of
conductors by colours or numerals
IEC 60447 1993 Man-machine-interface (MMI) - Actuating
principles
IEC 60947-1 2001 Low-voltage switchgear and controlgear -
Part 1: General rules
IEC 60947-2 2001 Low-voltage switchgear and controlgear -
Part 2: Circuit-breakers
IEC 60947-3 2001 Low-voltage switchgear and controlgear -
Part 3: Switches, disconnectors, switch-
disconnectors and fuse-combination
units
IEC 60947-4-1 2000 Low-voltage switchgear and controlgear -
Part 4-1: Contactors and motor-starters –
Electromechanical contactors and motor-
starters
IEC 60947-4-2 2002 Low-voltage switchgear and controlgear -
Part 4-2: Contactors and motor-starters –
AC semiconductor motor controllers and
starters
IEC 60947-4-3 1999 Low-voltage switchgear and controlgear -
Part 4-3: Contactors and motor-starters –
AC semiconductor controllers and
contactors for non-motor loads
IEC 60947-5-1 2000 Low-voltage switchgear and controlgear -
Part 5-1: Control circuit devices and
switching elements - Electromechanical
control circuit devices
IEC 60947-5-2 1999 Low-voltage switchgear and controlgear -
Part 5-2: Control circuit devices and
switching elements – Proximity switches
IEC 60947-5-3 1999 Low-voltage switchgear and controlgear -
Part 5-3: Control circuit devices and
switching elements – Requirements for
proximity devices with defined behaviour
under fault conditions
IEC 60947-5-4 1996 Low-voltage switchgear and controlgear -
Part 5: Control circuit devices and
switching elements – Section 4: Method
of assessing the performance of low
energy contacts. Special tests
IEC 60947-5-5 1997 Low-voltage switchgear and controlgear -
Part 5-5: Control circuit devices and
switching elements - Electrical
emergency stop device with mechanical
latching function
STANDARD YEAR TITLE
19
1.2 IEC standards for electrical installation
1 Standards
ABB SACE - Electrical devices
1.2 IEC standards for electrical installation
1 Standards
18 ABB SACE - Electrical devices
1994 Part 5: Lift cables
1994 Part 6: Arc welding electrode cables
1994 Part 7: Heat resistant ethylene-vinyl
acetate rubber insulated cables
1998 Part 8: Cords for applications requiring
high flexibility
IEC 60309-2 1999 Plugs, socket-outlets and couplers for
industrial purposes - Part 2: Dimensional
interchangeability requirements for pin
and contact-tube accessories
IEC 61008-1 1996 Residual current operated circuit-breakers
without integral overcurrent protection for
household and similar uses (RCCBs) -
Part 1: General rules
IEC 61008-2-1 1990 Residual current operated circuit-breakers
without integral overcurrent protection for
household and similar uses (RCCB’s).
Part 2-1: Applicability of the general rules
to RCCB’s functionally independent of
line voltage
IEC 61008-2-2 1990 Residual current operated circuit-breakers
without integral overcurrent protection for
household and similar uses (RCCB’s).
Part 2-2: Applicability of the general rules
to RCCB’s functionally dependent on line
voltage
IEC 61009-1 1996 Residual current operated circuit-breakers
with integral overcurrent protection for
household and similar uses (RCBOs) -
Part 1: General rules
IEC 61009-2-1 1991 Residual current operated circuit-breakers
with integral overcurrent protection for
household and similar uses (RCBO’s)
Part 2-1: Applicability of the general rules
to RCBO’s functionally independent of
line voltage
IEC 61009-2-2 1991 Residual current operated circuit-breakers
with integral overcurrent protection for
household and similar uses (RCBO’s) -
Part 2-2: Applicability of the general rules
to RCBO’s functionally
dependent on line voltage
IEC 60670 1989 General requirements for enclosures for
accessories for household and similar
fixed electrical installations
IEC 60669-2-1 2000 Switches for household and similar fixed
electrical installations - Part 2-1:
Particular requirements – Electronic
switches
IEC 60669-2-2 2000 Switches for household and similar fixed
electrical installations - Part 2: Particular
requirements – Section 2: Remote-control
switches (RCS)
IEC 606692-3 1997 Switches for household and similar fixed
electrical installations - Part 2-3:
Particular requirements – Time-delay
switches (TDS)
STANDARD YEAR TITLE
IEC 60890 1987 A method of temperature-rise assessment
by extrapolation for partially type-tested
assemblies (PTTA) of low-voltage
switchgear and controlgear
IEC 61117 1992 A method for assessing the short-circuit
withstand strength of partially type-tested
assemblies (PTTA)
IEC 60092-303 1980 Electrical installations in ships. Part 303:
Equipment - Transformers for power and
lighting
IEC 60092-301 1980 Electrical installations in ships. Part 301:
Equipment - Generators and motors
IEC 60092-101 1994 Electrical installations in ships - Part 101:
Definitions and general requirements
IEC 60092-401 1980 Electrical installations in ships. Part 401:
Installation and test of completed
installation
IEC 60092-201 1994 Electrical installations in ships - Part 201:
System design - General
IEC 60092-202 1994 Electrical installations in ships - Part 202:
System design - Protection
IEC 60092-302 1997 Electrical installations in ships - Part 302:
Low-voltage switchgear and controlgear
assemblies
IEC 60092-350 2001 Electrical installations in ships - Part 350:
Shipboard power cables - General
construction and test requirements
IEC 60092-352 1997 Electrical installations in ships - Part 352:
Choice and installation of cables for low-
voltage power systems
IEC 60364-5-52 2001 Electrical installations of buildings - Part
5-52: Selection and erection of electrical
equipment – Wiring systems
IEC 60227 Polyvinyl chloride insulated cables of
rated voltages up to and including 450/
750 V
1998 Part 1: General requirements
1997 Part 2: Test methods
1997 Part 3: Non-sheathed cables for fixed
wiring
1997 Part 4: Sheathed cables for fixed wiring
1998 Part 5: Flexible cables (cords)
2001 Part 6: Lift cables and cables for flexible
connections
1995 Part 7: Flexible cables screened and
unscreened with two or more conductors
IEC 60228 1978 Conductors of insulated cables
IEC 60245 Rubber insulated cables - Rated voltages
up to and including 450/750 V
1998 Part 1: General requirements
1998 Part 2: Test methods
1994 Part 3: Heat resistant silicone insulated
cables
STANDARD YEAR TITLE
21
1.2 IEC standards for electrical installation
1 Standards
ABB SACE - Electrical devices
1.2 IEC standards for electrical installation
1 Standards
20 ABB SACE - Electrical devices
IEC 61032 1997 Protection of persons and equipment by
enclosures - Probes for verification
IEC 61000-1-1 1992 Electromagnetic compatibility (EMC) -
Part 1: General - Section 1: Application
and interpretation of fundamental
definitions and terms
IEC 61000-1-2 2001 Electromagnetic compatibility (EMC) -
Part 1-2: General - Methodology for the
achievement of the functional safety of
electrical and electronic equipment with
regard to electromagnetic phenomena
IEC 61000-1-3 2002 Electromagnetic compatibility (EMC) -
Part 1-3: General - The effects of high-
altitude EMP (HEMP) on civil equipment
and systems
STANDARD YEAR TITLE
IEC 60079-10 1995 Electrical apparatus for explosive gas
atmospheres - Part 10: Classification of
hazardous areas
IEC 60079-14 1996 Electrical apparatus for explosive gas
atmospheres - Part 14: Electrical
installations in hazardous areas (other
than mines)
IEC 60079-17 1996 Electrical apparatus for explosive gas
atmospheres - Part 17: Inspection and
maintenance of electrical installations in
hazardous areas (other than mines)
IEC 60269-1 1998 Low-voltage fuses - Part 1: General
requirements
IEC 60269-2 1986 Low-voltage fuses. Part 2: Supplementary
requirements for fuses for use by
authorized persons (fuses mainly for
industrial application)
IEC 60269-3-1 2000 Low-voltage fuses - Part 3-1:
Supplementary requirements for fuses for
use by unskilled persons (fuses mainly for
household and similar applications) -
Sections I to IV
IEC 60127-1/10 Miniature fuses -
1999 Part 1: Definitions for miniature fuses and
general requirements for miniature fuse-links
1989 Part 2: Cartridge fuse-links
1988 Part 3: Sub-miniature fuse-links
1996 Part 4: Universal Modular Fuse-Links
(UMF)
1988 Part 5: Guidelines for quality assessment
of miniature fuse-links
1994 Part 6: Fuse-holders for miniature
cartridge fuse-links
2001 Part 10: User guide for miniature fuses
IEC 60730-2-7 1990 Automatic electrical controls for
household and similar use. Part 2:
Particular requirements for timers and
time switches
IEC 60364-1 2001 Electrical installations of buildings - Part 1:
Fundamental principles, assessment of
general characteristics, definitions
IEC 60364-4 2001 Electrical installations of buildings - Part 4:
Protection for safety
IEC 60364-5 2001…2002 Electrical installations of buildings - Part 5:
Selection and erection of electrical equipment
IEC 60364-6 2001 Electrical installations of buildings - Part 6:
Verification
IEC 60364-7 1983…2002 Electrical installations of buildings. Part 7:
Requirements for special installations or
locations
IEC 60529 2001 Degrees of protection provided by
enclosures (IP Code)
STANDARD YEAR TITLE
23 22 ABB SACE - Electrical devices ABB SACE - Electrical devices
2 Protection of feeders 2 Protection of feeders
Conventional operating current (of a protective device) A specified value of
the current which cause the protective device to operate within a specified
time, designated conventional time.
Overcurrent detection A function establishing that the value of current in a
circuit exceeds a predetermined value for a specified length of time.
Leakage current Electrical current in an unwanted conductive path other than
a short circuit.
Fault current The current flowing at a given point of a network resulting from
a fault at another point of this network.
Wiring systems
Wiring system An assembly made up of a cable or cables or busbars and the
parts which secure and, if necessary, enclose the cable(s) or busbars.
Electrical circuits
Electrical circuit (of an installation) An assembly of electrical equipment of
the installation supplied from the same origin and protected against overcurrents
by the same protective device(s).
Distribution circuit (of buildings) A circuit supplying a distribution board.
Final circuit (of building) A circuit connected directly to current using
equipment or to socket-outlets.
Other equipment
Electrical equipment Any item used for such purposes as generation,
conversion, transmission, distribution or utilization of electrical energy, such as
machines, transformers, apparatus, measuring instruments, protective devices,
equipment for wiring systems, appliances.
Current-using equipment Equipment intended to convert electrical energy
into another form of energy, for example light, heat, and motive power
Switchgear and controlgear Equipment provided to be connected to an
electrical circuit for the purpose of carrying out one or more of the following
functions: protection, control, isolation, switching.
Portable equipment Equipment which is moved while in operation or which
can easily be moved from one place to another while connected to the supply.
Hand-held equipment Portable equipment intended to be held in the hand
during normal use, in which the motor, if any, forms an integral part of the
equipment.
Stationary equipment Either fixed equipment or equipment not provided with
a carrying handle and having such a mass that it cannot easily be moved.
Fixed equipment Equipment fastened to a support or otherwise secured in a
specific location.
2.1 Introduction
2.1 Introduction
The following definitions regarding electrical installations are derived from the
Standard IEC 60050.
Characteristics of installations
Electrical installation (of a building) An assembly of associated electrical
equipment to fulfil a specific purpose and having coordinated characteristics.
Origin of an electrical installation The point at which electrical energy is
delivered to an installation.
Neutral conductor (symbol N) A conductor connected to the neutral point of
a system and capable of contributing to the transmission of electrical energy.
Protective conductor PE A conductor required by some measures for
protection against electric shock for electrically connecting any of the following
parts:
- exposed conductive parts;
- extraneous conductive parts;
- main earthing terminal;
- earth electrode;
- earthed point of the source or artificial neutral.
PEN conductor An earthed conductor combining the functions of both
protective conductor and neutral conductor
Ambient temperature The temperature of the air or other medium where the
equipment is to be used.
Voltages
Nominal voltage (of an installation) Voltage by which an installation or part of
an installation is designated.
Note: the actual voltage may differ from the nominal voltage by a quantity within
permitted tolerances.
Currents
Design current (of a circuit) The current intended to be carried by a circuit in
normal service.
Current-carrying capacity (of a conductor) The maximum current which can
be carried continuously by a conductor under specified conditions without its
steady-state temperature exceeding a specified value.
Overcurrent Any current exceeding the rated value. For conductors, the rated
value is the current-carrying capacity.
Overload current (of a circuit) An overcurrent occurring in a circuit in the
absence of an electrical fault.
Short-circuit current An overcurrent resulting from a fault of negligible
impedance between live conductors having a difference in potential under normal
operating conditions.
25 24 ABB SACE - Electrical devices ABB SACE - Electrical devices
2 Protection of feeders 2 Protection of feeders
Table 1: Selection of wiring systems
Conductors and
cables
Bare conductors
Insulated conductors
Sheathed cables
Multi-core
(including armoured and
mineral insulated)
Single-core
Without
fixings
-
-
+
0
Clipped
direct
-
-
+
+
Conduit
-
+
+
+
Cable trunking
(including skirting
trunking, flush floor
trunking)
-
+
+
+
Cable
ducting
-
+
+
+
Cable ladder
Cable tray
Cable brackets
-
-
+
+
On in-
sulators
+
+
0
0
Support
wire
-
-
+
+
Method of installation
+ Permitted.
– Not permitted.
0 Not applicable, or not normally used in practice.
For a correct dimensioning of a cable, it is necessary to:
• choose the type of cable and installation according to the environment;
• choose the cross section according to the load current;
• verify the voltage drop.
2.2 Installation and dimensioning of cables
Installation dimensioning
The flow chart below suggests the procedure to follow for the correct
dimensioning of a plant.
Dimensioning of conductors:
- eval uati on of the current (I
b
)
i n the si ngl e connecti on el ements;
- definition of the conductor type (conductors and insulation materials,
configuration,...);
- definition of the cross section and of the current carrying capacity;
- calculation of the voltage drop at the load current under specific reference
conditions (motor starting,…).
Load analysis:
- definition of the power absorbed by the loads and relevant position;
- definition of the position of the power distribution centers (switchboards);
- definition of the paths and calculation of the length of the connection elements;
- definition of the total power absorbed, taking into account the utilization factors
and demand factors.
Dimensioning of transformers and generators with margin connected to
future predictable power supply requirements (by approximation from +15÷30%)
Verification of the voltage drop limits at the final loads
Short-circuit current calculation maximum values at the busbars (beginning of
line) and minimum values at the end of line
Selection of protective circuit-breakers with:
- breaking capacity higher than the maximum prospective short-circuit current;
- rated current In not lower than the load curren Ib;
- characteristics compatible with the type of protected load (motors, capacitors...).
1
S
D
C
0
1
0
0
0
1
F
0
9
0
1
Verification of the coordination with other equipments (discrimination and
back-up, verification of the coordination with switch disconnectors...)
Verification of the protection of conductors:
- verification of the protection against overload: the rated current or the set current
of the circuit-breaker shall be higher than the load current, but lower than the
current carrying capacity of the conductor:
Ib ≤ In ≤ Iz
- verification of the protection against short-circuit: the specific let-through energy
by the circuit breaker under short-circuit conditions shall be lower than the specific
let-through energy which can be withstood by the cable:
I
2
t ≤ k
2
S
2
- verification of the protection against indirect contacts (depending on the
distribution system).
negati ve
outcome
negati ve
outcome
negati ve
outcome
Definition of the components (auxiliary circuits, terminals…) and switchboard
design
Selection of the cable
The international reference Standard ruling the installation and calculation of
the current carrying capacity of cables in residential and industrial buildings is
IEC 60364-5-52 “Electrical installations of buildings – Part 5-52 Selection and
Erection of Electrical Equipment- Wiring systems”.
The following parameters are used to select the cable type:
• conductive material (copper or aluminium): the choice depends on cost,
dimension and weight requirements, resistance to corrosive environments
(chemical reagents or oxidizing elements). In general, the carrying capacity of
a copper conductor is about 30% greater than the carrying capacity of an
aluminium conductor of the same cross section. An aluminium conductor of
the same cross section has an electrical resistance about 60% higher and a
weight half to one third lower than a copper conductor.
• insulation material (none, PVC, XLPE-EPR): the insulation material affects the
maximum temperature under normal and short-circuit conditions and therefore
the exploitation of the conductor cross section [see Chapter 2.4 “Protection
against short-circuit”].
• the type of conductor (bare conductor, single-core cable without sheath, single-
core cable with sheath, multi-core cable) is selected according to mechanical
resistance, degree of insulation and difficulty of installation (bends, joints along
the route, barriers...) required by the method of installation.
Table 1 shows the types of conductors permitted by the different methods of
installation.
2.2.1 Current carrying capacity and methods of installation
2.1 Introduction
27 26 ABB SACE - Electrical devices ABB SACE - Electrical devices
2.2 Installation and dimensioning of cables 2.2 Installation and dimensioning of cables
2 Protection of feeders 2 Protection of feeders
Table 2: Method of installation
Without
fixings
40, 46,
15, 16
56
72, 73
57, 58
-
-
With
fixings
0
56
0
3
20, 21
-
Conduit
15, 16
54, 55
70, 71
1, 2
59, 60
4, 5
0
Cable trunking
(including skirting
trunking, flush floor
trunking)
-
0
-
50, 51, 52,
53
6, 7, 8, 9,
12, 13, 14
10, 11
Cable
ducting
0
44
70, 71
44, 45
6, 7, 8, 9
-
Cable ladder
Cable tray
Cable brackets
30, 31,
32, 33, 34
30, 31, 32,
33, 34
0
0
30, 31,
32, 33, 34
30, 31, 32,
33, 34
On
insulators
-
-
-
-
36
36
Support
wire
-
-
-
-
-
35
Method of installation
The number in each box indicates the item number in Table 3.
- Not permitted.
0 Not applicable or not normally used in practice.
Situations
Building voids
Cable channel
Buried in
Ground
Embedded in
Structure
Surface
Mounted
Overhead
Room
Room
Room
TV
ISDN
TV
ISDN
Methods of
installation
Item n. Description
Reference
method of
installation to be
used to
obtain current-
carrying
capacity
1
Insulated conductors or single-core
cables in conduit in a thermally
insulated wall
A1
2
Multi-core cables in conduit in a
thermally insulated wall
A2
3
Multi-core cable direct in a thermally
insulated wall
A1
4
Insulated conductors or single-core
cables in conduit on a wooden, or
masonry wall or spaced less than 0.3
times conduit diameter from it
B1
5
Multi-core cable in conduit on a
wooden, or masonry wall or spaced
less than 0.3 times conduit diameter
from it
B2
6
7
Insulated conductors or single-core
cables in cable trunking on a wooden
wall – run horizontally (6)
– run vertically (7)
B1
8
9
Insulated conductors or single-core
cable in suspended cable trunking
(8)
Multi-core cable in suspended cable
trunking (9)
B1 (8) or B2 (9)
12
Insulated conductors or single-core
cable run in mouldings
A1
13
14
Insulated conductors or single-core
cables in skirting trunking (13)
Multi-core cable in skirting trunking
(14)
B1 (13)
or
B2 (14)
15
Insulated conductors in conduit or
single-core or multi-core cable in
architrave
A1
16
Insulated conductors in conduit or
single-core or multi-core cable in
window frames
A1
20
21
Single-core or multi-core cables:
– fixed on, or spaced less than 0.3
times (20)
cable diameter from a wooden wall
– fixed directly under a wooden
ceiling (21)
C
1
S
D
C
0
1
0
0
0
1
F
0
2
0
1
For industrial installations, multi-core cables are rarely used with cross section
greater than 95 mm
2
.
Methods of installation
To define the current carrying capacity of the conductor and therefore to identify
the correct cross section for the load current, the standardized method of
installation that better suits the actual installation situation must be identified
among those described in the mentioned reference Standard.
From Tables 2 and 3 it is possible to identify the installation identification number,
the method of installation (A1, A2, B1, B2, C, D, E, F, G) and the tables to
define the theoretical current carrying capacity of the conductor and any
correction factors required to allow for particular environmental and installation
situations.
Table 3: Examples of methods of installation
29 28 ABB SACE - Electrical devices ABB SACE - Electrical devices
2.2 Installation and dimensioning of cables 2.2 Installation and dimensioning of cables
2 Protection of feeders 2 Protection of feeders
≤ 0.3 D
e
≤ 0.3 D
e
≤ 0.3 D
e
≤ 0.3 D
e
≤ 0.3 D
e
≤ 0.3 D
e
D
e
V
D
e
V
V
D
e
V
V
D
e
TV
ISDN
TV
ISDN
1.5 D
e
≤ V <20 D
e
1.5 D
e
≤ V <20 D
e
1.5 D
e
≤ V <5 De
5 D
e
≤ V < 50D
e
5 D
e
≤ V < 50 D
e
1.5 De ≤ V <5 D
e
1.5 D
e ≤ V <20 D
e
30 On unperforated tray
1
C
31 On perforated tray
1
E or F
32 On brackets or on a wire mesh
1
E or F
33
Spaced more than 0.3 times cable
diameter from a wall
E or F or G
34 On ladder E or F
35
Single-core or multi-core cable
suspended from or incorporating a
support wire
E or F
36
Bare or insulated conductors on
insulators
G
Methods of
installation
Item n. Description
Reference
method of
installation to be
used to
obtain current-
carrying
capacity
1
S
D
C
0
1
0
0
0
2
F
0
2
0
1
40
Single-core or multi-core cable in a
building void
2
B2
V ≥ 20 D
e
B1
24
Insulated conductors in cable ducting
in a building void
2
B2
V ≥ 20 D
e
B1
44
Insulated conductors in cable ducting
in masonry having a thermal
resistivity not greater than 2 Km/W
B2
B1
46
Single-core or multi-core cable:
– in a ceiling void
– in a suspended floor
1
B2
B1
50
Insulated conductors or single-core
cable in flush cable trunking in the
floor
B1
51
Multi-core cable in flush cable
trunking in the floor
B2
52
53
Insulated conductors or single-core
cables in embedded trunking (52)
Multi-core cable in embedded
trunking (53)
B1 (52)
or
B2 (53)
54
Insulated conductors or single-core
cables in conduit in an unventilated
cable channel run horizontally or
vertically
2
B2
V ≥20 D
e
B1
Methods of
installation
Item n. Description
Reference
method of
installation to be
used to
obtain current-
carrying
capacity
31 30 ABB SACE - Electrical devices ABB SACE - Electrical devices
2.2 Installation and dimensioning of cables 2.2 Installation and dimensioning of cables
2 Protection of feeders 2 Protection of feeders
tot z
k I k k I I
0 2 1 0
= =
Methods of
installation
Item n. Description
Reference
method of
installation to be
used to
obtain current-
carrying
capacity
55
Insulated conductors in conduit in an
open or ventilated cable channel in
the floor
B1
56
Sheathed single-core or multi-core
cable in an open or ventilated cable
channel run horizontally or vertically
B1
57
Single-core or multi-core cable direct
in masonry having a thermal
resistivity not greater than 2 Km/W
Without added mechanical protection
C
58
Single-core or multi-core cable direct
in masonry having a thermal
resistivity not greater than 2 Km/W
With added mechanical protection
C
59
Insulated conductors or single-core
cables in conduit in masonry
B1
60
Multi-core cables in conduit in
masonry
B2
70
Multi-core cable in conduit or in cable
ducting in the ground
D
71
Single-core cable in conduit or in
cable ducting in the ground
D
72
Sheathed single-core or multi-core
cables direct in the ground
– without added mechanical
protection
D
73
Sheathed single-core or multi-core
cables direct in the ground
– with added mechanical protection
D
1
S
D
C
0
1
0
0
0
3
F
0
2
0
1
1
D
e
is the external diameter of a multi-core cable:
– 2.2 x the cable diameter when three single core cables are bound in trefoil, or
– 3 x the cable diameter when three single core cables are laid in flat formation.
2
D
e
is the external diameter of conduit or vertical depth of cable ducting.
V is the smaller dimension or diameter of a masonry duct or void, or the vertical depth of a rectangular duct, floor or ceiling void.
The depth of the channel is more important than the width.
Table 4: Correction factor for ambient air temperature other than 30 °C
Insulation
(a)
For higher ambient temperatures, consult manufacturer.
PVC
1.22
1.17
1.12
1.06
0.94
0.87
0.79
0.71
0.61
0.50
–
–
–
–
–
–
–
XLPE and EPR
1.15
1.12
1.08
1.04
0.96
0.91
0.87
0.82
0.76
0.71
0.65
0.58
0.50
0.41
–
–
–
Ambient
temperature (a)
°C
10
15
20
25
35
40
45
50
55
60
65
70
75
80
85
90
95
PVC covered or
bare and exposed
to touch 70 °C
1.26
1.20
1.14
1.07
0.93
0.85
0.87
0.67
0.57
0.45
–
–
–
–
–
–
–
Bare not exposed
to touch 105 °C
1.14
1.11
1.07
1.04
0.96
0.92
0.88
0.84
0.80
0.75
0.70
0.65
0.60
0.54
0.47
0.40
0.32
Mineral (a)
where:
• I
0
is the current carrying capacity of the single conductor at 30 °C reference
ambient temperature;
• k
1
is the correction factor if the ambient temperature is other than 30 °C;
• k
2
is the correction factor for cables installed bunched or in layers or for
cables installed in a layer on several supports.
Correction factor k
1
The current carrying capacity of the cables that are not buried in the ground
refers to 30 °C ambient temperature. If the ambient temperature of the place
of installation is different from this reference temperature, the correction factor
k
1
on Table 4 shall be used, according to the insulation material.
Installation not buried in the ground: choice of the
cross section according to cable carrying capacity and
type of installation
The cable carrying capacity of a cable that is not buried in the ground is obtained
by using this formula:
33 32 ABB SACE - Electrical devices ABB SACE - Electrical devices
2.2 Installation and dimensioning of cables 2.2 Installation and dimensioning of cables
2 Protection of feeders 2 Protection of feeders
> 2 De
2
De
1
De
2
a)
b)
c)
<
3
0
c
m
1
S
D
C
0
1
0
0
0
2
F
0
0
0
1
a)
b)
c)
1
S
D
C
0
1
0
0
0
3
F
0
0
0
1
Correction factor k
2
The cable current carrying capacity is influenced by the presence of other cables
installed nearby. The heat dissipation of a single cable is different from that of
the same cable when installed next to the other ones. The factor k
2
is tabled
according to the installation of cables laid close together in layers or bunches.
Definition of layer or bunch
layer: several circuits constituted by cables installed one next to another, spaced
or not, arranged horizontally or vertically. The cables on a layer are installed on
a wall, tray, ceiling, floor or on a cable ladder;
bunch: several circuits constituted by cables that are not spaced and are not
installed in a layer; several layers superimposed on a single support (e.g. tray)
are considered to be a bunch.
The value of correction factor k
2
is 1 when:
• the cables are spaced:
- two single-core cables belonging to different circuits are spaced when the
distance between them is more than twice the external diameter of the
cable with the larger cross section;
- two multi-core cables are spaced when the distance between them is at
least the same as the external diameter of the larger cable;
• the adjacent cables are loaded less than 30 % of their current carrying capacity.
The correction factors for bunched cables or cables in layers are calculated by
assuming that the bunches consist of similar cables that are equally loaded. A
group of cables is considered to consist of similar cables when the calculation
of the current carrying capacity is based on the same maximum allowed
operating temperature and when the cross sections of the conductors is in the
range of three adjacent standard cross sections (e.g. from 10 to 25 mm
2
).
The calculation of the reduction factors for bunched cables with different cross
sections depends on the number of cables and on their cross sections. These
factors have not been tabled, but must be calculated for each bunch or layer.
Cables in layers: a) spaced; b) not spaced; c) double layer
Bunched cables: a) in trunking; b) in conduit; c) on perforated tray
35 34 ABB SACE - Electrical devices ABB SACE - Electrical devices
2.2 Installation and dimensioning of cables 2.2 Installation and dimensioning of cables
2 Protection of feeders 2 Protection of feeders
n
k
1
2
=
NOTE 1 These factors are applicable to uniform groups of cables, equally loaded.
NOTE 2 Where horizontal clearances between adjacent cables exceeds twice their overall diameter, no reduction
factor need be applied.
NOTE 3 The same factors are applied to:
– groups of two or three single-core cables;
– multi-core cables.
NOTE 4 If a system consists of both two- and three-core cables, the total number of cables is taken as the number of
circuits, and the corresponding factor is applied to the tables for two loaded conductors for the two-core
cables, and to the tables for three loaded conductors for the three-core cables.
NOTE 5 If a group consists of n single-core cables it may either be considered as n/2 circuits of two loaded
conductors or n/3 circuits of three loaded conductors.
Number of circuits or multi-core cables
Item
1
2
3
4
5
Arrangement
(cables touching)
Bunched in air, on a
surface, embedded or
enclosed
Single layer on wall,
floor or unperforated
tray
Single layer fixed
directly under a
wooden ceiling
Single layer on a
perforated horizontal or
vertical tray
Single layer on ladder
support or cleats etc.
To be used with
current-carrying
capacities,
reference
Methods A to F
Method C
Methods E and F
1
1.00
1.00
0.95
1.00
1.00
2
0.80
0.85
0.81
0.88
0.87
3
0.70
0.79
0.72
0.82
0.82
4
0.65
0.75
0.68
0.77
0.80
5
0.60
0.73
0.66
0.75
0.80
6
0.57
0.72
0.64
0.73
0.79
7
0.54
0.72
0.63
0.73
0.79
8
0.52
0.71
0.62
0.72
0.78
9
0.50
0.70
0.61
0.72
0.78
12
0.45
16
0.41
20
0.38
No further
reduction
factor for more
than
nine circuits or
multicore cables
1
S
D
C
0
1
0
0
0
4
F
0
2
0
1
Number of three-phase
circuits (note 4)
Method of installation in Table 3
Number of
trays
1 2 3
Use as a
multiplier to
rating for
Perforated
trays
(note 2)
31
Touching
20 mm
1
2
3
0.98
0.96
0.95
0.91
0.87
0.85
0.87
0.81
0.78
Three cables in
horizontal
formation
Vertical
perforated
trays
(note 3)
31
Touching
225 mm
1
2
0.96
0.95
0.86
0.84
–
–
Three cables in
vertical
formation
Ladder
supports,
cleats, etc.
(note 2)
32
33
34
Touching
20 mm
1
2
3
1.00
0.98
0.97
0.97
0.93
0.90
0.96
0.89
0.86
Three cables in
horizontal
formation
Perforated
trays
(note 2)
31
20 mm
2D
e
D
e
1
2
3
1.00
0.97
0.96
0.98
0.93
0.92
0.96
0.89
0.86
Vertical
perforated
trays
(note 3)
31
Spaced
225 mm
1
2
1.00
1.00
0.91
0.90
0.89
0.86
Ladder
supports,
cleats, etc.
(note 2)
32
33
34
20 mm
1
2
3
1.00
0.97
0.96
1.00
0.95
0.94
1.00
0.93
0.90
Three cables in
trefoil formation
NOTE 1 Factors are given for single layers of cables (or trefoil groups) as shown in the table and do not apply
when cables are installed in more than one layer touching each other. Values for such installations may be
significantly lower and must be determined by an appropriate method.
NOTE 2 Values are given for vertical spacings between trays of 300 mm. For closer spacing the factors should be
reduced.
NOTE 3 Values are given for horizontal spacing between trays of 225 mm with trays mounted back to back and at
least 20 mm between the tray and any wall. For closer spacing the factors should be reduced.
NOTE 4 For circuits having more than one cable in parallel per phase, each three phase set of conductors should
be considered as a circuit for the purpose of this table.
D
e
D
e
D
e
≥2D
e
≥2D
e
≥2D
e
The reduction factor for a group containing different cross sections of insulated
conductors or cables in conduits, cable trunking or cable ducting is:
where:
• k
2
is the group reduction factor;
• n is the number of circuits of the bunch.
The reduction factor obtained by this equation reduces the danger of overloading
of cables with a smaller cross section, but may lead to under utilization of
cables with a larger cross section. Such under utilization can be avoided if large
and small cables are not mixed in the same group.
The following tables show the reduction factor (k
2
).
Table 5: Reduction factor for grouped cables
Table 6: Reduction factor for single-core cables with method of
installation F
37 36 ABB SACE - Electrical devices ABB SACE - Electrical devices
2.2 Installation and dimensioning of cables 2.2 Installation and dimensioning of cables
2 Protection of feeders 2 Protection of feeders
tot
b b
b
k
I
k k
I
I = =
2 1
'
1
S
D
C
0
1
0
0
0
5
F
0
2
0
1
Number of cables
Method of installation in Table 3
Number
of trays
1 2 3 4 6 9
Touching
20 mm
1
2
3
1.00
1.00
1.00
0.88
0.87
0.86
0.82
0.80
0.79
0.79
0.77
0.76
0.76
0.73
0.71
0.73
0.68
0.66
Perforated
trays
(note 2)
31
Spaced
20 mm
1
2
3
1.00
1.00
1.00
1.00
0.99
0.98
0.98
0.96
0.95
0.95
0.92
0.91
0.91
0.87
0.85
–
–
–
Touching
225 mm
1
2
1.00
1.00
0.88
0.88
0.82
0.81
0.78
0.76
0.73
0.71
0.72
0.70
Vertical
perforated
trays
(note 3)
31
Spaced
225 mm
De
1
2
1.00
1.00
0.91
0.91
0.89
0.88
0.88
0.87
0.87
0.85
–
–
Touching
20 mm
1
2
3
1.00
1.00
1.00
0.87
0,86
0.85
0.82
0.80
0.79
0.80
0.78
0.76
0.79
0.76
0.73
0.78
0.73
0.70
Ladder
supports,
cleats, etc.
(note 2)
32
33
34
Spaced
20 mm
D
e
1
2
3
1.00
1.00
1.00
1.00
0.99
0.98
1.00
0.98
0.97
1.00
0.97
0.96
1.00
0.96
0.93
–
–
–
NOTE 1 Factors apply to single layer groups of cables as shown above and do not apply when cables are installed in
more than one layer touching each other. Values for such installations may be significantly lower and must be
determined by an appropriate method.
NOTE 2 Values are given for vertical spacings between trays of 300 mm and at least 20 mm between trays and wall.
For closer spacing the factors should be reduced.
NOTE 3 Values are given for horizontal spacing between trays of 225 mm with trays mounted back to back. For closer
spacing the factors should be reduced.
D
e
D
e
D
e
To summarize:
The following procedure shall be used to determine the cross section
of the cable:
1. from Table 3 identify the method of installation;
2. from Table 4 determine the correction factor k
1
according to
insulation material and ambient temperature;
3. use Table 5 for cables installed in layer or bunch, Table 6 for single-
core cables in a layer on several supports, Table 7 for multi-core
cables in a layer on several supports or the formula shown in the
case of groups of cables with different sections to determine the
correction factor k
2
appropriate for the numbers of circuits or multi-
core cables;
4. calculate the value of current I’
b
by dividing the load current I
b
(or
the rated current of the protective device) by the product of the
correction factors calculated:
Table 7: Reduction factor for multi-core cables with method of
installation E
5. from Table 8 or from Table 9, depending on the method of installation, on
insulation and conductive material and on the number of live conductors,
determine the cross section of the cable with capacity I
0
≥ I’
b
;
6. the actual cable current carrying capacity is calculated by I
Z
= I
0
k
1
k
2
.
39 38 ABB SACE - Electrical devices ABB SACE - Electrical devices
2.2 Installation and dimensioning of cables 2.2 Installation and dimensioning of cables
2 Protection of feeders 2 Protection of feeders
1
S
D
C
0
1
0
0
0
6
F
0
2
0
1
Installation
method
Insulation
S[mm
2
]
Loaded
conductors
2 3 2 3 2 3 2 3 2 3 2 3 2 3 2 3 2 3
1.5 19 17 14.5 13.5 18.5 16.5 14 13.0 23 20
2.5 26 23 19.5 18 20 19 14.5 14 25 22 18.5 17.5 19.5 18 14.5 13.5 31 28
4 35 31 26 24 27 25 20 18.5 33 30 25 23 26 24 20 17.5 42 37
6 45 40 34 31 35 32 26 24 42 38 32 29 33 31 25 23 54 48
10 61 54 46 42 48 44 36 32 57 51 43 39 45 41 33 31 75 66
16 81 73 61 56 64 58 48 43 76 68 57 52 60 55 44 41 100 88
25 106 95 80 73 84 76 63 57 99 89 75 68 78 71 58 53 133 117
35 131 117 99 89 103 94 77 70 121 109 92 83 96 87 71 65 164 144
50 158 141 119 108 125 113 93 84 145 130 110 99 115 104 86 78 198 175
70 200 179 151 136 158 142 118 107 183 164 139 125 145 131 108 98 253 222
95 241 216 182 164 191 171 142 129 220 197 167 150 175 157 130 118 306 269
120 278 249 210 188 220 197 164 149 253 227 192 172 201 180 150 135 354 312
150 318 285 240 216 253 226 189 170 290 259 219 196 230 206 172 155
185 362 324 273 245 288 256 215 194 329 295 248 223 262 233 195 176
240 424 380 321 286 338 300 252 227 386 346 291 261 307 273 229 207
300 486 435 367 328 387 344 289 261 442 396 334 298 352 313 263 237
400
500
630
A1
Al
PVC
XLPE
EPR PVC
Cu
XLPE
EPR
A2
Cu Al
XLPE
EPR PVC
XLPE
EPR PVC
XLPE
EPR
Cu
2 3 2 3 2 3 2 3 2 3 2 3 2 3 2 3 2 3 2 3 2 3
17.5 15.5 22 19.5 16.5 15 24 22 19.5 17.5
24 21 25 22 18.5 16.5 30 26 23 20 23 21 17.5 15.5 33 30 27 24 26 24 21 18.5
32 28 33 29 25 22.0 40 35 30 27 31 28 24 21 45 40 36 32 35 32 28 25.0
41 36 43 38 32 28 51 44 38 34 40 35 30 27.0 58 52 46 41 45 41 36 32
57 50 59 52 44 39 69 60 52 46 54 48 41 36 80 71 63 57 62 57 49 44
76 68 79 71 60 53 91 80 69 62 72 64 54 48 107 96 85 76 84 76 66 59
101 89 105 93 79 70 119 105 90 80 94 84 71 62 138 119 112 96 101 90 83 73
125 110 130 116 97 86 146 128 111 99 115 103 86 77 171 147 138 119 126 112 103 90
151 134 157 140 118 104 175 154 133 118 138 124 104 92 209 179 168 144 154 136 125 110
192 171 200 179 150 133 221 194 168 149 175 156 131 116 269 229 213 184 198 174 160 140
232 207 242 217 181 161 265 233 201 179 210 188 157 139 328 278 258 223 241 211 195 170
269 239 281 251 210 186 305 268 232 206 242 216 181 160 382 322 299 259 280 245 226 197
441 371 344 299 324 283 261 227
506 424 392 341 371 323 298 259
599 500 461 403 439 382 352 305
693 576 530 464 508 440 406 351
Cu Al
XLPE
EPR PVC
XLPE
EPR PVC
B1
Al
PVC
XLPE
EPR PVC
C
Cu Al
XLPE
EPR PVC XLPE/EPR PVC
B2
Conductor
13
25
Table 8: Current carrying capacity of cables with PVC or EPR/XLPE
insulation (method A-B-C)
41 40 ABB SACE - Electrical devices ABB SACE - Electrical devices
2.2 Installation and dimensioning of cables 2.2 Installation and dimensioning of cables
2 Protection of feeders 2 Protection of feeders
Table 8: Current carrying capacity of cables with PVC or EPR/XLPE
insulation (method E-F-G)
C
1
S
D
C
0
1
0
1
0
0
F
0
2
0
1
D
e
D
e
or or
Installation
method
Insulation
XLPE
EPR
PVC
XLPE
EPR
PVC
XLPE
EPR
PVC
XLPE
EPR
PVC
XLPE
EPR
PVC
XLPE
EPR
PVC
XLPE
EPR
PVC
XLPE
EPR
PVC
S[mm
2
]
Loaded
conductors
1.5 26 22 23 18.5
2.5 36 30 28 23 32 2 5 24 19.5
4 49 40 38 31 42 34 32 26
6 63 51 49 39 54 43 42 33
10 86 70 67 54 75 60 58 46
16 115 94 91 73 100 80 77 61
25 149 119 108 89 127 101 97 78 161 131 121 98 13 5 110 103 84
35 185 148 135 111 158 126 120 96 200 162 150 122 169 137 129 105
50 225 180 164 135 192 153 146 117 242 196 184 149 207 167 159 128
70 289 232 211 173 246 196 187 150 310 251 237 192 268 216 206 166
95 352 282 257 210 298 238 227 183 377 304 289 235 328 264 253 203
120 410 328 300 244 346 276 263 212 437 352 337 273 383 308 296 237
150 473 379 346 282 399 319 304 245 504 406 389 316 444 356 343 274
185 542 434 397 322 456 364 347 280 575 463 447 363 510 409 395 315
240 641 514 470 380 538 430 409 330 679 546 530 430 607 485 471 375
300 741 593 543 439 621 497 471 381 783 629 613 497 703 561 547 434
400 940 754 740 600 823 656 663 526
500 1083 868 856 694 946 749 770 610
630 1254 1005 996 808 1088 855 899 711
F
Cu Al Cu Al
E
2 3
Al Cu Al
2 3
Cu
XLPE
EPR
PVC
XLPE
EPR
PVC
3H 3V 3H 3V 3H 3V 3H 3V
141 114 107 87 182 161 146 130 138 122 112 99
176 143 135 109 226 201 181 162 172 153 139 124
216 174 165 133 275 246 219 197 210 188 169 152
279 225 215 173 353 318 281 254 271 244 217 196
342 275 264 212 430 389 341 311 332 300 265 241
400 321 308 247 500 454 396 362 387 351 308 282
464 372 358 287 577 527 456 419 448 408 356 327
533 427 413 330 661 605 521 480 515 470 407 376
634 507 492 392 781 719 615 569 611 561 482 447
736 587 571 455 902 833 709 659 708 652 557 519
868 689 694 552 1085 1008 852 795 856 792 671 629
998 789 806 640 1253 1169 982 920 991 921 775 730
1151 905 942 746 1454 1362 1138 1070 1154 1077 900 852
G
3
Cu Al
PVC
Al
XLPE
EPR
PVC
Cu
XLPE
EPR
43 42 ABB SACE - Electrical devices ABB SACE - Electrical devices
2.2 Installation and dimensioning of cables 2.2 Installation and dimensioning of cables
2 Protection of feeders 2 Protection of feeders
1
S
D
C
0
1
0
0
0
7
F
0
2
0
1
Installation
method
Loaded
conductors
2 3 3 2 3 3 2 3 3 2
23 19 21 28 24 27 25 21 23 31
31 26 29 38 33 36 33 28 31 41
40 35 38 51 44 47 44 37 41 54
25 21 23 31 26 30 26 22 26 33
34 28 31 42 35 41 36 30 34 45
45 37 41 55 47 53 47 40 45 60
57 48 52 70 59 67 60 51 57 76
77 65 70 96 81 91 82 69 77 104
102 86 92 127 107 119 109 92 102 137
133 112 120 166 140 154 142 120 132 179
163 137 147 203 171 187 174 147 161 220
202 169 181 251 212 230 215 182 198 272
247 207 221 307 260 280 264 223 241 333
296 249 264 369 312 334 317 267 289 400
340 286 303 424 359 383 364 308 331 460
388 327 346 485 410 435 416 352 377 526
440 371 392 550 465 492 472 399 426 596
514 434 457 643 544 572 552 466 496 697
Note 1 For single-core cables the sheaths of the cables of the circuit are connected together at both ends.
Note 2 For bare cables exposed to touch, values should be multiplied by 0.9.
Note 3 D
e
is the external diameter of the cable.
Note 4 For metallic sheath temperature 105 °C no correction for grouping need to be applied.
500 V
750 V
C E or F
120
150
185
240
35
50
70
95
6
10
16
25
4
1.5
2.5
4
1.5
2.5
Bare cable not
exposed to touch
S[mm
2
]
PVC covered or
bare exposed to touch
PVC covered or
bare exposed to touch
Metallic sheath temperature 105 °C Metallic sheath temperature 70 °C Metallic sheath temperature 105 °C
Sheath
3 3 3 3 3 3
26 29 26 29 33.0 37.0
35 39 34 39 43 49
46 51 45 51 56 64
28 32 28 32 35 40
38 43 37 43 47 54
50 56 49 56 61 70
64 71 62 71 78 89
87 96 84 95 105 120
115 127 110 125 137 157
150 164 142 162 178 204
184 200 173 197 216 248
228 247 213 242 266 304
279 300 259 294 323 370
335 359 309 351 385 441
385 411 353 402 441 505
441 469 400 454 498 565
500 530 446 507 557 629
584 617 497 565 624 704
G
Metallic sheath temperature 70 °C
PVC covered or
bare exposed to touch
Bare cable not
exposed to touch
Bare cable not
e exposed to touch
Metallic sheath temperature 70 °C Metallic sheath temperature 105 °C
or or or or or or
D
e
D
e
D
e
D
e
33 37
Table 9: Current carrying capacity of cables with mineral insulation
45 44 ABB SACE - Electrical devices ABB SACE - Electrical devices
2.2 Installation and dimensioning of cables 2.2 Installation and dimensioning of cables
2 Protection of feeders 2 Protection of feeders
tot z
k I k k k I I
0 3 2 1 0
= =
' ' '
2 2
k k k
.
=
2
a a
a a
Table 10: Correction factors for ambient ground temperatures other
than 20 °C
Ground
temperature
°C
10
15
25
30
35
40
45
50
55
60
65
70
75
80
PVC
1.10
1.05
0.95
0.89
0.84
0.77
0.71
0.63
0.55
0.45
–
–
–
–
XLPE and EPR
1.07
1.04
0.96
0.93
0.89
0.85
0.80
0.76
0.71
0.65
0.60
0.53
0.46
0.38
Insulation
Table 11: Reduction factors for cables laid directly in the ground
Number
of circuits
2
3
4
5
6
Nil (cables
touching)
0.75
0.65
0.60
0.55
0.50
One cable
diameter
0.80
0.70
0.60
0.55
0.55
0.125 m
0.85
0.75
0.70
0.65
0.60
0.25 m
0.90
0.80
0.75
0.70
0.70
0.5 m
0.90
0.85
0.80
0.80
0.80
Cable to cable clearance (a)
NOTE The given values apply to an installation depth of 0.7 m and a soil thermal resistivity of 2.5 Km/W.
Multi-core cables
Single-core cables
Installation in ground: choice of the cross section according
to cable carrying capacity and type of installation
The current carrying capacity of a cable buried in the ground is calculated by
using this formula:
where:
• I
0
is the current carrying capacity of the single conductor for installation in the
ground at 20°C reference temperature;
• k
1
is the correction factor if the temperature of the ground is other than 20°C;
• k
2
is the correction factor for adjacent cables;
• k
3
is the correction factor if the soil thermal resistivity is different from the
reference value, 2.5 Km/W.
Correction factor k
1
The current carrying capacity of buried cables refers to a ground temperature
of 20 °C. If the ground temperature is different, use the correction factor k
1
shown in Table 10 according to the insulation material.
Correction factor k
2
The cable current carrying capacity is influenced by the presence of other cables
installed nearby. The heat dissipation of a single cable is different from that of
the same cable installed next to the other ones.
The correction factor k
2
is obtained by the formula:
Tables 11, 12, and 13 show the factor k
2
’ values for single-core and multi-core
cables that are laid directly in the ground or which are installed in buried ducts,
according to their distance from other cables or the distance between the ducts.
47 46 ABB SACE - Electrical devices ABB SACE - Electrical devices
2.2 Installation and dimensioning of cables 2.2 Installation and dimensioning of cables
2 Protection of feeders 2 Protection of feeders
a
a a
Table 12: Reduction factors for multi-core cables laid in single way
ducts in the ground
Number
of circuits
2
3
4
5
6
Nil (cables
touching)
0.85
0.75
0.70
0.65
0.60
0.25 m
0.90
0.85
0.80
0.80
0.80
0.5 m
0.95
0.90
0.85
0.85
0.80
1.0 m
0.95
0.95
0.90
0.90
0.90
Cable to cable clearance (a)
NOTE The given values apply to an installation depth of 0.7 m and a soil thermal resistivity of 2.5 Km/W.
Multi-core cables
Number of single-core
circuits of
two or three cables
2
3
4
5
6
Nil (ducts
touching)
0.80
0.70
0.65
0.60
0.60
0.25 m
0.90
0.80
0.75
0.70
0.70
0.5 m
0.90
0.85
0.80
0.80
0.80
1.0 m
0.95
0.90
0.90
0.90
0.90
Duct to duct clearance (a)
NOTE The given values apply to an installation depth of 0.7 m and a soil thermal resistivity of 2.5 Km/W.
Single-core cables
Table 13: Reduction factors for single-core cables laid in single way
ducts in the ground
Table 14: Correction factors for soil thermal resistivities other than
2.5 Km/W
Thermal resistivities Km/W 1 1.5 2 2.5 3
Correction factor 1.18 1.1 1.05 1 0.96
Note 1: the overall accuracy of correction factors is within ±5%.
Note 2: the correction factors are applicable to cables drawn into buried ducts; for cables
laid direct in the ground the correction factors for thermal resistivities less than 2.5 Km/W
will be higher. Where more precise values are required they may be calculated by methods
given in IEC 60287.
Note 3: the correction factors are applicable to ducts buried at depths of up to 0.8 m.
For correction factor k
2
’’:
• for cables laid directly in the ground or if there are not other conductors within
the same duct, the value of k
2
’’ is 1;
• if several conductors of similar sizes are present in the same duct (for the
meaning of “group of similar conductors”, see the paragraphs above), k
2
’’ is
obtained from the first row of Table 5;
• if the conductors are not of similar size, the correction factor is calculated by
using this formula:
where:
n is the number of circuits in the duct.
Correction factor k
3
Soil thermal resistivity influences the heat dissipation of the cable. Soil with low
thermal resistivity facilitates heat dissipation, whereas soil with high thermal
resistivity limits heat dissipation. IEC 60364-5-52 states as reference value for
the soil thermal resistivity 2.5 Km/W.
n
k
1
' '
2
=
49 48 ABB SACE - Electrical devices ABB SACE - Electrical devices
2.2 Installation and dimensioning of cables 2.2 Installation and dimensioning of cables
2 Protection of feeders 2 Protection of feeders
tot
b b
b
k
I
k k k
I
I = =
3 2 1
'
1
S
D
C
0
1
0
0
0
8
F
0
2
0
1
Installation
method
Insulation
S[mm
2
]
Loaded
conductors
2 3 2 3 2 3 2 3
1.5 26 22 22 18
2.5 34 29 29 24 26 22 22 18.5
4 44 37 38 31 34 29 29 24
6 56 46 47 39 42 36 36 30
10 73 61 63 52 56 47 48 40
16 95 79 81 67 73 61 62 52
25 121 101 104 86 93 78 80 66
35 146 122 125 103 112 94 96 80
50 173 144 148 122 132 112 113 94
70 213 178 183 151 163 138 140 117
95 252 211 216 179 193 164 166 138
120 287 240 246 203 220 186 189 157
150 324 271 278 230 249 210 213 178
185 363 304 312 258 279 236 240 200
240 419 351 361 297 322 272 277 230
300 474 396 408 336 364 308 313 260
XLPE
EPR
PVC
XLPE
EPR
PVC
D
Cu Al Conductor
k1 fromtable 4
1
S
D
C
0
1
0
0
0
9
F
0
2
0
1
START
END
yes
D method?
yes
no
yes
multi-core cable?
no
no
yes
single layer? multi-core cable?
no
yes
yes
no
no
for cables?
yes
no
yes
yes
no
yes
yes
no
no
yes
selection of wiring systems table 1
erection of wiring systems table 2
Ground temperature
<>
20 °C?
Ambient air temperature
<>
30 °C?
k1 = 1
k1 from table 10
k2' fromtable 11
(k 2''=1)
cables laid directly
in the ground?
k2' fromtable 13 k2' from table 12
more than one
cable per conduit?
similar
sections?
n
k
1
' '
2
=
k2'' fromtable 6
k2''=1
k1 = 1
similar
sections?
k2 fromtable 5 k2 fromtable 6
ktot =k 1*k 2
I'b=I b/ktot
table current carrying capacity
I0 > I' b
ktot =k 1*k 2*k 3
S [mm
2
]
Iz = I 0 *k tot
Thermal resistivity
<> 2.5 Km/W?
k3 = 1
k3 from table 14
k2=k 2'*k 2''
k2 fromtable 7
I
Method of installation table 3
b
n
k
1
' '
2
=
no
k2 = 1
To summarize:
Use this procedure to determine the cross section of the cable:
1. from Table 10, determine the correction factor k
1
according to the insulation
material and the ground temperature;
2. use Table 11, Table 12, Table 13 or the formula for groups of non-similar
cables to determine the correction factor k
2
according to the distance
between cables or ducts;
3. from Table 14 determine factor k
3
corresponding to the soil thermal resistivity;
4. calculate the value of the current I’
b
by dividing the load current I
b
(or the
rated current of the protective device) by the product of the correction factors
calculated:
5. from Table 15, determine the cross section of the cable with I
0
≥ I’
b
, according
to the method of installation, the insulation and conductive material and the
number of live conductors;
6. the actual cable current carrying capacity is calculated by.
Table 15: Current carrying capacity of cables buried in the ground
z
k k I I
2 1 0
= k
3
51 50 ABB SACE - Electrical devices ABB SACE - Electrical devices
2.2 Installation and dimensioning of cables 2.2 Installation and dimensioning of cables
2 Protection of feeders 2 Protection of feeders
1
S
D
C
0
1
0
0
0
7
F
0
0
0
1
C
N
B
A
tot
b
b
I
I =
'
k
86 . 0
'
.
=
tot
b
b
k
I
I
'
N
b
I
I =
0.86
N b
I I =
'
III
tot
b
N k
k
I
I . .
= 3
Effect of harmonic currents on balanced three-phase
systems: reduction factors for harmonic currents in four-
core and five-core cables with four cores carrying current
Where the neutral conductor carries current without a corresponding reduction
in load of the phase conductors, the current flowing in the neutral conductor
shall be taken into account in ascertaining the current-carrying capacity of the
circuit.
This neutral current is due to the phase currents having a harmonic content
which does not cancel in the neutral. The most significant harmonic which
does not cancel in the neutral is usually the third harmonic. The magnitude of
the neutral current due to the third harmonic may exceed the magnitude of the
power frequency phase current. In such a case the neutral current will have a
significant effect on the current-carrying capacity of the cables in the circuit.
Equipment likely to cause significant harmonic currents are, for example,
fluorescent lighting banks and dc power supplies such as those found in
computers (for further information on harmonic disturbances see the IEC 61000).
The reduction factors given in Table 16 only apply in the balanced three-phase
circuits (the current in the fourth conductor is due to harmonics only) to cables
where the neutral conductor is within a four-core or five-core cable and is of the
same material and cross-sectional area as the phase conductors. These
reduction factors have been calculated based on third harmonic currents. If
significant, i.e. more than 10 %, higher harmonics (e.g. 9th, 12th, etc.) are
expected or there is an unbalance between phases of more than 50 %, then
lower reduction factors may be applicable: these factors can be calculated only
by taking into account the real shape of the current in the loaded phases.
Where the neutral current is expected to be higher than the phase current then
the cable size should be selected on the basis of the neutral current.
Where the cable size selection is based on a neutral current which is not
significantly higher than the phase current, it is necessary to reduce the tabulated
current carrying capacity for three loaded conductors.
If the neutral current is more than 135 % of the phase current and the cable size
is selected on the basis of the neutral current, then the three phase conductors
will not be fully loaded. The reduction in heat generated by the phase conductors
offsets the heat generated by the neutral conductor to the extent that it is not
necessary to apply any reduction factor to the current carrying capacity for
three loaded conductors.
Table 16: Reduction factors for harmonic currents in four-core and
five-core cables
Third harmonic content
of phase current
%
0 ÷ 15
15 ÷ 33
33 ÷ 45
> 45
Size selection is
based on phase
current
1
0.86
-
-
Current to take in
account for the
cable selection
I
b
’
-
-
Size selection is
based on neutral
current
-
-
0.86
1
Current to take in
account for the
cable selection
I
b
’
-
-
Reduction factor
Where I
N
is the current flowing in the neutral calculated as follows:
I
b
is the load current;
k
tot
is the total correction factor;
k
III
is the third harmonic content of phase current;
Note on current carrying capacity tables and loaded conductors
Tables 8, 9 and 15 provide the current carrying capacity of loaded conductors
(current carrying conductors) under normal service conditions.
In single-phase circuits, the number of loaded conductors is two.
In balanced or slightly unbalanced three-phase circuits the number of loaded
conductors is three, since the current in the neutral conductor is negligible.
In three-phase systems with high unbalance, where the neutral conductor in a
multi-core cable carries current as a result of an unbalance in the phase currents
the temperature rise due to the neutral current is offset by the reduction in the
heat generated by one or more of the phase conductors. In this case the
conductor size shall be chosen on the basis of the highest phase current. In all
cases the neutral conductor shall have an adequate cross section.
53 52 ABB SACE - Electrical devices ABB SACE - Electrical devices
2.2 Installation and dimensioning of cables 2.2 Installation and dimensioning of cables
2 Protection of feeders 2 Protection of feeders
a
d
b
c
1
S
D
C
0
1
0
0
0
8
F
0
0
0
1
k
1
= 0.87
A
k k
I
I
b
b
212.85
54 . 0 87 . 0
100
2 1
'
=
.
= =
2
= 0.54 k
Procedure:
Type of installation
In Table 3, it is possible to find the reference number of the installation and the
method of installation to be used for the calculations. In this example, the
reference number is 31, which corresponds to method E (multi-core cable on
tray).
Correction factor of temperature k
1
From Table 4, for a temperature of 40 °C and PVC insulation material, k
1
=
0.87.
Correction factor for adjacent cables k
2
For the multi-core cables grouped on the perforated tray see Table 5.
As a first step, the number of circuits or multi-core cables present shall be
determined; given that:
• each circuit a), b) and d) constitute a separate circuit;
• circuit c) consists of three circuits, since it is composed by three cables in
parallel per phase;
• the cable to be dimensioned is a multi-core cable and therefore constitutes a
single circuit;
the total number of circuits is 7.
Referring to the row for the arrangement (cables bunched) and to the column
for the number of circuits (7)
After k
1
and k
2
have been determined, I’
b
is calculated by:
From Table 8, for a multi-core copper cable with PVC insulation, method of
installation E, with three loaded conductors, a cross section with current carrying
capacity of I
0
≥ I’
b
= 212.85 A, is obtained. A 95 mm
2
cross section cable can
carry, under Standard reference conditions, 238 A.
The current carrying capacity, according to the actual conditions of installation,
is I
z
= 238
.
0.87
.
0.54 = 111.81 A
Example of cable dimensioning in a balanced three-
phase circuit without harmonics
Dimensioning of a cable with the following characteristics:
• conductor material: : copper
• insulation material: : PVC
• type of cable: : multi-core
• installation: : cables bunched on horizontal
perforated tray
• load current: : 100 A
Installation conditions:
• ambient temperature: : 40 °C
• adjacent circuits with a) three-phase circuit consisting of 4
single-core cables, 4x50 mm
2
;
b) three-phase circuit consisting of one
multi-core cable, 1x(3x50) mm
2
;
c) three-phase circuit consisting of 9
single-core (3 per phase) cables,
9x95 mm
2
;
d) single-phase circuit consisting of 2
single-core cables, 2x70 mm
2
.
55 54 ABB SACE - Electrical devices ABB SACE - Electrical devices
2.2 Installation and dimensioning of cables 2.2 Installation and dimensioning of cables
2 Protection of feeders 2 Protection of feeders
k
1
= 1
2
= 1 k
A
k k
I
I
b
b
115
2 1
'
= =
A
k k
I
I
b
b
7 . 133
86 . 0
115
86 . 0
2 1
'
= =
. .
=
A k
k
I
I
III
tot
b
N
138 4 . 0 3 115 3 =
. .
=
. .
=
A
I
I
N
b
5 . 160
86 . 0
138
86 . 0
'
= = =
A k
k
I
I
III
tot
b
N
207 6 . 0 3 115 3 =
. .
=
. .
=
A I I
N b
207
'
= =
and current I’
b
is:
From Table 8, a 95 mm
2
cable with current carrying capacity of 238 A must be
selected.
Example of dimensioning a cable in a balanced three-
phase circuit with a significant third-harmonic content
Dimensioning of a cable with the following characteristics:
• conductor material: : copper
• insulation material: : PVC
• type of cable: : multi-core
• installation: : layer on horizontal perforated tray
• load current: : 115 A
Installation conditions:
• ambient temperature: : 30 °C
• no adjacent circuits.
Procedure:
Type of installation
On Table 3, it is possible to find the reference number of the installation and the
method of installation to be used for the calculations. In this example, the
reference number is 31, which corresponds to method E (multi-core cable on
tray).
Temperature correction factor k
1
From Table 4, for a temperature of 30 °C and PVC insulation material
Correction factor for adjacent cables k
2
As there are no adjacent cables, so
After k
1
and k
2
have been determined, I’
b
is calculated by:
If no harmonics are present, from Table 8, for a multi-core copper cable with
PVC insulation, method of installation E, with three loaded conductors, a cross
section with current carrying capacity of I
0
≥ I’
b
= 115 A, is obtained. A 35 mm
2
cross section cable can carry, under Standard reference conditions, 126 A.
The current carrying capacity, according to the actual conditions of installation,
is still 126 A, since the value of factors k
1
and k
2
is 1.
The third harmonic content is assumed to be 28%.
Table 16 shows that for a third harmonic content of 28% the cable must be
dimensioned for the current that flows through the phase conductors, but a
reduction factor of 0.86 must be applied. The current I’
b
becomes:
From Table 8, a 50 mm
2
cable with carrying capacity of 153 A shall be selected.
If the third harmonic content is 40 %, Table 16 shows that the cable shall be
dimensioned according to the current of the neutral conductor and a reduction
factor of 0.86 must be applied.
The current in the neutral conductor is:
and the value of current I’
b
is:
From Table 8, a 70 mm
2
cable with 196 A current carrying capacity shall be
selected.
If the third harmonic content is 60 %, Table 16 shows that the cable shall be
dimensioned according to the current of the neutral conductor, but a reduction
factor of 1 must be applied.
The current in the neutral conductor is:
57 56 ABB SACE - Electrical devices ABB SACE - Electrical devices
2.2 Installation and dimensioning of cables 2.2 Installation and dimensioning of cables
2 Protection of feeders 2 Protection of feeders
) sin cos ( x r
n
L
kI kZI U
b b
+ = = ∆ [V] (1)
2
cos 1 sin =
.
-
100 %
r
U
U
u
∆
= ∆
(2)
2.2.2 Voltage drop
In an electrical installation it is important to evaluate voltage drops from the
point of supply to the load.
The performance of a device may be impaired if supplied with a voltage different
from its rated voltage. For example:
• motors: the torque is proportional to the square of the supply voltage; therefore,
if the voltage drops, the starting torque shall also decrease, making it more
difficult to start up motors; the maximum torque shall also decrease;
• incandescent lamps: the more the voltage drops the weaker the beam
becomes and the light takes on a reddish tone;
• discharge lamps: in general, they are not very sensitive to small variations in
voltage, but in certain cases, great variation may cause them to switch off;
• electronic appliances: they are very sensitive to variations in voltage and that
is why they are fitted with stabilizers;
• electromechanical devices: the reference Standard states that devices such
as contactors and auxiliary releases have a minimum voltage below which
their performances cannot be guaranteed. For a contactor, for example, the
holding of the contacts becomes unreliable below 85% of the rated voltage.
To limit these problems the Standards set the following limits:
• IEC 60364-5-52 “Electrical installations of buildings. Selection and erection
of electrical equipment - Wiring systems” Clause 525 states that “in the
absence of other considerations it is recommended that in practice the voltage
drop between the origin of consumer’s installation and the equipment should
not be greater than 4% of the rated voltage of the installation. Other
considerations include start-up time for motors and equipment with high inrush
current. Temporary conditions such as voltage transients and voltage variation
due to abnormal operation may be disregarded”.
• IEC 60204-1”Safety of machinery – Electrical equipment of machines – General
requirements” Clause 13.5 recommends that: “the voltage drop from the
point of supply to the load shall not exceed 5% of the rated voltage under
normal operating conditions”.
• IEC 60364-7-714 “Electrical installations of buildings - Requirements for special
installations or locations - External lighting installations” Clause 714.512
requires that “the voltage drop in normal service shall be compatible with the
conditions arising from the starting current of the lamps”.
Voltage drop calculation
For an electrical conductor with impedance Z, the voltage drop is calculated by
the following formula:
where
• k is a coefficient equal to:
- 2 for single-phase and two-phase systems;
- for three-phase systems;
• I
b
[A] is the load current; if no information are available, the cable carrying
capacity I
z
shall be considered;
• L [km] is the length of the conductor;
• n is the number of conductors in parallel per phase;
• r [Ω/km] is the resistance of the single cable per kilometre;
• x [Ω/km] is the reactance of the single cable per kilometre;
• cosϕ is the power factor of the load:
Normally, the percentage value in relation to the rated value U
r
is calculated by:
Resistance and reactance values per unit of length are set out on the following
table by cross-sectional area and cable formation, for 50 Hz; in case of 60 Hz,
the reactance value shall be multiplied by 1.2.
59 58 ABB SACE - Electrical devices ABB SACE - Electrical devices
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2 Protection of feeders 2 Protection of feeders
Table 1: Resistance and reactance per unit of length of copper cables
single-core cable two-core/three-core cable
S r[Ω/km] x[Ω/km] r[Ω/km] x[Ω/km]
[mm
2
] @ 80 [°C] @ 80 [°C]
1.5 14.8 0.168 15.1 0.118
2.5 8.91 0.156 9.08 0.109
4 5.57 0.143 5.68 0.101
6 3.71 0.135 3.78 0.0955
10 2.24 0.119 2.27 0.0861
16 1.41 0.112 1.43 0.0817
25 0.889 0.106 0.907 0.0813
35 0.641 0.101 0.654 0.0783
50 0.473 0.101 0.483 0.0779
70 0.328 0.0965 0.334 0.0751
95 0.236 0.0975 0.241 0.0762
120 0.188 0.0939 0.191 0.074
150 0.153 0.0928 0.157 0.0745
185 0.123 0.0908 0.125 0.0742
240 0.0943 0.0902 0.0966 0.0752
300 0.0761 0.0895 0.078 0.075
Table 2: Resistance and reactance per unit of length of aluminium
cables
single-core cable two-core/three-core cable
S r[Ω/km] x[Ω/km] r[Ω/km] x[Ω/km]
[mm
2
] @ 80 [°C] @ 80 [°C]
1.5 24.384 0.168 24.878 0.118
2.5 14.680 0.156 14.960 0.109
4 9.177 0.143 9.358 0.101
6 6.112 0.135 6.228 0.0955
10 3.691 0.119 3.740 0.0861
16 2.323 0.112 2.356 0.0817
25 1.465 0.106 1.494 0.0813
35 1.056 0.101 1.077 0.0783
50 0.779 0.101 0.796 0.0779
70 0.540 0.0965 0.550 0.0751
95 0.389 0.0975 0.397 0.0762
120 0,310 0.0939 0.315 0.074
150 0.252 0.0928 0.259 0.0745
185 0.203 0.0908 0.206 0.0742
240 0.155 0.0902 0.159 0.0752
300 0.125 0.0895 0.129 0.075
The following tables show the ∆U
x
[V/(A
.
km)] values by cross section and
formation of the cable according to the most common cosϕ values.
Table 3: Specific voltage drop at cosϕ = 1 for copper cables
cosϕ = 1
single-core cable two-core cable three-core cable
S[mm
2
] single-phase three-phase single-phase three-phase
1.5 29.60 25.63 30.20 26.15
2.5 17.82 15.43 18.16 15.73
4 11.14 9.65 11.36 9.84
6 7.42 6.43 7.56 6.55
10 4.48 3.88 4.54 3.93
16 2.82 2.44 2.86 2.48
25 1.78 1.54 1.81 1.57
35 1.28 1.11 1.31 1.13
50 0.95 0.82 0.97 0.84
70 0.66 0.57 0.67 0.58
95 0.47 0.41 0.48 0.42
120 0.38 0.33 0.38 0.33
150 0.31 0.27 0.31 0.27
185 0.25 0.21 0.25 0.22
240 0.19 0.16 0.19 0.17
300 0.15 0.13 0.16 0.14
Table 4: Specific voltage drop at cosϕ = 0.9 for copper cables
cosϕ = 0.9
single-core cable two-core cable three-core cable
S[mm
2
] single-phase three-phase single-phase three-phase
1.5 26.79 23.20 27.28 23.63
2.5 16.17 14.01 16.44 14.24
4 10.15 8.79 10.31 8.93
6 6.80 5.89 6.89 5.96
10 4.14 3.58 4.16 3.60
16 2.64 2.28 2.65 2.29
25 1.69 1.47 1.70 1.48
35 1.24 1.08 1.25 1.08
50 0.94 0.81 0.94 0.81
70 0.67 0.58 0.67 0.58
95 0.51 0.44 0.50 0.43
120 0.42 0.36 0.41 0.35
150 0.36 0.31 0.35 0.30
185 0.30 0.26 0.29 0.25
240 0.25 0.22 0.24 0.21
300 0.22 0.19 0.21 0.18
61 60 ABB SACE - Electrical devices ABB SACE - Electrical devices
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2 Protection of feeders 2 Protection of feeders
Table 5: Specific voltage drop at cosϕ = 0.85 for copper cables
cosϕ = 0.85
single-core cable two-core cable three-core cable
S[mm
2
] single-phase three-phase single-phase three-phase
1.5 25.34 21.94 25.79 22.34
2.5 15.31 13.26 15.55 13.47
4 9.62 8.33 9.76 8.45
6 6.45 5.59 6.53 5.65
10 3.93 3.41 3.95 3.42
16 2.51 2.18 2.52 2.18
25 1.62 1.41 1.63 1.41
35 1.20 1.04 1.19 1.03
50 0.91 0.79 0.90 0.78
70 0.66 0.57 0.65 0.56
95 0.50 0.44 0.49 0.42
120 0.42 0.36 0.40 0.35
150 0.36 0.31 0.35 0.30
185 0.30 0.26 0.29 0.25
240 0.26 0.22 0.24 0.21
300 0.22 0.19 0.21 0.18
Table 6: Specific voltage drop at cosϕ = 0.8 for copper cables
cosϕ = 0.8
single-core cable two-core cable three-core cable
S[mm
2
] single-phase three-phase single-phase three-phase
1.5 23.88 20.68 24.30 21.05
2.5 14.44 12.51 14.66 12.69
4 9.08 7.87 9.21 7.98
6 6.10 5.28 6.16 5.34
10 3.73 3.23 3.74 3.23
16 2.39 2.07 2.39 2.07
25 1.55 1.34 1.55 1.34
35 1.15 0.99 1.14 0.99
50 0.88 0.76 0.87 0.75
70 0.64 0.55 0.62 0.54
95 0.49 0.43 0.48 0.41
120 0.41 0.36 0.39 0.34
150 0.36 0.31 0.34 0.29
185 0.31 0.26 0.29 0.25
240 0.26 0.22 0.24 0.21
300 0.23 0.20 0.21 0.19
Table 7: Specific voltage drop at cosϕ=0.75 for copper cables
cosϕ = 0.75
single-core cable two-core cable three-core cable
S[mm
2
] single-phase three-phase single-phase three-phase
1.5 22.42 19.42 22.81 19.75
2.5 13.57 11.75 13.76 11.92
4 8.54 7.40 8.65 7.49
6 5.74 4.97 5.80 5.02
10 3.52 3.05 3.52 3.05
16 2.26 1.96 2.25 1.95
25 1.47 1.28 1.47 1.27
35 1.10 0.95 1.08 0.94
50 0.84 0.73 0.83 0.72
70 0.62 0.54 0.60 0.52
95 0.48 0.42 0.46 0.40
120 0.41 0.35 0.38 0.33
150 0.35 0.31 0.33 0.29
185 0.30 0.26 0.29 0.25
240 0.26 0.23 0.24 0.21
300 0.23 0.20 0.22 0.19
Table 8: Specific voltage drop at cosϕ = 1 for aluminium cables
cosϕ = 1
single-core cable two-core cable three-core cable
S[mm
2
] single-phase three-phase single-phase three-phase
1.5 48.77 42.23 49.76 43.09
2.5 29.36 25.43 29.92 25.91
4 18.35 15.89 18.72 16.21
6 12.22 10.59 12.46 10.79
10 7.38 6.39 7.48 6.48
16 4.65 4.02 4.71 4.08
25 2.93 2.54 2.99 2.59
35 2.11 1.83 2.15 1.87
50 1.56 1.35 1.59 1.38
70 1.08 0.94 1.10 0.95
95 0.78 0.67 0.79 0.69
120 0.62 0.54 0.63 0.55
150 0.50 0.44 0.52 0.45
185 0.41 0.35 0.41 0.36
240 0.31 0.27 0.32 0.28
300 0.25 0.22 0.26 0.22
63 62 ABB SACE - Electrical devices ABB SACE - Electrical devices
2.2 Installation and dimensioning of cables 2.2 Installation and dimensioning of cables
2 Protection of feeders 2 Protection of feeders
Table 9: Specific voltage drop at cosϕ = 0.9 for aluminium cables
cosϕ = 0.9
single-core cable two-core cable three-core cable
S[mm
2
] single-phase three-phase single-phase three-phase
1.5 44.04 38.14 44.88 38.87
2.5 26.56 23.00 27.02 23.40
4 16.64 14.41 16.93 14.66
6 11.12 9.63 11.29 9.78
10 6.75 5.84 6.81 5.89
16 4.28 3.71 4.31 3.73
25 2.73 2.36 2.76 2.39
35 1.99 1.72 2.01 1.74
50 1.49 1.29 1.50 1.30
70 1.06 0.92 1.06 0.91
95 0.78 0.68 0.78 0.68
120 0.64 0.55 0.63 0.55
150 0.53 0.46 0.53 0.46
185 0.44 0.38 0.44 0.38
240 0.36 0.31 0.35 0.30
300 0.30 0.26 0.30 0.26
Table 10: Specific voltage drop at cosϕ = 0.85 for aluminium cables
cosϕ = 0.85
single-core cable two-core cable three-core cable
S[mm
2
] single-phase three-phase single-phase three-phase
1.5 41.63 36.05 42.42 36.73
2.5 25.12 21.75 25.55 22.12
4 15.75 13.64 16.02 13.87
6 10.53 9.12 10.69 9.26
10 6.40 5.54 6.45 5.58
16 4.07 3.52 4.09 3.54
25 2.60 2.25 2.63 2.27
35 1.90 1.65 1.91 1.66
50 1.43 1.24 1.43 1.24
70 1.02 0.88 1.01 0.88
95 0.76 0.66 0.76 0.65
120 0.63 0.54 0.61 0.53
150 0.53 0.46 0.52 0.45
185 0.44 0.38 0,43 0.37
240 0.36 0.31 0.35 0.30
300 0.31 0.27 0.30 0.26
Table 11: Specific voltage drop at cosϕ = 0.8 for aluminium cables
cosϕ = 0.8
single-core cable two-core cable three-core cable
S[mm
2
] single-phase three-phase single-phase three-phase
1.5 39.22 33.96 39.95 34.59
2.5 23.67 20.50 24.07 20.84
4 14.85 12.86 15.09 13.07
6 9.94 8.61 10.08 8.73
10 6.05 5.24 6.09 5.27
16 3.85 3.34 3.87 3.35
25 2.47 2.14 2.49 2.16
35 1.81 1.57 1.82 1.57
50 1.37 1.18 1.37 1.18
70 0.98 0.85 0.97 0.84
95 0.74 0.64 0.73 0.63
120 0.61 0.53 0.59 0.51
150 0.51 0.45 0.50 0.44
185 0.43 0.38 0.42 0.36
240 0.36 0.31 0.34 0.30
300 0.31 0.27 0.30 0.26
Table 12: Specific voltage drop at cosϕ = 0.75 for aluminium cables
cosϕ = 0.75
single-core cable two-core cable three-core cable
S[mm
2
] single-phase three-phase single-phase three-phase
1.5 36.80 31.87 37.47 32.45
2.5 22.23 19.25 22.58 19.56
4 13.95 12.08 14.17 12.27
6 9.35 8.09 9.47 8.20
10 5.69 4.93 5.72 4.96
16 3.63 3.15 3.64 3.15
25 2.34 2.02 2.35 2.03
35 1.72 1.49 1.72 1.49
50 1.30 1.13 1.30 1.12
70 0.94 0.81 0.92 0.80
95 0.71 0.62 0.70 0.60
120 0.59 0.51 0.57 0.49
150 0.50 0.43 0.49 0.42
185 0.42 0.37 0.41 0.35
240 0.35 0.31 0.34 0.29
300 0.31 0.27 0.29 0.25
65 64 ABB SACE - Electrical devices ABB SACE - Electrical devices
2.2 Installation and dimensioning of cables 2.2 Installation and dimensioning of cables
2 Protection of feeders 2 Protection of feeders
L I U U
b x
03 . 2 025 . 0 100 81 . 0 =
. .
=
. .
∆ = ∆ V
% 51 . 0 100
400
03 . 2
100 % =
.
=
.
∆
= ∆
r
U
U
u
L
I U U
b x
28 . 4
2
05 . 0
50 42 . 3
2
=
.
. =
. .
∆ = ∆ V
% 62 . 0 100
690
28 . 4
100 % =
.
=
.
∆
= ∆
r
U
U
u
L I
U u
U
b
r
x
. .
.
∆
= ∆
100
%
max
(3)
A
U
P
I
r
u
b
56
9 . 0 400 3
35000
cos 3
=
. .
=
. .
=
V L I U
b
2 . 28 14 . 0 56 6 . 3 60 . 3 =
. .
=
. .
= ∆
% 05 . 7 100
400
2 . 28
100 % =
.
=
.
∆
= ∆
r
U
U
u
02 . 1
14 . 0 56 100
400 % 2
100
%
max
=
. .
.
=
. .
.
∆
= ∆
L I
U u
U
b
r
x
V/(A km)
.
Example 1
To calculate a voltage drop on a three-phase cable with the following
specifications:
• rated voltage: 400 V;
• cable length: 25 m;
• cable formation: single-core copper cable, 3x50 mm
2
;
• load current I
b
: 100 A;
• power factor cosϕ: 0.9.
From Table 4, for a 50 mm
2
single-core cable it is possible to read that a ∆U
x
voltage drop corresponds to 0.81 V/(A⋅km). By multiplying this value by the
length in km and by the current in A, it results:
which corresponds to this percentage value:
Example 2
To calculate a voltage drop on a three-phase cable with the following
specifications:
• rated voltage: 690 V;
• cable length: 50 m;
• cable formation: multi-core copper cable, 2x(3x10) mm
2
;
• load current I
b
: 50 A;
• power factor cosϕ: 0.85.
From Table 5, for a multi-core 10 mm
2
cable it is possible to read that ∆U
x
voltage drop corresponds to 3.42 V/(A⋅km). By multiplying this value by the
length in km and by the current in A, and by dividing it by the number of cables
in parallel, it results:
which corresponds to this percentage value:
Method for defining the cross section of the conductor according to
voltage drop in the case of long cables
In the case of long cables, or if particular design specifications impose low
limits for maximum voltage drops, the verification using as reference the cross
section calculated on the basis of thermal considerations (calculation according
to chapter 2.2.1 “Current carrying capacity and methods of installation”) may
have a negative result.
To define the correct cross section, the maximum ∆U
xmax
value calculated by
using the formula:
is compared with the corresponding values on Tables 4÷12 by choosing the
smallest cross section with a ∆U
x
value lower than ∆U
xmax
.
Example:
Supply of a three-phase load with P
u
= 35 kW (U
r
=400 V, f
r
= 50 Hz, cosϕ=0.9)
with a 140 m cable installed on a perforated tray, consisting of a multi-core
copper cable with EPR insulation.
Maximum permitted voltage drop 2%.
Load current I
b
is:
The Table 8 of Chapter 2.2.1 shows S = 10 mm
2
.
From Table 4, for the multi-core 10 mm
2
cable it is possible to read that the
voltage drop per A and per km is 3.60 V/(A⋅km). By multiplying this value by the
length in km and by the current in A, it results:
which corresponds to this percentage value:
This value is too high.
Formula (3) shows:
67 66 ABB SACE - Electrical devices ABB SACE - Electrical devices
2 Protection of feeders 2 Protection of feeders
V L I U U
b x
35 . 6 14 . 0 56 81 . 0 =
. .
=
. .
∆ = ∆
% 6 . 1 100
400
35 . 6
100 % =
.
=
.
∆
= ∆
r
U
U
u
3
2
L I r
P
b
j
. . .
= [W]
1000
2
2
L I r
P
b
j
. . .
= [W]
1000
1.45Iz Iz Ib
In I2
1
S
D
C
0
1
0
0
0
9
F
0
0
0
1
I
b
≤ I
n
≤ I
z
(1)
I
2
≤ 1.45
.
I
z
(2)
From Table 4 a cross section of 50 mm
2
can be chosen.
For this cross section ∆U
x
= 0.81< 1.02 V/(A⋅km).
By using this value it results:
This corresponds to a percentage value of:
2.2.3 Joule-effect losses
Joule-effect losses are due to the electrical resistance of the cable.
The lost energy is dissipated in heat and contributes to the heating of the
conductor and of the environment.
A first estimate of three-phase losses is:
whereas single-phase losses are:
where:
• I
b
is the load current [A];
• r is the phase resistance per unit of length of the cable at 80 °C [Ω/km] (see
Table 1);
• L is the cable length [m].
Single-core cable Two-core/three-core cable
S
[mm
2
] Cu AI Cu AI
1.5 14.8 24.384 15.1 24.878
2.5 8.91 14.680 9.08 14.960
4 5.57 9.177 5.68 9.358
6 3.71 6.112 3.78 6.228
10 2.24 3.691 2.27 3.740
16 1.41 2.323 1.43 2.356
25 0.889 1.465 0.907 1.494
35 0.641 1.056 0.654 1.077
50 0.473 0.779 0.483 0.796
70 0.328 0.540 0.334 0.550
95 0.236 0.389 0.241 0.397
120 0.188 0.310 0.191 0.315
150 0.153 0.252 0.157 0.259
185 0.123 0.203 0.125 0.206
240 0.0943 0.155 0.0966 0.159
300 0.0761 0.125 0.078 0.129
Table 1: Resistance values [Ω/km] of single-core and multi-core
cables in copper and aluminium at 80 °C
The Standard IEC 60364-4-43 “Electrical installation of buildings - Protection
against overcurrent” specifies coordination between conductors and overload
protective devices (normally placed at the beginning of the conductor to be
protected) so that it shall satisfy the two following conditions:
Where:
• I
b
is the current for which the circuit is dimensioned;
• I
z
is the continuous current carrying capacity of the cable;
• I
n
is the rated current of the protective device; for adjustable protective releases,
the rated current I
n
is the set current;
• I
2
is the current ensuring effective operation in the conventional time of the
protective device.
According to condition (1) to correctly choose the protective device, it is
necessary to check that the circuit-breaker has a rated (or set) current that is:
• higher than the load current, to prevent unwanted tripping;
• lower than the current carrying capacity of the cable, to prevent cable overload.
The Standard allows an overload current that may be up to 45% greater than
the current carrying capacity of the cable but only for a limited period
(conventional trip time of the protective device).
The verification of condition (2) is not necessary in the case of circuit-breakers
because the protective device is automatically tripped if:
• I
2
= 1.3⋅I
n
for circuit-breakers complying with IEC 60947-2 (circuit-breakers
for industrial use);
• I
2
= 1.45⋅I
n
for circuit-breakers complying with IEC 60898 (circuit-breakers
for household and similar installations).
Therefore, for circuit-breakers, if I
n
≤ I
z
, the formula I
2
≤ 1.45⋅I
z
will also be
verified.
When the protective device is a fuse, it is also essential to check formula (2)
because IEC 60269-2-1 on “Low-voltage fuses” states that a 1.6⋅I
n
current
must automatically melt the fuse. In this case, formula (2) becomes 1.6⋅I
n
≤ 1.45⋅I
z
or I
n
≤ 0.9⋅I
z
.
2.3 Protection against overload
2.2 Installation and dimensioning of cables
69 68 ABB SACE - Electrical devices ABB SACE - Electrical devices
2.3 Protection against overload 2.3 Protection against overload
2 Protection of feeders 2 Protection of feeders
I
b
≤ I
n
≤ 0.9
.
I
z
I
b
1
S
D
C
0
1
0
0
1
0
F
0
0
0
1
I
n
I
z
I
b
1
S
D
C
0
1
0
0
1
1
F
0
0
0
1
I
n
I
z
0.9
To summarize: to carry out by a fuse protection against overload, the following
must be achieved:
and this means that the cable is not fully exploited.
Circuit-breaker: choice of rated current
Fuse: choice of rated current
Where the use of a single conductor per phase is not feasible, and the currents
in the parallel conductors are unequal, the design current and requirements for
overload protection for each conductor shall be considered individually.
Examples
Example 1
Load specifications
P
r
= 70 kW; U
r
= 400 V; cosϕ = 0.9; three-phase load so I
b
= 112 A
Cable specifications
I
z
= 134 A
Protective device specifications
T1B160 TMD I
n
125; set current I1 = 125 A
Example 2
Load specifications
P
r
= 80 kW; cosϕ = 0.9; U
r
= 400 V; three-phase load so I
b
= 128 A
Cable specifications
I
z
= 171 A
Protective device specifications
T2N160 PR221DS-LS I
n
160; set current I1 = 0.88 x I
n
= 140.8 A
Example 3
Load specifications
P
r
= 100 kW; cosϕ = 0.9; U
r
= 400 V ; three-phase load so I
b
= 160 A
Cable specifications
I
z
= 190 A
Protective device specifications
T3N250 TMD I
n
200; set current I1 = 0.9 x I
n
= 180 A
Example 4
Load specifications
P
r
= 25 kW; cosϕ = 0.9; U
r
= 230 V ; single-phase load so I
b
= 121 A
Cable specifications
I
z
= 134 A
Protective device specifications
T1B160 1P TMF I
n
125
71 70 ABB SACE - Electrical devices ABB SACE - Electrical devices
2 Protection of feeders 2 Protection of feeders
I
2
t ≤ k
2
S
2
(1)
1
S
D
C
0
1
0
0
1
0
F
0
2
0
1
PVC
≤300 mm
2
PVC
>300 mm
2
EPR
XLPE
Rubber
60 °C
Mineral
PVC Bare
Conductor insulation
Initial temperature °C
Final temperature °C
Material of conductor:
Copper
Aluminium
tin-soldered joints
in copper conductors
a
This value shall be used for bare cables exposed to touch.
NOTE 1 Other values of k are under consideration for.
- small conductors (particularly for cross section less than 10 mm
2
);
- duration of short-circuit exceeding 5 s;
- other types of joints in conductors;
- bare conductors.
NOTE 2 The nominal current of the short-circuit protective device may be greater than the current carrying
capacity of the cable.
NOTE 3 The above factors are based on IEC 60724.
70
160
115
76
115
70
140
103
68
-
90
250
143
94
-
60
200
141
93
-
70
160
115
-
-
105
250
135/115
a
-
-
Table 1: Values of k for phase conductor
2.4 Protection against short-circuit
Table 2 shows the maximum withstood energy for cables according to the
cross section, the conductor material and the type of insulation, which are
calculated by using the parameters of Table 1.
Table 2: Maximum withstood energy for cables k
2
S
2
[(kA)
2
s]
A cable is protected against short-circuit if the specific let-through energy of
the protective device (I
2
t) is lower or equal to the withstood energy of the cable
(k
2
S
2
):
where
• I
2
t is the specific let-through energy of the protective device which can be
read on the curves supplied by the manufacturer (see Electrical installation
handbook, Vol. 1, Chapter 3.4 “Specific let-through energy curves”) or from a
direct calculation in the case of devices that are not limiting and delaying;
• S is the cable cross section [mm
2
]; in the case of conductors in parallel it is
the cross section of the single conductor;
• k is a factor that depends on the cable insulating and conducting material.
The values of the most common installations are shown in Table 1; for a more
detailed calculation, see Annex D.
1
S
D
C
0
1
0
0
0
2
F
0
9
0
1
1.5 2.5 4 6 10 16 25 35
Cu 115 2.98·10
-2
8.27·10
-2
2.12·10
-1
4.76·10
-1
1.32 3.39 8.27 1.62·10
1
PVC
Al 76 1.30·10
-2
3.61·10
-2
9.24·10
-2
2.08·10
-1
5.78·10
-1
1.48 3.61 7.08
Cu 143 4.60·10
-2
1.28·10
-1
3.27·10
-1
7.36·10
-1
2.04 5.23 1.28·10
1
2.51·10
1
EPR/XLPE
Al 94 1.99·10
-2
5.52·10
-2
1.41·10
-1
3.18·10
-1
8.84·10
-1
2.26 5.52 1.08·10
1
Cu 141 4.47·10
-2
1.24·10
-1
3.18·10
-1
7.16·10
-1
1.99 5.09 1.24·10
1
2.44·10
1
Rubber
Al 93 1.95·10
-2
5.41·10
-2
1.38·10
-1
3.11·10
-1
8.65·10
-1
2.21 5.41 1.06·10
1
50 70 95 120 150 185 240 300
Cu 115 3.31·10
1
6.48·10
1
1.19·10
2
1.90·10
2
2.98·10
2
4.53·10
2
7.62·10
2
1.19·10
3
PVC
Al 76 1.44·10
1
2.83·10
1
5.21·10
1
8.32·10
1
1.30·10
2
1.98·10
2
3.33·10
2
5.20·10
2
Cu 143 5.11·10
1
1.00·10
1
1.85·10
1
2.94·10
2
4.60·10
2
7.00·10
2
1.18·10
3
1.84·10
3
EPR/XLPE
Al 94 2.21·10
1
4.33·10
1
7.97·10
1
1.27·10
2
1.99·10
2
3.02·10
2
5.09·10
2
7.95·10
2
Cu 141 4.97·10
1
9.74·10
1
1.79·10
1
2.86·10
2
4.47·10
2
6.80·10
2
1.15·10
3
1.79·10
3
G2
Al 93 2.16·10
1
4.24·10
1
7.81·10
1
1.25·10
2
1.95·10
2
2.96·10
2
4.98·10
2
7.78·10
2
Cable k
Cable k
Cross section [mm
2
]
Cross section [mm
2
]
The formula (1) must be verified along the whole length of the cable. Due to the
shape of the specific let-through energy curve of a circuit breaker, it is generally
sufficient to verify formula (1) only for the maximum and minimum short-circuit
current that may affect the cable. The maximum value is normally the value of
the three-phase short-circuit current at the beginning of the line, while the
minimum value is the value of the phase to neutral short-circuit current (phase
to phase if the neutral conductor is not distributed) or phase to earth at the end
of the cable.
2.4 Protection against short-circuit
73 72 ABB SACE - Electrical devices ABB SACE - Electrical devices
2.4 Protection against short-circuit 2.4 Protection against short-circuit
2 Protection of feeders 2 Protection of feeders
1
S
D
C
0
1
0
0
1
1
F
0
0
0
1
[(KA)
2
s]
10
-1
10
2
10
-1
10
-2
1
10
10
1
10
-3
[KA]
2L
1.5
k k U 0.8
I
par sec r
kmin
. .
. . .
=
S
S
L
m) (1 1.5
k k U 0.8
I
par sec 0
kmin
.
+
. .
. . .
=
I
kmin
>1.2
.
I
3
(3)
This verification can be simplified by comparing only the let-through energy
value of the circuit-breaker at the maximum short-circuit current with the
withstood energy of the cable and by ensuring that the circuit breaker trips
instantaneously at the minimum short-circuit current: the threshold of the short-
circuit protection (taking into consideration also the tolerances) shall therefore
be lower than the minimum short-circuit current at the end of the conductor.
Calculation of short-circuit current at end of the conductor
Minimum short-circuit current can be calculated by the following approximate
formulas:
where:
• I
kmin
is the minimum value of the prospective short-circuit current [kA];
• U
r
is the supply voltage [V];
• U
0
is the phase to earth supply voltage [V];
• ρ is the resistivity at 20 °C of the material of the conductors in Ωmm
2
/m and is:
- 0.018 for copper;
- 0.027 for aluminium;
• L is the length of the protected conductor [m];
• S is the cross section of the conductor [mm
2
];
• k
sec
is the correction factor which takes into account the reactance of the
cables with cross section larger than 95 mm
2
:
S[mm
2
] 120 150 180 240 300
k
sec
0.9 0.85 0.80 0.75 0.72
• k
par
is the correcting coefficient for conductors in parallel:
number of parallel
conductors 2 3 4 5
k
par
* 2 2.7 3 3.2
*k
par
= 4 (n-1)/n where: n = number of conductors in parallel per phase
• m is the ratio between the resistances of the neutral conductor and the phase
conductor (if they are made of the same material m is the ratio between the
cross section of the phase conductor and the cross section of the neutral
conductor).
After calculating the minimum short-circuit current, verify that
with non-distributed neutral conductor (2.1)
with distributed neutral conductor (2.2)
where:
• I
3
is the current that trips the magnetic protection of the circuit-breaker;
• 1.2 is the tolerance at the trip threshold.
75 74 ABB SACE - Electrical devices ABB SACE - Electrical devices
2.4 Protection against short-circuit 2.4 Protection against short-circuit
2 Protection of feeders 2 Protection of feeders
Example
Choice of CB1
System data:
Rated voltage 400 V
I
k
= 30 kA
Cable data:
Insulated copper conductor in PVC
Length = 150 m
S = 50 mm
2
I
z
= 134 A
1.98
S
2L
1.5
k k U 0.8
I
par sec
kmin
=
. .
. . .
= kA
The magnetic threshold of the circuit breaker T1N160 In160 is set at 1600 A. If
tolerance is 20%, the circuit breaker shall definitely trip if the values exceed
1920 A; the cable is therefore fully protected against short-circuit.
Maximum protected length
The formula (3), when solved for the length, enables the maximum length
protected by the protective device to be obtained for a precise instantaneous
trip threshold. In Table 3, the maximum protected length can be identified for a
given cross section of the cable and for the setting threshold of the instantaneous
protection of the circuit breaker against short-circuit:
- three-phase system, 400 V rated voltage;
- non-distributed neutral;
- copper conductor with resistivity equal to 0.018 Ωmm
2
/m.
The values on the table below take into account the 20% tolerance coefficient
for the magnetic trip value, the increase in cable resistivity due to heating caused
by the short-circuit current and the reduction of voltage due to the fault.
The correction factors shown after the table must be applied if the system
conditions are different from the reference conditions.
section [mm
2
]
I
3
[A] 1.5 2.5 4 6 10 16 25 35 50 70 95 120 150 185 240 300
20 370 617
30 246 412 658
40 185 309 494 741
50 148 247 395 593
60 123 206 329 494
70 105 176 282 423 705
80 92 154 246 370 617
90 82 137 219 329 549
100 74 123 197 296 494 790
120 61 102 164 246 412 658
140 52 88 141 211 353 564
150 49 82 131 197 329 527
160 46 77 123 185 309 494 772
180 41 68 109 164 274 439 686
200 37 61 98 148 247 395 617
220 33 56 89 134 224 359 561 786
250 29 49 79 118 198 316 494 691
280 26 44 70 105 176 282 441 617
300 24 41 65 98 165 263 412 576
320 23 38 61 92 154 247 386 540 772
350 21 35 56 84 141 226 353 494 705
380 19 32 52 78 130 208 325 455 650
400 18 30 49 74 123 198 309 432 617
420 17 29 47 70 118 188 294 412 588
450 16 27 43 65 110 176 274 384 549 768
480 15 25 41 61 103 165 257 360 514 720
500 14 24 39 59 99 158 247 346 494 691
520 14 23 38 57 95 152 237 332 475 665
550 13 22 35 53. 90 144 224 314 449 629
580 12 21 34 51 85 136 213 298 426 596 809
600 12 20 32 49 82 132 206 288 412 576 782
620 11 19 31 47 80 127 199 279 398 558 757
650 11 19 30 45 76 122 190 266 380 532 722
680 10 18 29 43 73 116 182 254 363 508 690
700 10 17 28 42 71 113 176 247 353 494 670 847
750 16 26 39 66 105 165 230 329 461 626 790 840
800 15 24 37 62 99 154 216 309 432 586 667 787
850 14 23 34 58 93 145 203 290 407 552 627 741
900 13 21 32 55 88 137 192 274 384 521 593 700
950 13 20 31 52 83 130 182 260 364 494 561 663
1000 12 19 29 49 79 123 173 247 346 469 533 630 731
1250 15 23 40 63 99 138 198 277 375 427 504 585 711
1500 13 19 33 53 82 115 165 230 313 356 420 487 593
1600 12 18 31 49 77 108 154 216 293 333 394 457 556 667
2000 14 25 40 62 86 123 173 235 267 315 365 444 533
2500 11 20 32 49 69 99 138 188 213 252 292 356 427
3000 16 26 41 58 82 115 156 178 210 244 296 356
3200 15 25 39 54 77 108 147 167 197 228 278 333
4000 12 20 31 43 62 86 117 133 157 183 222 267
5000 10 16 25 35 49 69 94 107 126 146 178 213
6300 13 20 27 39 55 74 85 100 116 141 169
8000 10 15 22 31 43 59 67 79 91 111 133
9600 13 18 26 36 49 56 66 76 93 111
10000 12 17 25 35 47 53 63 73 89 107
12000 10 14 21 29 39 44 52 61 74 89
15000 12 16 23 31 36 42 49 59 71
20000 12 17 23 27 31 37 44 53
24000 10 14 20 22 26 30 37 44
30000 12 16 20 25 30 40 49
Table 3: Maximum protected length
1
S
D
C
0
1
0
0
1
1
F
0
2
0
1
Ur = 400 V U
T1N160 In160
PVC Cu L = 150 m
L
Ik = 30 kA
CB1
Cable Section 50 mm
2
Iz = 134.0 A
Protection against short-circuit at the beginning of the conductor
T1N160 In160 (breaking capacity 36 kA@400 V)
I
2
t (@30 kA) = 7.5 10
-1
(kA)
2
s (for the curves of specific let-through energy, see
Volume 1, Chapter 3.4)
k
2
S
2
= 115
2
⋅ 50
2
= 3.31
.
10
1
(kA)
2
s
The cable is therefore protected against short-circuit at the beginning of the
conductor.
Protection against short-circuit at end of the conductor
The minimum short-circuit current at end of the conductor (k
sec
=1 and k
par
=1) is:
77 76 ABB SACE - Electrical devices ABB SACE - Electrical devices
2.4 Protection against short-circuit 2.4 Protection against short-circuit
2 Protection of feeders 2 Protection of feeders
N
d
S
S
k
+
.
=
1
1
3
2
if S = S
N
k
d
is 0.58;
if S = 2 S
N
k
d
is 0.39.
.
r d v
k k k L L
0
=
Example 1
Neutral not distributed
Rated voltage = 400 V
Protective device: T2N160 TMD In100
Magnetic threshold: I
3
= 1000 A
Phase cross section = Neutral cross section = 70 mm
2
The table shows that at I
3
= 1000 A, the 70 mm
2
cable is protected up to 346 m.
Example 2
Neutral distributed
Rated voltage = 400 V
Protective device: T3S250 TMD In200
Magnetic threshold: I
3
= 2000 A
Phase cross section = 300 mm
2
Neutral cross section = 150 mm
2
For I
3
= 2000 A and S = 300 mm
2
, a protected length equivalent of L
0
= 533 m
is obtained.
By applying the correction factor k
d
required when the neutral is distributed:
L= L
0
.
0.39 = 533
.
0.39 = 207.9 m
This is the maximum protected length with neutral distributed.
Correction factor for voltage other than 400 V: k
v
Multiply the length value obtained from the table by the correction factor k
v
:
U
r
[V] k
v
(three-phase value)
230
(*)
0.58
400 1
440 1.1
500 1.25
690 1.73
(*)
230 V single-phase is the equivalent of a three-phase 400 V system with distributed
neutral and with the cross section of the phase conductor the same as the cross section
area of the neutral conductor, so that k
v
is 0.58.
Correction factor for distributed neutral: k
d
Multiply the length value obtained from the table by the correction factor k
d
:
where
• S is the phase cross section [mm
2
];
• S
N
is the neutral cross section [mm
2
].
In particular:
Correction factor for aluminium conductors: k
r
If the cable is in aluminium, multiply the length value obtained from the table
above by the correction factor k
r
= 0.67.
To summarize:
On the table, for the cross section and magnetic trip threshold it is possible to
read a maximum protected value L
0
. This length shall then be multiplied, if
necessary, by the correction factors in order to obtain a value that is compatible
with the installation operating conditions:
39 . 0
150
300
1
1
3
2
1
1
3
=
+
=
+
=
N
d
S
S
k
2
. .
79 78 ABB SACE - Electrical devices ABB SACE - Electrical devices
2 Protection of feeders 2 Protection of feeders
1
S
D
C
0
1
0
0
1
3
F
0
0
0
1
P
P
P
N
R1 R2 U1
3
=
1
U
.
0
U
.
1
R
1
R +
2
R
Figure 2: Three-phase alternative power supply with a 4-pole switch
Power supply 1
L1
L2
L3
PEN
PE
L1
L2
L3
Power supply 2
Supplier
User
Current using equipment
1
S
D
C
0
1
0
0
1
2
F
0
2
0
1
NOTE - This method
prevents electromagnetic
fields due to stray currents
in the main supply system
of an installation. The sum
of the currents within one
cable must be zero. This
ensures that the neutral
current will flow only in the
neutral conductor of the
respective switched on
circuit. The 3rd harmonic
(150 Hz) current of the line
conductors will be added
with the same phase angle
to the neutral conductor
current.
Neutral conductor
The neutral conductor is a conductor that is connected to the system neutral
point (which generally but not necessarily coincides with the star centre of the
secondary windings of the transformer or the windings of the generator); it is
able to contribute to the transmission of electric power, thereby making available
a voltage that is different from the phase to phase voltage. In certain cases and
under specific conditions, the functions of neutral conductor and protective
conductor can be combined in a single conductor (PEN).
Protection and disconnection of the neutral conductor
If fault conditions arise, a voltage to earth may occur on the neutral conductor.
This may be caused by a phase to neutral short-circuit and by the disconnection
of the neutral conductor due to accidental breaking or to tripping of single-pole
devices (fuses or single-pole circuit breakers).
If the neutral conductor only is disconnected in a four-conductor circuit, the
supply voltage to the single-phase loads may be altered so that they are supplied
by a voltage different from the U
0
phase to neutral voltage (as shown in Fig. 1).
Therefore, all the necessary measures to prevent this type of fault shall be taken,
e.g. by not protecting the neutral conductor with single-pole devices.
2.5 Neutral and protective conductors
Figure 1: Disconnection of the neutral conductor
Moreover, in TN-C systems, voltage to earth arising on the neutral conductor
constitutes a hazard for people; in fact, since this conductor is also a protective
conductor, this voltage reaches the connected exposed conductive parts. For
TN-C systems, the Standards specify minimum cross sections (see next clause)
for the neutral conductor in order to prevent accidental breaking and they forbid
the use of any device (single-pole or multi-pole) that could disconnect the PEN.
The need for protection on the neutral conductor and the possibility of
disconnecting the circuit depend on the distribution system:
TT or TN systems:
• if the cross section of the neutral conductor is the same or larger than the
cross section of the phase conductor, there is neither the need to detect
overcurrents on the neutral conductor nor to use a breaking device (neutral
conductor is not protected or disconnected); this requirement applies only if
there are no harmonics that may, at any instant, cause r.m.s. current values
on the neutral conductor higher than the maximum current detected on the
phase conductors;
• if the cross section of the neutral conductor is less than the cross section of
the phase conductor, overcurrents on the neutral conductor must be detected
so as to have the phase conductors, but not necessarily the neutral conductor,
disconnected (neutral conductor protected but not disconnected): in this case
the overcurrents on the neutral conductor do not need to be detected if the
following conditions are simultaneously fulfilled:
1.the neutral conductor is protected against short-circuit by
the protective device of the phase conductors;
2.the maximum current that can flow through the neutral
conductor during normal service is lower than the neutral
current carrying capacity.
In TN-S systems, the neutral need not be disconnected if the supply conditions
are such that the neutral conductor can be considered to be reliable at earth potential.
As already mentioned, in TN-C systems, the neutral conductor is also a
protective conductor and cannot therefore be disconnected. Furthermore, if
the neutral conductor is disconnected, the exposed conductive parts of the
single-phase equipment could take the system rated voltage to earth.
In certain specific cases, the neutral conductor has to be disconnected to
prevent currents circulating between parallel supply sources (see Figures 2 and 3).
2.5 Neutral and protective conductors
81 80 ABB SACE - Electrical devices ABB SACE - Electrical devices
2.5 Neutral and protective conductors 2.5 Neutral and protective conductors
2 Protection of feeders 2 Protection of feeders
1
S
D
C
0
1
0
0
1
4
F
0
0
0
1
L1
L2
L3
PEN
PE
L1
L2
L3
1
S
D
C
0
1
0
0
1
3
F
0
2
0
1
It is not necessary:
-the presence of a
breaking device
for the neutral.
It is necessary to:
-detect the neutral current;
-open the phase contacts;
It is not necessary to:
-open the neutral contact.
yes
Neutral max current
<
Neutral carrying capacity (Iz)?
yes
no
no
It is necessary to:
detect the neutral current
in order to open all the contacts
(phase and neutral).
Neutral shall not be disconnected before the phase conductors
Neutral shall be reconnected at the same time as
or before the phase conductors
no
Is the neutral protected by
the short-circuit protection
of the phase conductor?
It is necessary to:
- open all the contacts
(phase and neutral)
It is not necessary to:
-detect the neutral current.
It is necessary to:
-open the phase contacts
It is not necessary to:
-detect the neutral overcurrent;
-open the neutral contact.
yes
TT/TNSystem?
yes
Upstream protection
for the neutral?
no
yes
Is the circuit protected
by a RCD with
I∆n≤
0.15 x Neutral
carrying capacity ?
no
no
yes
START
≥ S
N
S?
NOTE – A three-phase
alternative power supply
with a non-suitable 3-pole
switch, due to
unintentional circular stray
currents generating
electromagnetic fields.
Figure 3: Three-phase alternative power supply with non-suitable
3-pole switch
IT system:
The Standard advises against distributing the neutral conductor in IT systems.
If the neutral conductor is distributed, the overcurrents must be detected on
the neutral conductor of each circuit in order to disconnect all the live conductors
on the corresponding circuit, including the neutral one (neutral conductor
protected and disconnected).
Overcurrents do not need to be detected on the neutral conductor in any of the
following cases:
• the neutral conductor is protected against short-circuit by a protective device
fitted upstream;
• the circuit is protected by a residual current device with rated residual current
lower than 0.15 times the current carrying capacity of the corresponding neutral
conductor. This device must disconnect all the live conductors, the neutral
conductor included.
For all distribution systems, whenever necessary, connection and disconnection
of the neutral conductor, shall ensure that:
• the neutral conductor is not disconnected before the phase conductor;
• the neutral conductor is connected at the same moment or before the phase
conductor.
83 82 ABB SACE - Electrical devices ABB SACE - Electrical devices
2.5 Neutral and protective conductors 2.5 Neutral and protective conductors
2 Protection of feeders 2 Protection of feeders
k
t I
S
PE
2
=
(1)
1
S
D
C
0
1
0
0
1
4
F
0
2
0
1
[mm ]
2
[mm ]
2
S
.
1
k
16
1
.
k
2
k
1
S k
.
2
k
Cross section of
line conductor S
Minimum cross section of the corresponding
protective conductor
If the protective conductor is of the
same material as the line conductor
If the protective conductor is not of the same
material as the line conductor
S ≤ 16 S
16 < S ≤ 25 16
*
S > 25
2
S
*
2
Where
k
1
is the value of k for the line conductor, selected from Table 1 Chapter 2.4 according to the materials of
the conductor and insulation;
k
2
is the value of k for the protective conductor.
*
For a PEN conductor, the reduction of the cross section is permitted only in accordance with the rules for sizing of the neutral conductor.
2
k
Determination of the minimum cross section of the neutral conductor
The neutral conductor, if any, shall have the same cross section as the line
conductor:
• in single-phase, two-wire circuits whatever the section;
• in polyphase and single-phase three-wire circuits, when the size of the line
conductors is less than or equal to 16 mm
2
in copper, or 25 mm
2
in
aluminium.
1
The cross section of the neutral conductor can be less than the cross section
of the phase conductor when the cross section of the phase conductor is
greater than 16 mm
2
with a copper cable, or 25 mm
2
with an aluminium cable,
if both the following conditions are met:
• the cross section of the neutral conductor is at least 16 mm
2
for copper
conductors and 25 mm
2
for aluminium conductors;
• there is no high harmonic distortion of the load current. If there is high harmonic
distortion (the harmonic content is greater than 10%), as for example in
equipment with discharge lamps, the cross section of the neutral conductor
cannot be less than the cross section of the phase conductors.
Table 1: Minimum cross sections of the neutral conductor
Phase cross section Min. neutral cross section
S [mm
2
] S
N
[mm
2
]
Single-phase/two-phase circuits
Cu/Al Any S
*
Three-phase circuits S ≤ 16 S
*
Cu S > 16 16
Three-phase circuits S ≤ 25 S
*
Al S > 25 25
*
for TN-C systems, the Standards specify a minimum cross section of 10 mm
2
for copper
and 16 mm
2
for aluminium conductors
1
The cross section of phase conductors shall be dimensioned in compliance with the
instructions of the Chapter 2.2.1 “Current carrying capacity and methods of installation”
Protective conductor
Determination of the minimum cross sections
The minimum cross section of the protective conductor can be determined by
using the following table:
Table 2: Cross section of the protective conductor
For a more accurate calculation and if the protective conductor is subjected to
adiabatic heating from an initial known temperature to a final specified tempe-
rature (applicable for fault extinction time no longer than 5s), the minimum cross
section of the protective conductor S
PE
can be obtained by using the following
formula:
where:
• S
PE
is the cross section of the protective conductor [mm
2
];
• I is the r.m.s. current flowing through the protective conductor in the event of
a fault with low impedance [A];
• t is the trip time of the protective device [s];
85 84 ABB SACE - Electrical devices ABB SACE - Electrical devices
2.5 Neutral and protective conductors 2.5 Neutral and protective conductors
2 Protection of feeders 2 Protection of feeders
Table 3: Values of k for insulated protective conductors not
incorporated in cables and not bunched with other cables
1
S
D
C
0
1
0
0
1
5
F
0
2
0
1
Conductor insulation
Temperature
°C
b
Material of conductor
Copper Aluminium Steel
Initial Final Values for k
70 °C PVC
90 °C PVC
90 °C thermosetting
60 °C rubber
85 °C rubber
Silicon rubber
30
30
30
30
30
30
160/140
a
143/133
a
250
200
220
350
143/133
a
143/133
a
176
159
168
201
95/88
a
95/88
a
116
105
110
133
52/49
a
52/49
a
64
58
60
73
a
The lower value applies to PVC insulated conductors of cross section greater than 300 mm
2
.
b
Temperature limits for various types of insulation are given in IEC 60724.
Table 4: Values of k for protective conductors as a core incorporated
in a cable or bunched with other cables or insulated conductors
1
S
D
C
0
1
0
0
1
5
F
0
2
0
1
Conductor insulation
Temperature
°C
b
Material of conductor
Copper Aluminium Steel
Initial Final Values for k
70 °C PVC
90 °C PVC
90 °C thermosetting
60 °C rubber
85 °C rubber
Silicon rubber
70
90
90
60
85
180
160/140
a
160/140
a
250
200
220
350
115/103
a
100/86
a
143
141
134
132
76/68
a
66/57
a
94
93
89
87
42/37
a
36/31
a
52
51
48
47
a
The lower value applies to PVC insulated conductors of cross section greater than 300 mm
2
.
b
Temperature limits for various types of insulation are given in IEC 60724.
For current using equipment intended for permanent connection and with a
protective conductor current exceeding 10 mA, reinforced protective conductors
shall be designed as follows:
• either the protective conductor shall have a cross-sectional area of at least 10
mm
2
Cu or 16 mm
2
Al, through its total run;
• or a second protective conductor of at least the same cross-sectional area as
required for protection against indirect contact shall be laid up to a point
where the protective conductor has a cross-sectional area not less than 10
mm
2
Cu or 16 mm
2
Al. This requires that the appliance has a separate terminal
for a second protective conductor.
When overcurrent protective devices are used for protection against electric
shock, the protective conductor shall be incorporated in the same wiring system
as the live conductors or be located in their immediate proximity.
Further values of k can be taken from the Tables in Annex D, which provides
the formula for accurate calculation of the value of k.
If Table 2 or formula (1) do not provide a standardized cross section, a larger
standardized cross section shall be chosen.
Regardless of whether Table 2 or formula (1) are used, the cross section of the
protective conductor, which is not part of the supply cable, shall be at least:
- 2.5 mm
2
Cu/16 mm
2
Al, if a mechanical protection is provided;
- 4 mm
2
Cu/16 mm
2
Al, if no mechanical protection is provided.
• k is a constant which depends on the material of the protective conductor, on
the type of insulation and on initial and final temperature. The most common
values can be taken from Tables 3 and 4.
87 86 ABB SACE - Electrical devices ABB SACE - Electrical devices
2 Protection of feeders 2 Protection of feeders
m r
t
b
U
b P
I
cos 3
. .
.
= [A] (1)
Z t Z b
I k I I =
.
≤
0
(2)
Load current calculation for three-phase system
Load current I
b
for a three-phase system is calculated by the following formula:
where:
• P
t
is the sum of the active power of all the installed loads [W];
• b is the supply factor, which is:
- 1 if the BTS is supplied from one side only;
- 1/2 if the BTS is supplied from the centre or from both ends
simultaneously;
• U
r
is the operating voltage [V];
• cosϕ
m
is the average power factor of the loads.
Choice of BTS current carrying capacity
A BTS shall be chosen so that its current carrying capacity I
z
complies with the
following formula:
where:
• I
Z0
is the current that the BTS can carry for an indefinite time at the reference
temperature (40 °C);
• I
b
is the load current;
• k
t
is the correction factor for ambient temperature values other than the
reference ambient temperature shown on Table 1.
Table 1: Correction factor k
t
for ambient temperature other than 40 °C
Ambient
Temperature [°C] 15 20 25 30 35 40 45 50
k
t
1.2 1.17 1.12 1.08 1.05 1 0.95 0.85
BTS geometry
• Type of installation:
- flat;
- edge-on;
- vertical.
• Length.
NOTE: BTSs shall be placed at a distance from the walls and the ceilings in such a way as
to enable visual inspection of connections during assembly and to facilitate insertion of the
branch units.
If possible, it is preferable to install the BTS edge-on so as to improve mechanical resistance
and reduce any possible deposit of powder and polluting substances that might affect the
level of internal insulation.
2.6 Busbar trunking systems (BTSs)
In electrical installations for industrial environments, busbar trunking systems
(BTSs) optimize the power distribution despite the inevitable modifications that
are carried out (additions, displacements, replacement of loads) and to facilitate
maintenance work and safety verifications.
They are mainly used for:
- supplying sources of light, safety and low power distribution;
- lighting lines (medium power);
- power supply and distribution (medium and large power);
- supplying moving equipment (bridge cranes).
Busbar trunking systems are subject to the following Standards:
- IEC 60439 – 1 “Low-voltage switchgear and controlgear assemblies – Part 1:
Type-tested and partially type-tested assemblies”
- IEC 60439 – 2 “Low-voltage switchgear and controlgear assemblies – Part 2:
Particular requirements for busbar trunking systems (busways)”.
BTSs consist of:
- conductors/busbars;
- coupling: electrical and mechanical connecting elements for different elements;
- straight elements: base elements of the line for carrying energy from the source
to the loads;
- routing elements: flexible joints for the creation of curves or overcoming
obstacles, horizontal and vertical angles, tee joints and cross elements to
create any type of route;
- pull boxes: elements that enable lamps or operating machines to be supplied
directly with integrated protection (fuses or circuit breakers);
- suspensions/accessories: hanging and fixing elements for BTS and for any
support required for special loads (lighting components, etc).
Dimensioning of a BTS
To dimension a BTS, the load current must be determined using the following
data:
Power supply
• General type of load supply:
- single-phase
- three-phase.
• Type of BTS supply:
- from one end;
- from both ends;
- central power supply.
• Rated voltage
• Short-circuit current at the supply point
• Ambient temperature.
Loads
• Number, distribution, power and cosϕ and type of loads supplied by the same
BTS
2.6 Busbar trunking systems
89 88 ABB SACE - Electrical devices ABB SACE - Electrical devices
2.6 Busbar trunking systems 2.6 Busbar trunking systems
2 Protection of feeders 2 Protection of feeders
25 LB254 25A 4 cond. Cu 4 25 6.964 1.144 400
25 HL254 25A 4 cond. Cu 4 25 6.876 1.400 400
25 HL2544 25A 4+4 cond. Cu 4+4 25 6.876 1.400 400
40 LB404 40A 4 cond. Cu 4 40 3.556 0.792 400
40 HL404 40A 4 cond. Cu 4 40 3.516 1.580 400
40 HL4044 40A 4+4 cond. Cu 4+4 40 3.516 1.580 400
40 SL 40A 4 cond. Cu 4 40 2.173 0.290 400
63 SL 63A 4 cond. Cu 4 63 1.648 0.637 400
100 MS 100A 4 cond. Cu 4 100 0.790 0.366 400
160 MS 160A 4 cond. Cu 4 160 0.574 0.247 400
160 SB4 160A 4 cond. Cu 4 160 0.335 0.314 500
160 SB5 160A 5 cond. Cu 5 160 0.335 0.314 500
160 SB6 160A 5 cond. Cu 5 160 0.335 0.314 500
160 SB7 160A 4 cond. Cu 4 160 0.335 0.314 500
250 MR 250A 4 cond. Cu 4 250 0.285 0.205 1000
250 MRf 250A 5 cond. Cu 5 250 0.285 0.205 1000
250 SB4 250A 4 cond. Cu 4 250 0.194 0.205 500
250 SB5 250A 5 cond. Cu 5 250 0.194 0.205 500
250 SB6 250A 5 cond. Cu 5 250 0.194 0.205 500
250 SB7 250A 4 cond. Cu 4 250 0.194 0.205 500
315 MR 315A 4 cond. Cu 4 315 0.216 0.188 1000
315 MRf 315A 5 cond. Cu 5 315 0.216 0.188 1000
350 SB4 350A 4 cond. Cu 4 350 0.142 0.188 500
350 SB5 350A 5 cond. Cu 5 350 0.142 0.188 500
350 SB6 350A 5 cond. Cu 5 350 0.142 0.188 500
350 SB7 350A 4 cond. Cu 4 350 0.142 0.188 500
400 MR 400A 4 cond. Cu 4 400 0.115 0.129 1000
400 MRf 400A 5 cond. Cu 5 400 0.115 0.129 1000
500 SB4 500A 4 cond. Cu 4 500 0.092 0.129 500
500 SB5 500A 5 cond. Cu 5 500 0.092 0.129 500
500 SB6 500A 5 cond. Cu 5 500 0.092 0.129 500
500 SB7 500A 4 cond. Cu 4 500 0.092 0.129 500
630 MR 630A 4 cond. Cu 4 630 0.073 0.122 1000
630 MRf 630A 5 cond. Cu 5 630 0.073 0.122 1000
700 SB4 700A 4 cond. Cu 4 700 0.077 0.122 500
700 SB5 700A 5 cond. Cu 5 700 0.077 0.122 500
700 SB6 700A 5 cond. Cu 5 700 0.077 0.122 500
700 SB7 700A 4 cond. Cu 4 700 0.077 0.122 500
800 MR 800A 4 cond. Cu 4 800 0.047 0.122 1000
800 MRf 800A 5 cond. Cu 5 800 0.047 0.122 1000
800 SC 800A 4 cond. Cu 4 800 0.038 0.027 1000
800 SB4 800A 4 cond. Cu 4 800 0.072 0.122 500
800 SB5 800A 5 cond. Cu 5 800 0.072 0.122 500
800 SB6 800A 5 cond. Cu 5 800 0.072 0.122 500
800 SB7 800A 4 cond. Cu 4 800 0.072 0.122 500
1000 MR 1000A 4 cond. Cu 4 1000 0.038 0.120 1000
1000 MRf 1000A 5 cond. Cu 5 1000 0.038 0.120 1000
1000 SC 1000A 4 cond. Cu 4 1000 0.037 0.026 1000
1000 HRC1 1000A 4 cond. Cu 4 1000 0.038 0.097 1000
1000 SB4 1000A 4 cond. Cu 4 1000 0.068 0.120 500
1000 SB5 1000A 5 cond. Cu 5 1000 0.068 0.120 500
1000 SB6 1000A 5 cond. Cu 5 1000 0.068 0.120 500
1000 SB7 1000A 4 cond. Cu 4 1000 0.068 0.120 500
1200 SC 1200A 4 cond. Cu 4 1200 0.035 0.021 1000
1250 SC 1250A 4 cond. Cu 4 1250 0.034 0.023 1000
1250 HRC1 1250A 4 cond. Cu 4 1250 0.035 0.076 1000
1500 SC 1500A 4 cond. Cu 4 1500 0.030 0.022 1000
1600 SC 1600A 4 cond. Cu 4 1600 0.025 0.018 1000
1600 HRC1 1600A 4 cond. Cu 4 1600 0.034 0.074 1000
2000 SC 2000A 4 cond. Cu 4 2000 0.020 0.015 1000
2000 HRC1 2000A 4 cond. Cu 4 2000 0.025 0.074 1000
2400 SC 2400A 4 cond. Cu 4 2400 0.019 0.012 1000
2500 SC 2500A 4 cond. Cu 4 2500 0.016 0.011 1000
2500 HRC1 2500A 4 cond. Cu 4 2500 0.019 0.040 1000
3000 SC 3000A 4 cond. Cu 4 3000 0.014 0.011 1000
3000 HRC2 3000A 4 cond. Cu 4 3000 0.017 0.031 1000
3200 SC 3200A 4 cond. Cu 4 3200 0.013 0.009 1000
3200 HRC2 3200A 4 cond. Cu 4 3200 0.015 0.031 1000
4000 SC 4000A 4 cond. Cu 4 4000 0.011 0.007 1000
4000 HRC2 4000A 4 cond. Cu 4 4000 0.011 0.026 1000
5000 SC 5000A 4 cond. Cu 4 5000 0.008 0.005 1000
5000 HRC2 5000A 4 cond. Cu 4 5000 0.008 0.023 1000
*phase resistance at I
z0
Note: the following tables refer to Zucchini S.p.A. products
Table 2: Current carrying capacity I
Z0
of copper BTS
Number of I
Z0
r
ph
* x
ph
U
r
Size Type conductors [A] [mΩ/m] [mΩ/m] [V]
Number of I
Z0
r
ph
* x
ph
U
r
Size Type conductors [A] [mΩ/m] [mΩ/m] [V]
91 90 ABB SACE - Electrical devices ABB SACE - Electrical devices
2.6 Busbar trunking systems 2.6 Busbar trunking systems
2 Protection of feeders 2 Protection of feeders
160 MR 160A 4 cond. Al 4 160 0.591 0.260 1000
160 MRf 160A 5 cond. Al 5 160 0.591 0.260 1000
160 SB4 160A 4 cond. Al 4 160 0.431 0.260 500
160 SB5 160A 5 cond. Al 5 160 0.431 0.260 500
160 SB6 160A 5 cond. Al 5 160 0.431 0.260 500
160 SB7 160A 4 cond. Al 4 160 0.431 0.260 500
250 MR 250A 4 cond. Al 4 250 0.394 0.202 1000
250 MRf 250A 5 cond. Al 5 250 0.394 0.202 1000
250 SB4 250A 4 cond. Al 4 250 0.226 0.202 500
250 SB5 250A 5 cond. Al 5 250 0.226 0.202 500
250 SB6 250A 5 cond. Al 5 250 0.226 0.202 500
250 SB7 250A 4 cond. Al 4 250 0.226 0.202 500
315 MR 315A 4 cond. Al 4 315 0.236 0.186 1000
315 MRf 315A 5 cond. Al 5 315 0.236 0.186 1000
315 SB4 315A 4 cond. Al 4 315 0.181 0.186 500
315 SB5 315A 5 cond. Al 5 315 0.181 0.186 500
315 SB6 315A 5 cond. Al 5 315 0.181 0.186 500
315 SB7 315A 4 cond. Al 4 315 0.181 0.186 500
400 MR 400A 4 cond. Al 4 400 0.144 0.130 1000
400 MRf 400A 5 cond. Al 5 400 0.144 0.130 1000
400 SB4 400A 4 cond. Al 4 400 0.125 0.130 500
400 SB5 400A 5 cond. Al 5 400 0.125 0.130 500
400 SB6 400A 5 cond. Al 5 400 0.125 0.130 500
400 SB7 400A 4 cond. Al 4 400 0.125 0.130 500
500 SB4 500A 4 cond. Al 4 500 0.102 0.127 500
500 SB5 500A 5 cond. Al 5 500 0.102 0.127 500
500 SB6 500A 5 cond. Al 5 500 0.102 0.127 500
500 SB7 500A 4 cond. Al 4 500 0.102 0.127 500
630 MR 630A 4 cond. Al 4 630 0.072 0.097 1000
630 MRf 630A 5 cond. Al 5 630 0.072 0.097 1000
630 SC 630A 4 cond. Al 4 630 0.072 0.029 1000
630 SB4 630A 4 cond. Al 4 630 0.073 0.097 500
630 SB5 630A 5 cond. Al 5 630 0.073 0.097 500
630 SB6 630A 5 cond. Al 5 630 0.073 0.097 500
630 SB7 630A 4 cond. Al 4 630 0.073 0.097 500
800 MR 800A 4 cond. Al 4 800 0.062 0.096 1000
800 MRf 800A 5 cond. Al 5 800 0.062 0.096 1000
800 SC 800A 4 cond. Al 4 800 0.067 0.027 1000
800 SB4 800A 4 cond. Al 4 800 0.071 0.096 500
800 SB5 800A 5 cond. Al 5 800 0.071 0.096 500
800 SB6 800A 5 cond. Al 5 800 0.071 0.096 500
800 SB7 800A 4 cond. Al 4 800 0.071 0.096 500
1000 SC 1000A 4 cond. Al 4 1000 0.062 0.023 1000
1000 HRC1 1000A 4 cond. Al 4 1000 0.068 0.087 1000
1200 SC 1200A 4 cond. Al 4 1200 0.054 0.023 1000
1250 SC 1250A 4 cond. Al 4 1250 0.044 0.021 1000
1250 HRC1 1250A 4 cond. Al 4 1250 0.044 0.066 1000
1500 SC 1500A 4 cond. Al 4 1500 0.041 0.023 1000
1600 SC 1600A 4 cond. Al 4 1600 0.035 0.017 1000
1600 HRC1 1600A 4 cond. Al 4 1600 0.041 0.066 1000
2000 SC 2000A 4 cond. Al 4 2000 0.029 0.016 1000
2000 HRC1 2000A 4 cond. Al 4 2000 0.034 0.053 1000
2250 HRC2 2250A 4 cond. Al 4 2250 0.032 0.049 1000
2400 SC 2400A 4 cond. Al 4 2400 0.028 0.012 1000
2500 SC 2500A 4 cond. Al 4 2500 0.022 0.011 1000
2500 HRC2 2500A 4 cond. Al 4 2500 0.022 0.034 1000
3000 SC 3000A 4 cond. Al 4 3000 0.020 0.011 1000
3200 SC 3200A 4 cond. Al 4 3200 0.017 0.009 1000
3200 HRC2 3200A 4 cond. Al 4 3200 0.020 0.034 1000
4000 SC 4000A 4 cond. Al 4 4000 0.014 0.008 1000
4000 HRC2 4000A 4 cond. Al 4 4000 0.017 0.024 1000
4500 HRC2 4500A 4 cond. Al 4 4500 0.014 0.024 1000
*phase resistance at I
z0
Table 3: Current carrying capacity I
Z0
of aluminium BTS
Number of I
Z0
r
ph
* x
ph
U
r
Size Type conductors [A] [mΩ/m] [mΩ/m] [V]
Number of I
Z0
r
ph
* x
ph
U
r
Size Type conductors [A] [mΩ/m] [mΩ/m] [V]
93 92 ABB SACE - Electrical devices ABB SACE - Electrical devices
2.6 Busbar trunking systems 2.6 Busbar trunking systems
2 Protection of feeders 2 Protection of feeders
I
b
≤ I
n
≤ I
z
(3)
START
END
Ib
yes
yes
yes
yes
yes
no
no
no
no
1
S
D
C
0
1
0
0
1
7
F
0
2
0
1
no
kt=1
kt from
Table 1
Voltage drop
OK ?
BTS choice
(Ib < kt*I
Z0
=IZ )
Circuit-breaker
choice
Ib < InCB < I
Z
?
I
2
t
CB
< I
2
t
BTS
?
Ikp < I
kp
?
Temperature
<> 40 °C ?
CB BTS
BTS protection
Protection against overload
BTSs are protected against overload by using the same criterion as that used
for the cables. The following formula shall be verified:
where:
• I
b
is the current for which the circuit is designed;
• I
n
is the rated current of the protective device; for adjustable protective devices,
the rated current I
n
is the set current;
• I
z
is the continuous current carrying capacity of the BTS.
Protection against short-circuit
The BTS must be protected against thermal overload and electrodynamic effects
due to the short-circuit current.
Protection against thermal overload
The following formula shall be fulfilled:
where:
• I
2
t
CB
is the specific let-through energy of the circuit-breaker at the maximum
short-circuit current value at the installation point. This can be extrapolated
from the curves shown in Volume 1 Chapter 3.4;
• I
2
t
BTS
is the withstood energy of the BTS and it is normally given by the
manufacturer (see Tables 4 and 5).
Protection against electrodynamic effects
The following formula shall be fulfilled:
where:
• I
kp CB
is the peak limited by the circuit-breaker at the maximum short-circuit
current value at the installation point. This can be extrapolated from the
limitation curves shown in Volume 1, Chapter 3.3;
• I
kp BTS
is the maximum peak current value of the BTS (see Tables 4 and 5).
NOTE - The protection
against short-circuit does
not need to be checked if
MCBs up to 63 A are used
whenever correctly
dimensioned for overload
protection. In such cases,
in fact, protection against
both thermal and
electrodynamic effects is
certainly adequate
because of the energy and
peak limitations offered by
these protective devices.
I
2
t
CB
≤ I
2
t
BTS
(4)
I
kp CB
≤ I
kp BTS
(5)
95 94 ABB SACE - Electrical devices ABB SACE - Electrical devices
2.6 Busbar trunking systems 2.6 Busbar trunking systems
2 Protection of feeders 2 Protection of feeders
25 LB254 25A 4 cond. Cu 0.48 0.48 0.48 10 10
25 HL254 25A 4 cond. Cu 0.64 0.64 0.64 10 10
25 HL2544 25A 4+4 cond. Cu 0.64 0.64 0.64 10 10
40 LB404 40A 4 cond. Cu 0.73 0.73 0.73 10 10
40 HL404 40A 4 cond. Cu 1 1 1 10 10
40 HL4044 40A 4+4 cond. Cu 1 1 1 10 10
40 SL 40A 4 cond. Cu 7.29 7.29 7.29 10 10
63 SL 63A 4 cond. Cu 7.29 7.29 7.29 10 10
100 MS 100A 4 cond. Cu 20.25 20.25 20.25 10 10
160 MS 160A 4 cond. Cu 30.25 30.25 30.25 10 10
160 SB4 160A 4 cond. Cu 100 60 60 17 10.2
160 SB5 160A 5 cond. Cu 100 100 100 17 10.2
160 SB6 160A 5 cond. Cu 100 100 100 17 10.2
160 SB7 160A 4 cond. Cu 100 100 100 17 10.2
250 MR 250A 4 cond. Cu 312.5 187.5 187.5 52.5 31.5
250 MRf 250A 5 cond. Cu 312.5 312.5 312.5 52.5 31.5
250 SB4 250A 4 cond. Cu 169 101.4 101.4 26 15.6
250 SB5 250A 5 cond. Cu 169 169 169 26 15.6
250 SB6 250A 5 cond. Cu 169 169 169 26 15.6
250 SB7 250A 4 cond. Cu 169 169 169 26 15.6
315 MR 315A 4 cond. Cu 312.5 187.5 187.5 52.5 31.5
315 MRf 315A 5 cond. Cu 312.5 312.5 312.5 52.5 31.5
350 SB4 350A 4 cond. Cu 169 101.4 101.4 26 15.6
350 SB5 350A 5 cond. Cu 169 169 169 26 15.6
350 SB6 350A 5 cond. Cu 169 169 169 26 15.6
350 SB7 350A 4 cond. Cu 169 169 169 26 15.6
400 MR 400A 4 cond. Cu 900 540 540 63 37.8
400 MRf 400A 5 cond. Cu 900 900 900 63 37.8
500 SB4 500A 4 cond. Cu 756.25 453.75 453.75 58 34.8
500 SB5 500A 5 cond. Cu 756.25 756.25 756.25 58 34.8
500 SB6 500A 5 cond. Cu 756.25 756.25 756.25 58 34.8
500 SB7 500A 4 cond. Cu 756.25 756.25 756.25 58 34.8
630 MR 630A 4 cond. Cu 1296 777.6 777.6 75.6 45.4
630 MRf 630A 5 cond. Cu 1296 1296 1296 75.6 45.4
700 SB4 700A 4 cond. Cu 756.25 453.75 453.75 58 34.8
700 SB5 700A 5 cond. Cu 756.25 756.25 756.25 58 34.8
700 SB6 700A 5 cond. Cu 756.25 756.25 756.25 58 34.8
700 SB7 700A 4 cond. Cu 756.25 756.25 756.25 58 34.8
800 MR 800A 4 cond. Cu 1296 777.6 777.6 75.6 45.4
800 MRf 800A 5 cond. Cu 1296 1296 1296 75.6 45.4
800 SC 800A 4 cond. Cu 3969 3969 2381.4 139 83.4
800 SB4 800A 4 cond. Cu 756.25 453.75 453.75 58 34.8
800 SB5 800A 5 cond. Cu 756.25 756.25 756.25 58 34.8
800 SB6 800A 5 cond. Cu 756.25 756.25 756.25 58 34.8
800 SB7 800A 4 cond. Cu 756.25 756.25 756.25 58 34.8
1000 MR 1000A 4 cond. Cu 1296 777.6 777.6 75.6 45.4
1000 MRf 1000A 5 cond. Cu 1296 1296 1296 75.6 45.4
1000 SC 1000A 4 cond. Cu 3969 3969 2381.4 139 83.4
1000 HRC1 1000A 4 cond. Cu 1600 1600 960 84 50.4
1000 SB4 1000A 4 cond. Cu 1024 614.4 614.4 60 36
1000 SB5 1000A 5 cond. Cu 1024 1024 1024 60 36
1000 SB6 1000A 5 cond. Cu 1024 1024 1024 60 36
1000 SB7 1000A 4 cond. Cu 1024 1024 1024 60 36
1200 SC 1200A 4 cond. Cu 7744 7744 4646.4 194 116.4
1250 SC 1250A 4 cond. Cu 7744 7744 4646.4 194 116.4
1250 HRC1 1250A 4 cond. Cu 2500 2500 1500 105 63
1500 SC 1500A 4 cond. Cu 7744 7744 4646.4 194 116.4
1600 SC 1600A 4 cond. Cu 7744 7744 4646.4 194 116.4
1600 HRC1 1600A 4 cond. Cu 2500 2500 1500 105 63
2000 SC 2000A 4 cond. Cu 7744 7744 4646.4 194 116.4
2000 HRC1 2000A 4 cond. Cu 3600 3600 2160 132 79.2
2400 SC 2400A 4 cond. Cu 7744 7744 4646.4 194 116.4
2500 SC 2500A 4 cond. Cu 7744 7744 4646.4 194 116.4
2500 HRC1 2500A 4 cond. Cu 4900 4900 2940 154 92.4
3000 SC 3000A 4 cond. Cu 30976 30976 18585.6 387 232.2
3000 HRC2 3000A 4 cond. Cu 8100 8100 4860 198 118.8
3200 SC 3200A 4 cond. Cu 30976 30976 18585.6 387 232.2
3200 HRC2 3200A 4 cond. Cu 8100 8100 4860 198 118.8
4000 SC 4000A 4 cond. Cu 30976 30976 18585.6 387 232.2
4000 HRC2 4000A 4 cond. Cu 8100 8100 4860 198 118.8
5000 SC 5000A 4 cond. Cu 30976 30976 18585.6 387 232.2
5000 HRC2 5000A 4 cond. Cu 10000 10000 6000 220 132
Table 4: Values of the withstood energy and peak current of copper BTS
Size Type I
2
t
ph
I
2
t
N
I
2
t
PE
I
peakph
I
peakN
[(kA)
2
s] [(kA)
2
s] [(kA)
2
s] [kA] [kA]
Size Type I
2
t
ph
I
2
t
N
I
2
t
PE
I
peakph
I
peakN
[(kA)
2
s] [(kA)
2
s] [(kA)
2
s] [kA] [kA]
97 96 ABB SACE - Electrical devices ABB SACE - Electrical devices
2.6 Busbar trunking systems 2.6 Busbar trunking systems
2 Protection of feeders 2 Protection of feeders
160 MR 160A 4 cond. Al 112.5 67.5 67.5 30 18
160 MRf 160A 5 cond. Al 112.5 112.5 112.5 30 18
160 SB4 160A 4 cond. Al 100 60 60 17 10.2
160 SB5 160A 5 cond. Al 100 100 100 17 10.2
160 SB6 160A 5 cond. Al 100 100 100 17 10.2
160 SB7 160A 4 cond. Al 100 100 100 17 10.2
250 MR 250A 4 cond. Al 312.5 187.5 187.5 52.5 31.5
250 MRf 250A 5 cond. Al 312.5 312.5 312.5 52.5 31.5
250 SB4 250A 4 cond. Al 169 101.4 101.4 26 15.6
250 SB5 250A 5 cond. Al 169 169 169 26 15.6
250 SB6 250A 5 cond. Al 169 169 169 26 15.6
250 SB7 250A 4 cond. Al 169 169 169 26 15.6
315 MR 315A 4 cond. Al 625 375 375 52.5 31.5
315 MRf 315A 5 cond. Al 625 625 625 52.5 31.5
315 SB4 315A 4 cond. Al 169 101.4 101.4 26 15.6
315 SB5 315A 5 cond. Al 169 169 169 26 15.6
315 SB6 315A 5 cond. Al 169 169 169 26 15.6
315 SB7 315A 4 cond. Al 169 169 169 26 15.6
400 MR 400A 4 cond. Al 900 540 540 63 37.8
400 MRf 400A 5 cond. Al 900 900 900 63 37.8
400 SB4 400A 4 cond. Al 625 375 375 52.5 31.5
400 SB5 400A 5 cond. Al 625 625 625 52.5 31.5
400 SB6 400A 5 cond. Al 625 625 625 52.5 31.5
400 SB7 400A 4 cond. Al 625 625 625 52.5 31.5
500 SB4 500A 4 cond. Al 625 375 375 52.5 31.5
500 SB5 500A 5 cond. Al 625 625 625 52.5 31.5
500 SB6 500A 5 cond. Al 625 625 625 52.5 31.5
500 SB7 500A 4 cond. Al 625 625 625 52.5 31.5
630 MR 630A 4 cond. Al 1296 777.6 777.6 75.6 45.4
630 MRf 630A 5 cond. Al 1296 1296 1296 75.6 45.4
630 SC 630A 4 cond. Al 1444 1444 866.4 80 48
630 SB4 630A 4 cond. Al 1024 614.4 614.4 67.5 40.5
630 SB5 630A 5 cond. Al 1024 1024 1024 67.5 40.5
630 SB6 630A 5 cond. Al 1024 1024 1024 67.5 40.5
630 SB7 630A 4 cond. Al 1024 1024 1024 67.5 40.5
800 MR 800A 4 cond. Al 1296 777.6 777.6 75.6 45.4
800 MRf 800A 5 cond. Al 1296 1296 1296 75.6 45.4
800 SC 800A 4 cond. Al 1764 1764 1058.4 88 52.8
800 SB4 800A 4 cond. Al 1024 614.4 614.4 67.5 40.5
800 SB5 800A 5 cond. Al 1024 1024 1024 67.5 40.5
800 SB6 800A 5 cond. Al 1024 1024 1024 67.5 40.5
800 SB7 800A 4 cond. Al 1024 1024 1024 67.5 40.5
1000 SC 1000A 4 cond. Al 6400 6400 3840 176 105.6
1000 HRC1 1000A 4 cond. Al 1600 1600 960 84 50.4
1200 SC 1200A 4 cond. Al 6400 6400 3840 176 105.6
1250 SC 1250A 4 cond. Al 6400 6400 3840 176 105.6
1250 HRC1 1250A 4 cond. Al 2500 2500 1500 105 63
1500 SC 1500A 4 cond. Al 6400 6400 3840 176 105.6
1600 SC 1600A 4 cond. Al 6400 6400 3840 176 105.6
1600 HRC1 1600A 4 cond. Al 2500 2500 1500 105 63
2000 SC 2000A 4 cond. Al 6400 6400 3840 176 105.6
2000 HRC1 2000A 4 cond. Al 3600 3600 2160 132 79.2
2250 HRC2 2250A 4 cond. Al 4900 4900 2940 154 92.4
2400 SC 2400A 4 cond. Al 25600 25600 15360 352 211.2
2500 SC 2500A 4 cond. Al 25600 25600 15360 352 211.2
2500 HRC2 2500A 4 cond. Al 8100 8100 4860 198 118.8
3000 SC 3000A 4 cond. Al 25600 25600 15360 352 211.2
3200 SC 3200A 4 cond. Al 25600 25600 15360 352 211.2
3200 HRC2 3200A 4 cond. Al 8100 8100 4860 198 118.8
4000 SC 4000A 4 cond. Al 25600 25600 15360 352 211.2
4000 HRC2 4000A 4 cond. Al 8100 8100 4860 198 118.8
4500 HRC2 4500A 4 cond. Al 10000 10000 6000 220 132
Size Type I
2
t
ph
I
2
t
N
I
2
t
PE
I
peakph
I
peakN
[(kA)
2
s] [(kA)
2
s] [(kA)
2
s] [kA] [kA]
Table 5: Values of the withstood energy and peak current of
aluminium BTS
Size Type I
2
t
ph
I
2
t
N
I
2
t
PE
I
peakph
I
peakN
[(kA)
2
s] [(kA)
2
s] [(kA)
2
s] [kA] [kA]
99 98 ABB SACE - Electrical devices ABB SACE - Electrical devices
2.6 Busbar trunking systems 2.6 Busbar trunking systems
2 Protection of feeders 2 Protection of feeders
1000
) sin cos ( 3
m m t
x r L Ib a
u
+
.
=
[V] (6a)
. . . . .
∆
1000
) sin cos ( 2
m m t
x r L Ib a
u
+
.
= [V] (6b)
. . . . .
∆
1
S
D
C
0
1
0
0
1
5
F
0
0
0
1
L L
l1
L2
L3
L
l2 l3
L1
Table 6: Current distribution factor
Type of Arrangement Current distribution
supply of loads factor
From one end only Load concentrated at the end 1
Evenly distributed load 0.5
From both ends Evenly distributed load 0.25
Central Load concentrated at the ends 0.25
Evenly distributed load 0.125
• I
b
is the load current [A];
• L is the BTS length [m];
• r
t
is the phase resistance per unit of length of BTS, measured under thermal
steady-state conditions [mΩ/m];
• x is the phase reactance per unit of length of BTS [mΩ/m];
• cosϕ
m
is average power factor of the loads.
Percentage voltage drop is obtained from:
Protection of the outgoing feeders
If the outgoing feeder, which generally consists of cable duct, is not already
protected against short-circuit and overload by the device located upstream of
the cable, the following measures shall be taken:
- protection against short-circuit:
there is no need to protect the feeder against the short-circuit if simultaneously:
a. the length does not exceed 3 metres;
b. the risk of short-circuit is minimized;
c. there is no inflammable material nearby.
In explosive environments and environments with greater risk of fire, protection
against short-circuit is always required;
- protection against overload:
the current carrying capacity of the feeder is generally lower than that of the
BTS. It is therefore necessary to protect also the feeder against overload.
The protection device against overload can be placed inside the pull box or on
the incoming panel.
In the latter case, protection against overload can also be provided by the
circuit-breakers protecting the single outgoing feeder from the panel only if the
sum of their rated currents is lower or equal to the current carrying capacity I
z
of the outgoing feeder.
In locations with greater risk of fire, the overload protection device shall be
installed at the outgoing point, i.e. inside the pull box.
Voltage drop
If a BTS is particularly long, the value of the voltage drop must be verified.
For three-phase systems with a power factor (cosϕ
m
) not lower than 0.8, the
voltage drop can be calculated by using the following simplified formula:
For single-phase BTS the formula is:
where:
• a is the current distribution factor, which depends on the circuit supply and
the arrangement of the electric loads along the BTS, as shown in Table 6:
where U
r
is rated voltage.
To reduce the voltage drop in very long BTS the power can be supplied at an
intermediate position rather than at the end (see Table 6).
Calculation of voltage drop for unevenly distributed loads
If the loads cannot be considered to be evenly distributed, the voltage drop can
be calculated more accurately by using the formulas below.
For the distribution of the three-phase loads shown in the figure, the voltage
drop can be calculated by the following formula if the BTS has a constant cross
section (as usual):
100 %
.
=
r
U
u
u
(7)
∆
∆
)] sin sin sin ( ) cos cos cos ( [ 3
3 3 3 2 2 2 1 1 1 3 3 3 2 2 2 1 1 1
L I L I L I x L I L I L I r ∆u
t
+ + + + + =
L I L I
1000
sin cos 3 +
. .
=
mi i i mi i i t
x r
∆u [V] (8)
. . . .
1000
3
2
L I r
P
b t
j
.
= [W] (9a)
. .
1000
2
2
L I r
P
b t
j
.
= [W] (9b)
. .
Generally speaking, this formula becomes:
where:
• r
t
is the phase resistance per unit of length of BTS, measured under thermal
steady-state conditions [mΩ/m];
• x is the phase reactance per unit of length of BTS [mΩ/m];
• cosϕ
m
is average power factor of the i-th load;
• I
i
is i-th load current [A];
• L
i
is the distance of the i-th load from the beginning of the BTS [m].
Joule-effect losses
Joule-effect losses are due to the electrical resistance of the BTS.
The losses are dissipated in heat and contribute to the heating of the trunking
and of the environment. Calculation of power losses is useful for correctly
dimensioning the air-conditioning system for the building.
Three-phase losses are:
while single-phase losses are:
where:
• I
b
is the current used [A];
• r
t
is the phase resistance per unit of length of BTS measured under thermal
steady-state conditions [mΩ/m];
• L is the length of BTS [m].
For accurate calculations, losses must be assessed section by section on the
basis of the currents flowing through them; e.g. in the case of distribution of
loads shown in the previous figure:
Length Current Losses
1° section L
1
I
1
+I
2
+I
3
P
1
=3r
t
L
1
(I
1
+I
2
+I
3
)
2
2° section L
2
-L
1
I
2
+I
3
P
2
=3r
t
(L
2
-L
1
)(I
2
+I
3
)
2
3° section L
3
-L
2
I
3
P
3
=3r
t
(L
3
-L
2
)(I
3
)
2
Total losses in BTS P
tot
=P
1
+P
2
+P
3
101 100 ABB SACE - Electrical devices ABB SACE - Electrical devices
2.6 Busbar trunking systems
2 Protection of feeders 3 Protection of electrical equipment
Introduction
Upon supply of a lighting installation, for a brief period an initial current exceeding
the rated current (corresponding to the power of the lamps) circulates on the
network. This possible peak has a value of approximately 15÷20 times the
rated current, and is present for a few milliseconds; there may also be an inrush
current with a value of approximately 1.5÷3 times the rated current, lasting up
to some minutes. The correct dimensioning of the switching and protection
devices must take these problems into account.
The most commonly used lamps are of the following types:
- incandescent;
- halogen;
- fluorescent;
- high intensity discharge: mercury vapour, metal halide and sodium vapour.
Incandescent lamps
Incandescent lamps are made up of a glass bulb containing a vacuum or inert
gas and a tungsten filament. The current flows through this filament, heating it
until light is emitted.
The electrical behaviour of these lamps involves a high peak current, equal to
approximately 15 times the rated current; after a few milliseconds the current
returns to the rated value. The peak is caused by the lamp filament which,
initially cold, presents a very low electrical resistance. Subsequently, due to the
very fast heating of the element, the resistance value increases considerably,
causing the decrease in the current absorbed.
3.1 Protection and switching of lighting
circuits
1
S
D
C
0
1
0
0
0
3
F
0
9
0
1
4-5 milliseconds Time [milliseconds]
In
15÷20 In
Peak
I [A]
Peak current diagram Inrush current diagram
I [A]
Inrush
1.5÷3 In
Time [minutes] 3- 5 min.
103 102 ABB SACE - Electrical devices ABB SACE - Electrical devices
3 Protection of electrical equipment 3 Protection of electrical equipment
3.1 Protection and switching of lighting circuits 3.1 Protection and switching of lighting circuits
Lamp type Peak current Inrush current Turn-on time
Incandescent lamps 15In - -
Halogen lamps 15In - -
Fluorescent Non PFC − 2In 10 s
lamp PFC 20In 1÷6 s
High intensity Non PFC − 2In 2÷8 min
discharge lamps PFC 20In 2In 2÷8 min
High intensity discharge lamps: mercury vapour, metal
halide and sodium vapour
The functioning of high intensity discharge lamps is the same as that of
fluorescent lamps with the difference that the discharge occurs in the presence
of a gas at high pressure. In this case, the arc is able to vaporize the metallic
elements contained in the gas, releasing energy in the form of radiation which
is both ultraviolet and within the visible spectrum. The special type of bulb
glass blocks the ultraviolet radiation and allows only the visible radiation to
pass through. There are three main types of high intensity discharge lamps:
mercury vapour, metal halide and sodium vapour. The colour characteristics
and the efficiency of the lamp depend upon the different metallic elements
present in the gas, which are struck by the arc.
High intensity discharge lamps require a suitably sized controller and a heating
period which can last some minutes before the emission of the rated light output.
A momentary loss of power makes the restarting of the system and the heating
necessary.
Non PFC lamps have inrush currents of up to twice the rated current for
approximately 5 minutes.
PFC lamps have a peak current equal to 20 times the rated current, and an
inrush current of up to twice the rated current for approximately 5 minutes.
Protection and switching devices
IEC 60947-4-1 identifies two specific utilization categories for lamp control
contactors:
• AC-5a switching of electric discharge lamps;
• AC-5b switching of incandescent lamps.
The documentation supplied by the manufacturer includes tables for contactor
selection, according to the number of lamps to be controlled, and to their type.
Halogen lamps
Halogen lamps are a special type of incandescent lamp in which the gas
contained within the bulb prevents the vaporized material of the tungsten filament
from depositing on the surface of the bulb and forces re-deposition on the
filament. This phenomenon slows the deterioration of the filament, improves
the quality of the light emitted and increases the life of the lamp.
The electrical behaviour of these lamps is the same as that of incandescent
lamps.
Fluorescent lamps
Fluorescent lamps are a so-called discharge light source. The light is produced
by a discharge within a transparent enclosure (glass, quartz, etc. depending on
the type of lamp) which contains mercury vapour at low pressure.
Once the discharge has started, the gas within the enclosure emits energy in
the ultraviolet range which strikes the fluorescent material; in turn, this material
transforms the ultraviolet radiation into radiation which has a wavelength within
the visible spectrum. The colour of the light emitted depends upon the fluorescent
material used.
The discharge is created by an appropriate peak in voltage, generated by a
starter. Once the lamp has been switched on, the gas offers an ever lower
resistance, and it is necessary to stabilize the intensity of the current, using a
controller (reactor); this lowers the power factor to approximately 0.4÷0.6;
normally a capacitor is added to increase the power factor to a value of more
than 0.9
There are two types of controllers, magnetic (conventional) and electronic, which
absorb from 10% to 20% of the rated power of the lamp. Electronic controllers
offer specific advantages such as a saving in the energy absorbed, a lower
dissipation of heat, and ensure a stable, flicker-free light. Some types of
fluorescent lamps with electronic reactors do not need a starter.
Compact fluorescent lamps are made up of a folded tube and a plastic base
which contains, in some cases, a conventional or electronic controller.
The value of the inrush current depends upon the presence of a power factor
correction capacitor:
- non PFC lamps have inrush currents equal to approximately twice the rated
current and a turn-on time of about ten seconds;
- in PFC lamps, the presence of the capacitor allows the reduction of the turn-
on time to a few seconds, but requires a high peak current, determined by
the charge of the capacitor, which can reach 20 times the rated current.
If the lamp is fitted with an electronic controller, the initial transient current may
lead to peak currents equal to, at maximum, 10 times the rated current.
105 104 ABB SACE - Electrical devices ABB SACE - Electrical devices
3 Protection of electrical equipment 3 Protection of electrical equipment
3.1 Protection and switching of lighting circuits 3.1 Protection and switching of lighting circuits
1
S
D
C
0
1
0
0
0
4
F
0
9
0
1
Turning-on characteristics
Circuit-breaker characteristics
Contactor Icw
[t]
[A]
Figure 1: Approximate diagram for the coordination of lamps with
protection and switching devices
1
S
D
C
0
1
0
0
3
2
F
0
2
0
1
Ur= 400 V Ik= 15 kA
Incandescent/halogen lamps
Circuit-breaker type
Setting PR221 DS
Contactor type
Rated Power [W]
60
100
200
300
500
1000
Rated current Ib [A]
0.27
0.45
0.91
1.37
2.28
4.55
S270 D20
----
A26
57
34
17
11
6
3
S270 D20
----
A26
65
38
19
12
7
4
S270 D25
----
A26
70
42
20
13
8
4
S270 D32
----
A26
103
62
30
20
12
6
S270 D50
----
A30
142
85
42
28
16
8
T2N160 In63
L= 0.68- A S= 8- B
A40
155
93
46
30
18
9
T2N160 In63
L= 0.92- A S= 10- B
A50
220
132
65
43
26
13
T2N160 In100
L= 0.68- A S= 8- B
A63
246
147
73
48
29
14
T2N160 In100
L= 0.76- A S= 8- B
A75
272
163
80
53
32
16
T2N160 In100
L= 1- A S= 10- B
A95
355
210
105
70
42
21
T2N160 In160
L= 0.68- A S= 7- B
A110
390
240
120
80
48
24
N° lamps per phase
Table 1: Incandescent and halogen lamps
For the selection of a protection device the following verifications shall be carried
out:
- the trip characteristic curve shall be above the turning-on characteristic curve
of the lighting device to avoid unwanted trips; an approximate example is
shown in Figure1;
- coordination shall exist with the contactor under short-circuit conditions (lighting
installations are not generally characterized by overloads).
With reference to the above verification criteria, the following tables show the
maximum number of lamps per phase which can be controlled by the
combination of ABB circuit-breakers and contactors for some types of lamps,
according to their power and absorbed current I
b
(
*
)
, for three phase installations
with a rated voltage of 400 V and a maximum short-circuit current of 15 kA.
(
*
)
For calculation see Annex B Calculation of load current I
b
107 106 ABB SACE - Electrical devices ABB SACE - Electrical devices
3 Protection of electrical equipment 3 Protection of electrical equipment
3.1 Protection and switching of lighting circuits 3.1 Protection and switching of lighting circuits
1
S
D
C
0
1
0
0
3
3
F
0
2
0
1
Ur= 400 V Ik= 15 kA
Fluorescent lamps non PFC
Circuit-breaker type
Setting PR221 DS
Contactor type
Rated Power [W]
20
40
65
80
100
110
Rated current Ib [A]
0.38
0.45
0.7
0.8
1.15
1.2
S270 D16
A26
40
33
21
18
13
12
S270 D20
A26
44
37
24
21
14
14
S270 D20
A26
50
42
27
23
16
15
S270 D32
A26
73
62
40
35
24
23
S270 D40
A30
100
84
54
47
33
31
S270 D50
A40
110
93
60
52
36
35
S270 D63
A50
157
133
85
75
52
50
T2N160 In100
L= 0.68- A S= 10- B
A63
173
145
94
82
57
55
T2N160 In100
L= 0.76- A S= 10- B
A75
192
162
104
91
63
60
T2N160 In100
L= 0.96- A- S= 10- B
A95
250
210
135
118
82
79
T2N160 In160
S= 0.68- A S= 10- B
A110
278
234
150
132
92
88
N° lamps per phase
Ur= 400 V Ik= 15 kA
Fluorescent lamps PFC
Circuit-breaker type
Setting PR221 DS
Contactor type
Rated Power [W]
20
40
65
80
100
110
Rated current Ib [A]
0.18
0.26
0.42
0.52
0.65
0.7
S270 D25
---
A26
83
58
35
28
23
21
S270 D25
---
A26
94
65
40
32
26
24
S270 D32
---
A26
105
75
45
36
29
27
S270 D40
---
A26
155
107
66
53
43
40
S270 D63
---
A30
215
150
92
74
59
55
T2N160 In63
L= 0.68- A S= 8- B
A40
233
160
100
80
64
59
T2N160 In63
L= 1- A S= 10- B
A50
335
230
142
115
92
85
T2N160 In100
L= 0.68- A S= 10- B
A63
360
255
158
126
101
94
T2N160 In100
L= 0.76- A S= 10- B
A75
400
280
173
140
112
104
T2N160 In100
L= 0.96- A S= 10- B
A95
530
365
225
180
145
135
N° lamps per phase Capacitor [µF]
5
5
7
7
16
18
Table 2: Fluorescent lamps
109 108 ABB SACE - Electrical devices ABB SACE - Electrical devices
3 Protection of electrical equipment 3 Protection of electrical equipment
3.1 Protection and switching of lighting circuits 3.1 Protection and switching of lighting circuits
Example:
Switching and protection of a lighting system, supplied by a three phase network
at 400 V 15 kA, made up of 55 incandescent lamps, of 200 W each, per phase.
In Table 1, on the row corresponding to 200 W, select the cell showing the
number of controllable lamps immediately above the number of lamps per phase
present in the installation. In the specific case, corresponding to the cell for 65
lamps per phase the following equipment are suggested:
- ABB Tmax T2N160 In63 circuit-breaker with PR221/DS type electronic release,
with protection L set at 0.92, curve A and protection S set at 10, curve B;
- A50 contactor.
1
S
D
C
0
1
0
0
3
4
F
0
2
0
1
Ur= 400 V Ik= 15 kA
Fluorescent lamps non PFC
Fluorescent lamps PFC
Ur= 400 V Ik= 15 kA
Circuit-breaker type
Setting PR221 DS
Contactor type
Rated Power [W]
150
250
400
600
1000
Rated current Ib [A]
1.8
3
4.4
6.2
10.3
S270 D16
A26
6
4
3
1
-
S270 D2
A26
7
4
3
2
1
S270 D20
A26
8
5
3
2
1
S270 D32
A26
11
7
4
3
2
S270 D40
A30
15
9
6
4
3
S270 D40
A40
17
10
7
5
3
S270 D50
A50
23
14
9
7
4
S270 D63
A63
26
16
10
8
5
T2N160 In100
L= 0.8- B S= 6.5- B
A75
29
17
12
8
5
T2N160 In100
L= 1- B S= 8- B
A95
38
23
15
11
6
T2N160 In160
L= 0.8- B S= 6.5- B
A110
41
25
17
12
7
N° lamps per phase
Circuit-breaker type
Setting PR221 DS
Contactor type
Rated Power [W]
150
250
400
600
1000
Rated current Ib [A]
1
1.5
2.5
3.3
6.2
S270 D16
---
A26
13
8
5
4
-
S270 D20
---
A26
14
9
5
4
-
S270 D20
---
A26
15
10
6
5
-
S270 D32
---
A26
23
15
9
7
4
S270 D40
---
A30
28
18
11
8
4
S270 D40
---
A40
30
20
12
9
5
T2N160 In100
L= 0.8- B S= 6.5- B
A50
50
33
20
15
8
T2N160 In100
L= 0.88- B S= 6.5- B
A63
58
38
23
17
9
T2N160 In100
L= 1- B S= 6.5- B
A75
63
42
25
19
10
T2N160 In160
L= 0.84- B S= 4.5- B
A95
81
54
32
24
13
N° lamps per phase Capacitor [µF]
20
36
48
65
100
T2N160 In160
L= 0.88- B S= 4.5- B
A110
88
59
36
27
14
Table 3: High intensity discharge lamps
111 110 ABB SACE - Electrical devices ABB SACE - Electrical devices
3 Protection of electrical equipment 3 Protection of electrical equipment
%
100
' '
d
rg
kg
X
I
I
.
=
r
rg
rg
U
S
I
.
=
3
I
3
≥ I
kg
As a first approximation, it can be estimated that the maximum value of the
short-circuit current of a generator, with rated power S
rg
, at the rated voltage of
the installation U
r
, is equal to:
where
I
rg
is the rated current of the generator:
The circuit-breaker for the protection of the generator shall be selected according
to the following criteria:
• the set current higher than the rated current of the generator: I
1
≥ I
rg
;
• breaking capacity I
cu
or I
cs
higher than the maximum value of short-circuit
current at the installation point:
- in the case of a single generator: I
cu
(I
cs
) ≥ I
kg
;
- in the case of n identical generators in parallel: I
cu
(I
cs
) ≥ I
kg
·(n-1);
- in the case of operation in parallel with the network: I
cu
(I
cs
) ≥ I
kNet,
as the short-circuit contribution from the network is normally
greater than the contribution from the generator;
• for circuit-breakers with thermomagnetic releases: low magnetic trip threshold:
I
3
=2.5/3·I
n
;
• for circuit-breakers with electronic releases:
- trip threshold of the delayed short-circuit protection function (S), set
between 1.5 and 4 times the rated current of the generator, in such
a way as to “intercept” the decrement curve of the generator:
I
2
= (1.5÷4)·I
rg
; if the function S is not present, function I can be set
at the indicated values I
3
= (1.5÷4)·I
rg
;
- trip threshold of the instantaneous short-circuit protection function
(I
3
) set at a value greater than the rated short-circuit current of the
generator, so as to achieve discrimination with the devices installed
downstream, and to allow fast tripping in the event of a short-circuit
upstream of the device (working in parallel with other generators or
with the network):
1
S
D
C
0
1
0
0
1
8
F
0
2
0
1
Synchronous
phase
Transient
phase
Subtransient
phase
x I
rg
10 1
1
t [s]
10
1
10
-1
10
-2
10
-3
10
2
The need to guarantee an ever greater continuity of service has led to an increase
in the use of emergency supply generators, either as an alternative to, or in
parallel with the public utility supply network.
Typical configurations include:
• “Island supply” (independent functioning) of the priority loads in the case of a
lack of energy supply through the public network;
• supply to the user installation in parallel with the public supply network.
Unlike the public supply network, which has a constant contribution, in case of
a short-circuit, the current supplied by the generator is a function of the
parameters of the machine itself, and decreases with time; it is possible to
identify the following successive phases:
1. a subtransient phase: with a brief duration (10÷50 ms), characterized
by the subtransient reactance X”
d
(5÷20% of the rated impedance value),
and by the subtransient time constant T”
d
(5÷30 ms);
2. a transitory phase: may last up to some seconds (0.5÷2.5 s), and is
characterized by the transitory reactance X’
d
(15÷40% of the rated
impedance value), and by the transitory time constant T’
d
(0.03÷2.5 s);
3. a synchronous phase: may persist until the tripping of external protection,
and is characterized by the synchronous reactance X
d
(80÷300% of
the rated impedance value).
3.2 Protection and switching of generators
3.2 Protection and switching of generators
113 112 ABB SACE - Electrical devices ABB SACE - Electrical devices
3 Protection of electrical equipment 3 Protection of electrical equipment
3.2 Protection and switching of generators 3.2 Protection and switching of generators
1
S
D
C
0
1
0
0
1
7
F
0
0
0
1
4
6
7
9
11
14
17
19
21
22
28
31
35
38
42
44
48
55
69
80
87
100
111
138
159
173
180
190
208
218
242
277
308
311
346
381
415
436
484
554
692
727
865
1107 S7 1600 E2/E3 1600
1730 S8 2500 E3 2500
2180
2214
2250
2500
2800
3150
3500 E6 5000/6300
S
rg
[kVA] MCB MCCB ACB
T2 160 In=10
T2 160 In=25
T2 160 In=63
T2 160 In=100
T2 160 In=160
T4 250
T4 320
T5 400
S8 3200 E3 3200
E4 4000
T3 250
T4 250
T5 630
S6 800
E1/E2 1250
S6 800
S7 1000
S7 1250
4
6
7
9
11
14
17
19
21
22
28
31
35
38
42
44
48
55
69
80
87
100
111
138
159
173
180
190
208
218
242
277
308
311
346
381
415
436
484 T5 630
554
692
727
865 S6 800
1107 S7 1000 E1/E2 1250
1730 S7 1600 E2/E3 1600
2180
2214
2250
2500
2800
3150
3500
MCB MCCB ACB
T2 160 In=10
T2 160 In=25
T2 160 In=63
T2 160 In=100
T2 160 In=160
T3 250
T4 250
T4 320
S8 3200 E3 3200
T5 400
E1 800
T5 630
S6 800
S8 2500
E2 2000
E3 2500
E3 2500
1
S
D
C
0
1
0
0
1
6
F
0
0
0
1
4 S20L/S260 B6
6
7
9 S20L/S260 B13
11 S20L/S260 B16
14
17
19
21
22
28
31
35
38
42
44
48
55
69 S280 B100
80
87
100 T2 160
111
138
159
173
180
190
208
218
242
277
308
311
346
381
415
436
484
554
692
727
865 E2/E3 1600
1107 S7 1600 E2/E3 2000
1730 E3 3200
2180 E3 3200/E4 4000
2214
2250
2500
2800
3150
3500
E6 5000/6300
S6 800
S7 1250
E1/E2 1250
S7 1250
S8 3200
E4 4000
T3 250
T4 250
T4 320
T5 400
T5 630
S6 800
S280 B80
T2 160 In=100
T2 160 In=160
T4 250
S20L/S260 B32
T2 160 In=63 S20L/S260 B50
S20L/S260 B63
T2 160 In=10
S20L/S260 B10
T2 160 In=25
S20L/S260 B25
S
rg
[kVA] MCB MCCB ACB
4 S20L/S260 B6
6 S20L/S260 B8
7 S20L/S260 B10
9 S20L/S260 B13
11 S20L/S260 B16
14 S20L/S260 B20
17 S20L/S260 B25
19
21
22
28 S20L/S260 B40
31
35
38
42
44
48
55
69 S280 B100
80
87
100
111
138 T4 250
159
173
180
190
208
218
242
277 T5 400
308
311
346
381
415
436
484
554
692
727
865 S7 1250
1107 S7 1600 E2/E3 1600
1730 E3 2500
2180
2214
2250
2500 E4 3600
2800 E4 4000
3150
3500
E6 5000/6300
T2 160 In=63 S20L/S260 B50
S20L/S260 B63
S280 B80
T2 160 In=100
T2 160 In=160
T4 320
E1/E2 1250
S7 1000
S6 800
S7 1000
S8 3200
E3 3200
T3 250
T4 250
T5 630
S6 800
T2 160 In=160
S20L/S260 B32
T2 160 In=10
T2 160 In=25
S
rg
[kVA] MCB MCCB ACB
Table 3 500 V Table 4 690 V
Note: It is always advisable to check that the settings of the releases are correct with respect to the
effective decrement curve of the current of the generator to be protected.
The following tables give ABB SACE suggestions for the protection and switching
of generators; the tables refer to 400 V (Table 1), 440 V (Table 2), 500 V (Table 3)
and 690 V (Table 4).
Table 1 400 V Table 2 440 V
115 114 ABB SACE - Electrical devices ABB SACE - Electrical devices
3 Protection of electrical equipment 3 Protection of electrical equipment
Table 1: Utilization categories and typical applications
Current type Utilization categories Typical applications
Slip-ring motors: starting,
AC-2
switching off
Alternating Current ac
Squirrel-cage motors: starting,
AC-3
switching off during running
(1)
Squirrel-cage motors: starting,
AC-4
plugging, inching
(1)
AC-3 categories may be used for occasionally inching or plugging for limited time periods
such as machine set-up; during such limited time periods the number of such operations
should not exceed five per minutes or more than ten in a 10 minutes period.
3.3 Protection and switching of motors
Electromechanical starter
The starter is designed to:
- start motors;
- ensure continuous functioning of motors;
- disconnect motors from the supply line;
- guarantee protection of motors against working overloads.
The starter is typically made up of a switching device (contactor) and an overload
protection device (thermal release).
The two devices must be coordinated with equipment capable of providing
protection against short-circuit (typically a circuit-breaker with magnetic release
only), which is not necessarily part of the starter.
The characteristics of the starter must comply with the international Standard
IEC 60947-4-1, which defines the above as follows:
Contactor: a mechanical switching device having only one position of rest,
operated otherwise than by hand, capable of making, carrying and breaking
currents under normal circuit conditions including operating overload conditions.
Thermal release: thermal overload relay or release which operates in the case
of overload and also in case of loss of phase.
Circuit-breaker: defined by IEC 60947-2 as a mechanical switching device,
capable of making, carrying and breaking currents under normal circuit
conditions and also making, carrying for a specified time and breaking currents
under specified abnormal circuit conditions.
The main types of motor which can be operated and which determine the
characteristics of the starter are defined by the following utilization categories:
Time-Current Curves
1
S
D
C
0
1
0
0
1
9
F
0
2
0
1
10
-2
10
-1
10
1
10
2
10
3
10 s
4
s
s
s
s
s
T2 160
100 kVA generator
decrement curve
1s
10
-1
kA 1kA 10
1
kA
Example:
Protection of a generator with S
rg
= 100 kVA, in a system with a rated voltage
of 440 V.
The generator parameters are:
U
r
= 440 V
S
rg
= 100 kVA
f = 50 Hz
I
rg
= 131.2 A
X
’’
d
= 6.5 % (subtransient reactance)
X
’
d
= 17.6 % (transient reactance)
X
d
= 230 % (synchronous reactance)
T
’’
d
= 5.5 ms (subtransient time constant)
T
’
d
= 39.3 ms (transient time constant)
From table 2, an ABB SACE T2N160 circuit-breaker is selected, with I
n
= 160
A, with electronic release PR221-LS. For correct protection of the generator,
the following settings are selected:
function L: 0.84 – A, corresponding to 134.4 A, value greater than I
rg
function I: 1.5
3.2 Protection and switching of generators
117 116 ABB SACE - Electrical devices ABB SACE - Electrical devices
3 Protection of electrical equipment 3 Protection of electrical equipment
3.3 Protection and switching of motors 3.3 Protection and switching of motors
1
S
D
C
0
1
0
0
1
9
F
0
0
0
1
MCCB
KL
TOR
Motor
K∆
KY
MCCB
KL
TOR
Motor
1
S
D
C
0
1
0
0
1
8
F
0
0
0
1
Other types of starting for squirrel-cage motors are accomplished by reducing
the supply voltage of the motor: this leads to a reduction in the starting current
and of the motor torque, and an increase in the acceleration time.
Star-Delta starter
The most common reduced voltage starter is the Star-Delta starter (Y-∆), in
which:
- on starting, the stator windings are star-connected, thus achieving the
reduction of peak inrush current;
- once the normal speed of the motor is nearly reached, the switchover to delta
is carried out.
After the switchover, the current and the torque follow the progress of the curves
associated with normal service connections (delta).
As can be easily checked, starting the motor with star-connection gives a voltage
reduction of √3, and the current absorbed from the line is reduced by 1/3
compared with that absorbed with delta-connection.
The start-up torque, proportional to the square of the voltage, is reduced by 3
times, compared with the torque that the same motor would supply when del-
ta-connected.
This method is generally applied to motors with power from 15 to 355 kW, but
intended to start with a low initial resistant torque.
Starting sequence
By pressing the start button, contactors KL and KY are closed. The timer starts
to measure the start time with the motor connected in star. Once the set time
has elapsed, the first contact of the timer opens the KY contactor and the
second contact, delayed by approximately 50 ms, closes the K∆ contactor.
With this new configuration, contactors KL and K∆ closed, the motor becomes
delta-connected.
The choice of the starting method and also, if necessary, of the type of motor to
be used depends on the typical resistant torque of the load and on the short-
circuit power of the motor supplying network.
With alternating current, the most commonly used motor types are as follows:
- asynchronous three-phase squirrel-cage motors (AC-3): the most widespread
type due to the fact that they are of simple construction, economical and
sturdy; they develop high torque with short acceleration times, but require
elevated starting currents;
- slip-ring motors (AC-2): characterized by less demanding starting conditions,
and have quite a high starting torque, even with a supply network of low
power.
Starting methods
The most common starting methods for asynchronous squirrel-cage motors
are detailed below:
Direct starting
With direct starting, the DOL (Direct On Line) starter, with the closing of line
contactor KL, the line voltage is applied to the motor terminals in a single
operation. Hence a squirrel-cage motor develops a high starting torque with a
relatively reduced acceleration time. This method is generally used with small
and medium power motors which reach full working speed in a short time.
These advantages are, however, accompanied by a series of drawbacks,
including, for example:
- high current consumption and associated voltage drop which may cause
damages to the other parts of the system connected to the network;
- violent acceleration which has negative effects on mechanical transmission
components (belts, chains and mechanical joints), reducing working life.
119 118 ABB SACE - Electrical devices ABB SACE - Electrical devices
3 Protection of electrical equipment 3 Protection of electrical equipment
3.3 Protection and switching of motors 3.3 Protection and switching of motors
1
S
D
C
0
1
0
0
2
1
F
0
0
0
1
TOR
Motor
K2 K1
Inductance
3
r
I
3
r
I
3
r
I
1
S
D
C
0
1
0
0
2
0
F
0
0
0
1
MCCB
TOR
Motor
K1 K3 K2
Starting with inductive reactors or resistors
This type of starting is used for simple or double-cage rotors. The reduction of
the supply voltage is achieved by the insertion of inductive reactors or resistors,
in series to the stator. On start-up, the current is limited to 2.5÷3.5 times the
rated value.
On starting, the motor is supplied via contactor K2; once the normal speed is
reached, the reactors are short-circuited by the closing of contactor K1, and
are then excluded by the opening of contactor K2.
It is possible to achieve exclusions by step of the resistors or reactors with
time-delayed commands, even for motors with power greater than 100 kW.
The use of reactors notably reduces the power factor, while the use of resistors
causes the dissipation of a high power (Joule effect), even if limited to the
starting phase.
For a reduction K (0.6÷0.8) of the motor voltage, the torque is reduced by K
2
times (0.36÷0.64).
In compliance with the above mentioned Standard, starters can also be classified
according to tripping time (trip classes), and according to the type of coordination
achieved with the short-circuit protection device (Type 1 and Type 2).
Therefore, the motor starts at a reduced voltage, and when it has reached
approximately 80% of its normal speed, contactor K1 is opened and main
contactor K3 is closed. Subsequently, contactor K2 is opened, excluding the
autotransformer so as to supply the full network voltage.
The thermal release TOR, inserted in the delta circuit, can detect any 3
rd
harmonic
currents, which may occur due to saturation of the magnetic pack and by
adding to the fundamental current, overload the motor without involving the line.
With reference to the connection diagram, the equipment used for a Star/Delta
starter must be able to carry the following currents:
KL line contactor and K∆ delta contactor
KY star contactor
overload protection release
where I
r
is the rated current of the motor.
Starting with autotransformers
Starting with autotransformers is the most functional of the methods used for
reduced voltage starting, but is also the most expensive. The reduction of the
supply voltage is achieved by using a fixed tap autotransformer or a more
expensive multi tap autotransformer.
Applications can be found with squirrel-cage motors which generally have a
power from 50 kW to several hundred kilowatts, and higher power double-
cage motors.
The autotransformer reduces the network voltage by the factor K (K=1.25÷1.8),
and as a consequence the start-up torque is reduced by K
2
times compared
with the value of the full rated voltage.
On starting, the motor is connected to the taps of the autotransformer and the
contactors K2 and K1 are closed.
121 120 ABB SACE - Electrical devices ABB SACE - Electrical devices
3 Protection of electrical equipment 3 Protection of electrical equipment
3.3 Protection and switching of motors 3.3 Protection and switching of motors
The following is an example of the type of tables available:
Table 3: 400 V 50 kA DOL Normal Type 2
(Tmax, Isomax – Contactor – TOR)
Table 2: Trip class
Trip Class Tripping time in seconds (Tp)
10A 2 < Tp ≤ 10
10 4 < Tp ≤ 10
20 6 < Tp ≤ 20
30 9 < Tp ≤ 30
where Tp is the cold trip time of the thermal release at 7.2 times the set current
value (for example: a release in class 10 at 7.2 times the set current value must
not trip within 4 s, but must trip within 10 s).
It is normal procedure to associate class 10 with a normal start-up type, and
class 30 with a heavy duty start-up type.
Coordination type
Type 1
It is acceptable that in the case of short-circuit the contactor and the thermal
release may be damaged. The starter may still not be able to function and must
be inspected; if necessary, the contactor and/or the thermal release must be
replaced, and the breaker release reset.
Type 2
In the case of short-circuit, the thermal release must not be damaged, while
the welding of the contactor contacts is allowed, as they can easily be separated
(with a screwdriver, for example), without any significant deformation.
In order to clearly determine a coordination type, and therefore the equipment
necessary to achieve it, the following must be known:
• power of the motor in kW and type;
• rated system voltage;
• rated motor current;
• short-circuit current at installation point;
• starting type: DOL or Y/∆ - normal or heavy duty – Type 1 or Type 2.
The requested devices shall be coordinated with each other in accordance
with the prescriptions of the Standard.
For the most common voltages and short-circuit values (400 V - 440 V - 500 V
- 690 V 35 kA - 50 kA) and for the most frequently used starting types, such as
direct starting and Star/Delta starting, for asynchronous squirrel-cage motor
(AC-3), ABB supplies solutions with:
• magnetic circuit-breaker - contactor - thermal release;
• thermomagnetic circuit-breaker - contactor;
• thermomagnetic circuit-breaker with PR212 MP electronic release – contactor.
Trip classes
The trip classes differentiate between the thermal releases according to their
trip curve.
The trip classes are defined in the following table 2:
MA: magnetic only adjustable release
MF: fixed magnetic only release
1
S
D
C
0
1
0
0
2
2
F
0
2
0
1
Motor MCCB Contactor Thermal Overload Release
[kW] [A] [A] [A] [A]
0.37 1.1 T2S160 MF 1.6 21 A9 TA25DU1.4 1 1.4
0.55 1.5 T2S160 MF 1.6 21 A9 TA25DU1.8 1.3 1.8
0.75 1.9 T2S160 MF 2 26 A9 TA25DU2.4 1.7 2.4
1.1 2.8 T2S160 MF 3.2 42 A9 TA25DU4 2.8 4
1.5 3.5 T2S160 MF 4 52 A16 TA25DU5 3.5 5
2.2 5 T2S160 MF 5 65 A26 TA25DU6.5 4.5 6.5
3 6.6 T2S160 MF 8.5 110 A26 TA25DU8.5 6 8.5
4 8.6 T2S160 MF 11 145 A30 TA25DU11 7.5 11
5.5 11.5 T2S160 MF 12.5 163 A30 TA25DU14 10 14
7.5 15.2 T2S160 MA 20 210 A30 TA25DU19 13 19
11 22 T2S160 MA 32 288 A30 TA42DU25 18 25
15 28.5 T2S160 MA 52 392 A50 TA75DU42 29 42
18.5 36 T2S160 MA 52 469 A50 TA75DU52 36 52
22 42 T2S160 MA 52 547 A50 TA75DU52 36 52
30 56 T2S160 MA 80 840 A63 TA75DU80 60 80
37 68 T2S160 MA 80 960 A75 TA75DU80 60 80
45 83 T2S160 MA 100 1200 A95 TA110DU110 80 110
55 98 T3S250 MA 160 1440 A110 TA110DU110 80 110
75 135 T3S250 MA 200 1800 A145 TA200DU175 130 175
90 158 T3S250 MA 200 2400 A185 TA200DU200 150 200
110 193 T4S320 PR221-I In320 2720 A210 E320DU320 100 320
132 232 T5S400 PR221-I In400 3200 A260 E320DU320 100 320
160 282 T5S400 PR221-I In400 4000 A300 E320DU320 100 320
200 349 T5S630 PR221-I In630 5040 AF400 E500DU500 150 500
250 430 T5S630 PR221-I In630 6300 AF460 E500DU500 150 500
290 520 S6S800 PR211-I In800 8000 AF580 E800DU800 250 800
315 545 S6S800 PR211-I In800 9600 AF580 E800DU800 250 800
355 610 S6S800 PR211-I In800 9600 AF750 E800DU800 250 800
P
e
I
r
Type I
3
Type Type
Current
setting
min. max.
123 122 ABB SACE - Electrical devices ABB SACE - Electrical devices
3 Protection of electrical equipment 3 Protection of electrical equipment
3.3 Protection and switching of motors 3.3 Protection and switching of motors
Table 4: 400 V 50 kA DOL Heavy duty Type 2
(Tmax, Isomax – Contactor – TOR)
1
S
D
C
0
1
0
0
2
0
F
0
2
0
1
[kW] [A] [A] [A] [A]
0.37 1.1 T2S160 MF 1.6 21 A9 TA25DU1.4* 1 1.4
0.55 1.5 T2S160 MF 1.6 21 A9 TA25DU1.8* 1.3 1.8
0.75 1.9 T2S160 MF 2 26 A9 TA25DU2.4* 1.7 2.4
1.1 2.8 T2S160 MF 3.2 42 A9 TA25DU4* 2.8 4
1.5 3.5 T2S160 MF 4 52 A16 TA25DU5* 3.5 5
2.2 5 T2S160 MF 5 65 A26 TA25DU6.5* 4.5 6.5
3 6.6 T2S160 MF 8.5 110 A26 TA25DU8.5* 6 8.5
4 8.6 T2S160 MF 11 145 A30 TA25DU11* 7.5 11
5.5 11.5 T2S160 MF 12.5 163 A30 TA450SU60 4 10 15
7.5 15.2 T2S160 MA 20 210 A30 TA450SU60 3 13 20
11 22 T2S160 MA 32 288 A30 TA450SU60 2 20 30
15 28.5 T2S160 MA 52 392 A50 TA450SU80 2 23 40
18.5 36 T2S160 MA 52 469 A50 TA450SU80 2 23 40
22 42 T2S160 MA 52 547 A50 TA450SU60 40 60
30 56 T2S160 MA 80 840 A63 TA450SU80 55 80
37 68 T2S160 MA 80 960 A95 TA450SU80 55 80
45 83 T2S160 MA 100 1200 A110 TA450SU105 70 105
55 98 T3S250 MA 160 1440 A145 TA450SU140 95 140
75 135 T3S250 MA 200 1800 A185 TA450SU185 130 185
90 158 T3S250 MA 200 2400 A210 TA450SU185 130 185
110 193 T4S320 PR221-I In320 2720 A260 E320DU320 100 320
132 232 T5S400 PR221-I In400 3200 A300 E320DU320 100 320
160 282 T5S400 PR221-I In400 4000 AF400 E500DU500 150 500
200 349 T5S630 PR221-I In630 5040 AF460 E500DU500 150 500
250 430 T5S630 PR221-I In630 6300 AF580 E500DU500*** 150 500
290 520 S6S800 PR211-I In800 8000 AF750 E800DU800 250 800
315 545 S6S800 PR211-I In800 9600 AF750 E800DU800 250 800
355 610 S6S800 PR211-I In800 9600 AF750 E800DU800 250 800
Motor MCCB Contactor
P
e
I
r
Type
Setting
range
min. max.
Setting of
the
magnetic
release
Type Type**
No. of
turns of
the CT
primary
coil
* Provide a by-pass contactor of the same size during motor start-up
** For type E releases choose tripping class 30
*** Connecting kit not available. To use the connecting kit, replacement with release E800DU800 is necessary
MA: magnetic only adjustable release
MF: fixed magnetic only release
Thermal Overload Release
MA : magnetic only adjustable release
18.5 36 T2S160 MA52 469 A50 A50 A26 TA75DU25 18-25
22 42 T2S160 MA52 547 A50 A50 A26 TA75DU32 22-32
30 56 T2S160 MA80 720 A63 A63 A30 TA75DU42 29-42
37 68 T2S160 MA80 840 A75 A75 A30 TA75DU52 36-52
45 83 T2S160 MA100 1050 A75 A75 A30 TA75DU63 45 - 63
55 98 T2S160 MA100 1200 A75 A75 A40 TA75DU63 45 - 63
75 135 T3S250 MA160 1700 A95 A95 A75 TA110DU90 66 - 90
90 158 T3S250 MA200 2000 A110 A110 A95 TA110DU110 80 - 110
110 193 T3S250 MA200 2400 A145 A145 A95 TA200DU135 100 - 135
132 232 T4S320 PR221-I In320 2880 A145 A145 A110 E200DU200 60 - 200
160 282 T5S400 PR221-I In400 3600 A185 A185 A145 E200DU200 60 - 200
200 349 T5S630 PR221-I In630 4410 A210 A210 A185 E320DU320 100 - 320
250 430 T5S630 PR221-I In630 5670 A260 A260 A210 E320DU320 100 - 320
I3
LINE DELTA STAR
[kW] [A] Type [A] Type Type Type [A]
MOTOR MCCB Contactor
Type P
e
I
r
1
S
D
C
0
1
0
0
2
3
F
0
2
0
1
Thermal Overload Release
Table 5: 400 V 50 kA Y/∆ Normal Type 2
(Tmax, Isomax – Contactor – TOR)
125 124 ABB SACE - Electrical devices ABB SACE - Electrical devices
3 Protection of electrical equipment 3 Protection of electrical equipment
3.3 Protection and switching of motors 3.3 Protection and switching of motors
Contactor
min. max.
[kW] [A] [A]
* Connection kit not available
MA: magnetic only adjustable release
MF: fixed magnetic only release
Motor
Current
Type Type Type
MCCB
setting
I3 P
e
I
r
[A] [A]
0.37 1 T2H160 MF 1 13 A9 TA25DU1.4 1 1.4
0.55 1.4 T2H160 MF 1.6 21 A9 TA25DU1.8 1.3 1.8
0.75 1.7 T2H160 MF 2 26 A9 TA25DU2.4 1.7 2.4
1.1 2.2 T2H160 MF 2.5 33 A9 TA25DU3.1 2.2 3.1
1.5 3 T2H160 MF 3.2 42 A16 TA25DU4 2.8 4
2.2 4.4 T2H160 MF 5 65 A26 TA25DU5 3.5 5
3 5.7 T2H160 MF 6.5 84 A26 TA25DU6.5 4.5 6.5
4 7.8 T2H160 MF 8.5 110 A30 TA25DU11 7.5 11
5.5 10.5 T2H160 MF 11 145 A30 TA25DU14 10 14
7.5 13.5 T2H160 MA 20 180 A30 TA25DU19 13 19
11 19 T2H160 MA 32 240 A30 TA42DU25 18 25
15 26 T2H160 MA 32 336 A50 TA75DU32 22 32
18.5 32 T2H160 MA 52 469 A50 TA75DU42 29 42
22 38 T2H160 MA 52 547 A50 TA75DU52 36 52
30 52 T2H160 MA 80 720 A63 TA75DU63 45 63
37 63 T2H160 MA 80 840 A75 TA75DU80 60 80
45 75 T2H160 MA 100 1050 A95 TA110DU90 65 90
55 90 T4H250 PR221-I In160 1200 A110 TA110DU110 80 110
75 120 T4H250 PR221-I In250 1750 A145 E200DU200 60 200
90 147 T4H250 PR221-I In250 2000 A185 E200DU200 60 200
110 177 T4H250 PR221-I In250 2500 A210 E320DU320 100 320
132 212 T4H320 PR221-I In320 3200 A260 E320DU320 100 320
160 260 T5H400 PR221-I In400 3600 A300 E320DU320 100 320
200 320 T5H630 PR221-I In630 4410 AF 400 E500DU500 150 500
250 410 T5H630 PR221-I In630 5355 AF 460 E500DU500 150 500
290 448 S6H630 PR211-I In630 7560 AF 580 E500DU500* 150 500
315 500 S6H800 PR211-I In800 8000 AF 580 E800DU800 250 800
355 549 S6H800 PR211-I In800 9600 AF 580 E800DU800 250 800
1
S
D
C
0
1
0
0
2
4
F
0
2
0
1
Thermal Overload Release
Table 6: 440 V 50 kA DOL Normal Type 2
(Tmax, Isomax – Contactor – TOR)
1
S
D
C
0
1
0
0
2
1
F
0
2
0
1
* Provide a by-pass contactor of the same size during motor start-up
** For type E releases choose tripping class 30
*** Connecting kit not available. To use the connecting kit, replacement with release E800DU800 is necessary
No. of
turns of
the CT
primary
coil
Motor MCCB Contactor
P
e
I
r
Type Setting
range
min. max.
Type** Type
Setting of
the
magnetic
release
[kW] [A] [A] [A] [A]
0.37 1 T2H160 MF 1 13 A9 TA25DU1.4* 1 1.4
0.55 1.4 T2H160 MF 1.6 21 A9 TA25DU1.8* 1.3 1.8
0.75 1.7 T2H160 MF 2 26 A9 TA25DU2.4* 1.7 2.4
1.1 2.2 T2H160 MF 2.5 33 A9 TA25DU3.1* 2.2 3.1
1.5 3 T2H160 MF 3.2 42 A16 TA25DU4* 2.8 4
2.2 4.4 T2H160 MF 5 65 A26 TA25DU5* 3.5 5
3 5.7 T2H160 MF 6.5 84 A26 TA25DU6.5* 4.5 6.5
4 7.8 T2H160 MF 8.5 110 A30 TA25DU11* 7.5 11
5.5 10.5 T2H160 MF 11 145 A30 TA25DU14* 10 14
7.5 13.5 T2H160 MA 20 180 A30 TA450SU60 4 10 15
11 19 T2H160 MA 32 240 A30 TA450SU80 3 18 27
15 26 T2H160 MA 32 336 A50 TA450SU60 2 20 30
18.5 32 T2H160 MA 52 469 A50 TA450SU80 2 28 40
22 38 T2H160 MA 52 547 A50 TA450SU80 2 28 40
30 52 T2H160 MA 80 720 A63 TA450SU60 40 60
37 63 T2H160 MA 80 840 A95 TA450SU80 55 80
45 75 T2H160 MA 100 1050 A110 TA450SU105 70 105
55 90 T4H250 PR221-I In160 1200 A145 E200DU200 60 200
75 120 T4H250 PR221-I In250 1750 A185 E200DU200 60 200
90 147 T4H250 PR221-I In250 2000 A210 E320DU320 100 320
110 177 T4H250 PR221-I In250 2500 A260 E320DU320 100 320
132 212 T4H320 PR221-I In320 3200 A300 E320DU320 100 320
160 260 T5H400 PR221-I In400 3600 AF400 E500DU500 150 500
200 320 T5H630 PR221-I In630 4410 AF460 E500DU500 150 500
250 410 T5H630 PR221-I In630 5355 AF580 E500DU500*** 150 500
290 448 S6H630 PR211-I In630 7560 AF750 E500DU500*** 150 500
315 500 S6H800 PR211-I In800 8000 AF 750 E800DU800 250 800
355 549 S6H800 PR211-I In800 9600 AF 750 E800DU800 250 800
MA: magnetic only adjustable release
MF: fixed magnetic only release
Thermal Overload Release
Table 7: 440 V 50 kA DOL Heavy duty Type 2
(Tmax, Isomax – Contactor – TOR)
127 126 ABB SACE - Electrical devices ABB SACE - Electrical devices
3 Protection of electrical equipment 3 Protection of electrical equipment
3.3 Protection and switching of motors 3.3 Protection and switching of motors
Thermal Overload Release
1
S
D
C
0
1
0
0
2
6
F
0
2
0
1
* Connection kit not available
MA: magnetic only adjustable release
MF: fixed magnetic only release
min. max.
[kW] [A] [A]
Type Type Type
setting
MCCB
I3 P
e
I
r
Contactor Motor
Current
[A] [A]
0.37 0.88 T2L160 MF 1 13 A9 TA25DU1.0 0.63 1
0.55 1.2 T2L160 MF 1.6 21 A9 TA25DU1.4 1 1.4
0.75 1.5 T2L160 MF 1.6 21 A9 TA25DU1.8 1.3 1.8
1.1 2.2 T2L160 MF 2.5 33 A9 TA25DU3.1 2.2 3.1
1.5 2.8 T2L160 MF 3.2 42 A16 TA25DU4 2.8 4
2.2 4 T2L160 MF 4 52 A26 TA25DU5 3.5 5
3 5.2 T2L160 MF 6.5 84 A26 TA25DU6.5 4.5 6.5
4 6.9 T2L160 MF 8.5 110 A30 TA25DU8.5 6 8.5
5.5 9.1 T2L160 MF 11 145 A30 TA25DU11 7.5 11
7.5 12.2 T2L160 MF 12.5 163 A30 TA25DU14 10 14
11 17.5 T2L160 MA 20 240 A30 TA25DU19 13 19
15 23 T2L160 MA 32 336 A50 TA75DU25 18 25
18.5 29 T2L160 MA 52 392 A50 TA75DU32 22 32
22 34 T2L160 MA 52 469 A50 TA75DU42 29 42
30 45 T2L160 MA 52 624 A63 TA75DU52 36 52
37 56 T2L160 MA 80 840 A75 TA75DU63 45 63
45 67 T2L160 MA 80 960 A95 TA80DU80 60 80
55 82 T2L160 MA 100 1200 A110 TA110DU90 65 90
75 110 T4H250 PR221-I In160 1440 A145 E200DU200 60 200
90 132 T4H250 PR221-I In250 1875 A145 E200DU200 60 200
110 158 T4H250 PR221-I In250 2250 A185 E200DU200 60 200
132 192 T4H320 PR221-I In320 2720 A210 E320DU320 100 320
160 230 T5H400 PR221-I In400 3600 A260 E320DU320 100 320
200 279 T5H400 PR221-I In400 4000 A300 E320DU320 100 320
250 335 T5H630 PR221-I In630 4725 AF 400 E 500DU500 150 500
290 394 T5H630 PR221-I In630 5040 AF 460 E 500DU500 150 500
315 440 S6L630 PR211-I In630 7560 AF 580 E 500DU500* 150 500
355 483 S6L630 PR211-I In630 7560 AF 580 E 800DU800 250 800
1
S
D
C
0
1
0
0
2
5
F
0
2
0
1
I3 LINE DELTA STAR
[kW] [A]
Type [A] Type Type Type Type [A]
MA : Magnetic only adjustable release
MOTOR MCCB Contactor
P
e
I
r
18.5 32 T2H160 MA52 392 A 50 A 50 A 16 TA75DU25 18-25
22 38 T2H160 MA52 469 A 50 A 50 A 26 TA75DU25 18-25
30 52 T2H160 MA80 720 A 63 A 63 A 26 TA75DU42 29-42
37 63 T2H160 MA80 840 A 75 A 75 A 30 TA75DU42 29-42
45 75 T2H160 MA80 960 A 75 A 75 A30 TA75DU52 36-52
55 90 T2H160 MA100 1150 A 75 A 75 A40 TA75DU63 45 - 63
75 120 T4H250 PR221-I In250 1625 A95 A95 A75 TA80DU80 60-80
90 147 T4H250 PR221-I In250 1875 A95 A95 A75 TA110DU110 80-110
110 177 T4H250 PR221-I In250 2250 A145 A145 A95 E200DU200 60-200
132 212 T4H320 PR221-I In320 2720 A145 A145 A110 E200DU200 60-200
160 260 T5H400 PR221-I In400 3200 A185 A185 A145 E200DU200 60-200
200 320 T5H630 PR221-I In630 4095 A210 A210 A185 E320DU320 100-320
250 410 T5H630 PR221-I In630 5040 A260 A260 A210 E320DU320 100-320
Thermal Overload Release
Table 8: 440 V 50 kA Y/∆ Normal Type 2
(Tmax, Isomax – Contactor – TOR)
Table 9: 500 V 50 kA DOL Normal Type 2
(Tmax, Isomax – Contactor – TOR)
129 128 ABB SACE - Electrical devices ABB SACE - Electrical devices
3 Protection of electrical equipment 3 Protection of electrical equipment
3.3 Protection and switching of motors 3.3 Protection and switching of motors
1
S
D
C
0
1
0
0
2
7
F
0
2
0
1
Thermal Overload Release
I3 LINE DELTA STAR
[kW] [A] Type [A] Type Type Type Type [A]
MA: magnetic only adjustable release
MOTOR MCCB Contactor
P
e
I
r
22 34 T2L160 MA52 430 A 50 A 50 A 16 TA75DU25 18-25
30 45 T2L160 MA52 547 A 63 A 63 A 26 TA75DU32 22-32
37 56 T2L160 MA80 720 A 75 A 75 A 30 TA75DU42 29-42
45 67 T2L160 MA80 840 A 75 A 75 A30 TA75DU52 36 - 52
55 82 T2L160 MA100 1050 A 75 A 75 A30 TA75DU52 36 - 52
75 110 T4H250 PR221-I In250 1375 A95 A95 A50 TA80DU80 60-80
90 132 T4H250 PR221-I In250 1750 A95 A95 A75 TA110DU90 65-90
110 158 T4H250 PR221-I In250 2000 A110 A110 A95 TA110DU110 80-110
132 192 T4H320 PR221-I In320 2560 A145 A145 A95 E200DU200 60-200
160 230 T4H320 PR221-I In320 2880 A145 A145 A110 E200DU200 60-200
200 279 T5H400 PR221-I In400 3400 A210 A210 A145 E320DU320 100-320
250 335 T5H630 PR221-I In630 4410 A210 A210 A185 E320DU320 100-320
290 394 T5H630 PR221-I In630 5040 A260 A260 A210 E320DU320 100-320
Table 11: 500 V 50 kA Y/∆ Normal Type 2
(Tmax, Isomax – Contactor – TOR)
1
S
D
C
0
1
0
0
2
1
F
0
2
0
1
* Provide a by-pass contactor of the same size during motor start-up
** For type E releases choose tripping class 30
*** Connecting kit not available. To use the connecting kit, replacement with release E800DU800 is necessary
No. of
turns of
the CT
primary
coil
Motor MCCB Contactor
P
e
I
r
Type Setting
range
min. max.
Type** Type
Setting of
the
magnetic
release
[kW] [A] [A] [A] [A]
0.37 0.88 T2L160 MF 1 13 A9 TA25DU1.0* 0.63 1
0.55 1.2 T2L160 MF 1.6 21 A9 TA25DU1.4* 1 1.4
0.75 1.5 T2L160 MF 1.6 21 A9 TA25DU1.8* 1.3 1.8
1.1 2.2 T2L160 MF 2.5 33 A9 TA25DU3.1* 2.2 3.1
1.5 2.8 T2L160 MF 3.2 42 A16 TA25DU4* 2.8 4
2.2 4 T2L160 MF 4 52 A26 TA25DU5* 3.5 5
3 5.2 T2L160 MF 6.5 84 A26 TA25DU6.5* 4.5 6.5
4 6.9 T2L160 MF 8.5 110 A30 TA25DU8.5* 6 8.5
5.5 9.1 T2L160 MF 11 145 A30 TA25DU11* 7.5 11
7.5 12.2 T2L160 MF 12.5 163 A30 TA450SU60 4 10 15
11 17.5 T2L160 MA 20 240 A30 TA450SU60 3 13 20
15 23 T2L160 MA 32 336 A50 TA450SU60 2 20 30
18.5 29 T2L160 MA 52 392 A50 TA450SU80 2 27.5 40
22 34 T2L160 MA 52 469 A50 TA450SU80 2 27.5 40
30 45 T2L160 MA 52 624 A63 TA450SU60 40 60
37 56 T2L160 MA 80 840 A75 TA450SU60 40 60
45 67 T2L160 MA 80 960 A95 TA450SU80 55 80
55 82 T2L160 MA 100 1200 A145 TA450SU105 70 105
75 110 T4H250 PR221-I In160 1440 A145 E200DU200 60 200
90 132 T4H250 PR221-I In250 1875 A185 E200DU200 60 200
110 158 T4H250 PR221-I In250 2123 A210 E320DU320 100 320
132 192 T4H320 PR221-I In320 2720 A260 E320DU320 100 320
160 230 T5H400 PR221-I In400 3200 A300 E320DU320 100 320
200 279 T5H400 PR221-I In400 3600 AF400 E500DU500 150 500
250 335 T5H630 PR221-I In630 4725 AF460 E500DU500 150 500
290 394 T5H630 PR221-I In630 5040 AF580 E500DU500*** 150 500
315 440 S6L630 PR211-I In630 7560 AF750 E500DU500*** 150 500
355 483 S6L630 PR211-I In630 7560 AF750 E500DU500 150 500
MA: magnetic only adjustable release
MF: fixed magnetic only release
Thermal Overload Release
Table 10: 500 V 50 kA DOL Heavy duty Type 2
(Tmax, Isomax – Contactor – TOR)
131 130 ABB SACE - Electrical devices ABB SACE - Electrical devices
3 Protection of electrical equipment 3 Protection of electrical equipment
10
-2
10
-3
10
-2
10
-1
1
10
-1
1
[s]
1
S
D
C
0
1
0
0
2
2
F
0
0
0
1
[kA]
3.4 Protection and switching of
transformers
General aspects
Transformers are used to achieve a change in the supply voltage, for both
medium and low voltage supplies.
The choice of the protection devices must take into account transient insertion
phenomena, during which the current may reach values higher than the rated
full load current; the phenomenon decays in a few seconds.
The curve which represents these transient phenomena in the time-current
diagram, termed “inrush current I0”, depends on the size of the transformer
and can be evaluated with the following formula (the short-circuit power of the
network is assumed to be equal to infinity)
where:
K ratio between the maximum peak inrush current value ( I
0
) and the rated
current of the transformer (I
1r
): (K= I
0
/ I
1r
);
τ time constant of the inrush current;
I
1r
rated current of the primary;
t time.
The table below shows the indicative values for t and K parameters referred to
rated power Sr for oil transformers.
Sr [kVA] 50 100 160 250 400 630 1000 1600 2000
K = Io/I1r 15 14 12 12 12 11 10 9 8
τ ττ ττ [s] 0.10 0.15 0.20 0.22 0.25 0.30 0.35 0.40 0.45
Further to the above consideration, the follwing diagram shows the inrush
current curve for a 20/0.4kV of 400kVA transformer. This transformer has an
inrush current during the very first moments equal to about 8 times the rated
current; this transient phenomenon stops after a few tenths of a second.
Example:
For a Y/∆ Normal starting Type 2, of a three phase asynchronous squirrel-cage
motor with the following data:
rated voltage U
r
= 400 V
short-circuit current I
k
= 50 kA
rated motor power P
e
= 200 kW
from Table 5, on the relevant row, the following information can be found:
• I
r
(rated current): 349 A;
• short-circuit protection device: circuit-breaker T5S630 PR221-I In630;
• magnetic trip threshold: I
3
= 4410 A;
• line contactor: A210;
• delta contactor: A210;
• star contactor: A185;
• thermal release E320DU320, setting range 100÷320 A
(to be set at ).
A
I
r
202
3
=
3.3 Protection and switching of motors
=
0
I
2
) / (
1
t
r
e I K
–
⋅ ⋅
τ
133 132 ABB SACE - Electrical devices ABB SACE - Electrical devices
3 Protection of electrical equipment 3 Protection of electrical equipment
3.4 Protection and switching of transformers 3.4 Protection and switching of transformers
20
3
1000
r
r
r
U
S
I
⋅
⋅
= [A] (4)
1
S
D
C
0
1
0
0
2
4
F
0
0
0
1
kA 1kA 10kA
250 kVA Trafo
T4N250 PR221 In=250 A
10
-2
10
-1
10
1
10
2
10
3
10 s
4
s
s
s
s
s
1s
10
-1
) ( 3
t Net
r
k
Z Z
U
I
+ ⋅
= [A] (1)
r
r k
t
S
U u
Z
2
100
%
⋅ = [Ω] (2)
r k
r
r
r k
r
t
r
k
U u
S
S
U u
U
Z
U
I
⋅ ⋅
=
⎟
⎟
⎠
⎞
⎜
⎜
⎝
⎛
⋅ ⋅
=
⋅
=
% 3
100
100
%
3
) ( 3
2
[A] (3)
1
S
D
C
0
1
0
0
2
3
F
0
0
0
1
1kA 10kA
1s
10
-2
s
10
-1
s
In summary: for the correct protection of the transformer and to avoid unwanted
trips, the trip curve of the protection device must be above the inrush current
curve and below the overload point.
The diagram below shows a possible position of the time-current curve of an
upstream protection device of a 690/400 V, 250 kVA transformer with u
k
% = 4 %.
Criteria for the selection of protection devices
For the protection at the LV side of MV/LV transformers, the selection of a
circuit-breaker shall take into account:
• the rated current at LV side of the protected transformer (this value is the
reference value for the rated current of the circuit-breaker and the setting of
the protections);
• the maximum short-circuit current at the point of installation (this value
determines the minimum breaking capacity (I
cu
/I
cs
) of the protection device).
MV/LV unit with single transformer
The rated current at the LV side of the transformer (I
r
) is determined by the
following formula:
where:
• S
r
is the rated power of the transformer [kVA];
• U
r20
is the rated LV no-load voltage of the transformer [V].
The transformer protection devices must also guarantee that the transformer
cannot operate above the point of maximum thermal overload under short-
circuit conditions; this point is defined on the time-current diagram by the value
of short-circuit current which can pass through the transformer and by a time
equal to 2 s, as stated by Standard IEC 60076-5. The short-circuit current (I
k
)
flowing for a fault with low impedance at the LV terminals of the transformer is
calculated by using the following formula:
where:
• U
r
is the rated voltage of the transformer [V];
• Z
Net
is the short-circuit impedance of the network [Ω];
• Z
t
is the short-circuit impedance of the transformer; from the rated power of
the transformer (S
r
[VA]) and the percentage short-circuit voltage (u
k
%) it is
equal to:
Considering the upstream short-circuit power of the network to be infinite
(Z
Net
=0), formula (1) becomes:
The diagram below shows the inrush current curve for a 20/0.4 kV of 400 kVA
transformer (u
k
% = 4 %) and the point referred to the thermal ability to withstand
the short-circuit current (Ik; 2 sec.).
135 134 ABB SACE - Electrical devices ABB SACE - Electrical devices
3 Protection of electrical equipment 3 Protection of electrical equipment
3.4 Protection and switching of transformers 3.4 Protection and switching of transformers
1
S
D
C
0
1
0
0
2
5
F
0
0
0
1
I
k
= I
k1
+ I
k2
+ I
k3
I
k2
+ I
k3
I
k1
I
k2
I
k3
A
B
%
100
k
r
k
u
I
I
⋅
= [A] (5)
For a correct dimensioning, a circuit-breaker with a breaking capacity higher
than twice the short-circuit current of one of the transformers must be chosen
(assuming that all the transformers are equal and the loads are passive).
The circuit-breakers positioned on the outgoing feeders (circuit-breakers B)
shall have a breaking capacity higher than the sum of the short-circuit currents
of the three transformers, according to the hypothesis that the upstream network
short-circuit power is 750 MVA and the loads are passive.
The full voltage three-phase short-circuit current (I
k
), at the LV terminals of the
transformer, can be expressed as (assuming that the short-circuit power of the
network is infinite):
where:
u
k
% is the short-circuit voltage of the transformer, in %.
The protection circuit-breaker must have:
I
n
≥ I
r
;
I
cu
(I
cs
) ≥ I
k
.
If the short-circuit power of the upstream network is not infinite and cable or
busbar connections are present, it is possible to obtain a more precise value
for I
k
by using formula (1), where Z
Net
is the sum of the impedance of the
network and of the impedance of the connection.
MV/LV substation with more than one transformer in parallel
For the calculation of the rated current of the transformer, the above applies
(formula 4).
The breaking capacity of each protection circuit-breaker on the LV side shall be
higher than the short-circuit current equivalent to the short-circuit current of
each equal transformer multiplied by the number of them minus one.
As can be seen from the diagram below, in the case of a fault downstream of a
transformer circuit-breaker (circuit-breaker A), the short-circuit current that flows
through the circuit-breaker is equal to the contribution of a single transformer.
In the case of a fault upstream of the same circuit-breaker, the short-circuit
current that flows is equal to the contribution of the other two transformers in
parallel.
137 136 ABB SACE - Electrical devices ABB SACE - Electrical devices
3 Protection of electrical equipment 3 Protection of electrical equipment
3.4 Protection and switching of transformers 3.4 Protection and switching of transformers
Selection of the circuit-breaker
The following tables show some possible choices of ABB SACE circuit-breakers,
according to the characteristics of the transformer to be protected.
Table 1: Protection and switching of 230 V transformers
1
S
D
C
0
1
0
0
3
5
F
0
2
0
1
Sr uk Trafo Ir Busbar Ib
Trafo
Feeder Ik
Busbar Ik
[kVA] % [A] [A] [kA] size setting [kA] 32 A 63 A 125 A 160 A
1 x 63 158 158 3.9 T1B160 In=160 1 3.9 T1B160
2 x 63 158 316 3.9 T1B160 In=160 1 7.9
1 x 100 251 251 6.3 T4N320 In=320 0.9 6.3
2 x 100 251 502 6.2 T4N320 In=320 0.9 12.5
1 x 125 314 314 7.8 T5N400 In=400 0.9 7.8
2 x 125 314 628 7.8 T5N400 In=400 0.9 15.6
1 x 160 402 402 10.0 T5N630 In=630 0.7 10.0
2 x 160 402 803 9.9 T5N630 In=630 0.7 19.9
1 x 200 502 502 12.5 T5N630 In=630 0.9 12.5
2 x 200 502 1004 12.4 T5N630 In=630 0.9 24.8
1 x 250 628 628 15.6 T5N630 In=630 1 15.6
2 x 250 628 1255 15.4 T5N630 In=630 1 30.9
1 x 315 791 791 19.6 S6N800 In=800 1 19.6
2 x 315 791 1581 19.4 S6N800 In=800 1 38.7
1 x 400 1004 1004 24.8 S7S1250/E1B1250 In=1250 0.9 24.8
2 x 400 1004 2008 24.5 S7S1250/E1B1250 In=1250 0.9 48.9
1 x 500 1255 1255 30.9 S7S1600/E2B1600 In=1600 0.9 30.9
2 x 500 1255 2510 30.4 S7S1600/E2B1600 In=1600 0.9 60.7
1 x 630 1581 1581 38.7 S7S1600/E2B1600 In=1600 1 38.7
2 x 630 1581 3163 37.9 S7S1600/E2B1600 In=1600 1 75.9
3 x 630 1581 4744 74.4 S7S1600/E3S1600 In=1600 1 111.6
1 x 800 2008 2008 39.3 E3N2500 In=2500 0.9 39.3
2 x 800 2008 4016 38.5 E3N2500 In=2500 0.9 77.0
3 x 800 2008 6025 75.5 E3H2500 In=2500 0.9 113.2
1 x 1000 2510 2510 48.9 E3N3200 In=3200 0.8 48.9
2 x 1000 2510 5020 47.7 E3N3200 In=3200 0.8 95.3
3 x 1000 2510 7531 93.0 E3H3200 In=3200 0.8 139.5
1 x 1250 3138 3138 60.7 E3N3200 In=3200 1 60.7
2 x 1250 3138 6276 58.8 E3N3200 In=3200 1 117.7
3 x 1250 3138 9413 114.1 S8V3200/E6V3200 In=3200 1 171.2
5
4
4
5
5
4
4
4
4
4
4
4
4
Transformer Circuit-breaker "A" (LV side)
Release ABB SACE
Circuit-breaker
S250/S260
S250/S260
S250/S260
S250/S260
T1B160
T1B160
T1B160
S250/S260
S250/S260
S250/S260
T1B160
T1B160
T1B160
T1B160
T1B160
T1B160
T1C160
T1B160
S250/S260
T1B160
S250/S260
T1C160
T1B160
T1N160
T1C160
T2N160
T1C160
T2S160
T2L160
T1C160
T2S160
T2L160
T1N160
T4L250
T2H160
T4L250
T2N160
T2L160
250 A 400 A 630 A 800 A 1250 A 1600 A 2000 A 2500 A 3200 A 4000 A
T3N250
T3N250 T5N400
T3N250
T3N250 T5N400
T3N250
T3N250 T5N400 T5N630
T3N250 T5N400
T3N250 T5N400 T5N630
T3N250 T5N400
T3N250 T5N400 T5N630 S6N800
T3N250 T5N400 T5N630
T3N250 T5N400 T5N630 S6N800 S7S1250
T3N250 T5N400 T5N630 S6N800
T3N250 T5N400 T5N630 S6N800 S7S1250/E1N1250 S7S1600/E2N1600
T3N250 T5N400 T5N630 S6N800
T3S250 T5N400 T5N630 S6N800 S7S1250/E2N1250 S7S1600/E2N1600 E2N2000
T3N250 T5N400 T5N630 S6N800 S7S1250/E1N1250
T3S250 T5S400 T5S630 S6S800 S7S1250/E2L1250 S7S1600/E2L1600 E3H2000 E3H2500
T4L250 T5L400 T5L630 S6L800 S7L1250/E2L1250 S7L1600/E2L1600 E3L2000 E3L2500 E6V3200
T3N250 T5N400 T5N630 S6N800 S7S1250/E1B1250 S7S1600/E2B1600
T3S250 T5S400 T5S630 S6S800 S7S1250/E2L1250 S7S1600/E2L1600 E3H2000 E3H2500 E3H3200
T4L250 T5L400 T5L630 S6L800 S7L1250/E2L1250 S7L1600/E2L1600 E3L2000 E3L2500 E6V3200 E6V4000
T3N250 T5N400 T5N630 S6N800 S7S1250/E1N1250 S7S1600/E2N1600 E2N2000
T4H250 T5H400 T5H630 S6H800 S7H1250/E2L1250 S7H1600/E2L1600 E3H2000 E3H2500 E3H3200 E4H4000
T4L250 T5L400 T5L630 S6L800 S7L1250 S7L1600 E6V3200 E6V3200 E6V3200 E6V4000
T3S250 T5N400 T5N630 S6N800 S7S1250/E2N1250 S7S1600/E2N1600 E2N2000 E3N2500
T4L250 T5L400 T5L630 S6L800 S7L1250/E2L1250 S7L1600/E2L1600 E3L2000 E3L2500 E6V3200 E6V4000
T4L250 T5L400 T5L630 S6L800 S7L1250 S7L1600
Circuit-breaker "B" (Feeder circuit-breaker )
Feeder circuit-breaker type and rated current
139 138 ABB SACE - Electrical devices ABB SACE - Electrical devices
3 Protection of electrical equipment 3 Protection of electrical equipment
3.4 Protection and switching of transformers 3.4 Protection and switching of transformers
1
S
D
C
0
1
0
0
3
6
F
0
2
0
1
S
r
u
k
Trafo I
r
Busbar I
b
Trafo
Feeder I
k
Busbar I
k
[kVA] % [A] [A] [kA] size setting [kA] 32 A 63 A 125 A 160 A 250 A
1 x 63 91 91 2.2 T1B/T2N160 In=100 0.96 2.2
2 x 63 91 182 2.2 T1B/T2N160 In=100 0.96 4.4 T1B160
1 x 100 144 144 3.6 T1B/T2N160 In=160 0.92 3.6 T1B160
2 x 100 144 288 3.6 T1B/T2N160 In=160 0.92 7.2 T1B160
1 x 125 180 180 4.5 T3N250 In=250 0.95/0.8 4.5
2 x 125 180 360 4.4 T3N250 In=250 0.95/0.8 8.8
1 x 160 231 231 5.7 T3N250 In=250 0.95/0.95 5.7
2 x 160 231 462 5.7 T3N250 In=250 0.95/0.95 11.4 T3N250
1 x 200 289 289 7.2 T4N320 In=320 0.95 7.2 T3N250
2 x 200 289 578 7.1 T4N320 In=320 0.95 14.2 T3N250
1 x 250 361 361 8.9 T5N400 In=400 0.95 8.9 T3N250
2 x 250 361 722 8.8 T5N400 In=400 0.95 17.6 T3N250
1 x 315 455 455 11.2 T5N630 In=630 0.8 11.2 T3N250
2 x 315 455 910 11.1 T5N630 In=630 0.8 22.2 T3N250
1 x 400 577 577 14.2 T5N630/S6N800 In=630/800 0.95/0.8 14.2 T3N250
2 x 400 577 1154 14 T5N630/S6N800 In=630/800 0.95/0.8 28 T3N250
1 x 500 722 722 17.7 S6N800/S7S1250 In=800/1000 0.95/0.8 17.7 T3N250
2 x 500 722 1444 17.5 S6N800/S7S1250 In=800/1000 0.95/0.8 35.9 T3N250
1 x 630 909 909 22.3 S7S1250/E1B1250 In=1000 0.95 22.3 T3N250
2 x 630 909 1818 21.8 S7S1250/E1B1250 In=1000 0.95 43.6 T3S250
3 x 630 909 2727 42.8 S7S1250/E1N1250 In=1000 0.95 64.2 T4H250
1 x 800 1155 1155 22.6 S7S1250/E1B1250 In=1250 0.95 22.6 T3N250
2 x 800 1155 2310 22.1 S7S1250/E1B1250 In=1250 0.95 44.3 T3S250
3 x 800 1155 3465 43.4 S7S1250/E1N1250 In=1250 0.95 65 T4H250
1 x 1000 1443 1443 28.1 S7S1600/E2B1600 In=1600 0.95 28.1 T3N250
2 x 1000 1443 2886 27.4 S7S1600/E2B1600 In=1600 0.95 54.8 T4H250
3 x 1000 1443 4329 53.5 S7H1600/E2N1600 In=1600 0.95 80.2 T4L250
1 x 1250 1804 1804 34.9 E2B2000 In=2000 0.95 34.9 T3N250
2 x 1250 1804 3608 33.8 E2B2000 In=2000 0.95 67.7 T4H250
3 x 1250 1804 5412 65.6 E3S2000 In=2000 0.95 98.4 T4L250
1 x 1600 2309 2309 35.7 E3N2500 In=2500 0.95 35.7 T3N250
2 x 1600 2309 4618 34.6 E3N2500 In=2500 0.95 69.2 T4H250
3 x 1600 2309 6927 67 E3S2000 In=2500 0.95 100.6 T4L250
1 x 2000 2887 2887 44.3 E3N3200 In=3200 0.95 44.3 T3S250
2 x 2000 2887 5774 42.6 E3N3200 In=3200 0.95 85.1 T4L250
3 x 2000 2887 8661 81.9 E3H3200 In=3200 0.95 122.8 T4V250
1 x 2500 6.25 3608 3608 54.8 E4S4000 In=4000 1 54.8 T4H250
1 x 3125 6.25 4510 4510 67.7 E6H5000 In=5000 1 67.7 T4H250
T4L250
T2H160
T2S160
T4L250
T4L250
T2H160
T1N160
T2H160
T2L160
T1N160
T1C160
T1N160
T1B160
4
S250/S260
S250/S260
T1B160 S250/S260
S250/S260
Transformer Circuit-breaker "A" (LV side)
Release
S250/S260
4
S250/S260
T1C160
T1B160
T1C160
T1B160
T1C160
T2S160
T2H160
4
T1B160 S250/S260
4
T1B160 S250/S260
T1B160
S250/S260 T1B160
T1B160
T2H160
T2S160 5
5
5
6.25
T1C160
T1N160
T2H160
T2N160
T4L250
6.25
ABB SACE
Circuit-breaker
T2H160
4
4
4
4
4
4
400 A 630 A 800 A 1250 A 1600 A 2000 A 2500 A 3200 A 4000 A
T5N400
T5N400
T5N400
T5N400 T5N630
T5N400
T5N400 T5N630
T5N400 T5N630
T5N400 T5N630 S6N800
T5N400 T5N630 S6N800/E1B800
T5S400 T5S630 S6S800/E1N800 S7S1250/E1N1250
T5H400 T5H630 S6L800/E2N1250 S7L1250/E2N1250 S7L1600/E2N1600
T5N400 T5N630 S6N800/E1B800
T5S400 T5S630 S6S800/E1N800 S7S1250/E1N1250 S7S1600/E2N1600
T5H400 T5H630 S6L800/E2N1250 S7L1250/E2N1250 S7L1600/E2N1600 E2N2000 E3N2500
T5N400 T5N630 S6N800/E1B800 S7S1250/E1B1250
T5H400 T5H400 S6H800/E2N1250 S7H1250/E2N1250 S7H1600/E2N1600 E2N2000
T5L400 T5L630 S6L800/E3H1250 S7L1250/E3H1250 S7L1600/E3H1600 E3H2000 E3H2500 E3H3200
T5N400 T5N630 S6N800/E1B800 S7S1250/E1B1250 S7S1600/E2B1600
T5H400 T5H630 S6L800/E3H1250 S7L1250/E3S1250 S7L1600/E3S1600 E3S2000 E3S2500 E3S3200
T5L400 T5L630 S6L800/E3H1250 S7L1250/E3H1250 S7L1600/E3H1600 E3H2000 E3H2500 E3H3200 E4H4000
T5N400 T5N630 S6N800/E1B800 S7S1250/E1B1250 S7S1600/E2B1600
T5H400 T5H630 S6L800/E3S1250 S7L1250/E3S1250 S7L1600/E3S1600 E3S2000 E3S2500 E3S3200 E4S4000
T5L400 T5L630 S8V2000/E2L1600 E3L2000 E3L2500 E6V3200 E6V4000
T5S400 T5S630 S6S800/E1N800 S7S1250/E1N1250 S7S1600/E2N1600 E2N2000
T5L400 T5L630 S6L800/E3H1250 S7L1250/E3H1250 S7L1600/E3H1600 E3H2000 E3H2500 E3H3200 E4H4000
T5V400 T5V630 E2L1600 E3L2000 E3L2500 E6V3200 E6V4000
T5H400 T5H630 S6H800/E2N1250 S7H1250/E2N1250 S7H1600/E2N1600 E2N2000 E3N2500 E3N3200
T5H400 T5H630 S6L800/E3S1250 S7L1250/E3S1250 S7L1600/E3S1600 E3S2000 E3S2500 E3S3200 E4S4000
Circuit-breaker "B" (Feeder circuit-breaker )
Feeder circuit-breaker type and rated current
S8V2000/E2L1250
E2L1250
Table 2: Protection and switching of 400 V transformers
141 140 ABB SACE - Electrical devices ABB SACE - Electrical devices
3 Protection of electrical equipment 3 Protection of electrical equipment
3.4 Protection and switching of transformers 3.4 Protection and switching of transformers
1
S
D
C
0
1
0
0
3
7
F
0
2
0
1
S
r
u
k
Trafo I
r
Busbar I
b
Trafo
Feeder I
k
Busbar I
k
[kVA] % [A] [A] [kA] size setting [kA] 32 A 63 A 125 A 160 A 250 A
1 x 63 83 83 2.1 T1B/T2N160 In=100 0.9/0.88 2.1
2 x 63 83 165 2.1 T1B/T2N160 In=100 0.9/0.88 4.1 T1B160
1 x 100 131 131 3.3 T1B/T2N160 In=160 0.85/0.88 3.3
2 x 100 131 262 3.3 T1B/T2N160 In=160 0.85/0.88 6.5
1 x 125 164 164 4.1 T3N/T4N250 In=250 0.9/0.7 4.1 T1B160
2 x 125 164 328 4.1 T3N/T4N250 In=250 0.9/0.7 8.1 T3N250
1 x 160 210 210 5.2 T3N/T4N250 In=250 0.9 5.2
2 x 160 210 420 5.2 T3N/T4N250 In=250 0.9 10.4 T3N250
1 x 200 262 262 6.5 T5N400 In=320 0.9 6.5
2 x 200 262 525 6.5 T5N400 In=320 0.9 12.9 T3N250
1 x 250 328 328 8.1 T5N400 In=400 0.9 8.1 T3N250
2 x 250 328 656 8.1 T5N400 In=400 0.9 16.1 T3N250
1 x 315 413 413 10.2 T5N630 In=630 0.7 10.2 T3N250
2 x 315 413 827 10.1 T5N630 In=630 0.7 20.2 T3N250
1 x 400 525 525 12.9 T5N630 In=630 0.9 12.9 T3N250
2 x 400 525 1050 12.8 T5N630 In=630 0.9 25.6 T3S250
1 x 500 656 656 16.1 S6N800 In=800 0.9 16.1 T3N250
2 x 500 656 1312 15.9 S6N800 In=800 0.9 31.7 T3S250
1 x 630 827 827 20.2 S7S1250/E1B1250 In=1000 0.9 20.2 T3N250
2 x 630 827 1653 19.8 S7S1250/E1B1250 In=1000 0.9 39.7 T3S250
3 x 630 827 2480 38.9 S7S1250/E1B1250 In=1000 0.9 58.3 T4H250
1 x 800 1050 1050 20.6 S7S1250/E1B1250 In=1250 0.9 20.6 T3N250
2 x 800 1050 2099 20.1 S7S1250/E1B1250 In=1250 0.9 40.3 T4H250
3 x 800 1050 3149 39.5 S7S1250/E1B1250 In=1250 0.9 59.2 T4H250
1 x 1000 1312 1312 25.6 S7S1600/E2B1600 In=1600 0.9 25.6 T3S250
2 x 1000 1312 2624 24.9 S7S1600/E2B1600 In=1600 0.9 49.8 T4H250
3 x 1000 1312 3936 48.6 S7H1600/E2N1600 In=1600 0.9 72.9 T4L250
1 x 1250 1640 1640 31.7 E2B2000 In=2000 0.9 31.7 T3S250
2 x 1250 1640 3280 30.8 E2B2000 In=2000 0.9 61.5 T4H250
3 x 1250 1640 4921 59.6 E2N2000 In=2000 0.9 89.5 T4L250
1 x 1600 2099 2099 32.5 E2N2500 In=2500 0.9 32.5 T3S250
2 x 1600 2099 4199 31.4 E2N2500 In=2500 0.9 62.9 T4H250
3 x 1600 2099 6298 60.9 E2N2500 In=2500 0.9 91.4 T4L250
1 x 2000 2624 2624 40.3 E3N3200 In=3200 0.9 40.3 T4H250
2 x 2000 2624 5249 38.7 E3N3200 In=3200 0.9 77.4 T4L250
3 x 2000 2624 7873 74.4 E3S3200 In=3200 0.9 111.7 T4V250
1 x 2500 6.25 3280 3280 49.8 E4S4000 In=4000 0.9 49.8 T4H250
1 x 3125 6.25 4100 4100 61.5 E6H5000 In=5000 0.9 61.5 T4H250 T2L160
T4V250
T4L250
T4L250
5
6.25
6.25
T2H160
T2L160
T2S160
S4L160
4
4
5
5
4
4
4
4
4
4
4
4
Transformer Circuit-breaker "A" (LV side)
Release ABB SACE
Circuit-breaker
S250/S260
S250/S260
S250/S260
T1B160
T1C160
T1C160
S250/S260
S250/S260
T1B160
T1B160
T1B160
T1N160
T1C160
T1N160
T1C160
T2L160
T1N160
T2S160
T2N160
T1N160
T2S160
T1N160
T1B160
T2L160
T2S160
T2S160
T2L160
T2N160
T2H160
T2L160
T2S160
400 A 630 A 800 A 1250 A 1600 A 2000 A 2500 A 3200 A 4000 A
T5N400
T5N400
T5N400 T5N630
T5N400
T5N400 T5N630
T5N400
T5S400 T5S630 S6S800
T5N400 T5N630
T5S400 T5S630 S6S800/E1B800 S7S1250/E1B1250
T5H400 T5H630 S6L800/E2N1250 S7L1250/E2N1250 S7L1600/E2N1600 E2N2000
T5N400 T5N630 S6N800/E1B800
T5H400 T5H630 S6S800/E1B800 S7H1250/E1B1250 S7H1600/E2B1600
T5H400 T5H630 S6L800/E2N1250 S7L1250/E2N1250 S7L1600/E2N1600 E2N2000 E3N2500 E3N3200 E4S4000
T5N400 T5N630 S6N800/E1B800
T5H400 T5H630 S6L800/E2N1250 S7H1250/E1N1250 S7H1600/E2N1600 E2N2000
T5L400 T5L630 S6L800/E3S1250 S7L1250/E3S1250 S7L1600/E3S1600 E3S2000 E3S2500 E3S3200
T5S400 T5S630 S6S800/E1B800 S7S1250/E1B1250
T5H400 T5H630 S6L800/E2N1250 S7L1250/E2N1250 S7L1600/E2N1600 E2N2000 E3N2500
T5L400 T5L630 S8V2000/E2L1600 E3H2000 E3H2500 E3H3200 E4H4000
T5S400 T5S630 S6S800/E1B800 S7S1250/E1B1250 S7S1600/E2B1600
T5H400 T5H630 S6L800/E2N1250 S7L1250/E2N1250 S7L1600/E2N1600 E2N2000 E3N2500 E3N3200
T5L400 T5L630 S8V2000/E2L1600 E3H2000 E3H2500 E3H3200 E4H4000
T5H400 T5H630 S6S800/E1B800 S7H1250/E1N1250 S7H1600/E2B1600 E2B2000
T5L400 T5L630 S6L800/E3H1250 S7L1250/E3H1250 S7L1600/E3H1600 E3H2000 E3H2500 E3H3200 E4H4000
T5V400 T5V630 E6V4000
T5H400 T5H630 S6L800/E2N1250 S7H1250/E1N1250 S7H1600/E2N1600 E2N2000 E3N2500
T5H400 T5H630 S6L800/E2N1250 S7L1250/E2N1250 S7L1600/E2N1600 E2N2000 E3N2500 E3N3200
S8V2000/E2L1250
S8V2000/E2L1250
E6V3200
Circuit-breaker "B" Feeder circuit-breaker
Feeder circuit-breaker type and rated current
Table 3: Protection and switching of 440 V transformers
143 142 ABB SACE - Electrical devices ABB SACE - Electrical devices
3 Protection of electrical equipment 3 Protection of electrical equipment
3.4 Protection and switching of transformers 3.4 Protection and switching of transformers
1
S
D
C
0
1
0
0
3
7
F
0
2
0
1
S
r
u
k
Trafo I
r
Busbar I
b
Trafo
Feeder I
k
Busbar I
k
[kVA] % [A] [A] [kA] size setting [kA] 32 A 63 A 125 A 160 A
1 x 63 53 53 1.3 T1B/T2N160 In=63 0.9/0.88 1.3 T1B160
2 x 63 53 105 1.3 T1B/T2N160 In=63 0.9/0.88 2.6
1 x 100 84 84 2.1 T1B/T2N160 In=100 0.9/0.92 2.1
2 x 100 84 167 2.1 T1B/T2N160 In=100 0.9/0.92 4.2
1 x 125 105 105 2.6 T1B/T2N160 In=160 0.9/0.72 2.6
2 x 125 105 209 2.6 T1B/T2N160 In=160 0.9/0.72 5.2
1 x 160 134 134 3.3 T1C/T2N160 In=160 0.9/0.88 3.3
2 x 160 134 268 3.3 T1C/T2N160 In=160 0.9/0.88 6.6
1 x 200 167 167 4.2 T3N250/T4N250 In=250 0.9/0.8 4.2
2 x 200 167 335 4.1 T3N250/T4N250 In=250 0.9/0.8 8.3
1 x 250 209 209 5.2 T3S250/T4N250 In=250 0.9 5.2
2 x 250 209 418 5.1 T3S250/T4N250 In=250 0.9 10.3
1 x 315 264 264 6.5 T4N320 In=320 0.9 6.5
2 x 315 264 527 6.5 T4N320 In=320 0.9 12.9
1 x 400 335 335 8.3 T5N400 In=400 0.9 8.3
2 x 400 335 669 8.2 T5N400 In=400 0.9 16.3
1 x 500 418 418 10.3 T5N630 In=630 0.7 10.3
2 x 500 418 837 10.1 T5N630 In=630 0.7 20.2
1 x 630 527 527 12.9 T5N630 In=630 0.9 12.9
2 x 630 527 1054 12.6 T5N630 In=630 0.9 25.3
3 x 630 527 1581 24.8 T5S630 In=630 0.9 37.2
1 x 800 669 669 13.1 S6N800 In=800 0.9 13.1
2 x 800 669 1339 12.8 S6N800 In=800 0.9 25.7
3 x 800 669 2008 25.2 S6L800 In=800 0.9 37.7
1 x 1000 837 837 16.3 S7S1250/E1B1250 In=1000 0.9 16.3
2 x 1000 837 1673 15.9 S7S1250/E1B1250 In=1000 0.9 31.8
3 x 1000 837 2510 31.0 S7L1250/E1B1250 In=1000 0.9 46.5
1 x 1250 1046 1046 20.2 S7H1250/E1B1250 In=1250 0.9 20.2
2 x 1250 1046 2092 19.6 S7S1250/E1B1250 In=1250 0.9 39.2
3 x 1250 1046 3138 38.0 E2B1250 In=1600 0.7 57.1
1 x 1600 1339 1339 20.7 E2B1600 In=1600 0.9 20.7
2 x 1600 1339 2678 20.1 E2B1600 In=1600 0.9 40.1
3 x 1600 1339 4016 38.9 E2B1600 In=1600 0.9 58.3
1 x 2000 1673 1673 25.7 E2B2000 In=2000 0.9 25.7
2 x 2000 1673 3347 24.7 E2B2000 In=2000 0.9 49.3
3 x 2000 1673 5020 47.5 E2B2000 In=2000 0.9 71.2
1 x 2500 6.25 2092 2092 31.8 E3N2500 In=2500 0.9 31.8
1 x 3125 6.25 2615 2615 39.2 E3N3200 In=3200 0.9 39.2
T4H250
T4L250
T4L250
T4L250
T4H250
T4H250
T4H250
T4V250
T4L250
5
6.25
6.25
T4S250
T4H250
4
4
5
5
T4S250
T4N250
T4H250
T4N250
4
4
4
4
4
4
4
4
Transformer Circuit-breaker "A" (LV side)
Release ABB SACE
Circuit-breaker
T1B160
T1B160
T1B160
T1N160
T1N160
T1C160
T1N160
T2S160
T2L160
T1N160
T4N250
T2S160
T4N250
T2L160
T4N250
T4N250
T4H250
T4N250
T4H250
T4H250
T4S250
T4L250
A 250 A 400 A 630 A 800 A 1250 A 1600 A 2000 A 2500 A 3200 A 4000 A
T4N250
T4N250
T4N250 T5N400
T4N250
T4N250 T5N400
T4N250
T4S250 T5S400 T5S630
T4N250 T5N400
T4H250 T5H400 T5H630
T4H250 T5H400 T5H630
T4N250 T5N400
T4H250 T5H400 T5H630 S6L800
T4H250 T5H400 T5H630
T4N250 T5N400 T5N630
T4H250 T5H400 T5H630 S7L1250/E1B800 S7L1250/E1B1250
T4L250 T5L400 T5L630 S8V2000/E2N1600 E2N2000
T4S250 T5S400 T5S630 S6S800/E1B800
T4H250 T5H400 T5H630 S8H2000/E2B1600
T4L250 T5L400 T5L630
T4S250 T5S400 T5S630 S6S800/E1B800
T4L250 T5L400 T5L630 S8V2000/E2B1600 E2B2000
T4L250 T5L400 T5L630 E3N3200
T4H250 T5H400 T5H630 S6L800/E1B800 S7L1250/E1B1250
T4L250 T5L400 T5L630 S8V2000/E2N1600 E2N2000 E3N2500
T4V250 T5V400 T5V630 E2L1600 E3S2000 E3S2500 E3S3200 E4S4000
T4H250 T5H400 T5H630 S7L1250/E1B800 S7L1250/E1B1250 S7L1600/E2B1600
T4H250 T5H400 T5H630 S8H2000/E2B1600 E2B2000 S8H2000/E2B1250
E2B1600
E2B1600
S8V2000/E2N1250
S8H2000/E2B1250
E3N2500
S8V2000/E2B1250
E3N2500
S8V2000/E2N1250
E2L1250
Circuit-breaker "B" Feeder circuit-breaker
Feeder circuit-breaker type and rated current
Table 4: Protection and switching of 690 V transformers
145 144 ABB SACE - Electrical devices ABB SACE - Electrical devices
3 Protection of electrical equipment 3 Protection of electrical equipment
3.4 Protection and switching of transformers 3.4 Protection and switching of transformers
1
S
D
C
0
1
0
0
2
6
F
0
0
0
1
A1 A2 A3
B1 B2 B3
63 A 400 A 800 A
From Table 2, corresponding to the row relevant to 3x630 kVA transformers, it
can be read that:
Level A circuit-breakers (LV side of transformer)
• Trafo I
r
(909 A) is the current that flows through the transformer circuit-breakers;
• Busbar I
b
(2727 A) is the maximum current that the transformers can supply;
• Trafo Feeder I
k
(42.8 kA) is the value of the short-circuit current to consider for
the choice of the breaking capacity of each of the transformer circuit-breakers;
• S7S1250 or E1N1250 is the size of the transformer circuit-breaker;
• In (1000 A) is the rated current of the transformer circuit-breaker (electronic
release chosen by the user);
• Setting (0.95) indicates the set value of function L of the electronic release.
Level B circuit-breakers (outgoing feeder)
• Busbar I
k
(64.2 kA) is the short-circuit current due to the contribution of all
three transformers;
• corresponding to 63 A, read circuit-breaker B1 Tmax T2H160;
• corresponding to 400 A, read circuit-breaker B2 Tmax T5H400;
• corresponding to 800 A, read circuit-breaker B3 Isomax S6L800 or E2N1250.
The choice made does not take into account discrimination/back-up
requirements. Refer to the relevant chapters for selections appropriate to the
various cases.
NOTE
The tables refer to the previously specified conditions; the information for the
selection of circuit-breakers is supplied only with regard to the current in use
and the prospective short-circuit current. For a correct selection, other factors
such as selectivity, back-up protection, the decision to use limiting circuit-
breakers etc. must also be considered. Therefore, it is essential that the design
engineers carry out precise checks.
It must also be noted that the short-circuit currents given are determined using
the hypothesis of 750 MVA power upstream of the transformers, disregarding
the impedances of the busbars or the connections to the circuit-breakers.
Example:
Supposing the need to size breakers A1/A2/A3, on the LV side of the three
transformers of 630 kVA 20/0.4 kV with u
k
% equal to 4% and outgoing feeder
circuit-breakers B1/B2/B3 of 63-400-800 A:
147 146 ABB SACE - Electrical devices ABB SACE - Electrical devices
4 Power factor correction 4 Power factor correction
S
Q
P
I
IQ
IR
U
cos
S
P
= =
I
I
R
(1)
tan =
Q
(2)
P
In alternating current circuits, the current absorbed by the user can be
represented by two components:
- the active component I
R
, in phase with the supply voltage, is directly correlated
to the output (and therefore to the part of electrical energy transformed into
energy of a different type, usually electrical with different characteristics,
mechanical, light and/or thermal);
- the reactive component I
Q
, in quadrature to the voltage, is used to produce
the flow necessary for the conversion of powers through the electric or
magnetic field. Without this, there could be no flow of power, such as in the
core of a transformer or in the air gap of a motor.
In the most common case, in the presence of ohmic-inductive type loads, the
total current (I) lags in comparison with the active component I
R
.
In an electrical installation, it is necessary to generate and transmit, other than
the active power P, a certain reactive power Q, which is essential for the
conversion of electrical energy, but not available to the user. The complex of
the power generated and transmitted constitutes the apparent power S.
Power factor (cosϕ) is defined as the ratio between the active component I
R
and the total value of the current l; ϕ is the phase shifting between the voltage
U and the current l.
It results:
The reactive demand factor (tanϕ) is the relationship between the reactive power
and the active power:
Load cosϕ tanϕ
power factor reactive demand factor
Transformers (no load condition) 0.1÷0.15 9.9÷6.6
Motor (full load) 0.7÷0.85 1.0÷0.62
Motor (no load) 0.15 6.6
Metal working apparatuses:
- Arc welding 0.35÷0.6 2.7÷1.3
- Arc welding compensated 0.7÷0.8 1.0÷0.75
- Resistance welding: 0.4÷0.6 2.3÷1.3
- Arc melting furnace 0.75÷0.9 0.9÷0.5
Fluorescent lamps
- compensated 0.9 0.5
- uncompensated 0.4÷0.6 2.3÷1.3
Mercury vapour lamps 0.5 1.7
Sodium vapour lamp 0.65÷0.75 1.2÷0.9
AC DC converters 0.6÷0.95 1.3÷0.3
DC drives 0.4÷0.75 2.3÷0.9
AC drives 0.95÷0.97 0.33÷0.25
Resistive load 1 0
Table 1: Typical power factor
The power factor correction is the action increasing the power factor in a specific
section of the installation by locally supplying the necessary reactive power, so
as to reduce the current value to the equivalent of the power required, and
therefore the total power absorbed from the upstream side. Thus, both the line
as well as the supply generator can be sized for a lower apparent power value
required by the load.
In detail, as shown by Figure 1 and Figure 2, increasing the power factor of the
load:
- decreases the relative voltage drop u
rp
per unit of active power transmitted;
- increases the transmittable active power and decreases the losses, the other
dimensioning parameters remaining equal.
Table 1 shows some typical power factors:
4.1 General aspects
4.1 General aspects
149 148 ABB SACE - Electrical devices ABB SACE - Electrical devices
4 Power factor correction 4 Power factor correction
4.1 General aspects 4.1 General aspects
) (
2 1 1 2
tan P Q Q Q
c
- ⋅ = - = (3) tan
1
10
0.50
Load power factor
R
e
l
a
t
i
v
e
v
o
l
t
a
g
e
d
r
o
p
Cable cross section
1
S
D
C
0
1
0
0
3
9
F
0
2
0
1
Active power increase with equal dimensioning factors
1
S
D
C
0
1
0
0
4
0
F
0
2
0
1
1
10
100
1000
0.70 0.80 0.90 1.00
Improved power factor
A
c
t
i
v
e
P
o
w
e
r
%
i
n
c
r
e
a
s
e
0.4 0.5 0.6
0.7 0.8 0.9
original power factor
1
S
D
C
0
1
0
0
4
1
F
0
2
0
1
P Q
2
S
2
Motor Power factor correction unit
(reactive power generator)
Q
c
P Q
1
S
1
P
Q
2
S
2
Q
1
Q
c
S
1
The distribution authority is responsible for the production and transmission of
the reactive power required by the user installations, and therefore has a series
of further inconveniences which can be summarized as:
- oversizing of the conductors and of the components of the transmission lines;
- higher Joule-effect losses and higher voltage drops in the components and
lines.
The same inconveniences are present in the distribution installation of the final
user. The power factor is an excellent index of the size of the added costs and
is therefore used by the distribution authority to define the purchase price of
the energy for the final user.
The ideal situation would be to have a cosϕ slightly higher than the set reference
so as to avoid payment of legal penalties, and at the same time not to risk
having, with a cosϕ too close to the unit, a leading power factor when the
power factor corrected device is working with a low load.
The distribution authority generally does not allow others to supply reactive
power to the network, also due to the possibility of unexpected overvoltages.
In the case of a sinusoidal waveform, the reactive power necessary to pass
from one power factor cosϕ
1
to a power factor cosϕ
2
is given by the formula:
where:
P is the active power;
Q
1
,ϕ
1
are the reactive power and the phase shifting before power factor correction;
Q
2
,ϕ
2
are the reactive power and the phase shifting after power factor correction;
Q
c
is the reactive power for the power factor correction.
Figure 1: Relative voltage drop
Figure 2: Transmittable active power
Voltage drop per unit of active power transmitted
151 150 ABB SACE - Electrical devices ABB SACE - Electrical devices
4 Power factor correction 4 Power factor correction
4.1 General aspects 4.1 General aspects
.
= P K
c
Q
c
= 0.355
.
300 = 106.5 kvar
= =
P
K
c
Q
c
-
(4) 2 1
tan tan
Table 2 shows the value of the relationship
for different values of the power factor before and after the correction.
Table 2: Factor K
c
K
c
cosϕ
2
cosϕ
1
0.80 0.85 0.90 0.91 0.92 0.93 0.94 0.95 0.96 0.97 0.98 0.99 1
0.60 0.583 0.714 0.849 0.878 0.907 0.938 0.970 1.005 1.042 1.083 1.130 1.191 1.333
0.61 0.549 0.679 0.815 0.843 0.873 0.904 0.936 0.970 1.007 1.048 1.096 1.157 1.299
0.62 0.515 0.646 0.781 0.810 0.839 0.870 0.903 0.937 0.974 1.015 1.062 1.123 1.265
0.63 0.483 0.613 0.748 0.777 0.807 0.837 0.870 0.904 0.941 0.982 1.030 1.090 1.233
0.64 0.451 0.581 0.716 0.745 0.775 0.805 0.838 0.872 0.909 0.950 0.998 1.058 1.201
0.65 0.419 0.549 0.685 0.714 0.743 0.774 0.806 0.840 0.877 0.919 0.966 1.027 1.169
0.66 0.388 0.519 0.654 0.683 0.712 0.743 0.775 0.810 0.847 0.888 0.935 0.996 1.138
0.67 0.358 0.488 0.624 0.652 0.682 0.713 0.745 0.779 0.816 0.857 0.905 0.966 1.108
0.68 0.328 0.459 0.594 0.623 0.652 0.683 0.715 0.750 0.787 0.828 0.875 0.936 1.078
0.69 0.299 0.429 0.565 0.593 0.623 0.654 0.686 0.720 0.757 0.798 0.846 0.907 1.049
0.70 0.270 0.400 0.536 0.565 0.594 0.625 0.657 0.692 0.729 0.770 0.817 0.878 1.020
0.71 0.242 0.372 0.508 0.536 0.566 0.597 0.629 0.663 0.700 0.741 0.789 0.849 0.992
0.72 0.214 0.344 0.480 0.508 0.538 0.569 0.601 0.635 0.672 0.713 0.761 0.821 0.964
0.73 0.186 0.316 0.452 0.481 0.510 0.541 0.573 0.608 0.645 0.686 0.733 0.794 0.936
0.74 0.159 0.289 0.425 0.453 0.483 0.514 0.546 0.580 0.617 0.658 0.706 0.766 0.909
0.75 0.132 0.262 0.398 0.426 0.456 0.487 0.519 0.553 0.590 0.631 0.679 0.739 0.882
0.76 0.105 0.235 0.371 0.400 0.429 0.460 0.492 0.526 0.563 0.605 0.652 0.713 0.855
0.77 0.079 0.209 0.344 0.373 0.403 0.433 0.466 0.500 0.537 0.578 0.626 0.686 0.829
0.78 0.052 0.183 0.318 0.347 0.376 0.407 0.439 0.474 0.511 0.552 0.599 0.660 0.802
0.79 0.026 0.156 0.292 0.320 0.350 0.381 0.413 0.447 0.484 0.525 0.573 0.634 0.776
0.80 0.130 0.266 0.294 0.324 0.355 0.387 0.421 0.458 0.499 0.547 0.608 0.750
0.81 0.104 0.240 0.268 0.298 0.329 0.361 0.395 0.432 0.473 0.521 0.581 0.724
0.82 0.078 0.214 0.242 0.272 0.303 0.335 0.369 0.406 0.447 0.495 0.556 0.698
0.83 0.052 0.188 0.216 0.246 0.277 0.309 0.343 0.380 0.421 0.469 0.530 0.672
0.84 0.026 0.162 0.190 0.220 0.251 0.283 0.317 0.354 0.395 0.443 0.503 0.646
0.85 0.135 0.164 0.194 0.225 0.257 0.291 0.328 0.369 0.417 0.477 0.620
0.86 0.109 0.138 0.167 0.198 0.230 0.265 0.302 0.343 0.390 0.451 0.593
0.87 0.082 0.111 0.141 0.172 0.204 0.238 0.275 0.316 0.364 0.424 0.567
0.88 0.055 0.084 0.114 0.145 0.177 0.211 0.248 0.289 0.337 0.397 0.540
0.89 0.028 0.057 0.086 0.117 0.149 0.184 0.221 0.262 0.309 0.370 0.512
0.90 0.029 0.058 0.089 0.121 0.156 0.193 0.234 0.281 0.342 0.484
Example
Supposing the need to change from 0.8 to 0.93 the power factor of a three-
phase installation (U
r
= 400 V) which absorbs an average power of 300 kW.
From Table 2, at the intersection of the column corresponding to the final power
factor (0.93), and the row corresponding to the starting power factor (0.8), the
value of K
c
(0.355) can be read. The reactive power Q
c
which must be generated
locally shall be:
Due to the effect of power factor correction, the current absorbed decreases
from 540 A to 460 A (a reduction of approximately 15%).
Characteristics of power factor correction capacitor banks
The most economical means of increasing the power factor, especially for an
installation which already exists, is installing capacitors.
Capacitors have the following advantages:
- low cost compared with synchronous compensators and electronic power
converters;
- ease of installation and maintenance;
- reduced losses (less than 0.5 W/kvar in low voltage);
- the possibility of covering a wide range of powers and different load profiles,
simply supplying in parallel different combinations of components, each with
a relatively small power.
The disadvantages are sensitivity to overvoltages and to the presence of non-
linear loads.
The Standards applicable to power factor correction capacitors are as follows:
- IEC 60831-1 “Shunt power capacitors of the self-healing type for a.c. systems
having a rated voltage up to and including 1000 V - Part 1: General - Perfor-
mance, testing and rating - Safety requirements - Guide for installation and
operation”;
- IEC 60931-1 “Shunt power capacitors of the non-self-healing type for a.c.
systems having a rated voltage up to and including 1000 V - Part 1: General-
Performance, testing and rating - Safety requirements - Guide for installation
and operation”.
153 152 ABB SACE - Electrical devices ABB SACE - Electrical devices
4 Power factor correction 4 Power factor correction
1000
3
9 . 0 9 . 0
0
0
I U
Q Q
r
c
⋅ ⋅
⋅ = ⋅ = [kvar] (6)
1
S
D
C
0
1
0
0
2
8
F
0
0
0
1
M
c
M
c
M
c
The characteristics of a capacitor, given on its nameplate, are:
• rated voltage U
r
, which the capacitor must withstand indefinitely;
• rated frequency f
r
(usually equal to that of the network);
•rated power Q
c
, generally expressed in kvar (reactive power of the capacitor
bank).
From this data it is possible to find the size characteristics of the capacitors by
using the following formulae (5):
Individual PFC of motors
The usual connection diagrams are shown in the following Figure:
With three-phase systems, for the same reactive power, the star-connection
requires a capacity 3 times larger and subjects the capacitors to a voltage and
a current times less than the analogous delta-connection.
Capacitors are generally supplied with connected discharge resistance,
calculated so as to reduce the residual voltage at the terminals to 75 V in 3
minutes, as stated in the reference Standard.
In the case of direct connection (diagrams 1 and 2) there is a risk that after
disconnection of the supply, the motor will continue to rotate (residual kinetic
energy) and self-excite with the reactive energy supplied by the capacitor bank,
acting as an asynchronous generator. In this case, the voltage is maintained on
the load side of the switching and control device, with the risk of dangerous
overvoltages of up to twice the rated voltage value.
However, in the case of diagram 3, to avoid the risk detailed above, the normal
procedure is to connect the PFC bank to the motor only when it is running, and
to disconnect it before the disconnection of the motor supply.
As a general rule, for a motor with power P
r
, it is advisable to use a PFC with
reactive power Q
c
below 90% of the reactive power absorbed by the no-load
motor Q
0
, at rated voltage U
r
, to avoid a leading power factor.
Considering that under no-load conditions, the current absorbed I
0
[A] is solely
reactive, if the voltage is expressed in volts, it results:
The current I
0
is generally given in the documentation supplied by the
manufacturer of the motor.
4.2 Power factor correction method
Single PFC
Single or individual power factor correction is carried out by connecting a
capacitor of the correct value directly to the terminals of the device which absorbs
reactive power.
Installation is simple and economical: capacitors and load can use the same
overload and short-circuit protection, and are connected and disconnected
simultaneously.
The adjustment of cosϕ is systematic and automatic with benefit not only to
the energy distribution authority, but also to the whole internal distribution system
of the user.
This type of power factor correction is advisable in the case of large users with
constant load and power factor and long connection times.
Individual PFC is usually applied to motors and fluorescent lamps. The capacitor
units or small lighting capacitors are connected directly to loads.
1
S
D
C
0
1
0
0
0
5
F
0
9
0
1
Single-phase
connection
Capacity of the capacitor bank
Three-phase
star-connection
Three-phase
delta-connection
Rated current of the components
Line current
2
2
r r
c
U f
Q
C
⋅
=
π
2
2
r r
c
U f
Q
C
⋅
=
π f 3 2
2
⋅ ⋅
=
r r
c
U
Q
C
π
2
r r rc
U C f I ⋅ ⋅ = π
3 ⋅ =
rc l
I I
rc l
I I =
rc l
I I =
2
r r rc
U C f I ⋅ ⋅ = π 3 / 2
r r rc
U C f I ⋅ ⋅ = π
Starter Starter
Starter
Diagram 1 Diagram 2 Diagram 3
4.1 General aspects 4.2 Power factor connection method
155 154 ABB SACE - Electrical devices ABB SACE - Electrical devices
4 Power factor correction 4 Power factor correction
4.2 Power factor connection method 4.2 Power factor connection method
Table 3 shows the values of reactive power for power factor correction of some
ABB motors, according to the power and the number of poles.
P
r
Q
c
Before PFC After PFC
[kW] [kvar] cosϕ
r
I
r
[A] cosϕ
2
I
2
[A]
400V / 50 Hz / 2 poles / 3000 r/min
7.5 2.5 0.89 13.9 0.98 12.7
11 2.5 0.88 20 0.95 18.6
15 5 0.9 26.5 0.98 24.2
18.5 5 0.91 32 0.98 29.7
22 5 0.89 38.5 0.96 35.8
30 10 0.88 53 0.97 47.9
37 10 0.89 64 0.97 58.8
45 12.5 0.88 79 0.96 72.2
55 15 0.89 95 0.97 87.3
75 15 0.88 131 0.94 122.2
90 15 0.9 152 0.95 143.9
110 20 0.86 194 0.92 181.0
132 30 0.88 228 0.95 210.9
160 30 0.89 269 0.95 252.2
200 30 0.9 334 0.95 317.5
250 40 0.92 410 0.96 391.0
315 50 0.92 510 0.96 486.3
400V / 50 Hz / 4 poles / 1500 r/min
7.5 2.5 0.86 14.2 0.96 12.7
11 5 0.81 21.5 0.96 18.2
15 5 0.84 28.5 0.95 25.3
18.5 7.5 0.84 35 0.96 30.5
22 10 0.83 41 0.97 35.1
30 15 0.83 56 0.98 47.5
37 15 0.84 68 0.97 59.1
45 20 0.83 83 0.97 71.1
55 20 0.86 98 0.97 86.9
75 20 0.86 135 0.95 122.8
90 20 0.87 158 0.94 145.9
110 30 0.87 192 0.96 174.8
132 40 0.87 232 0.96 209.6
160 40 0.86 282 0.94 257.4
200 50 0.86 351 0.94 320.2
250 50 0.87 430 0.94 399.4
315 60 0.87 545 0.93 507.9
P
r
Q
c
Before PFC After PFC
[kW] [kvar] cosϕ
r
I
r
[A] cosϕ
2
I
2
[A]
400V / 50 Hz / 6 poles / 1000 r/min
7.5 5 0.79 15.4 0.98 12.4
11 5 0.78 23 0.93 19.3
15 7.5 0.78 31 0.94 25.7
18.5 7.5 0.81 36 0.94 30.9
22 10 0.81 43 0.96 36.5
30 10 0.83 56 0.94 49.4
37 12.5 0.83 69 0.94 60.8
45 15 0.84 82 0.95 72.6
55 20 0.84 101 0.96 88.7
75 25 0.82 141 0.93 123.9
90 30 0.84 163 0.95 144.2
110 35 0.83 202 0.94 178.8
132 45 0.83 240 0.95 210.8
160 50 0.85 280 0.95 249.6
200 60 0.85 355 0.95 318.0
250 70 0.84 450 0.94 404.2
315 75 0.84 565 0.92 514.4
400V / 50 Hz / 8 poles / 750 r/min
7.5 5 0.7 18.1 0.91 13.9
11 7.5 0.76 23.5 0.97 18.4
15 7.5 0.82 29 0.97 24.5
18.5 7.5 0.79 37 0.93 31.5
22 10 0.77 45 0.92 37.5
30 12.5 0.79 59 0.93 50.0
37 15 0.78 74 0.92 62.8
45 20 0.78 90 0.93 75.4
55 20 0.81 104 0.93 90.2
75 30 0.82 140 0.95 120.6
90 30 0.82 167 0.93 146.6
110 35 0.83 202 0.94 178.8
132 50 0.8 250 0.93 214.6
Table 3: Reactive power for power factor motor correction
157 156 ABB SACE - Electrical devices ABB SACE - Electrical devices
4 Power factor correction 4 Power factor correction
4.2 Power factor connection method 4.2 Power factor connection method
⎟
⎠
⎞
⎜
⎝
⎛
⋅ ⋅ + ⎟
⎠
⎞
⎜
⎝
⎛
⋅ ≈ − ⎟
⎠
⎞
⎜
⎝
⎛
⋅ ⋅ + − ⎟
⎠
⎞
⎜
⎝
⎛
⋅ =
r
k
L r cu r
k
L fe r c
S
u
K S
i
P S
u
K P S
i
Q
100
%
100
%
100
%
100
% 2 0 2
2
2 2
2
0
[kvar] (7)
8 . 19 9 . 8 630
100
% 4
6 . 0 2 . 1 630
100
% 8 . 1
100
%
100
%
2
2
2 2
2
2
2
2 2
2
0
= − ⎟
⎠
⎞
⎜
⎝
⎛
⋅ ⋅ + − ⎟
⎠
⎞
⎜
⎝
⎛
⋅ = − ⎟
⎠
⎞
⎜
⎝
⎛
⋅ ⋅ + − ⎟
⎠
⎞
⎜
⎝
⎛
⋅ =
cu r
k
L fe r c
P S
u
K P S
i
Q kvar
4 . 20 630
100
% 4
6 . 0 630
100
% 8 . 1
100
%
100
%
2 2 0
= ⎟
⎠
⎞
⎜
⎝
⎛
⋅ ⋅ + ⎟
⎠
⎞
⎜
⎝
⎛
⋅ = ⎟
⎠
⎞
⎜
⎝
⎛
⋅ ⋅ + ⎟
⎠
⎞
⎜
⎝
⎛
⋅ =
r
k
L r c
S
u
K S
i
Q kvar
Example
For a three-phase asynchronous motor, 110 kW (400 V - 50 Hz - 4 poles), the
PFC power suggested in the table is 30 kvar.
Individual power factor correction of three-phase transformers
A transformer is an electrical device of primary importance which, due to the
system requirements, is often constantly in service.
In particular, in installations constituted by several transformer substations, it is
advisable to carry out power factor correction directly at the transformer.
In general, the PFC power (Q
c
) for a transformer with rated power S
r
[kVA]
should not exceed the reactive power required under minimum reference load
conditions.
Reading the data from the transformer nameplate, the percentage value of the
no-load current i
0
%, the percentage value of the short-circuit voltage u
k
%, the
iron losses P
fe
and the copper losses P
cu
[kW], the PFC power required is
approximately:
where K
L
is the load factor, defined as the relationship between the minimum
reference load and the rated power of the transformer.
Example
Supposing the need for PFC of a 630 kVA oil-distribution transformer which
supplies a load which is less than 60% of its rated power.
From the data on the transformer nameplate:
i
0
% = 1.8%
u
k
% = 4%
P
cu
= 8.9 kW
P
fe
= 1.2 kW
The PFC power of the capacitor bank connected to the transformer is:
while, when using the simplified formula, the result is:
Table 4 shows the reactive power of the capacitor bank Q
c
[kvar] to be connected
on the secondary side of an ABB transformer, according to the different minimum
estimated load levels.
Table 4: PFC reactive power for ABB transformers
Qc [kvar]
Sr uk% io% Pfe Pcu load factor KL
[kVA] [%] [%] [kW] [kW] 0 0.25 0.5 0.75 1
Oil Distribution Transformer MV-LV
50 4 2.9 0.25 1.35 1.4 1.5 1.8 2.3 2.9
100 4 2.5 0.35 2.30 2.5 2.7 3.3 4.3 5.7
160 4 2.3 0.48 3.20 3.6 4 5 6.8 9.2
200 4 2.2 0.55 3.80 4.4 4.8 6.1 8.3 11
250 4 2.1 0.61 4.50 5.2 5.8 7.4 10 14
315 4 2 0.72 5.40 6.3 7 9.1 13 18
400 4 1.9 0.85 6.50 7.6 8.5 11 16 22
500 4 1.9 1.00 7.40 9.4 11 14 20 28
630 4 1.8 1.20 8.90 11 13 17 25 35
800 6 1.7 1.45 10.60 14 16 25 40 60
1000 6 1.6 1.75 13.00 16 20 31 49 74
1250 6 1.6 2.10 16.00 20 24 38 61 93
1600 6 1.5 2.80 18.00 24 30 47 77 118
2000 6 1.2 3.20 21.50 24 31 53 90 142
2500 6 1.1 3.70 24.00 27 37 64 111 175
3150 7 1.1 4.00 33.00 34 48 89 157 252
4000 7 1.4 4.80 38.00 56 73 125 212 333
Cast Resin Distribution Transformer MV-LV
100 6 2.3 0.50 1.70 2.2 2.6 3.7 5.5 8
160 6 2 0.65 2.40 3.1 3.7 5.5 8.4 12
200 6 1.9 0.85 2.90 3.7 4.4 6.6 10 15
250 6 1.8 0.95 3.30 4.4 5.3 8.1 13 19
315 6 1.7 1.05 4.20 5.3 6.4 9.9 16 24
400 6 1.5 1.20 4.80 5.9 7.3 12 19 29
500 6 1.4 1.45 5.80 6.8 8.7 14 23 36
630 6 1.3 1.60 7.00 8 10 17 29 45
800 6 1.1 1.94 8.20 8.6 12 20 35 56
1000 6 1 2.25 9.80 9.7 13 25 43 69
1250 6 0.9 3.30 13.00 11 15 29 52 85
1600 6 0.9 4.00 14.50 14 20 38 67 109
2000 6 0.8 4.60 15.50 15 23 45 82 134
2500 6 0.7 5.20 17.50 17 26 54 101 166
3150 8 0.6 6.00 19.00 18 34 81 159 269
Example
For a 630 kVA oil-distribution transformer with a load factor of 0.5, the necessary
PFC power is 17 kvar.
159 158 ABB SACE - Electrical devices ABB SACE - Electrical devices
4 Power factor correction 4 Power factor correction
4.2 Power factor connection method 4.2 Power factor connection method
rc
r
c
c
I
U
Q
I ⋅ ≈
⋅
⋅ ⋅ = 5 . 1
3
15 . 1 3 . 1
max
(8)
1
S
D
C
0
1
0
0
2
9
F
0
0
0
1
1
S
D
C
0
1
0
0
3
0
F
0
0
0
1
C
LV
Feeders
PFC in groups
This consists of local power factor correction of groups of loads with similar
functioning characteristics by installing a dedicated capacitor bank.
This method achieves a compromise between the economical solution and the
correct operation of the installation, since only the line downstream of the
installation point of the capacitor bank is not correctly exploited.
Centralized PFC
The daily load profile is of fundamental importance for the choice of the most
suitable type of power factor correction.
In installations, in which not all loads function simultaneously and/or in which
some loads are connected for only a few hours a day, the solution of using
single PFC becomes unsuitable as many of the capacitors installed could stay
idle for long periods.
In the case of installations with many loads occasionally functioning, thus having
a high installed power and a quite low average power absorption by the loads
which function simultaneously, the use of a single PFC system at the installation
origin ensures a remarkable decrease in the total power of the capacitors to be
installed.
Centralized PFC normally uses automatic units with capacitor banks divided
into several steps, directly installed in the main distribution switchboards; the
use of a permanently connected capacitor bank is only possible if the absorption
of reactive energy is fairly regular throughout the day.
The main disadvantage of centralized PFC is that the distribution lines of the
installation, downstream of the PFC device, must be dimensioned taking into
account the full reactive power required by the loads.
4.3 Circuit-breakers for the protection and
switching of capacitor banks
The circuit-breakers for the protection and switching of capacitor banks in LV
shall:
1. withstand the transient currents which occur when connecting and
disconnecting the banks. In particular, the instantaneous magnetic and
electronic releases shall not trip due to these peak currents;
2. withstand the periodic or permanent overcurrents due to the voltage
harmonics and to the tolerance (+15%) of the rated value of capacity;
3. perform a high number of no-load and on-load operations, also with high
frequency;
4. be coordinated with any external device (contactors).
Furthermore, the making and breaking capacity of the circuit-breaker must be
adequate to the short- circuit current values of the installation.
Standards IEC 60831-1 and 60931-1 state that:
- the capacitors shall normally function with an effective current value up to
130% of their rated current I
rc
(due to the possible presence of voltage
harmonics in the network);
- a tolerance of +15% on the value of the capacity is allowed.
The maximum current which can be absorbed by the capacitor bank I
cmax
is:
Therefore:
- the rated current of the circuit-breaker shall be greater than 1.5⋅I
rc
;
- the overload protection setting shall be equal to 1.5⋅I
rc
.
The connection of a capacitor bank, similar to a closing operation under short-
circuit conditions, associated with transient currents with high frequency (1÷15
kHz), of short duration (1÷3 ms), with high peak (25÷200 I
rc
).
Therefore:
- the circuit-breaker shall have an adequate making capacity;
- the setting of the instantaneous short-circuit protection must not cause
unwanted trips.
Group of loads to be power factor corrected
161 160 ABB SACE - Electrical devices ABB SACE - Electrical devices
4 Power factor correction 4 Power factor correction
4.3 Circuit-breakers for the protection and switching of capacitor banks 4.3 Circuit-breakers for the protection and switching of capacitor banks
≥ 10⋅ I
cmax
= 15⋅I
rc
=
r
r
U
Q
⋅
⋅
3
15 (9) I
3
• for electronic releases, the instantaneous short-circuit protection shall be
deactivated (I
3
= OFF).
The second condition is generally respected:
• for thermomagnetic releases, the magnetic protection shall be set at a value
not less than 10⋅I
cmax
Hereunder, the selection tables for circuit-breakers: for the definition of the version
according to the required breaking capacity, refer to Volume 1, Chapter 3.1
“General characteristics”.
The following symbols are used in the tables (they refer to maximum values):
- I
nCB
= rated current of the protection release [A];
- I
rc
= rated current of the connected capacitor bank [A];
- Q
C
= power of the capacitor bank which can be connected [kvar] with reference
to the indicated voltage and 50 Hz frequency;
- N
mech
= number of mechanical operations;
- f
mech
= frequency of mechanical operations [op/h];
- N
el
= number of electrical operations with reference to a voltage of 415 V for
Tmax and Isomax moulded-case circuit breakers (Tables 5 and 6), and to a
voltage of 440 V for Emax air circuit-breakers (Table 7);
- f
el
= frequency of electrical operations [op/h].
Table 7: Selection table for SACE Emax air circuit-breakers
I
nCB
I
rc
Q
C
[kvar] N
mech
f
mech
N
el
f
el
CB Type [A] [A] 400 V 440 V 500 V 690 V [op/h] [op/h]
E1 B N 1250 834 578 636 722 997 25000 60 10000 30
E2 B-N 1250 834 578 636 722 997 25000 60 15000 30
E2 B-N 1600 1067 739 813 924 1275 25000 60 12000 30
E2 B-N 2000 1334 924 1017 1155 1594 25000 60 10000 30
E3 N-S-H 1250 834 578 636 722 997 20000 60 12000 20
E3 N-S-H 1600 1067 739 813 924 1275 20000 60 10000 20
E3 N-S-H 2000 1334 924 1017 1155 1594 20000 60 9000 20
E3 N-S-H 2500 1667 1155 1270 1444 1992 20000 60 8000 20
E3 N-S-H 3200 2134 1478 1626 1848 2550 20000 60 6000 20
E4 S-H 3200 2134 1478 1626 1848 2550 15000 60 7000 10
E6 H-V 3200 2134 1478 1626 1848 2550 12000 60 5000 10
Table 6: Selection table for SACE Isomax S moulded-case circuit-breakers
I
nCB
I
rc
Q
C
[kvar] N
mech
f
mech
N
el
f
el
S6 N-S-H-L 800 800 533 369 406 462 637 20000 120 5000 60
S7 S-H-L 1250 1250 833 577 635 722 996 10000 120 7000 20
S7 S-H-L 1600 1600 1067 739 813 924 1275 10000 120 5000 20
S8 H-V 2000 2000 1333 924 1016 1155 1593 10000 120 3000 20
S8 H-V 2500 2500 1667 1155 1270 1443 1992 10000 120 2500 20
S8 H-V 3200 3200 2133 1478 1626 1847 2550 10000 120 1500 10
Table 5: Selection table for Tmax moulded-case circuit-breakers
I
nCB
I
rc
Q
C
[kvar] N
mech
f
mech
N
el
f
el
CB Type [A] [A] 400 V 440 V 500 V 690 V [op/h] [op/h]
T1 B-C-N 160 160 107 74 81 92 127 25000 240 8000 120
T2 N-S-H-L 160* 160 107 74 81 92 127 25000 240 8000 120
T3 N-S 250* 250 167 115 127 144 199 25000 240 8000 120
T4 N-S-H-L-V 250 250 167 115 127 144 199 20000 240 8000 120
T4 N-S-H-L-V 320 320 213 147 162 184 254 20000 240 6000 120
T5 N-S-H-L-V 400 400 267 185 203 231 319 20000 120 7000 60
T5 N-S-H-L-V 630 630 420 291 320 364 502 20000 120 5000 60
* for plug-in version reduce the maximum power of the capacitor bank by 10%
163 162 ABB SACE - Electrical devices ABB SACE - Electrical devices
5 Protection of human beings 5 Protection of human beings
Zone
designation
AC-1
AC-2
AC-3
AC-4
AC-4.1
AC-4.2
AC-4.3
Zone
limits
Up to 0.5 mA
line a
0.5 mA
up to
line b*
Line b
up to
curve c
1
Above
curve c
1
c
1
- c
2
c
2
- c
3
Beyond
curve c
3
Physiological effects
Usually no reaction.
Usually no harmful physiological effects.
Usually no organic damage to be expected. Likelihood of cramplike
muscular contractions and difficulty in breathing for durations of
current-flow longer than 2 s. Reversible disturbances of formation and
conduction of impulses in the heart, including atrial fibrillation and
transient cardiac arrest without ventricular fibrillation increasing with
current magnitude and time.
Increasing with magnitude and time, dangerous pathophysiological
effects such as cardiac arrest, breathing arrest and severe burns may
occur in addition to the effects of zone 3.
Probability of ventricular fibrillation increasing up to about 5%.
Probability of ventricular fibrillation up to about 50%.
Probability of ventricular fibrillation above 50%.
* For durations of current-flow below 10 ms, the limit for the body current for line b
remains constant at a value of 200 mA.
1
S
D
C
0
1
0
0
4
2
F
0
2
0
1
Body current I
B
AC-4 AC-3 AC-2 AC-1
a b c
2
c
1
c
3
10.000
5.000
ms
2.000
1.000
500
200
100
50
20
10
0,1 0,2 0,5 1 2 5 10 20 50 100 200 500 1.000 2.000 5.000 10.000
mA
D
u
r
a
t
i
o
n
o
f
c
u
r
r
e
n
t
f
l
o
w
t
AC-4
.
1
AC-4
.
2
AC-4
.
3
Danger to persons due to contact with live parts is caused by the flow of the
current through the human body. The effects are:
- tetanization: the muscles affected by the current flow involuntary contract
and letting go of gripped conductive parts is difficult. Note: very high currents
do not usually induce muscular tetanization because, when the body touches
such currents, the muscular contraction is so sustained that the involuntary
muscle movements generally throw the subject away from the conductive
part;
- breathing arrest: if the current flows through the muscles controlling the
lungs, the involuntary contraction of these muscles alters the normal respiratory
process and the subject may die due to suffocation or suffer the consequences
of traumas caused by asphyxia;
- ventricular fibrillation: the most dangerous effect is due to the superposition
of the external currents with the physiological ones which, by generating
uncontrolled contractions, induce alterations of the cardiac cycle. This anomaly
may become an irreversible phenomenon since it persists even when the
stimulus has ceased;
- burns: they are due to the heating deriving, by Joule effect, from the current
passing through the human body.
The Standard IEC 60479-1 “Effects of current on human being and livestock”
is a guide about the effects of current passing through the human body to
be used for the definition of electrical safety requirements. This Standard shows,
on a time-current diagram, four zones to which the physiological effects of
alternating current (15 ÷100 Hz) passing through the human body have been
related.
5.1 General aspects: effects of current on
human beings
Figure 1: Time-current zones of the effects of alternating current on
the human body
This Standard gives also a related figure for direct current.
By applying Ohm’s law it is possible to define the safety curve for the allowable
voltages, once the human body impedance has been calculated. The electrical
impedance of the human body depends on many factors. The above mentioned
Standard gives different values of impedance as a function of the touch voltage
and of the current path.
5.1 General aspect: effects of current on human beings
165 164 ABB SACE - Electrical devices ABB SACE - Electrical devices
5 Protection of human beings 5 Protection of human beings
1
S
D
C
0
1
0
0
3
1
F
0
0
0
1
10
1
10
U [V]
t [s]
T
10
3
10
2
10
-1
10
-2
10
2
1
S
D
C
0
1
0
0
3
2
F
0
0
0
1
L
1
L
2
L
3
N
PE
1
S
D
C
0
1
0
0
3
3
F
0
0
0
1
L
1
L
2
L
3
PEN N
PE
(TN-C) (TN-S)
From this safety curve it results that for all voltage values below 50 V, the tolerance
time is indefinite; at 50 V the tolerance time is 5 s. The curve shown in the figure
refers to an ordinary location; in particular locations, the touch resistance of the
human body towards earth changes and consequently the tolerable voltage
values for an indefinite time shall be lower than 25 V.
Therefore, if the protection against indirect contact is obtained through the
disconnection of the circuit, it is necessary to ensure that such breaking is
carried out in compliance with the safety curve for any distribution system.
The Standard IEC 60479-1 has adopted precautionary values for the impedance
reported in the figure so as to get the time-voltage safety curve (Figure 2) related
to the total touch voltage U
T
(i.e. the voltage which, due to an insulation failure,
is present between a conductive part and a point of the ground sufficiently far,
with zero potential).
This represents the maximum no-load touch voltage value; thus, the most
unfavorable condition is taken into consideration for safety’s sake.
5.2 Distribution systems
The earth fault modalities and the consequences caused by contact with live
parts, are strictly related to the neutral conductor arrangement and to the
connections of the exposed conductive parts.
For a correct choice of the protective device, it is necessary to know which is
the distribution system of the plant.
IEC 60364-1 classifies the distribution systems with two letters.
The first letter represents the relationship of the power system to earth:
- T: direct connection of one point to earth, in alternating current systems,
generally the neutral point;
- I: all live parts isolated from earth, or one point, in alternating current systems,
generally the neutral point, connected to earth through an impedance.
The second letter represents the relationship of the exposed conductive parts
of the installation to earth:
- T: direct electrical connection of the exposed conductive parts to earth;
- N: direct electrical connection of the exposed conductive parts to the earthed
point of the power system.
Subsequent letters, if any, represent the arrangement of neutral and protective
conductors:
- S: protective function is provided by a conductor separate from the neutral
conductor;
- C: neutral and protective functions combined as a single conductor (PEN
conductor).
Three types of distribution system are considered:
TT System
TN System
Figure 2: Safety curve
5.1 General aspect: effects of current on human beings
167 166 ABB SACE - Electrical devices ABB SACE - Electrical devices
5 Protection of human beings 5 Protection of human beings
5.2 Distribution systems 5.2 Distribution systems
1
S
D
C
0
1
0
0
3
4
F
0
0
0
1
L
1
L
2
L
3
N
PE
1
S
D
C
0
1
0
0
3
5
F
0
0
0
1
L
1
L
2
L
3
N
I
k
I
k
R
A
R
B
1
S
D
C
0
1
0
0
3
6
F
0
0
0
1
L
1
L
2
L
3
PEN
I
k
I
k N PE
(TN-C) (TN-S)
0
1
S
D
C
0
1
0
0
3
7
F
0
0
0
1
L
1
L
2
L
3
I
k
C
3
C
2
C
1
I
k
Figure 1: Earth fault in TT systems
In TT installations, the neutral conductor is connected to the supply star center,
it is usually distributed and has the function of making the phase voltage (e.g.
230 V) available, useful for single-phase load supply. The exposed conductive
parts, on the contrary, singularly or collectively, are locally connected to earth.
TT systems are generally used for civil installations.
TN systems are typically used when the power supply is distributed to loads
having their own electrical substation. The neutral conductor is directly earthed
in the substation; the exposed conductive parts are connected to the same
earthing point of the neutral conductor, and can be locally earthed.
Three types of TN system are considered according to the arrangement of
neutral and protective conductors:
1. TN-C neutral and protective functions are combined in a single conductor
(PEN conductor);
2. TN-S neutral and protective conductors are always separated;
3. TN-C-S neutral and protective functions are combined in a single conductor
in a part of the system (PEN) and are separated in another part (PE + N).
In TT systems, the neutral conductor and the exposed conductive parts are
connected to earth electrodes electrically independent; the fault current flows
towards the power supply neutral point through earth (Fig. 1):
In TN systems, the fault current flows towards the power supply neutral point
through a solid metallic connection, practically without involving the earth
electrode (Figure 2).
These distribution systems are used for particular plants, where the continuity
of supply is a fundamental requirement, where the absence of the supply can
cause hazards to people or considerable economical losses, or where a low
value of a first earth fault is required. In these cases, an insulation monitoring
device shall be provided for optical or acoustic signalling of possible earth
faults, or failure of the supplied equipment.
Figure 2: Earth fault in TN systems
Figure 3: Earth fault in IT systems
IT systems have no live parts directly connected to earth, but they can be
earthed through a sufficiently high impedance. Exposed conductive parts shall
be earthed individually, in groups or collectively to an independent earthing
electrode.
The earth fault current flows towards the power supply neutral point through
the earthing electrode and the line conductor capacitance (Figure 3).
IT System
169 168 ABB SACE - Electrical devices ABB SACE - Electrical devices
5 Protection of human beings 5 Protection of human beings
Contacts of a person with live parts can be divided in two categories:
- direct contacts;
- indirect contacts.
A direct contact occurs when a part of the human body touches a part of the
plant, usually live (bare conductors, terminals, etc.).
A contact is indirect when a part of the human body touches an exposed
conductive parts, usually not live, but with voltage presence due to a failure or
wear of the insulating materials.
The measures of protection against direct contact are:
- insulation of live parts with an insulating material which can only be removed
by destruction (e.g. cable insulation);
- barriers or enclosures: live parts shall be inside enclosures or behind barriers
providing at least the degree of protection IPXXB or IP2X; for horizontal surfaces
the degree of protection shall be of at least IPXXD or IP4X (for the meaning of
the degree of protection codes please refer to Volume 1, Chapter 6.1 Electrical
switchboards);
- obstacles: the interposition of an obstacle between the live parts and the
operator prevents unintentional contacts only, but not an intentional contact
by the removal of the obstacle without particular tools;
- placing out of reach: simultaneously accessible parts at different potentials
shall not be within arm’s reach.
An additional protection against direct contact can be obtained by using residual
current devices with a rated operating residual current not exceeding 30 mA. It
must be remembered that the use of a residual current device as a mean of
protection against direct contacts does not obviate the need to apply one of
the above specified measures of protection.
The measures of protection against indirect contact are:
- automatic disconnection of the supply: a protective device shall automatically
disconnect the supply to the circuit so that the touch voltage on the exposed
conductive part does not persist for a time sufficient to cause a risk of harmful
physiological effect for human beings;
- supplementary insulation or reinforced insulation, e.g. by the use of Class II
components;
5.3 Protection against both direct and
indirect contact
- non-conducting locations: locations with a particular resistance value of
insulating floors and walls (≥ 50 kΩ for U
r
≤ 500 V; ≥ 100 kΩ for U
r
> 500 V)
and without protective conductors inside
- electrical separation, e.g. by using an isolating transformer to supply the circuit;
- earth-free local equipotential bonding: locations where the exposed conductive
parts are connected together but not earthed.
Finally, the following measures provide combined protection against both direct
and indirect contact:
- SELV (Safety Extra Low Voltage) system and PELV (Protective Extra Low
Voltage) system;
- FELV (Functional Extra Low Voltage) system.
The protection against both direct and indirect contact is ensured if the
requirements stated in 411 from IEC 60364-4-41 are fulfilled; particularly:
- the rated voltage shall not exceeds 50 V ac r.m.s. and 120 V ripple-free dc;
- the supply shall be a SELV or PELV source;
- all the installation conditions provided for such types of electrical circuits shall
be fulfilled.
A SELV circuit has the following characteristics:
1) it is supplied by an independent source or by a safety source. Independent
sources are batteries or diesel-driven generators. Safety sources are supplies
obtained through an isolating transformer;
2) there are no earthed points. The earthing of both the exposed conductive
parts as well as of the live parts of a SELV circuit is forbidden;
3) it shall be separated from other electrical systems. The separation of a SELV
system from other circuits shall be guaranteed for all the components; for
this purpose, the conductors of the SELV circuit may be contained in multi-
conductor cables or may be provided with an additional insulating sheath.
A PELV circuit has the same prescription of a SELV system, except for the
prohibition of earthed points; in fact in PELV circuits, at least one point is always
earthed.
5.3 Protection against both direct and indirect contact
171 170 ABB SACE - Electrical devices ABB SACE - Electrical devices
5 Protection of human beings 5 Protection of human beings
a
t
I
R
50
≤
n
t
I
R
∆
≤
50
1
S
D
C
0
1
0
0
3
5
F
0
0
0
1
L
1
L
2
L
3
N
I
k
I
k
R
A
R
B
1
S
D
C
0
1
0
0
4
3
F
0
2
0
1
no safety source,
connection to earth
is admissible
safety isolating transformer
or equivalent source,
connection to earth
is admissible
L1
L2
L3
N
SELV
safety isolating
transformer
or equivalent
source,
no earthing
PELV FELV
FELV circuit PELV circuit
PE
E
PE
E
Class II
equipment
voltage limits for
extra-low voltages:
50 V ac
120 V dc
earth connections by estraneous conductive parts,
e.g. by metal pipe or structural steelwork
protective conductor
earth electrode
PE
E
PE
Note 1: Overcurrent protective devices are not shown in this figure.
FELV circuits are used when for functional reasons the requirements for SELV
or PELV circuits cannot be fulfilled; they require compliance with the following rules:
a) protection against direct contact shall be provided by either:
- barriers or enclosures with degree of protection in accordance with what
stated above (measures of protection against direct contact);
- insulation corresponding to the minimum test voltage specified for the
primary circuit. If this test is not passed, the insulation of accessible non-
conductive parts of the equipment shall be reinforced during erection so
that it can withstand a test voltage of 1500 V ac r.m.s. for 1 min.;
b) protection against indirect contact shall be provided by:
- connection of the exposed conductive parts of the equipment of the FELV
circuit to the protective conductor of the primary circuit, provided that the
latter is subject to one of the measures of protection against direct contact;
- connection of a live conductor of the FELV circuit to the protective
conductor of the primary circuit provided that an automatic disconnection
of the supply is applied as measure of protection;
c) plugs of FELV systems shall not be able to enter socket-outlets of other
voltage systems, and plugs of other voltage systems shall not be able to
enter socket-outlets of FELV systems.
Figure 1 shows the main features of SELV, PELV and FELV systems.
Figure 1: SELV, PELV, FELV systems
5.4 TT System
An earth fault in a TT system involves the circuit represented in Figure 1:
Figure 1: Earth fault in TT system
The fault current involves the secondary winding of the transformer, the phase
conductor, the fault resistance, the protective conductor and the earth electrode
resistance (plant earthing system (R
A
) and earthing system which the neutral is
connected to (R
B
)).
According to IEC 60364-4 requirements, the protective devices must be co-
ordinated with the earthing system in order to rapidly disconnect the supply, if
the touch voltage reaches harmful values for the human body.
Assuming 50 V (25 V for particular locations) as limit voltage value, the condition
to be fulfilled in order to limit the touch voltage on the exposed conductive
parts under this limit value is:
or
where:
R
t
is the total resistance, equal to the sum of the earth electrode (R
A
)
and the protective conductor for the exposed conductive parts [Ω];
I
a
is the current causing the automatic operation within 5 s of the
overcurrent protective device, read from the tripping curve of the
device [A];
I
∆n
is the rated residual operating current, within one second, of the
circuit-breaker [A].
5.3 Protection against both direct and indirect contact
173 172 ABB SACE - Electrical devices ABB SACE - Electrical devices
5 Protection of human beings 5 Protection of human beings
5.4 TT System 5.4 TT System
Ω = ≤ 06 . 0
750
50
t
R
1
S
D
C
0
1
0
0
3
8
F
0
0
0
1
750 A
10kA 1kA 0.1kA
s
1s
5s
10s
10
2
10
-1
10
-2
10
3
s
s
s
10
4
s
which can be easily obtained in practice.
From the above, it is clear that R
t
value is considerably different when using
automatic circuit-breakers instead of residual current devices.
In fact, with the former, it is necessary to obtain very low earth resistance values
(usually less than 1 Ω) since the 5 s tripping current is generally high, whereas,
with the latter, it is possible to realize earthing systems with resistance value of
thousands of ohms, which are easier to be carried out.
Table 1 reports the maximum earth resistance values which can be obtained
using residual current devices, with reference to an ordinary location (50 V):
Table 1: Earth resistance values
I
∆n
R
t
[A] [Ω]
0.01 5000
0.03 1666
0.1 500
0.3 166
0.5 100
3 16
10 5
30 1.6
Example:
Assuming to provide protection by using an automatic circuit-breaker Tmax
T1B160 In125, the trip current value in less than 5 s, read from the tripping
characteristic curve, is about 750 A, when starting from cold conditions (the
worst case for thermomagnetic releases).
So:
In order to provide the required protection, it must be necessary to carry out an
earthing system with an earth resistance R
t
≤ 0.06 Ω, which is not an easily
obtainable value.
On the contrary, by using the same circuit-breaker mounting ABB SACE RC221
residual current release, with rated residual operating current I
∆n
= 0.03 A, the
required value of earth resistance is:
. Ω = ≤ 6 1666
03 . 0
50
t
R
In an electrical installation with a common earthing system and loads protected
by devices with different tripping currents, for the achievement of the coordination
of all the loads with the earthing system, the worst case - represented by the
device with the highest tripping current - shall be considered.
As a consequence, when some feeders are protected by overcurrent devices
and some others by residual current devices, all the advantages deriving from
the use of residual current releases are nullified, since the R
t
shall be calculated
on the basis of the I
5s
of the overcurrent device and since it is the highest
tripping current between these two kind of devices.
Therefore, it is advisable to protect all the loads of a TT system by means of
residual current circuit-breakers coordinated with the earthing system to obtain
the advantages of both a quick disconnection of the circuit when the fault occurs
as well as an earthing system which can be easily accomplished.
175 174 ABB SACE - Electrical devices ABB SACE - Electrical devices
5 Protection of human beings 5 Protection of human beings
1
S
D
C
0
1
0
0
3
6
F
0
0
0
1
L
1
L
2
L
3
PEN
I
k
I
k N PE
(TN-C) (TN-S)
0
0
U I Z
a s
≤
.
kA I
Z
U
s I
kLG
s
a
3 ) 4 . 0 (
0
= = ≤
1
S
D
C
0
1
0
0
3
9
F
0
0
0
1
U
L
-U1
U
r
= 400 V
LLLN / TN-S
-QF1
T1B 160 In125
-WC1
3x(1x50)+1x(1x25)+1G25
PVC Cu
dV = 0.38%
I
z
= 134.0 A
L
= 20 m
-B1
I
kLG
= 3.0 kA
S
r
= 70.00 kVA
cosϕ = 0.90
5.5 TN System
An earth fault in a TN system involves the circuit represented in Figure 1:
The fault loop does not affect the earthing system and is basically formed by
the connection in series of the phase conductor and of the protective conductor.
To provide a protection with automatic disconnection of the circuit, according
to IEC 60364-4 prescriptions, the following condition shall be fulfilled:
where:
Z
s
is the impedance of the fault loop comprising the source, the live
conductor up to the point of the fault and the protective conductor
between the point of the fault and the source [Ω];
U
0
is the nominal ac r.m.s. voltage to earth [V];
I
a
is the current causing the automatic operation of the disconnecting
protective device within the time stated in Table 1, as a function of
the rated voltage U
0
or, for distribution circuits, a conventional
disconnecting time not exceeding 5 s is permitted [A]; if the protection
is provided by means of a residual current device, I
a
is the rated
residual operating current I
∆n
.
Table 1: Maximum disconnecting times for TN system
U
0
[V] Disconnecting time [s]
120 0.8
230 0.4
400 0.2
> 400 0.1
Figure 1: Earth fault in TN system
In TN installations, an earth fault with low impedance occurring on the LV side
causes a short circuit current with quite high value, due to the low value of the
impedance of the fault loop. The protection against indirect contact can be
provided by automatic circuit-breakers: it is necessary to verify that the operating
current within the stated times is lower than the short-circuit current.
The use of residual current devices improves the conditions for protection in
particular when the fault impedance doesn’t have a low value, thus limiting the
short-circuit current; this current can persist for quite long time causing
overheating of the conductors and fire risks.
Finally, it is important to highlight the fact that the residual current devices cannot
be used in TN-C system, since the neutral and protective functions are provided
by a unique conductor: this configuration prevents the residual current device
from working.
Example:
In the plant represented in Figure 2, the earth fault current is:
I
kLG
= 3 kA
The rated voltage to earth is 230 V, therefore, according to Table 1, it shall be
verified that:
Figure 2
5.5 TN System
177 176 ABB SACE - Electrical devices ABB SACE - Electrical devices
5 Protection of human beings 5 Protection of human beings
1
S
D
C
0
1
0
0
4
0
F
0
0
0
1
10kA 1kA 0.1kA
10
-1
s
0.4s
1s
10
1
s
10
2
s
10
3
s
10
4
s
950 A
T1B160
In125
3x(1x50)+1x(1x25)+1G25
I
kLG
=3.0 kA
1
S
D
C
0
1
0
0
3
7
F
0
0
0
1
L
1
L
2
L
3
I
k
C
3
C
2
C
1
I
k
L d t
U I R ≤
.
Figure 3: LG Time-Current curves
5.6 IT System
From the tripping curve (Figure 3), it is clear that the circuit-breaker trips in 0.4 s
for a current value lower than 950 A. As a consequence, the protection against
indirect contact is provided by the same circuit-breaker which protects the
cable against short-circuit and overload, without the necessity of using an
additional residual current device.
As represented in Figure 1, the earth fault current in an IT system flows through
the line conductor capacitance to the power supply neutral point. For this reason,
the first earth fault is characterized by such an extremely low current value to
prevent the overcurrent protections from disconnecting; the deriving touch
voltage is very low.
Figure1: Earth fault in IT system
According to IEC 60364-4, the automatic disconnection of the circuit in case of
the first earth fault is not necessary only if the following condition is fulfilled:
where:
R
t
is the resistance of the earth electrode for exposed conductive parts [Ω];
I
d
is the fault current, of the first fault of negligible impedance between
a phase conductor and an exposed conductive part [A];
U
L
is 50 V for ordinary locations (25 V for particular locations).
If this condition is fulfilled, after the first fault, the touch voltage value on the
exposed conductive parts is lower than 50 V, tolerable by the human body for
an indefinite time, as shown in the safety curve (see Chapter 5.1 “General
aspects: effects of current on human beings”).
In IT system installations, an insulation monitoring device shall be provided to
5.5 TN System
179 178 ABB SACE - Electrical devices ABB SACE - Electrical devices
5 Protection of human beings 5 Protection of human beings
a
r
s
U
Z
.
≤
2 I
a
s
I
U
Z
.
≤
2
'
0
1
S
D
C
0
1
0
0
4
1
F
0
0
0
1
R
T
L N
indicate the occurrence of a first earth fault; in the event of a second fault, the
supply shall be disconnected according to the following modalities:
a) where exposed conductive parts are earthed in groups or individually,
the conditions for protection are the same as for TT systems (see
Chapter 5.4 “TT system”);
b) where exposed conductive parts are interconnected by a protective
conductor collectively earthed, the conditions of a TN system apply;
in particular, the following conditions shall be fulfilled:
if the neutral is not distributed:
if the neutral is distributed:
where
• U
0
is the rated voltage between phase and neutral [V];
• U
r
is the rated voltage between phases [V];
• Z
s
is the impedance of the fault loop comprising the phase conductor and the
protective conductor of the circuit [Ω];
• Z’
s
is the impedance of the fault loop comprising the neutral conductor and
the protective conductor of the circuit [Ω];
• I
a
is the operating current of the protection device in the disconnecting time
specified in Table 1, or within 5 s for distribution circuits.
Table 1: Maximum disconnecting time in IT systems
Rated voltage disconnecting time [s]
U
0
/U
r
[V] neutral not distributed neutral distributed
120/240 0.8 5
230/400 0.4 0.8
400/690 0.2 0.4
580/1000 0.1 0.2
IEC 60364-4 states that, if the requirements mentioned at point b) cannot be
fulfilled by using an overcurrent protective device, the protection of every supplied
load shall be provided by means of a residual current device.
The residual current device threshold shall be carefully chosen in order to avoid
unwanted tripping, due also to the particular path followed by the first fault
current through the line conductor capacitance to the power supply neutral
point (instead of the faulted line, another sound line with higher capacitance
could be affected by a higher fault current value).
Generalities on residual current circuit-breakers
The operating principle of the residual current release is basically the detection
of an earth fault current, by means of a toroid transformer which embraces all
the live conductors, included the neutral if distributed.
In absence of an earth fault, the vectorial sum of the currents I
∆
is equal to zero;
in case of an earth fault if the I
∆
value exceeds the rated residual operating
current I
∆n
, the circuit at the secondary side of the toroid sends a command
signal to a dedicated opening coil causing the tripping of the circuit-breaker.
A first classification of RCDs can be made according to the type of the fault
current they can detect:
- AC type: the tripping is ensured for residual sinusoidal alternating currents,
whether suddenly applied or slowly rising;
- A type: tripping is ensured for residual sinusoidal alternating currents and
residual pulsating direct currents, whether suddenly applied or slowly rising;
- B type: tripping is ensured for residual direct currents, for residual sinusoidal
alternating currents and residual pulsating direct currents, whether suddenly
applied or slowly rising.
Another classification referred to the operating time delay is:
- undelayed type;
- time delayed S-type.
Figure 1: Operating principle of the residual current device
5.7 Residual current devices (RCDs)
5.6 IT System
181 180 ABB SACE - Electrical devices ABB SACE - Electrical devices
5 Protection of human beings 5 Protection of human beings
5.7 Residual current devices 5.7 Residual current devices
I
∆
1 A
t 1 s
I∆
I∆
I
∆
0.3 A
t 0.5 s
I∆
I
∆
0.03 A
t inst.
I∆ I∆
I
∆
0.3 A
t 0.5 s
I
∆
0.3 A
t 0.5 s
RCDs can be coupled, or not, with other devices; it is possible to distinguish
among:
- pure residual current circuit-breakers (RCCBs): they have only the residual
current release and can protect only against earth fault. They must be coupled
with thermomagnetic circuit-breakers or fuses, for the protection against
thermal and dynamical stresses;
- residual current circuit-breakers with overcurrent protection (RCBOs): they
are the combination of a thermomagnetic circuit-breaker and a RCD; for this
reason, they provide the protection against both overcurrents as well as earth
fault current;
- residual current circuit-breakers with external toroid: they are used in industrial
plants with high currents. They are composed by a release connected to an
external toroid with a winding for the detection of the residual current; in case
of earth fault, a signal commands the opening mechanism of a circuit-breaker
or a line contactor.
Given I
∆n
the operating residual current, a very important parameter for residual
current devices is the residual non-operating current, which represents the
maximum value of the residual current which does not cause the circuit-breaker
trip; it is equal to 0.5 I
∆n
. Therefore, it is possible to conclude that:
183 182 ABB SACE - Electrical devices ABB SACE - Electrical devices
5 Protection of human beings 5 Protection of human beings
n
n
k
1
4
2
=
−
2 1
0
min
) 1 ( 2 . 1 5 . 1
8 . 0
k k
L m
S U
I
k
⋅ ⋅
⋅ + ⋅ ⋅ ⋅
=
ρ
⋅ ⋅
2 1
min
0
) 1 ( 2 . 1 5 . 1
8 . 0
k k
I m
S U
L
k
⋅ ⋅
⋅ + ⋅ ⋅ ⋅
=
ρ
⋅ ⋅
1
S
D
C
0
1
0
0
4
3
F
0
0
0
1
Dy
L1
L2
L3
N
PE
PE PE
R
EN
I
k
L1 L2 L3 N
5.8 Maximum protected length for the
protection of human beings
As described in the previous chapters, the Standards give indications about
the maximum disconnecting time for the protective devices, in order to avoid
pathophysiological effects for people touching live parts.
For the protection against indirect contact, it shall be verified that the circuit-
breaker trips within a time lower than the maximum time stated by the Standard;
this verification is carried out by comparing the minimum short-circuit current
of the exposed conductive part to be protected with the operating current
corresponding to the time stated by the Standard.
The minimum short-circuit current occurs when there is a short-circuit between
the phase and the protective conductors at the farthest point on the protected
conductor.
For the calculation of the minimum short-circuit current, an approximate method
can be used, assuming that:
- a 50 % increasing of the conductors resistance, with respect to the 20 °C
value, is accepted, due to the overheating caused by the short-circuit
current;
- a 80 % reduction of the supply voltage is considered as effect of the
short-circuit current;
- the conductor reactance is considered only for cross sections larger
than 95 mm
2
.
The formula below is obtained by applying Ohm’s law between the protective
device and the fault point.
Legend of the symbols and constants of the formula:
- 0.8 is the coefficient representing the reduction of the voltage;
- 1.5 is the coefficient representing the increasing in the resistance;
- U
r
is the rated voltage between phases;
- U
0
is the rated voltage between phase and ground;
- S is the phase conductor cross section;
- S
N
is the neutral conductor cross section;
- S
PE
is the protection conductor cross section;
- ρ is the conductor resistivity at 20 °C;
- L is the length of the cable;
-
PE
S
n S
m=
⋅
is the ratio between the total phase conductor cross section
(single phase conductor cross section S multiplied by n, number of
conductors in parallel) and the protective conductor cross section S
PE
assuming they are made of the same conductor material;
-
PE
N
S
n S
m =
1
⋅
is the ratio between the total neutral conductor cross section
(single neutral conductor cross section S
N
multiplied by n, number of
conductors in parallel) and the protective conductor cross section S
PE
assuming they are made of the same conductor material;
- k
1
is the correction factor which takes into account the reactance of
cables with cross section larger than 95 mm
2
, obtainable from the
following table:
Phase conductor cross section
[mm
2
] 120 150 185 240 300
k
1
0.90 0.85 0.80 0.75 0.72
- k
2
is the correction factor for conductors in parallel, obtainable by the
following formula:
where n is the number of conductor in parallel per phase;
- 1.2 is the magnetic threshold tolerance allowed by the Standard.
TN system
The formula for the evaluation of the minimum short circuit current is:
and consequently:
IT system
The formulas below are valid when a second fault turns the IT system into a TN
system.
It is necessary to separately examine installations with neutral not distributed
and neutral distributed.
5.8 Maximum protected length for the protection of human beings
185 184 ABB SACE - Electrical devices ABB SACE - Electrical devices
5 Protection of human beings 5 Protection of human beings
5.8 Maximum protected length for the protection of human beings 5.8 Maximum protected length for the protection of human beings
2 1 min
) 1 ( 2 . 1 5 . 1 2
8 . 0
k k
L m
S U
I
r
k
⋅ ⋅
⋅ + ⋅ ⋅ ⋅ ⋅
=
ρ
⋅ ⋅
2 1
min
) 1 ( 2 . 1 5 . 1 2
8 . 0
k k
I m
S U
L
k
r
⋅ ⋅
⋅ + ⋅ ⋅ ⋅ ⋅
=
ρ
⋅ ⋅
2 1
0
min
) 1 ( 2 . 1 5 . 1 2
8 . 0
k k
L m
S U
I
k
⋅ ⋅
⋅ + ⋅ ⋅ ⋅ ⋅
=
ρ
⋅ ⋅
2 1
min
0
) 1 ( 2 . 1 5 . 1 2
8 . 0
k k
I m
S U
L
k
⋅ ⋅
⋅ + ⋅ ⋅ ⋅ ⋅
=
ρ
⋅ ⋅
2 1
1
0
min
) 1 ( 2 . 1 5 . 1 2
8 . 0
k k
L m
S U
I
N
k
⋅ ⋅
⋅ + ⋅ ⋅ ⋅ ⋅
=
ρ
⋅ ⋅
2 1
min 1
0
) 1 ( 2 . 1 5 . 1 2
8 . 0
k k
I m
S U
L
k
N
⋅ ⋅
⋅ + ⋅ ⋅ ⋅ ⋅
=
ρ
⋅ ⋅
1
S
D
C
0
1
0
0
4
5
F
0
0
0
1
Dy
L1
L2
L3
N
PE
PE
PE
R
EN
I
k
L1 L2 L3 N
Z
PE
I
k
L1 L2 L3
A B
1
S
D
C
0
1
0
0
4
4
F
0
0
0
1
Dy
L1
L2
L3
PE
PE
PE
R
EN
I
k
L1 L2 L3
Z
PE
I
k
L1 L2 L3
Neutral not distributed
When a second fault occurs, the formula becomes:
and consequently:
Neutral distributed
Case A: three-phase circuits in IT system with neutral distributed
The formula is:
and consequently:
Note for the use of the tables
The tables showing the maximum protected length (MPL) have been defined
considering the following conditions:
- one cable per phase;
- rated voltage equal to 400 V (three-phase system);
- copper cables;
- neutral not distributed, for IT system only;
- protective conductor cross section according to Table 1:
Table 1: Protective conductor cross section
Phase conductor cross section S Protective conductor cross section S
PE
[mm
2
] [mm
2
]
S ≤ 16 S
16 < S ≤ 35 16
S > 35 S/2
Note: phase and protective conductors having the same isolation and conductive materials
Whenever the S function (delayed short-circuit) of electronic releases is used
for the definition of the maximum protected length, it is necessary to verify that
the tripping time is lower than the time value reported in Chapter 5.5 Table 1 for
TN systems and in Chapter 5.6 Table 1 for IT systems.
For conditions different from the reference ones, the following correction factors
shall be applied.
Case B: three-phase + neutral circuits in IT system with neutral distributed
The formula is:
and consequently:
187 186 ABB SACE - Electrical devices ABB SACE - Electrical devices
5 Protection of human beings 5 Protection of human beings
5.8 Maximum protected length for the protection of human beings 5.8 Maximum protected length for the protection of human beings
CURVE Z Z Z Z Z Z Z Z Z
In ≤10 13 16 20 25 32 40 50 63
I3 30 39 48 60 75 96 120 150 189
S S
PE
1.5 1.5 173 133 108 86 69 54 43
2.5 2.5 288 221 180 144 115 90 72 58 45
4 4 461 354 288 231 185 144 115 92 72
6 6 692 532 432 346 277 216 173 138 108
10 10 1153 886 721 577 461 360 288 231 180
16 16 1845 1419 1153 923 738 577 461 369 288
25 16 2250 1730 1406 1125 900 703 563 450 352
CURVE B B B B B B B B B B B B B
In ≤6 8 10 13 16 20 25 32 40 50 63 80 100
I3 30 40 50 65 80 100 125 160 200 250 315 400 500
S S
PE
1.5 1.5 173 130 104 80 65 52 42 32 26
2.5 2.5 288 216 173 133 108 86 69 54 43 35 27
4 4 461 346 277 213 173 138 111 86 69 55 44 35 28
6 6 692 519 415 319 259 208 166 130 104 83 66 52 42
10 10 1153 865 692 532 432 346 277 216 173 138 110 86 69
16 16 1845 1384 1107 852 692 554 443 346 277 221 176 138 111
25 16 2250 1688 1350 1039 844 675 540 422 338 270 214 169 135
35 16 190 152
CURVE C C C C C C C C C C C C C C C C
In ≤3 4 6 8 10 13 16 20 25 32 40 50 63 80 100 125
I3 30 40 60 80 100 130 160 200 250 320 400 500 630 800 1000 1250
S S
PE
1.5 1.5 173 130 86 65 52 40 32 26 21 16 13
2.5 2.5 288 216 144 108 86 67 54 43 35 27 22 17 14
4 4 461 346 231 173 138 106 86 69 55 43 35 28 22 17 14 11
6 6 692 519 346 259 208 160 130 104 83 65 52 42 33 26 21 17
10 10 1153 865 577 432 346 266 216 173 138 108 86 69 55 43 35 28
16 16 1845 1384 923 692 554 426 346 277 221 173 138 111 88 69 55 44
25 16 2250 1688 1125 844 675 519 422 338 270 211 169 135 107 84 68 54
35 16 95 76 61
Correction factors
Correction factor for cable in parallel per phase: the value of the maximum
protected length read in Table 2 (TN system) or Table 3 (IT system) shall be
multiplied by the following factor:
n 2 3 4 5 6 7 8
k
p
2 2.7 3 3.2 3.3 3.4 3.5
n is the number of conductors in parallel per phase.
Correction factor for three-phase voltage different from 400 V: the value
of the maximum protected length read in Table 2 (TN system) or Table 3 (IT
system) shall be multiplied by the following factor:
voltage [V] 230 400 440 500 690
kV 0.58 1 1.1 1.25 1.73
For 230 V single-phase systems, no correction factor is necessary.
Correction factor for aluminium cables: the value of the maximum protected
length read in Table 2 (TN system) or Table 3 (IT system) shall be multiplied by
the following factor:
kAl 0.64
Correction factor for protective conductor cross section S
PE
different
from the cross sections stated in Table 1: the value of the maximum
protected length shall be multiplied by the coefficient corresponding to the
phase conductor cross section and to the ratio between the protective conductor
(PE) and the phase cross sections:
SPE/S 0.5 0.55 0.6 0.66 0.75 0.87 1 1.25 1.5 2
S kPE
≤16 mm2 0.67 0.71 0.75 0.80 0.86 0.93 1.00 1.11 1.20 1.33
25 mm2 0.85 0.91 0.96 1.02 1.10 1.19 1.28 1.42 1.54 1.71
35 mm2 1.06 1.13 1.20 1.27 1.37 1.48 1.59 1.77 1.91 2.13
>35 mm2 1.00 1.06 1.13 1.2 1.29 1.39 1.5 1.67 1.8 2.00
Correction factor for neutral distributed in IT systems (for Table 3 only):
the value of the maximum protected length shall be multiplied by 0.58.
Table 2.2: Curve B
Table 2.3: Curve C
TN system MPL
by MCB Table 2.1: Curve Z
189 188 ABB SACE - Electrical devices ABB SACE - Electrical devices
5 Protection of human beings 5 Protection of human beings
5.8 Maximum protected length for the protection of human beings 5.8 Maximum protected length for the protection of human beings
CURVE K K K K K K K K K K K K K K K K K K K K K K
In ≤2 ≤3 4 4.2 5.8 6 8 10 11 13 15 16 20 25 26 32 37 40 41 45 50 63
I3 28 42 56 59 81 84 112 140 154 182 210 224 280 350 364 448 518 560 574 630 700 882
S S
PE
1.5 1.5 185 123 92 88 64 62 46 37 34 28 25 23 18 15 14 12 10 9
2.5 2.5 308 205 154 146 106 103 77 62 56 47 41 38 31 25 24 19 17 15 15 14
4 4 492 328 246 234 170 164 123 98 89 76 66 62 49 39 38 31 27 25 24 22 20 16
6 6 738 492 369 350 255 246 185 148 134 114 98 92 74 59 57 46 40 37 36 33 30 23
10 10 1231 820 615 584 425 410 308 246 224 189 164 154 123 98 95 77 67 62 60 55 49 39
16 16 1969 1313 984 934 681 656 492 394 358 303 263 246 197 158 151 123 106 98 96 88 79 63
25 16 2401 1601 12011140 830 800 600 480 437 369 320 300 240 192 185 150 130 120 117 107 96 76
CURVE D D D D D D D D D D D D D D D D
In ≤2 3 4 6 8 10 13 16 20 25 32 40 50 63 80 100
I3 40 60 80 120 160 200 260 320 400 500 640 800 1000 1260 1600 2000
S S
PE
1.5 1.5 130 86 65 43 32 26 20 16 13 10 8 6
2.5 2.5 216 144 108 72 54 43 33 27 22 17 14 11 9 7
4 4 346 231 173 115 86 69 53 43 35 28 22 17 14 11 9 7
6 6 519 346 259 173 130 104 80 65 52 42 32 26 21 16 13 10
10 10 865 577 432 288 216 173 133 108 86 69 54 43 35 27 22 17
16 16 1384 923 692 461 346 277 213 173 138 111 86 69 55 44 35 28
25 16 1688 1125 844 563 422 338 260 211 169 135 105 84 68 54 42 34
35 16 47 38
T1 T1 T1 T1 T1 T1
In ≤50 63 80 100 125 160
I3 500 A 10 In 10 In 10 In 10 In 10 In
S S
PE
1.5 1.5 6
2.5 2.5 10
4 4 15 12 10 8 6
6 6 23 18 14 12 9 7
10 10 38 31 24 19 15 12
16 16 62 49 38 31 25 19
25 16 75 60 47 38 30 23
35 16 84 67 53 42 34 26
50 25 128 102 80 64 51 40
70 35 179 142 112 90 72 56
95 50 252 200 157 126 101 79
T2 T2 T2 T2 T2 T2 T2 T2 T2 T2 T2 T2 T2 T2 T2 T2
In 1.6 2 2.5 3.2 4 5 6.3 8 10 12.5 16÷50 63 80 100 125 160
I3 10 In 10 In 10 In 10 In 10 In 10 In 10 In 10 In 10 In 10 In 500 A 10 In10 In 10 In 10 In 10 In
S S
PE
1.5 1.5 246 197 157 123 98 79 62 49 39 31 8
2.5 2.5 410 328 262 205 164 131 104 82 66 52 13
4 4 655 524 419 328 262 210 166 131 105 84 21 17 13 10 8
6 6 983 786 629 491 393 315 250 197 157 126 31 25 20 16 13 10
10 10 1638 1311 1048 819 655 524 416 328 262 210 52 42 33 26 21 16
16 16 2621 2097 1677 1311 1048 839 666 524 419 335 84 67 52 42 34 26
25 16 1598 1279 1023 812 639 511 409 102 81 64 51 41 32
35 16 1151 914 720 576 460 115 91 72 58 46 36
50 25 1092 874 699 175 139 109 87 70 55
70 35 979 245 194 153 122 98 76
95 50 343 273 215 172 137 107
120 70 417 331 261 209 167 130
150 95 518 411 324 259 207 162
185 95 526 418 329 263 211 165
Table 2.4: Curve K
Table 2.5: Curve D
Table 2.7: Tmax T2 TMD
TN system MPL
by MCB
TN system MPL
by MCCB
Table 2.6: TmaxT1 TMD
191 190 ABB SACE - Electrical devices ABB SACE - Electrical devices
5 Protection of human beings 5 Protection of human beings
5.8 Maximum protected length for the protection of human beings 5.8 Maximum protected length for the protection of human beings
T3 T3 T3 T3 T3 T3 T3
In 63 80 100 125 160 200 250
I3 10 In 10 In 10 In 10 In 10 In 10 In 10 In
S S
PE
4 4 17 13 10 8
6 6 25 20 16 13 10 8
10 10 42 33 26 21 16 13 10
16 16 67 52 42 34 26 21 17
25 16 81 64 51 41 32 26 20
35 16 91 72 58 46 36 29 23
50 25 139 109 87 70 55 44 35
70 35 194 153 122 98 76 61 49
95 50 273 215 172 137 107 86 69
120 70 331 261 209 167 130 104 83
150 95 411 324 259 207 162 130 104
185 95 418 329 263 211 165 132 105
240 120 499 393 315 252 197 157 126
T2 T2 T2 T2 T2
In 10 25 63 100 160
I3 5.5 In 5.5 In 5.5 In 5.5 In 5.5 In
S S
PE
1.5 1.5 79 31 12
2.5 2.5 131 52 21
4 4 210 84 33 21
6 6 315 126 50 31 20
10 10 524 210 83 52 33
16 16 839 335 133 84 52
25 16 1023 409 162 102 64
35 16 1151 460 183 115 72
50 25 1747 699 277 175 109
70 35 2446 979 388 245 153
95 50 3434 1374 545 343 215
120 70 4172 1669 662 417 261
150 95 5183 2073 823 518 324
185 95 5265 2106 836 526 329
TN system MPL
by MCCB
Table 2.9: Tmax T4 TMD/TMA
Table 2.8: Tmax T3 TMD
T4 T4 T4 T4 T4 T4 T4 T4 T4 T4
In 20 32 50 80 100 125 160 200 250 320
I
3
320 A 10 In 10 In 5...10 In 5...10 In 5...10 In 5...10 In 5...10 In 5...10 In 5...10 In
S S
PE
1.5 1.5 14 14 9 11…5 9…4 7…3 5…3 4…2 3…2 3…1
2.5 2.5 23 23 14 18…9 14…7 12…6 9…5 7…4 6…3 5…2
4 4 36 36 23 29…14 23…12 18…9 14…7 12…6 9…5 7…4
6 6 54 54 35 43…22 35…17 28…14 22…11 17…9 14…7 11…5
10 10 90 90 58 72…36 58…29 46…23 36…18 29…14 23…12 18…9
16 16 144 144 92 115…58 92…46 74…37 58…29 46…23 37…18 29…14
25 16 176 176 113 141…70 113…56 90…45 70…35 56…28 45…23 35…18
35 16 198 198 127 158…79 127…63 101…51 79…40 63…32 51…25 40…20
50 25 300 300 192 240…120 192…96 154…77 120…60 96…48 77…38 60…30
70 35 420 420 269 336…168 269…135 215…108 168…84 135…67 108…54 84…42
95 50 590 590 378 472…236 378…189 302…151 236…118 189…94 151…76 118…59
120 70 717 717 459 574…287 459…229 367…184 287…143 229…115 184…92 143…72
150 95 891 891 570 713…356 570…285 456…228 356…178 285…143 228…114 178…89
185 95 905 905 579 724…362 579…290 463…232 362…181 290…145 232…116 181…90
240 120 1081 1081 692 865…432 692…346 554…277 432…216 346…173 277…138 216…108
300 150 1297 1297 830 1038…519 830…415 664…332 519…259 415…208 332…166 259…130
TN system MPL
by MCCB Table 2.10: Tmax T5 TMA
T5 T5 T5 T5
In 320 400 500 630
I3 5...10 In 5...10 In 5...10 In 5...10 In
S SPE
1,5 1,5 3…1 2…1 2…1 1…1
2,5 2,5 5…2 4…2 3…1 2…1
4 4 7…4 6…3 5…2 4…2
6 6 11…5 9…4 7…3 5…3
10 10 18…9 14…7 12…6 9…5
16 16 29…14 23…12 18…9 15…7
25 16 35…18 28…14 23…11 18…9
35 16 40…20 32…16 25…13 20…10
50 25 60…30 48…24 38…19 31…15
70 35 84…42 67…34 54…27 43…21
95 50 118…59 94…47 76…38 60…30
120 70 143…72 115…57 92…46 73…36
150 95 178…89 143…71 114…57 91…45
185 95 181…90 145…72 116…58 92…46
240 120 216…108 173…86 138…69 110…55
300 150 259…130 208…104 166…83 132…66
Note: if the setting of function I is different from the reference value (5.5), the value of the
MPL shall be multiplied by the ratio between the reference value and the set value.
Table 2.11: Tmax T2 with PR221 DS-LS
193 192 ABB SACE - Electrical devices ABB SACE - Electrical devices
5 Protection of human beings 5 Protection of human beings
5.8 Maximum protected length for the protection of human beings 5.8 Maximum protected length for the protection of human beings
CURVE Z Z Z Z Z Z Z Z Z Z
In ≤8 10 13 16 20 25 32 40 50 63
I3 30 30 39 48 60 75 96 120 150 189
S S
PE
1.5 1.5 150 150 115 94 75 60 47 37
2.5 2.5 250 250 192 156 125 100 78 62 50 40
4 4 400 400 307 250 200 160 125 100 80 63
6 6 599 599 461 375 300 240 187 150 120 95
10 10 999 999 768 624 499 400 312 250 200 159
16 16 1598 1598 1229 999 799 639 499 400 320 254
25 16 1949 1949 1499 1218 974 780 609 487 390 309
CURVE B B B B B B B B B B B B B
In ≤6 8 10 13 16 20 25 32 40 50 63 80 100
I3 30 40 50 65 80 100 125 160 200 250 315 400 500
S S
PE
1.5 1.5 150 112 90 69 56 45 36 28 22
2.5 2.5 250 187 150 115 94 75 60 47 37 30 24
4 4 400 300 240 184 150 120 96 75 60 48 38 30 24
6 6 599 449 360 277 225 180 144 112 90 72 57 45 36
10 10 999 749 599 461 375 300 240 187 150 120 95 75 60
16 16 1598 1199 959 738 599 479 384 300 240 192 152 120 96
25 16 1949 1462 1169 899 731 585 468 365 292 234 186 146 117
35 16 165 132
CURVE C C C C C C C C C C C C C C C C
In ≤3 4 6 8 10 13 16 20 25 32 40 50 63 80 100 125
I3 30 40 60 80 100 130 160 200 250 320 400 500 630 800 1000 1250
S S
PE
1.5 1.5 150 112 75 56 45 35 28 22 18 14 11
2.5 2.5 250 187 125 94 75 58 47 37 30 23 19 15 12
4 4 400 300 200 150 120 92 75 60 48 37 30 24 19 15 12 10
6 6 599 449 300 225 180 138 112 90 72 56 45 36 29 22 18 14
10 10 999 749 499 375 300 230 187 150 120 94 75 60 48 37 30 24
16 16 1598 1199 799 599 479 369 300 240 192 150 120 96 76 60 48 38
25 16 1949 1462 974 731 585 450 365 292 234 183 146 117 93 73 58 47
35 16 82 66 53
Table 3.1: Curve Z
IT system MPL
by MCB
Table 3.3: Curve C
Table 3.2: Curve B
S6 S7 S7 S7 S8 S8 S8 S8
In 800 1000 1250 1600 1600 2000 2500 3200
I3 6 In 6 In 6 In 6 In 6 In 6 In 6 In 6 In
S S
PE
2.5 2.5
4 4
6 6
10 10
16 16
25 16
35 16
50 25 20
70 35 28 22 18 14 14
95 50 39 31 25 20 20 16 13 10
120 70 48 38 31 24 24 19 15 12
150 95 59 48 38 30 30 24 19 15
185 95 60 48 39 30 30 24 19 15
240 120 72 58 46 36 36 29 23 18
300 150 86 69 55 43 43 35 28 22
Table 2.13: SACE Isomax S6÷S8 with PR211- PR212
Note: if the setting of function S or I is different from the reference value (6), the MPL value
shall be multiplied by the ratio between the reference value and the set value. Besides,
using function S the MPL shall be multiplied by 1.1.
TN system MPL
by MCCB
T4 T4 T4 T4 T5 T5 T5
In 100 160 250 320 320 400 630
I
3
6.5 In 6.5 In 6.5 In 6.5 In 6.5 In 6.5 In 6.5 In
S S
PE
1,5 1,5
2,5 2,5
4 4
6 6 29 18
10 10 48 30 19
16 16 77 48 31 24 24 19
25 16 94 59 38 30 30 24 15
35 16 106 66 43 33 33 27 17
50 25 161 101 65 50 50 40 26
70 35 226 141 90 71 71 56 36
95 50 317 198 127 99 99 79 50
120 70 385 241 154 120 120 96 61
150 95 478 299 191 150 150 120 76
185 95 486 304 194 152 152 121 77
240 120 581 363 232 181 181 145 92
300 150 697 435 279 218 218 174 111
Table 2.12: Tmax T4-T5 with PR221 - PR222
Note: if the setting of function I is different from the reference value (6.5), the value of the
MPL shall be multiplied by the ratio between the reference value and the set value.
195 194 ABB SACE - Electrical devices ABB SACE - Electrical devices
5 Protection of human beings 5 Protection of human beings
5.8 Maximum protected length for the protection of human beings 5.8 Maximum protected length for the protection of human beings
T1 T1 T1 T1 T1 T1
In ≤50 63 80 100 125 160
I3 500 A 10 In 10 In 10 In 10 In 10 In
S S
PE
1.5 1.5 5
2.5 2.5 8
4 4 13 11 8 7 5
6 6 20 16 12 10 8 6
10 10 33 26 21 17 13 10
16 16 53 42 33 27 21 17
25 16 65 52 41 32 26 20
35 16 73 58 46 37 29 23
50 25 111 88 69 55 44 35
70 35 155 123 97 78 62 49
95 50 218 173 136 109 87 68
T2 T2 T2 T2 T2 T2 T2 T2 T2 T2 T2 T2 T2 T2 T2 T2
In 1.6 2 2.5 3.2 4 5 6.3 8 10 12.5 16÷50 63 80 100 125 160
I3 10 In 10 In 10 In 10 In 10 In 10 In 10 In 10 In 10 In 10 In 500 A 10 In 10 In 10 In 10 In 10 In
S S
PE
1.5 1.5 213 170 136 106 85 68 54 43 34 27 7
2.5 2.5 355 284 227 177 142 113 90 71 57 45 11
4 4 567 454 363 284 227 182 144 113 91 73 18 14 11 9 7
6 6 851 681 545 426 340 272 216 170 136 109 27 22 17 14 11 9
10 10 1419 1135 908 709 567 454 360 284 227 182 45 36 28 23 18 14
16 16 2270 1816 1453 1135 908 726 576 454 363 291 73 58 45 36 29 23
25 16 1384 1107 886 703 554 443 354 89 70 55 44 35 28
35 16 997 791 623 498 399 100 79 62 50 40 31
50 25 946 757 605 151 120 95 76 61 47
70 35 847 212 168 132 106 85 66
95 50 297 236 186 149 119 93
120 70 361 287 226 181 145 113
150 95 449 356 281 224 180 140
185 95 456 362 285 228 182 142
CURVE K K K K K K K K K K K K K K K K K K K K K K
In ≤2 ≤3 4 4.2 5.8 6 8 10 11 13 15 16 20 25 26 32 37 40 41 45 50 63
I3 28 42 56 59 81 84 112 140 154 182 210 224 280 350 364 448 518 560 574 630 700 882
S S
PE
1.5 1.5 161 107 80 76 55 54 40 32 29 25 21 20 16 13 12 10 9 8
2.5 2.5 268 178 134 127 92 89 67 54 49 41 36 33 27 21 21 17 14 13 13 12
4 4 428 285 214 204 148 143 107 86 78 66 57 54 43 34 33 27 23 21 21 19 17 14
6 6 642 428 321 306 221 214 161 128 117 99 86 80 64 51 49 40 35 32 31 29 26 20
10 10 1070 713 535 510 369 357 268 214 195 165 143 134 107 86 82 67 58 54 52 48 43 34
16 16 1712 1141 856 815 590 571 428 342 311 263 228 214 171 137 132 107 93 86 84 76 68 54
25 16 2088 1392 1044 994 720 696 522 418 380 321 278 261 209 167 161 130 113 104 102 93 84 66
CURVE D D D D D D D D D D D D D D D D
In ≤2 3 4 6 8 10 13 16 20 25 32 40 50 63 80 100
I3 40 60 80 120 160 200 260 320 400 500 640 800 1000 1260 1600 2000
S S
PE
1.5 1.5 112 75 56 37 28 22 17 14 11 9 7 6
2.5 2.5 187 125 94 62 47 37 29 23 19 15 12 9 7 6
4 4 300 200 150 100 75 60 46 37 30 24 19 15 12 10 7 6
6 6 449 300 225 150 112 90 69 56 45 36 28 22 18 14 11 9
10 10 749 499 375 250 187 150 115 94 75 60 47 37 30 24 19 15
16 16 1199 799 599 400 300 240 184 150 120 96 75 60 48 38 30 24
25 16 1462 974 731 487 365 292 225 183 146 117 91 73 58 46 37 29
35 41 33
Table 3.6: Tmax T1 TMD
Table 3.7: Tmax T2 TMD
IT system MPL
by MCCB Table 3.4: Curve K
IT system MPL
by MCB
Table 3.5: Curve D
197 196 ABB SACE - Electrical devices ABB SACE - Electrical devices
5 Protection of human beings 5 Protection of human beings
5.8 Maximum protected length for the protection of human beings 5.8 Maximum protected length for the protection of human beings
T2 T2 T2 T2 T2
In 10 25 63 100 160
I3 5.5 In 5.5 In 5.5 In 5.5 In 5.5 In
S S
PE
1.5 1.5 68 27 11
2.5 2.5 113 45 18
4 4 182 73 29 18
6 6 272 109 43 27 17
10 10 454 182 72 45 28
16 16 726 291 115 73 45
25 16 886 354 141 89 55
35 16 997 399 158 100 62
50 25 1513 605 240 151 95
70 35 2119 847 336 212 132
95 50 2974 1190 472 297 186
120 70 3613 1445 573 361 226
150 95 4489 1796 713 449 281
185 95 4559 1824 724 456 285
T3 T3 T3 T3 T3 T3 T3
In 63 80 100 125 160 200 250
I3 10 In 10 In 10 In 10 In 10 In 10 In 10 In
S S
PE
4 4 14 11 9 7
6 6 22 17 14 11 9 7
10 10 36 28 23 18 14 11 9
16 16 58 45 36 29 23 18 15
25 16 70 55 44 35 28 22 18
35 16 79 62 50 40 31 25 20
50 25 120 95 76 61 47 38 30
70 35 168 132 106 85 66 53 42
95 50 236 186 149 119 93 74 59
120 70 287 226 181 145 113 90 72
150 95 356 281 224 180 140 112 90
185 95 362 285 228 182 142 114 91
240 120 432 340 272 218 170 136 109
T4 T4 T4 T4 T4 T4 T4 T4 T4 T4
In 20 32 50 80 100 125 160 200 250 320
I
3
320 A 10 In 10 In 5...10 In 5...10 In 5...10 In 5...10 In 5...10 In 5...10 In 5...10 In
S S
PE
1.5 1.5 12 12 7 9…5 7…4 6…3 5…2 4…2 3…1 2…1
2.5 2.5 20 20 12 16…8 12…6 10…5 8…4 6…3 5…2 4…2
4 4 31 31 20 25…12 20…10 16…8 12…6 10…5 8…4 6…3
6 6 47 47 30 37…19 30…15 24…12 19…9 15…7 12…6 9…5
10 10 78 78 50 62…31 50…25 40…20 31…16 25…12 20…10 16…8
16 16 125 125 80 100…50 80…40 64…32 50…25 40…20 32…16 25…12
25 16 152 152 97 122…61 97…49 78…39 61…30 49…24 39…19 30…15
35 16 171 171 110 137…69 110…55 88…44 69…34 55…27 44…22 34…17
50 25 260 260 166 208…104 166…83 133…67 104…52 83…42 67…33 52…26
70 35 364 364 233 291…146 233…117 186…93 146…73 117…58 93…47 73…36
95 50 511 511 327 409…204 327…164 262…131 204…102 164…82 131…65 102…51
120 70 621 621 397 497…248 397…199 318…159 248…124 199…99 159…79 124…62
150 95 772 772 494 617…309 494…247 395…198 309…154 247…123 198…99 154…77
185 95 784 784 502 627…313 502…251 401…201 313…157 251…125 201…100 157…78
240 120 936 936 599 749…375 599…300 479…240 375…187 300…150 240…120 187…94
300 150 1124 1124 719 899…449 719…360 575…288 449…225 360…180 288…144 225…112
Table 3.11: Tmax T2 with PR221 DS-LS
IT system MPL
by MCCB
Note: if the setting of function I is different from the reference value (5.5), the MPL value
shall be multiplied by the ratio between the reference value and the set value.
Table 3.8: Tmax T3 TMD
IT system MPL
by MCCB
Table 3.9: Tmax T4 TMD/TMA
T5 T5 T5 T5
In 320 400 500 630
I
3
5...10 In 5...10 In 5...10 In 5...10 In
S S
PE
1.5 1.5 2…1 2…1 1…1 1…1
2.5 2.5 4…2 3…2 2…1 2…1
4 4 6…3 5…2 4…2 3…2
6 6 9…5 7…4 6…3 5…2
10 10 16…8 12…6 10…5 8…4
16 16 25…12 20…10 16…8 13…6
25 16 30…15 24…12 19…10 15…8
35 16 34…17 27…14 22…11 17…9
50 25 52…26 42…21 33…17 26…13
70 35 73…36 58…29 47…23 37…18
95 50 102…51 82…41 65…33 52…26
120 70 124…62 99…50 79…40 63…32
150 95 154…77 123…62 99…49 78…39
185 95 157…78 125…63 100…50 80…40
240 120 187…94 150…75 120…60 95…48
300 150 225…112 180…90 144…72 114…57
Table 3.10: Tmax T5 TMA
199 198 ABB SACE - Electrical devices ABB SACE - Electrical devices
5 Protection of human beings 5 Protection of human beings
5.8 Maximum protected length for the protection of human beings 5.8 Maximum protected length for the protection of human beings
S6 S7 S7 S7 S8 S8 S8 S8
In 800 1000 1250 1600 1600 2000 2500 3200
I3 6 In 6 In 6 In 6 In 6 In 6 In 6 In 6 In
S S
PE
2.5 2.5
4 4
6 6
10 10
16 16
25 16
35 16
50 25 17
70 35 24 19 16 12 12
95 50 34 27 22 17 17 14 11 9
120 70 41 33 26 21 21 17 13 10
150 95 51 41 33 26 26 21 16 13
185 95 52 42 33 26 26 21 17 13
240 120 62 50 40 31 31 25 20 16
300 150 75 60 48 37 37 30 24 19
Table 3.13: SACE Isomax S6-S8 with PR211-212
Note: if the setting of function S or I is different from the reference value (6), the MPL value
shall be multiplied by the ratio between the reference value and the set value. Besides,
using function S, the MPL shall be multiplied by 1.1.
IT system MPL
by MCCB
Table 3.12: Tmax T4-T5 with PR221-PR222 IT system MPL
by MCCB
T4 T4 T4 T4 T5 T5 T5
In 100 160 250 320 320 400 630
I3 6.5 In 6.5 In 6.5 In 6.5 In 6.5 In 6.5 In 6.5 In
S SPE
1.5 1.5
2.5 2.5
4 4
6 6 25 16
10 10 42 26 17
16 16 67 42 27 21 21 17
25 16 82 51 33 26 26 20 13
35 16 92 58 37 29 29 23 15
50 25 140 87 56 44 44 35 22
70 35 196 122 78 61 61 49 31
95 50 275 172 110 86 86 69 44
120 70 333 208 133 104 104 83 53
150 95 414 259 166 129 129 104 66
185 95 421 263 168 132 132 105 67
240 120 503 314 201 157 157 126 80
300 150 603 377 241 189 189 151 96
Note: if the setting of function I is different from the reference value (6.5), the value of the
MPL shall be multiplied by the ratio between the reference value and the set value.
201 200 ABB SACE - Electrical devices ABB SACE - Electrical devices
Annex A: Calculation tools Annex A: Calculation tools
1
S
D
C
0
0
8
0
5
9
F
0
0
0
1
A.1 Slide rules
Yellow slide rule: cable sizing
Side
Definition of the current carrying capacity, impedance and voltage drop of cables.
Side
Calculation of the short-circuit current for three-phase fault on the load side of
a cable line with known cross section and length.
In addition, a diagram for the calculation of the short-circuit current on the load
side of elements with known impedance.
These slide rules represent a valid instrument for a quick and approximate
dimensioning of electrical plants.
All the given information is connected to some general reference conditions;
the calculation methods and the data reported are gathered from the IEC
Standards in force and from plant engineering practice. The instruction manual
enclosed with the slide rules offers different examples and tables showing the
correction coefficients necessary to extend the general reference conditions to
those actually required.
These two-sided slide rules are available in four different colors, easily identified
by subject:
- yellow slide rule: cable sizing;
- orange slide rule: cable verification and protection;
- green slide rule: protection coordination;
- blue slide rule: motor and transformer protection.
A.1 Slide rules
203 202 ABB SACE - Electrical devices ABB SACE - Electrical devices
Annex A: Calculation tools Annex A: Calculation tools
A.1 Slide rules A.1 Slide rules
1
S
D
C
0
0
8
0
6
1
F
0
0
0
1
1
S
D
C
0
0
8
0
6
0
F
0
0
0
1
Orange slide rule: cable verification and protection
Side
Verification of cable protection against indirect contact and short-circuit with
ABB SACE MCCBs (moulded-case circuit-breakers).
Side
Verification of cable protection against indirect contact and short-circuit with
ABB MCBs (modular circuit-breakers).
Green slide rule: protection coordination
Side
Selection of the circuit-breakers when back-up protection is provided.
Side
Definition of the limit selectivity current for the combination of two circuit-breakers
in series.
205 204 ABB SACE - Electrical devices ABB SACE - Electrical devices
Annex A: Calculation tools Annex A: Calculation tools
1
S
D
C
0
0
8
0
6
2
F
0
0
0
1
A.2 DOCWin
DOCWin is a software for the dimensioning of electrical networks, with low or
medium voltage supply.
Networks can be completely calculated through simple operations starting from
the definition of the single-line diagram and thanks to the drawing functions
provided by an integrated CAD software.
Drawing and definition of networks
Creation of the single-line diagram, with no limits to the network complexity.
Meshed networks can also be managed.
• The diagram can be divided into many pages.
• The program controls the coherence of drawings in real time.
• It is possible to enter and modify the data of the objects which form the
network by using a table.
• It is possible to define different network configurations by specifying the status
(open/closed) of the operating and protective devices.
Supplies
• There are no pre-defined limits: the software manages MV and LV power
supplies and generators, MV/LV and LV/LV transformers, with two or three
windings, with or without voltage regulator, according to the requirements.
Network calculation
• Load Flow calculation using the Newton-Raphson method. The software can
manage networks with multiple slacks and unbalances due to single- or two-
phase loads. Magnitude and phase shift of the node voltage and of the branch
current are completely defined for each point of the network, for both MV as
well as LV.
• Calculation of the active and reactive power required by each single power
source.
Blue slide rule: motor and transformer protection
Side
Selection and coordination of the protection devices for the motor starter, DOL
start-up (type 2 coordination in compliance with the Standard IEC 60947-4-1).
Side
Sizing of a transformer feeder.
In addition, a diagram for the calculation of the short-circuit current on the load
side of transformers with known rated power.
A.1 Slide rules A.2 DOCWin
207 206 ABB SACE - Electrical devices ABB SACE - Electrical devices
Annex A: Calculation tools Annex A: Calculation tools
A.2 DOCWin A.2 DOCWIN
• Representation of the curves of circuit-breakers, cables, transformers, motors
and generators.
• Possibility of entering the curve of the utility and of the MV components point
by point, to verify the tripping discrimination of protection devices.
• Verification of the maximum voltage drop at each load.
• Verification of the protection devices, with control over the setting parameters
of the adjustable releases (both thermomagnetic as well as electronic).
Selection of operating and protection devices
• Automatic selection of protection devices (circuit-breakers and fuses)
• Automatic selection of operating devices (contactors and switch disconnectors)
• Discrimination and back-up managed as selection criteria, with discrimination
level adjustable for each circuit-breaker combination.
• Discrimination and back-up verification also through quick access to
coordination tables.
• Management of local (motors) and centralized power factor correction with
capacitor banks.
• Management of the demand factor for each single node of the network and
of the utilization factor on the loads.
• Short-circuit current calculation for three-phase, phase-to-phase, phase-to-
neutral, phase-to-ground faults. The calculation is also carried out for MV
sections, in compliance with the Standards IEC 60909-1, IEC 61363-1 (naval
installations) or with the method of symmetric components, taking into account
also the time-variance contribution of rotary machines (generators and motors).
• Calculation of switchboard overtemperature in compliance with Standard IEC
60890. The power dissipated by the single apparatus is automatically derived
by the data files of the software, and can be considered as a function of the
rated current or of the load current.
Cable line sizing
• Cable line sizing according to thermal criteria in compliance with the following
Standards: CEI 64-8 (tables CEI UNEL 35024-35026), IEC 60364, VDE 298-
4, NFC 15-100, IEC 60092 (naval installations) and IEC 60890.
• Possibility of setting, as additional calculation criterion, the economic criteria
stated in the Standard IEC 60827-3-2.
• Possibility of setting, as additional calculation criterion, the maximum allowed
voltage drop.
• Automatic sizing of busbar trunking system.
• Sizing and check on the dynamic withstand of busbars in compliance with
the Standard IEC 60865.
Curves and verifications
• Representation of:
- time / current curves (I-t),
- current / let-through energy curves (I-I
2
t),
- current limiting curves (peak): visual check of the effects of the settings on the
trip characteristics of protection devices.
• Motor coordination management through quick access to ABB tables.
Printouts
• Single-line diagram, curves and reports of the single components of the
network can be printed by any printer supported by the hardware
configuration.
• All information can be exported in the most common formats of data exchange.
• All print modes can be customized.
208 ABB SACE - Electrical devices
Annex A: Calculation tools
A.2 DOCWIN
U
r
[V]
230 400 415 440 500 600 690
P [kW] I
b
[A]
0.03 0.08 0.05 0.05 0.04 0.04 0.03 0.03
0.04 0.11 0.06 0.06 0.06 0.05 0.04 0.04
0.06 0.17 0.10 0.09 0.09 0.08 0.06 0.06
0.1 0.28 0.16 0.15 0.15 0.13 0.11 0.09
0.2 0.56 0.32 0.31 0.29 0.26 0.21 0.19
0.5 1.39 0.80 0.77 0.73 0.64 0.53 0.46
1 2.79 1.60 1.55 1.46 1.28 1.07 0.93
2 5.58 3.21 3.09 2.92 2.57 2.14 1.86
5 13.95 8.02 7.73 7.29 6.42 5.35 4.65
10 27.89 16.04 15.46 14.58 12.83 10.69 9.30
20 55.78 32.08 30.92 29.16 25.66 21.38 18.59
30 83.67 48.11 46.37 43.74 38.49 32.08 27.89
40 111.57 64.15 61.83 58.32 51.32 42.77 37.19
50 139.46 80.19 77.29 72.90 64.15 53.46 46.49
60 167.35 96.23 92.75 87.48 76.98 64.15 55.78
70 195.24 112.26 108.20 102.06 89.81 74.84 65.08
80 223.13 128.30 123.66 116.64 102.64 85.53 74.38
90 251.02 144.34 139.12 131.22 115.47 96.23 83.67
100 278.91 160.38 154.58 145.80 128.30 106.92 92.97
110 306.80 176.41 170.04 160.38 141.13 117.61 102.27
120 334.70 192.45 185.49 174.95 153.96 128.30 111.57
130 362.59 208.49 200.95 189.53 166.79 138.99 120.86
140 390.48 224.53 216.41 204.11 179.62 149.68 130.16
150 418.37 240.56 231.87 218.69 192.45 160.38 139.46
200 557.83 320.75 309.16 291.59 256.60 213.83 185.94
Table 1: Load current for three-phase systems with cosϕ = 0.9
Generic loads
The formula for the calculation of the load current of a generic load is:
where:
• P is the active power [W];
• k is a coefficient which has the value:
- 1 for single-phase systems or for direct current systems;
- for three-phase systems;
• U
r
is the rated voltage [V] (for three-phase systems it is the line voltage, for
single-phase systems it is the phase voltage);
• cosϕ is the power factor.
Table 1 allows the load current to be determined for some power values
according to the rated voltage. The table has been calculated considering cosϕ
to be equal to 0.9; for different power factors, the value from Table 1 must be
multiplied by the coefficient given in Table 2 corresponding to the actual value
of the power factor (cosϕ
act
).
Annex B: Calculation of load current I
b
ϕ cos ⋅ ⋅
=
r
b
U k
P
I
209 ABB SACE - Electrical devices
211 210 ABB SACE - Electrical devices
Annex B: Calculation of load current I
b
ABB SACE - Electrical devices
Annex B: Calculation of load current I
b
Annex B: calculation of load curremt I
b
Annex B: calculation of load curremt I
b
cosϕ
act
1 0.95 0.9 0.85 0.8 0.75 0.7
k
cosϕ
*
1 1.053 1.111 1.176 1.25 1.333 1.429
U
r
[V]
230 400 415 440 500 600 690
P [kW] I
b
[A]
30 130.43 75.00 72.29 68.18 60.00 50.00 43.48
40 173.91 100.00 96.39 90.91 80.00 66.67 57.97
50 217.39 125.00 120.48 113.64 100.00 83.33 72.46
60 260.87 150.00 144.58 136.36 120.00 100.00 86.96
70 304.35 175.00 168.67 159.09 140.00 116.67 101.45
80 347.83 200.00 192.77 181.82 160.00 133.33 115.94
90 391.30 225.00 216.87 204.55 180.00 150.00 130.43
100 434.78 250.00 240.96 227.27 200.00 166.67 144.93
110 478.26 275.00 265.06 250.00 220.00 183.33 159.42
120 521.74 300.00 289.16 272.73 240.00 200.00 173.91
130 565.22 325.00 313.25 295.45 260.00 216.67 188.41
140 608.70 350.00 337.35 318.18 280.00 233.33 202.90
150 652.17 375.00 361.45 340.91 300.00 250.00 217.39
200 869.57 500.00 481.93 454.55 400.00 333.33 289.86
250 1086.96 625.00 602.41 568.18 500.00 416.67 362.32
300 1304.35 750.00 722.89 681.82 600.00 500.00 434.78
350 1521.74 875.00 843.37 795.45 700.00 583.33 507.25
400 1739.13 1000.00 963.86 909.09 800.00 666.67 579.71
450 1956.52 1125.00 1084.34 1022.73 900.00 750.00 652.17
500 2173.91 1250.00 1204.82 1136.36 1000.00 833.33 724.64
550 2391.30 1375.00 1325.30 1250.00 1100.00 916.67 797.10
600 2608.70 1500.00 1445.78 1363.64 1200.00 1000.00 869.57
650 2826.09 1625.00 1566.27 1477.27 1300.00 1083.33 942.03
700 3043.48 1750.00 1686.75 1590.91 1400.00 1166.67 1014.49
750 3260.87 1875.00 1807.23 1704.55 1500.00 1250.00 1086.96
800 3478.26 2000.00 1927.71 1818.18 1600.00 1333.33 1159.42
850 3695.65 2125.00 2048.19 1931.82 1700.00 1416.67 1231.88
900 3913.04 2250.00 2168.67 2045.45 1800.00 1500.00 1304.35
950 4130.43 2375.00 2289.16 2159.09 1900.00 1583.33 1376.81
1000 4347.83 2500.00 2409.64 2272.73 2000.00 1666.67 1449.28
act
ϕ cos
1
= k
ϕ cos
ϕ cos
rL
N B L L
b
U
k k n P
I =
• U
rL
is the rated voltage of the lamps;
• cosϕ is the power factor of the lamps which has the value:
- 0.4 for lamps without compensation;
- 0.9 for lamps with compensation.
U
r
[V]
230 400 415 440 500 600 690
P [kW] I
b
[A]
250 697.28 400.94 386.45 364.49 320.75 267.29 232.43
300 836.74 481.13 463.74 437.39 384.90 320.75 278.91
350 976.20 561.31 541.02 510.28 449.05 374.21 325.40
400 1115.65 641.50 618.31 583.18 513.20 427.67 371.88
450 1255.11 721.69 695.60 656.08 577.35 481.13 418.37
500 1394.57 801.88 772.89 728.98 641.50 534.58 464.86
550 1534.02 882.06 850.18 801.88 705.65 588.04 511.34
600 1673.48 962.25 927.47 874.77 769.80 641.50 557.83
650 1812.94 1042.44 1004.76 947.67 833.95 694.96 604.31
700 1952.39 1122.63 1082.05 1020.57 898.10 748.42 650.80
750 2091.85 1202.81 1159.34 1093.47 962.25 801.88 697.28
800 2231.31 1283.00 1236.63 1166.36 1026.40 855.33 743.77
850 2370.76 1363.19 1313.92 1239.26 1090.55 908.79 790.25
900 2510.22 1443.38 1391.21 1312.16 1154.70 962.25 836.74
950 2649.68 1523.56 1468.49 1385.06 1218.85 1015.71 883.23
1000 2789.13 1603.75 1545.78 1457.96 1283.00 1069.17 929.71
cosϕact 1 0.95 0.9 0.85 0.8 0.75 0.7
kcosϕ
*
0.9 0.947 1 1.059 1.125 1.2 1.286
U
r
[V]
230 400 415 440 500 600 690
P [kW] I
b
[A]
0.03 0.13 0.08 0.07 0.07 0.06 0.05 0.04
0.04 0.17 0.10 0.10 0.09 0.08 0.07 0.06
0.06 0.26 0.15 0.14 0.14 0.12 0.10 0.09
0.1 0.43 0.25 0.24 0.23 0.20 0.17 0.14
0.2 0.87 0.50 0.48 0.45 0.40 0.33 0.29
0.5 2.17 1.25 1.20 1.14 1.00 0.83 0.72
1 4.35 2.50 2.41 2.27 2.00 1.67 1.45
2 8.70 5.00 4.82 4.55 4.00 3.33 2.90
5 21.74 12.50 12.05 11.36 10.00 8.33 7.25
10 43.48 25.00 24.10 22.73 20.00 16.67 14.49
20 86.96 50.00 48.19 45.45 40.00 33.33 28.99
act
ϕ cos
9 . 0
= k
ϕ cos
Table 4: Correction factors for load current with cosϕ other than 1
*
For cosϕ
act
values not present in the table,
Lighting circuits
The current absorbed by the lighting system may be deduced from the lighting
equipment catalogue, or approximately calculated using the following formula:
where:
• P
L
is the power of the lamp [W];
• n
L
is the number of lamps per phase;
• k
B
is a coefficient which has the value:
- 1 for lamps which do not need any auxiliary starter;
- 1.25 for lamps which need auxiliary starters;
• k
N
is a coefficient which has the value:
- 1 for star-connected lamps;
- for delta-connected lamps;
*
For cosϕ
act
values not present in the table,
Table 3 allows the load current to be determined for some power values
according to the rated voltage. The table has been calculated considering cosϕ
to be equal to 1; for different power factors, the value from Table 3 must be
multiplied by the coefficient given in Table 4 corresponding to the actual value
of the power factor (cosϕ
act
).
Table 2: Correction factors for load current with cosϕ other than 0.9
Table 3: Load current for single-phase systems with cosϕ = 1 or dc
systems
213 212 ABB SACE - Electrical devices ABB SACE - Electrical devices
2
C
Z R =
C
+
2
X
C
kLLL kLLL
L
r
kLL
I I
Z
U
I 87 . 0
2
3
2
= = =
Z
L
Z
L
Z
L
Z
N
I
kLLL
I
kLLL
I
kLLL
Z
L
Z
L
Z
L
Z
N
I
kLL
[kW]
0.06
0.09
0.12
0.18
0.25
0.37
0.55
0.75
1.1
1.5
2.2
2.5
3
3.7
4
5
5.5
6.5
7.5
8
9
11
12.5
15
18.5
20
22
25
30
37
40
45
51
55
59
75
80
90
100
110
129
132
140
147
160
180
184
200
220
250
257
295
315
355
400
450
475
500
560
600
670
PS = hp
1/12
1/8
1/6
1/4
1/3
1/2
3/4
1
1.5
2
3
3.4
4
5
5.5
6.8
7.5
8.8
10
11
12.5
15
17
20
25
27
30
34
40
50
54
60
70
75
80
100
110
125
136
150
175
180
190
200
220
245
250
270
300
340
350
400
430
480
545
610
645
680
760
810
910
220-230 V
[A]
0.38
0.55
0.76
1.1
1.4
2.1
2.7
3.3
4.9
6.2
8.7
9.8
11.6
14.2
15.3
18.9
20.6
23.7
27.4
28.8
32
39.2
43.8
52.6
64.9
69.3
75.2
84.4
101
124
134
150
168
181
194
245
260
292
325
358
420
425
449
472
502
578
590
626
700
803
826
948
990
1080
1250
1410
1490
1570
1750
–
–
240 V
[A]
0.35
0.50
0.68
1
1.38
1.93
2.3
3.1
4.1
5.6
7.9
8.9
10.6
13
14
17.2
18.9
21.8
24.8
26.4
29.3
35.3
40.2
48.2
58.7
63.4
68
77.2
92.7
114
123
136
154
166
178
226
241
268
297
327
384
393
416
432
471
530
541
589
647
736
756
868
927
1010
1130
1270
1340
1420
1580
–
–
380-400 V
[A]
0.22
0.33
0.42
0.64
0.88
1.22
1.5
2
2.6
3.5
5
5.7
6.6
8.2
8.5
10.5
11.5
13.8
15.5
16.7
18.3
22
25
30
37
40
44
50
60
72
79
85
97
105
112
140
147
170
188
205
242
245
260
273
295
333
340
370
408
460
475
546
580
636
710
800
850
890
1000
1080
1200
415 V
[A]
0.20
0.30
0.40
0.60
0.85
1.15
1.40
2
2.5
3.5
5
5.5
6.5
7.5
8.4
10
11
12.5
14
15.4
17
21
23
28
35
37
40
47
55
66
72
80
90
96
105
135
138
165
182
200
230
242
250
260
280
320
325
340
385
425
450
500
535
580
650
740
780
830
920
990
1100
440 V
[A]
0.19
0.28
0.37
0.55
0.76
1.06
1.25
1.67
2.26
3.03
4.31
4.9
5.8
7.1
7.6
9.4
10.3
12
13.5
14.4
15.8
19.3
21.9
26.3
32
34.6
37.1
42.1
50.1
61.9
67
73.9
83.8
90.3
96.9
123
131
146
162
178
209
214
227
236
256
289
295
321
353
401
412
473
505
549
611
688
730
770
860
920
1030
500 V
[A]
0.16
0.24
0.33
0.46
0.59
0.85
1.20
1.48
2.1
2.6
3.8
4.3
5.1
6.2
6.5
8.1
8.9
10.4
11.9
12.7
13.9
16.7
19
22.5
28.5
30.6
33
38
44
54
60
64.5
73.7
79
85.3
106
112
128
143
156
184
186
200
207
220
254
259
278
310
353
363
416
445
483
538
608
645
680
760
810
910
600 V
[A]
0.12
0.21
0.27
0.40
0.56
0.77
1.02
1.22
1.66
2.22
3.16
3.59
4.25
5.2
5.6
6.9
7.5
8.7
9.9
10.6
11.6
14.1
16.1
19.3
23.5
25.4
27.2
30.9
37.1
45.4
49.1
54.2
61.4
66.2
71.1
90.3
96.3
107
119
131
153
157
167
173
188
212
217
235
260
295
302
348
370
405
450
508
540
565
630
680
760
660-690 V
[A]
–
–
–
–
–
0.7
0.9
1.1
1.5
2
2.9
3.3
3.5
4.4
4.9
6
6.7
8.1
9
9.7
10.6
13
15
17.5
21
23
25
28
33
42
44
49
56
60
66
82
86
98
107
118
135
140
145
152
170
190
200
215
235
268
280
320
337
366
410
460
485
510
570
610
680
Three-phase fault
Two-phase fault
Motors
Table 5 gives the approximate values of the load current for some three-phase
squirrel-cage motors, 1500 rpm at 50 Hz, according to the rated voltage.
Motor power Rated current of the motor at:
Table 5: Motor load current
Note: these values are given for information only, and may vary according to the motor manifacturer
and depending on the number of poles
Annex B: Calculation of load current I
b
Annex C: Calculation of short-circuit current
Annex B: calculation of load curremt I
b
A short-circuit is a fault of negligible impedance between live conductors having
a difference in potential under normal operating conditions.
Fault typologies
In a three-phase circuit the following types of fault may occur:
• three-phase fault;
• two-phase fault;
• phase to neutral fault;
• phase to PE fault.
In the formulas, the following symbols are used:
• I
k
short-circuit current;
• U
r
rated voltage;
• Z
L
phase conductor impedance;
• Z
N
neutral conductor impedance;
• Z
PE
protective conductor impedance.
The following table briefly shows the type of fault and the relationships between
the value of the short-circuit current for a symmetrical fault (three phase) and
the short-circuit current for asymmetrical faults (two phase and single phase) in
case of faults far from generators. For more accurate calculation, the use of
DOCWin software is recommended.
215 214 ABB SACE - Electrical devices
Annex C: Calculation of short-circuit current
ABB SACE - Electrical devices
Annex C: Calculation of short-circuit current
Annex C: calculation of short-circuit current Annex C: calculation of short-circuit current
r
k
k
U 3
S
I
⋅
=
r
k
k
U 2
S
I
⋅
=
Three-phase short-circuit
Two-phase short-circuit
where:
• S
k
is the short-circuit apparent power seen at the point of the fault;
• U
r
is the rated voltage.
To determine the short-circuit apparent power S
k
, all the elements of the network
shall be taken into account, which may be:
• elements which contribute to the short-circuit current:
network, generators, motors;
• elements which limit the value of the short-circuit current:
conductors and transformers.
The procedure for the calculation of the short-circuit current involves the following
steps:
1. calculation of the short-circuit power for the different elements of the
installation;
2. calculation of the short-circuit power at the fault point;
3. calculation of the short-circuit current.
Determination of the short-circuit current
In order to determine the short-circuit current the “short-circuit power method”
can be used. This method allows the determination of the approximate short-
circuit current at a point in an installation in a simple way; the resultant value is
generally acceptable. However, this method is not conservative and gives more
accurate values, the more similar the power factors of the considered
components are (network, generators, transformers, motors and large section
cables etc.).
For more accurate calculation, the use of DOCWin software for the dimensioning
of installations is recommended.
The “short-circuit power method” calculates the short-circuit current I
k
based
on the formula:
Calculation of the short-circuit power for the different elements of
the installation
The short-circuit apparent power S
k
shall be determined for all the
components which are part of the installation:
Network
An electrical network is considered to include everything upstream of the point
of energy supply.
Phase to neutral fault
Phase to PE fault
( ) ( )
kLLL
L
r
N L
r
kLN
I
Z
U
Z Z
U
I = =
+
=
3 3
If ZN≅ limit condition:
U U
( ) ( )
kLLL
L
r
N L
r
kLN
I
Z Z Z
I 33 . 0
3 3 3
= =
+
=
(cross section of neutral conductor half the phase
conductor one):
If ZN= 2ZL
( ) ( )
kLLL
L
r
N L
r
kLN
I
Z
U
Z Z
U
I 5 . 0
2 3 3
= =
+
=
(cross section of neutral conductor equal to the
phase conductor one):
If ZL = ZN
( )
N L
r
kLN
Z Z
U
I
+
=
3
0
( )
kLLL
L
r
PE L
r
kLPE
I
Z
U
Z Z
U
I
= =
+
=
3 3 ( )
If ZPE ≅ limit condition:
( )
kLLL
L
r
PE L
r
kLPE
I
Z
U
Z Z
U
I 33 . 0
3 3 3
= =
+
=
( )
If ZPE = 2ZL (cross section of protective conductor
half to the phase conductor one):
( ) ( )
kLLL
L
r
PE L
r
kLPE I
Z
U
Z Z
U
I
5 . 0
2 3 3
= =
+
=
If ZL = ZPE (cross section of protective conductor equal
to the phase conductor one):
( )
PE L
r
kLPE
Z Z
U
I
+
=
3
0
Z
L
Z
L
Z
L
Z
N I
kLN
Z
L
Z
L
Z
L
Z
PE I
kLPE
Note
IkLLL
IkLL
I
kLN
Three-phase
short-circuit
I
kLLL
-
I
kLLL
=1.16I
kLL
I
kLLL
=2I
kLN
(Z
L
= Z
N
)
I
kLLL
=3I
kLN
(Z
L
= 2Z
N
)
I
kLLL
=I
kLN
(Z
N
≅ 0)
Two-phase
short-circuit
I
kLL
I
kLL
=0.87I
kLLL
-
I
kLL
=1.73I
kLN
(Z
L
= Z
N
)
I
kLL
=2.6I
kLN
(Z
L
= 2Z
N
)
I
kLL
=0.87I
kLN
(Z
N
≅ 0)
Phase to neutral
short-circuit
I
kLN
I
LN
=0.5I
kLLL
(Z
L
= Z
N
)
I
LN
=0.33I
kLLL
(Z
L
= 0,5Z
N
)
I
LN
=I
kLLL
(Z
N
≅ 0)
I
kLN
=0.58I
kLL
(Z
L
= Z
N
)
I
kLN
=0.38I
kLL
(Z
L
= 0,5Z
N
)
I
kLN
=1.16I
kLL
(Z
N
≅ 0)
-
Phase to PE short-circuit
(TN system)
I
kLPE
I
LPE
=0.5I
kLLL
(Z
L
= Z
PE
)
I
LPE
=0.33I
kLLL
(Z
L
= 0.5Z
PE
)
I
LPE
=I
kLLL
(Z
PE
≅ 0)
I
kLPE
=0.58I
kLL
(Z
L
= Z
PE
)
I
kLPE
=0.38I
kLL
(Z
L
= 0.5Z
PE
)
I
kLPE
=1.16I
kLL
(Z
PE
≅ 0)
The following table allows the approximate value of a short-circuit current to be
found quickly.
217 216 ABB SACE - Electrical devices
Annex C: Calculation of short-circuit current
ABB SACE - Electrical devices
Annex C: Calculation of short-circuit current
Annex C: calculation of short-circuit current Annex C: calculation of short-circuit current
k r kmot
I U S ⋅ ⋅ = 3
r
k
ktrafo
S
u
S ⋅ =
%
100
c
r
kcable
Z
U
S
2
=
et kn r knet
I U 3 S =
d%
*
r
kgen
X
100 S
S =
⋅
r
r
d
S
U
Z
2
=
2
C
Z
R
=
C
+
2
X
C
Cables
A good approximation of the short-circuit power of cables is:
where the impedance of the cable (Z
c
) is:
The following table gives the approximate values of the short-circuit power of
cables, at 50 and 60 Hz, according to the supply voltage (cable length = 10 m):
Asynchronous three-phase motors
Under short-circuit conditions, electric motors contribute to the fault for a brief
period (5-6 periods).
The power can be calculated according to the short-circuit current of the motor
(I
k
), by using the following expression:
Typical values are:
S
kmot
= 5÷7 S
rmot
(I
k
is about 5÷7 I
rmot
: 5 for motors of small size, and 7 for larger motors).
Transformers
The short-circuit power of a transformer (S
ktrafo
) can be calculated by using the
following formula:
The following table gives the approximate values of the short-circuit power of
transformers:
S
r
[kVA] 50 63 125 160 200 250 320 400 500 630 800 1000 1250 1600 2000 2500 3200 4000
u
k
% 4 4 4 4 4 4 4 4 4 4 5 5 5 6 6 6 6 6
S
ktrafo
[MVA] 1.3 1.6 3.1 4 5 6.3 8 10 12.5 15.8 16 20 25 26.7 33.3
Generally, the energy distribution authority supplies the short-circuit apparent
power (S
knet
) value at the point of energy supply. However, if the value of the
short-circuit current I
knet
is known, the value of the power can be obtained by
using, for three-phase systems, the following formula:
where U
r
is the rated voltage at the point of energy supply.
If the aforementioned data are not available, the values for S
knet
given in the
following table can be taken as reference values:
Net voltage U
r
[kV] Short-circuit power S
knet
[MVA]
Up to 20 500
Up to 32 750
Up to 63 1000
Generator
The short-circuit power is obtained from:
where X
*
d%
is the percentage value of the subtransient reactance (X
d
”
) or of the
transient reactance (X
d
’
) or of the synchronous reactance (X
d
), according to the
instant in which the value of the short-circuit power is to be evaluated.
In general, the reactances are expressed in percentages of the rated impedance
of the generator (Z
d
) given by:
where U
r
and S
r
are the rated voltage and power of the generator.
Typical values can be:
- X
d
”
from 10 % to 20 %;
- X
d
’ from 15 % to 40 %;
- X
d
from 80 % to 300 %.
Normally, the worst case is considered, that being the subtransient reactance.
The following table gives the approximate values of the short-circuit power of
generators (X
d
”
= 12.5 %):
S
r
[kVA] 50 63 125 160 200 250 320 400 500 630 800 1000 1250 1600 2000 2500 3200 4000
S
kgen
[MVA] 0.4 0.5 1.0 1.3 1.6 2.0 2.6 3.2 4.0 5.0 6.4 8.0 10.0 12.8 16.0 20.0 25.6 32.0
219 218 ABB SACE - Electrical devices
Annex C: Calculation of short-circuit current
ABB SACE - Electrical devices
Annex C: Calculation of short-circuit current
Annex C: calculation of short-circuit current Annex C: calculation of short-circuit current
r
k
k
U 3
S
I
⋅
=
r
k
k
U 2
S
I
⋅
=
1
S
D
C
0
1
0
0
5
0
F
0
0
0
1
CB1 CB2 CB3
Fault
1
S
D
C
0
1
0
0
5
1
F
0
0
0
1
CB1 CB2 CB3
Fault
230 [V] 400 [V] 440 [V] 500 [V] 690 [V] 230 [V] 400 [V] 440 [V] 500 [V] 690 [V]
S [mm
2
] S
kcable
[MVA] @50 Hz S
kcable
[MVA] @60 Hz
1.5 0.44 1.32 1.60 2.07 3.94 0.44 1.32 1.60 2.07 3.94
2.5 0.73 2.20 2.66 3.44 6.55 0.73 2.20 2.66 3.44 6.55
4 1.16 3.52 4.26 5.50 10.47 1.16 3.52 4.26 5.50 10.47
6 1.75 5.29 6.40 8.26 15.74 1.75 5.29 6.40 8.26 15.73
10 2.9 8.8 10.6 13.8 26.2 2.9 8.8 10.6 13.7 26.2
16 4.6 14.0 16.9 21.8 41.5 4.6 13.9 16.9 21.8 41.5
25 7.2 21.9 26.5 34.2 65.2 7.2 21.9 26.4 34.1 65.0
35 10.0 30.2 36.6 47.3 90.0 10.0 30.1 36.4 47.0 89.6
50 13.4 40.6 49.1 63.4 120.8 13.3 40.2 48.7 62.9 119.8
70 19.1 57.6 69.8 90.1 171.5 18.8 56.7 68.7 88.7 168.8
95 25.5 77.2 93.4 120.6 229.7 24.8 75.0 90.7 117.2 223.1
120 31.2 94.2 114.0 147.3 280.4 29.9 90.5 109.5 141.5 269.4
150 36.2 109.6 132.6 171.2 326.0 34.3 103.8 125.6 162.2 308.8
185 42.5 128.5 155.5 200.8 382.3 39.5 119.5 144.6 186.7 355.6
240 49.1 148.4 179.5 231.8 441.5 44.5 134.7 163.0 210.4 400.7
300 54.2 164.0 198.4 256.2 488.0 48.3 146.1 176.8 228.3 434.7
act
L
10
∑
=
i
k
S
S
1
1
∑
=
i k
S S
Once the short-circuit power equivalent at the fault point has been determined,
the short-circuit current can be calculated by using the following formula:
Three-phase short-circuit
Two-phase short-circuit
Calculation of the short-circuit current
To determine the short-circuit current in an installation, both the fault point as
well as the configuration of the system which maximize the short-circuit current
involving the device shall be considered. If appropriate, the contribution of the
motors shall be taken into account.
For example, in the case detailed below, for circuit-breaker CB1, the worst
condition occurs when the fault is right upstream of the circuit-breaker itself. To
determine the breaking capacity of the circuit-breaker, the contribution of two
transformers in parallel must be considered.
Fault right downstream of CB1
Fault right upstream of CB1
(worst condition for CB1)
With n cables in parallel, it is necessary to multiply the value given in the table
by n. If the length of the cable (L
act
) is other than 10 m, it is necessary to
multiply the value given in the table by the following coefficient:
Calculation of the short-circuit power at the fault point
The rule for the determination of the short-circuit power at a point in the
installation, according to the short-circuit power of the various elements of the
circuit, is analogue to that relevant to the calculation of the equivalent admittance.
In particular:
• the power of elements in series is equal to the inverse of the sum of the
inverses of the single powers (as for the parallel of impedances);
• the short-circuit power of elements in parallel is equal to the sum of the single
short-circuit powers (as for the series of impedances).
The elements of the circuit are considered to be in series or parallel, seeing the
circuit from the fault point.
In the case of different branches in parallel, the distribution of the current between
the different branches shall be calculated once the short-circuit current at the
fault point has been calculated. This must be done to ensure the correct choice
of protection devices installed in the branches.
221 220 ABB SACE - Electrical devices
Annex C: Calculation of short-circuit current
ABB SACE - Electrical devices
Annex C: Calculation of short-circuit current
Annex C: calculation of short-circuit current Annex C: calculation of short-circuit current
267
cos η
P
S
r
rmot
=
⋅
=
r
ϕ
kVA
26.7 S
u
100
S
r
k
ktrafo
= ⋅ = MVA
%
U
L M
A
CB1
B
CB2 CB3
1
S
D
C
0
1
0
0
5
3
F
0
0
0
1
S
kEL
I
k
S
kUP
S
kUP
=
∞
S
kUP
=
1000 MVA
S
kUP
=
750 MVA
S
kUP
=
500 MVA
S
kUP
=
250 MVA
S
kUP
=
100 MVA
S
kUP
=
50 MVA
S
kUP
=
40 MVA
S
kUP
=
30 MVA
S
kUP
=
20 MVA
S
kUP
=
10 MVA
S
kEL
[MVA]
I
k
[kA]
0
10
20
30
40
50
60
70
80
90
100
110
120
130
140
150
0 10 20 30 40 50 60 70 80 90 100
1
S
D
C
0
1
0
0
5
2
F
0
0
0
1
Examples:
The following examples demonstrate the calculation of the short-circuit current
in some different types of installation.
Example 1
Upstream network: U
r
= 20000 V
S
knet
= 500 MVA
Transformer: S
r
= 1600 kVA
u
k
% = 6%
U
1r
/ U
2r
=20000/400
Motor: P
r
= 220 kW
I
kmot
/I
r
= 6.6
cosϕ
r
= 0.9
η = 0.917
Generic load: I
rL
= 1443.4 A
cosϕ
r
= 0.9
Calculation of the short-circuit power of different elements
Network: S
knet
= 500 MVA
Transformer:
Motor:
S
kmot
= 6.6
.
S
rmot
= 1.76 MVA for the first 5-6 periods (at 50 Hz about 100 ms)
Calculation of the short-circuit current for the selection of circuit-breakers
Selection of CB1
For circuit-breaker CB1, the worst condition arises when the fault occurs right
downstream of the circuit-breaker itself. In the case of a fault right upstream,
the circuit-breaker would be involved only by the fault current flowing from the
motor, which is remarkably smaller than the network contribution.
As a first approximation, by using the following graph, it is possible to evaluate
the three-phase short-circuit current downstream of an object with short-circuit
power (S
kEL
) known; corresponding to this value, knowing the short-circuit
power upstream of the object (S
kUP
), the value of I
k
can be read on the y-axis,
expressed in kA, at 400 V.
Figure 1: Chart for the calculation of the three-phase short-circuit
current at 400 V
223 222 ABB SACE - Electrical devices
Annex C: Calculation of short-circuit current
ABB SACE - Electrical devices
Annex C: Calculation of short-circuit current
Annex C: calculation of short-circuit current Annex C: calculation of short-circuit current
36.6
U 3
S
I
r
kCB1
kCB1
=
⋅
= kA
39.13
U 3
S
I
r
kCB3
kCB3
=
⋅
= kA
27.11
S
1
S
1
1
S S
ktrafo knet
kmot kCB3
=
+
+ = MVA
1
S
D
C
0
1
0
0
5
5
F
0
0
0
1
A
CB1
B
CB3 CB4 CB5
CB2
Trafo 1 Trafo 2
U
L2 L1 L3
25.35
S S
S S
S
ktrafo knet
ktrafo knet
kCB1
=
+
= MVA
⋅
36.6
U 3
S
I
r
kCB1
kCB1
=
⋅
= kA
S
kUP
=
500 MVA
S
kEL
[MVA]
I
k
[kA]
0
10
20
30
40
50
60
70
80
90
100
110
120
130
140
150
0 10 20 30 40 50 60 70 80 90 100
S
kUP
=
26.7 MVA
I
k
=
36.5 kA
1
S
D
C
0
1
0
0
5
4
F
0
0
0
1
Selection of CB2
For circuit-breaker CB2, the worst condition arises when the fault occurs right
downstream of the circuit-breaker itself. The circuit, seen from the fault point, is
represented by the series of the network with the transformer. The short-circuit
current is the same used for CB1.
The rated current of the motor is equal to 385 A; the circuit-breaker to select is
a Tmax T5H 400.
Selection of CB3
For CB3 too, the worst condition arises when the fault occurs right downstream
of the circuit-breaker itself.
The circuit, seen from the fault point, is represented by two branches in parallel:
the motor and the series of the network and transformer. According to the
previous rules, the short-circuit power is determined by using the following
formula:
Motor // (Network + Transformer)
The rated current of the load L is equal to 1443 A; the circuit-breaker to select
is a SACE Isomax S7S 1600, or an Emax E2N1600.
Example 2
The circuit shown in the diagram is constituted by the supply, two transformers
in parallel and three loads.
Upstream network: U
r1
=20000 V
S
knet
= 500 MVA
Transformers 1 and 2: S
r
= 1600 kVA
u
k
% = 6%
U
1r
/U
2r
=20000/400
Load L1: S
r
= 1500 kVA; cosϕ = 0.9;
Load L2: S
r
= 1000 kVA; cosϕ = 0.9;
Load L3: S
r
= 50 kVA; cosϕ = 0.9.
The circuit, seen from the fault point, is represented by the series of the network
with the transformer. According to the previous rules, the short-circuit power is
determined by using the following formula:
the maximum fault current is:
The transformer LV side rated current is equal to 2309 A; therefore the circuit-
breaker to select is an Emax E3N 2500.
Using the chart shown in Figure 1, it is possible to find I
kCB1
from the curve with
S
kUP
= S
knet
= 500 MVA corresponding to S
kEL
= S
ktrafo
= 26.7 MVA:
225 224 ABB SACE - Electrical devices
Annex C: Calculation of short-circuit current
ABB SACE - Electrical devices
Annex C: Calculation of short-circuit current
Annex C: calculation of short-circuit current Annex C: calculation of short-circuit current
Sknet = 500 MVA
26.7 100
.
% u
S
S
k
r
ktrafo
= = MVA
48.2
) S (S S
) S (S S
S
ktrafo2 ktrafo1 knet
ktrafo2 rtrafo1 knet
kbusbar
=
+ +
+ ⋅
= MVA
69.56
U 3
S
I
r
kbusbar
kbusbar
=
⋅
= kA
34.78
2
I
I
kbusbar
kCB1(2)
= = kA
I
k
upstream I
k
downstream
[kA] [kA]
100 96 92 89 85 82 78 71 65 60 50 43 36 31 27 24 20 17 13 11 7.8 5.6 3.7 2.7 2.0 1.3
90 86 83 81 78 76 72 67 61 57 48 42 35 31 27 24 20 17 13 11 7.8 5.6 3.7 2.7 2.0 1.3
80 77 75 73 71 69 66 62 57 53 46 40 34 30 27 24 20 17 13 10 7.7 5.5 3.7 2.7 2.0 1.3
70 68 66 65 63 62 60 56 53 49 43 38 33 29 26 23 19 16 13 10 7.6 5.5 3.7 2.7 2.0 1.3
60 58 57 56 55 54 53 50 47 45 40 36 31 28 25 23 19 16 12 10 7.5 5.4 3.7 2.7 2.0 1.3
50 49 48 47 46 45 44 43 41 39 35 32 29 26 23 21 18 15 12 10 7.3 5.3 3.6 2.6 2.0 1.3
40 39 39 38 38 37 37 35 34 33 31 28 26 24 22 20 17 15 12 10 7.1 5.2 3.6 2.6 2.0 1.3
35 34 34 34 33 33 32 32 31 30 28 26 24 22 20 19 16 14 11 10 7.1 5.1 3.5 2.6 2.0 1.3
30 30 29 29 29 28 28 28 27 26 25 23 22 20 19 18 16 14 11 9.3 7.0 5.0 3.5 2.6 1.9 1.3
25 25 24 24 24 24 24 23 23 22 21 21 19 18 17 16 14 13 11 9.0 6.8 5.0 3.4 2.6 1.9 1.3
20 20 20 20 19 19 19 19 18 18 18 17 16 15 15 14 13 12 10 8.4 6.5 4.8 3.3 2.5 1.9 1.3
15 15 15 15 15 15 14 14 14 14 14 13 13 12 12 12 11 10 8.7 7.6 6.1 4.6 3.2 2.5 1.9 1.3
12 12 12 12 12 12 12 12 11 11 11 11 11 10 10 10 9.3 8.8 7.8 7.0 5.7 4.4 3.1 2.4 1.9 1.3
10 10 10 10 10 10 10 10 9.5 9.4 9.2 9.0 8.8 8.5 8.3 8.1 7.7 7.3 6.5 5.9 5.0 3.9 2.9 2.3 1.8 1.2
8.0 8.0 7.9 7.9 7.9 7.8 7.8 7.7 7.7 7.6 7.5 7.4 7.2 7.1 6.9 6.8 6.5 6.2 5.7 5.2 4.5 3.7 2.8 2.2 1.7 1.2
6.0 6.0 5.9 5.9 5.9 5.9 5.8 5.8 5.8 5.7 5.6 5.5 5.4 5.3 5.2 5.1 4.9 4.8 4.4 4.1 3.6 3.1 2.4 2.0 1.6 1.1
3.0 3.0 3.0 3.0 3.0 3.0 3.0 2.9 2.9 2.9 2.9 2.9 2.8 2.8 2.8 2.7 2.7 2.6 2.5 2.4 2.2 2.0 1.7 1.4 1.2 0.9
Cable
section Length
[mm
2
] [m]
1.5 0.9 1.1 1.4 1.8 2.5 3.5 5.3 7 9.4 14
2.5 0.9 1 1.2 1.5 1.8 2.3 2.9 4.1 5.9 8.8 12 16 24
4 0.9 1.2 1.4 1.6 1.9 2.3 2.8 3.7 4.7 6.6 9.4 14 19 25 38
6 0.8 1.1 1.4 1.8 2.1 2.5 2.8 3.5 4.2 5.6 7 10 14 21 28 38 56
10 0.9 1.2 1.4 1.9 2.3 2.9 3.5 4.1 4.7 5.8 7 9.4 12 16 23 35 47 63 94
16 0.9 1.1 1.5 1.9 2.2 3 3.7 4.7 5.6 6.5 7.5 9.3 11 15 19 26 37 56 75 100 150
25 0.9 1.2 1.4 1.7 2.3 2.9 3.5 4.6 5.8 7.2 8.7 10 12 14 17 23 29 41 58 87 116 155 233
35 1.2 1.6 2 2.4 3.2 4 4.8 6.4 8 10 12 14 16 20 24 32 40 56 80 121 161 216 324
50 1.1 1.7 2.3 2.8 3.4 4.5 5.7 6.8 9 11 14 17 20 23 28 34 45 57 79 113 170 226 303 455
70 0.8 1.5 2.3 3.1 3.8 4.6 6.2 7.7 9.2 12 15 19 23 27 31 38 46 62 77 108 154 231 308 413
95 1 2 3 4 5 6 8 10 12 16 20 25 30 35 40 50 60 80 100 140 200 300 400
120 1.2 2.4 3.6 4.8 6 7.2 10 12 14 19 24 30 36 42 48 60 72 96 120 168 240 360 481
150 1.4 2.8 4.2 5.6 7 8.4 11 14 17 23 28 35 42 49 56 70 84 113 141 197 281 422
185 1.6 3.2 4.8 6.4 8 10 13 16 19 26 32 40 48 56 64 80 96 128 160 224 320 480
240 1.8 3.7 5.5 7.3 9.1 11 15 18 22 29 37 46 55 64 73 91 110 146 183 256 366 549
300 2 4 6 8 10 12 16 20 24 32 40 50 60 70 80 100 120 160 200 280 400
2x120 2.4 4.8 7.2 10 12 14 19 24 29 38 48 60 72 84 96 120 144 192 240 336 481
2x150 2.8 5.6 8.4 11 14 17 23 28 34 45 56 70 84 98 113 141 169 225 281 394 563
2x185 3.2 6.4 10 13 16 19 26 32 38 51 64 80 96 112 128 160 192 256 320 448
3x120 3.6 7.2 11 14 18 22 29 36 43 58 72 90 108 126 144 180 216 288 360 505
3x150 4.2 8.4 13 17 21 25 34 42 51 68 84 105 127 148 169 211 253 338 422
3x185 4.8 10 14 19 24 29 38 48 58 77 96 120 144 168 192 240 288 384 480
Determination of the short-circuit current I
k
downstream
of a cable as a function of the upstream one
The table below allows the determination, in a conservative way, of the three-
phase short-circuit current at a point in a 400 V network downstream of a
single pole copper cable at a temperature of 20 °C. Known values:
- the three-phase short-circuit current upstream of the cable;
- the length and cross section of the cable.
Calculation of the short-circuit powers of different elements:
Network
Transformers 1 and 2
Selection of CB1 (CB2)
For circuit-breaker CB1 (CB2) the worst condition arises when the fault occurs
right downstream of the circuit-breaker itself. According to the previous rules,
the circuit seen from the fault point, is equivalent to the parallel of the two
transformers in series with the network: Network + (Trafo 1 // Trafo 2).
The short-circuit current obtained in this way corresponds to the short-circuit
current at the busbar. This current, given the symmetry of the circuit, is distributed
equally between the two branches (half each). The current which flows through
CB1 (CB2) is therefore equal to half of that at the busbar.
The circuit-breakers CB1(CB2) to select, with reference to the rated current of
the transformers, are Emax E3N 2500.
Selection of CB3-CB4-CB5
For these circuit-breakers the worst condition arises when the fault occurs
right downstream of the circuit-breakers themselves. Therefore, the short-circuit
current to be taken into account is that at the busbar:
I
kCB3
= I
kbusbar
= 69.56 kA
The circuit-breakers to select, with reference to the current of the loads, are:
CB3: Emax E3S 2500
CB4: Emax E3S 1600
CB5: Tmax T2H 160
227 226 ABB SACE - Electrical devices ABB SACE - Electrical devices
S=
I t
k
2
√
(1)
k=
Qc (B+20)
ln (2)
(
1+
)
θf - θi
B+θi
ρ20
√
Qc (B+20)
ρ20
√
1
S
D
C
0
1
0
0
5
6
F
0
0
0
1
400 V
Ik upstream = 32 kA
Ik downstream = ?
QF C QF B
QF A
120 mm
2
Cu/PVC
L = 29 m
Table 1: Value of parameters for different materials
Material B Q
c
ρ
20
[°C] [J/°Cmm
3
] [Ωmm]
Copper 234.5 3.45⋅10
-3
17.241⋅10
-6
226
Aluminium 228 2.5⋅10
-3
28.264⋅10
-6
148
Lead 230 1.45⋅10
-3
214⋅10
-6
41
Steel 202 3.8⋅10
-3
138⋅10
-6
78
By using the formula (1), it is possible to determine the conductor minimum
section S, in the hypothesis that the generic conductor is submitted to an
adiabatic heating from a known initial temperature up to a specific final tempe-
rature (applicable if the fault is removed in less than 5 s):
where:
• S is the cross section [mm
2
];
• I is the value (r.m.s) of prospective fault current for a fault of negligible
impedance, which can flow through the protective device [A];
• t is the operating time of the protective device for automatic disconnection [s];
k can be evaluated using the tables 2÷7 or calculated according to the formula (2):
where:
• Q
c
is the volumetric heat capacity of conductor material [J/°Cmm
3
] at 20 °C;
• B is the reciprocal of temperature coefficient of resistivity at 0 °C for the
conductor [°C];
• ρ
20
is the electrical resistivity of conductor material at 20 °C [Ωmm];
• θ
i
initial temperature of conductor [°C];
• θ
f
final temperature of conductor [°C].
Table 1 shows the values of the parameters described above.
Procedure
In the row corresponding to the cable cross section 120 mm
2
, it is possible to
find the column for a length equal to 29 m or right below (in this case 24). In the
column of upstream short-circuit current it is possible to identify the row with a
value of 32 kA or right above (in this case 35). From the intersection of this last
row with the previously identified column, the value of the downstream short-
circuit current can be read as being equal to 26 kA.
Note:
• In the case of the I
k
upstream and the length of the cable not being included
in the table, it is necessary to consider:
- the value right above I
k
upstream;
- the value right below for the cable length.
These approximations allow calculations which favour safety.
• In the case of cables in parallel not present in the table, the length must be
divided by the number of cables in parallel.
Example
Data
Rated voltage = 400 V
Cable section = 120 mm
2
Conductor = copper
Length = 29 m
Upstream short-
circuit current = 32 kA
Annex C: Calculation of short-circuit current
Annex C: calculation of short-circuit current
Annex D: Calculation of the coefficient k for
the cables (k
2
S
2
)
229 228 ABB SACE - Electrical devices
Annex D: Calculation of the coefficient k for
the cables (k
2
S
2
)
ABB SACE - Electrical devices
Annex D: Calculation of the coefficient k for
the cables (k
2
S
2
)
Annex D: calculation for the cables Annex D: calculation for the cables
Table 5: Values of k for protective conductors as a core incorporated in
a cable or bunched with other cables or insulated conductors
Initial
70
90
90
60
85
180
Final
160/140
a
160/140
a
250
200
220
350
Copper
115/103
a
100/86
a
143
141
134
132
Aluminium
Value for k
76/68
a
66/57
a
94
93
89
87
Steel
42/37
a
36/31
a
52
51
48
47
Temperature °C
b
Conductor insulation
70 °C PVC
90 °C PVC
90 °C thermosetting
60 °C rubber
85 °C rubber
Silicone rubber
Material of conductor
a
The lower value applies to PVC insulated conductors of cross section greater than
300 mm
2
.
b
Temperature limits for various types of insulation are given in IEC 60724.
Table 6: Values of k for protective conductors as a metallic layer of a
cable e.g. armour, metallic sheath, concentric conductor, etc.
Initial
60
80
80
55
75
70
105
Final
200
200
200
200
220
200
250
Copper
141
128
128
144
140
135
135
Aluminium
93
85
85
95
93
-
-
Lead
26
23
23
26
26
-
-
Temperature °C
Conductor insulation
70 °C PVC
90 °C PVC
90 °C thermosetting
60 °C rubber
85 °C rubber
Mineral PVC covered
a
Mineral bare sheath
Material of conductor
a
This value shall also be used for bare conductors exposed to touch or in contact with
combustible material.
Steel
51
46
46
52
51
-
-
Value for k
Table 7: Value of k for bare conductors where there is no risk of damage
to any neighbouring material by the temperature indicated
Initial
temperature
°C
30
30
30
k value
228
159
138
Conductor insulation
Visible and in restricted area
Normal conditions
Fire risk
Material of conductor
Copper
Maximum
temperature
°C
500
200
150
k value
125
105
91
Maximum
temperature
°C
300
200
150
k value
82
58
50
Maximum
temperature
°C
500
200
150
Aluminium Steel
Table 2: Values of k for phase conductor
Initial temperature °C
Final temperature °C
Material of conductor:
copper
aluminium
tin-soldered joints
in copper conductors
a
This value shall be used for bare cables exposed to touch.
Table 3: Values of k for insulated protective conductors not
incorporated in cables and not bunched with other cables
Initial
30
30
30
30
30
30
Final
160/140
a
160/140
a
250
200
220
350
Copper
143/133
a
143/133
a
176
159
166
201
Aluminium
Value for k
95/88
a
95/88
a
116
105
110
133
Steel
52/49
a
52/49
a
64
58
60
73
Temperature °C
b
Conductor insulation
70 °C PVC
90 °C PVC
90 °C thermosetting
60 °C rubber
85 °C rubber
Silicone rubber
Material of conductor
a
The lower value applies to PVC insulated conductors of cross section greater than
300 mm
2
.
b
Temperature limits for various types of insulation are given in IEC 60724.
Table 4: Values of k for bare protective conductors in contact with
cable covering but not bunched with other cables
Initial
30
30
30
Final
200
150
220
Copper
159
138
166
Aluminium
Value for k
105
91
110
Steel
58
50
60
Temperature °C
a
Cable covering
PVC
Polyethylene
CSP
Material of conductor
a
Temperature limits for various types of insulation are given in IEC 60724.
PVC
≤ 300 mm
2
70
160
115
76
115
PVC
≤ 300 mm
2
70
140
103
68
-
EPR
XLPE
90
250
143
94
-
Rubber
60 °C
60
200
141
93
-
PVC
70
160
115
-
-
Bare
105
250
135/115
a
-
-
Mineral
Conductor insulation
The International System of Units (SI)
Main quantities and SI units
1°=
π
180
.
rad
Quantity SI unit Other units Conversion
Symbol Name Symbol Name Symbol Name
Length, area, volume
in inch 1 in = 25.4 mm
ft foot i ft = 30.48 cm
l length m metre fathom fathom 1 fathom = 6 ft = 1.8288 m
mile mile 1 mile = 1609.344 m
sm sea mile 1 sm = 1852 m
yd yard 1 yd = 91.44 cm
A area m2 square metre
a are 1 a = 102 m2
ha hectare 1 ha = 104 m2
l litre 1 l = 1 dm
3
= 10
-3
m
3
V
volume m3 cubic metre
UK pt pint 1 UK pt = 0.5683 dm3
UK gal gallon 1 UK gal = 4.5461 dm3
US gal gallon 1 US gal = 3.7855 dm
3
Angles
α, β, γ plane angle rad radian ° degrees
Ω solid angle sr steradian
Mass
m mass, weight kg kilogram lb pound 1 lb = 0.45359 kg
ρ density kg/m3 kilogram
υ specific volume m
3
/kg
cubic metre
for kilogram
M moment of inertia kg⋅m2
kilogram for
square metre
Time
t duration s second
f frequency Hz Hertz 1 Hz = 1/s
ω
angular
1/s reciprocal second ω = 2pf
frequency
v speed m/s metre per second km/h
kilometre
1 km/h = 0.2777 m/s
per hour
mile/h mile per hour 1 mile/h = 0.4470 m/s
knot kn 1 kn = 0.5144 m/s
g acceleration m/s2 metre per second
squared
Force, energy, power
F force N newton 1 N = 1 kg⋅m/s
2
kgf 1 kgf = 9.80665 N
p pressure/stress Pa pascal 1 Pa = 1 N/m2
bar bar 1 bar = 105 Pa
W energy, work J joule 1 J = 1 W⋅s = 1 N⋅m
P power W watt Hp horsepower 1 Hp = 745.7 W
Temperature and heat
T temperature K kelvin
°C Celsius T[K] = 273.15 + T [°C]
°F Fahrenheit T[K] = 273.15 + (5/9)⋅(T [°F]-32)
Q quantity of heat J joule
S entropy J/K joule per kelvin
Photometric quantities
I luminous intensity cd candela
L luminance cd/m2 candela per square metre
Φ luminous flux lm lumen 1 lm = 1 cd⋅sr
E illuminance lux 1 lux = 1 lm/m
2
SI Base Units
Quantity Symbol Unit name
Length m metre
Mass kg kilogram
Time s Second
Electric Current A ampere
Thermodynamic Temperature K kelvin
Amount of Substance mol mole
Luminous Intensity cd candela
Metric Prefixes for Multiples and Sub-multiples of Units
Decimal power Prefix Symbol Decimal power Prefix Symbol
10
24
yotta Y 10
-1
deci d
10
21
zetta Z 10
-2
centi c
10
18
exa E 10
-3
milli m
10
15
peta P 10
-6
mikro µ
10
12
tera T 10
-9
nano n
109 giga G 10-12 pico p
106 mega M 10-15 femto f
103 kilo k 10-18 atto a
102 etto h 10-21 zepto z
10 deca da 10-24 yocto y
231 230 ABB SACE - Electrical devices
Annex E: Main physical quantities and
electrotechnical formulas
ABB SACE - Electrical devices
Annex E: Main physical quantities and
electrotechnical formulas
Annex E: main physical quantities
233 232 ABB SACE - Electrical devices
Annex E: Main physical quantities and
electrotechnical formulas
ABB SACE - Electrical devices
Annex E: Main physical quantities and
electrotechnical formulas
Annex E: main physical quantities Annex E: main physical quantities
Main electrical and magnetic quantities and SI units
Quantity SI unit Other units Conversion
Symbol Name Symbol Name Symbol Name
I current A ampere
V voltage V volt
R resistance Ω ohm
G conductance S siemens G = 1/R
X reactance Ω ohm
X
L
= ωL
X
C
=-1/ωC
B susceptance S siemens
BL = -1/ωL
BC = ωC
Z impedance Ω ohm
Y admittance S siemens
P active power W watt
Q reactive power var
reactive volt
ampere
S apparent power VA volt ampere
Q electric charge C coulomb Ah ampere/hour
1 C = 1 A⋅s
1 Ah = 3600 A⋅s
E
electric field
V/m volt per metre
strength
C electric capacitance F farad 1 F = 1 C/V
H magnetic field A/m ampere per metre
B magnetic induction T tesla G gauss
1 T = 1 V⋅s/m2
1 G = 10-4 T
L inductance H henry 1 H = 1 Ω⋅s
conductor conductivity temperature
resistivity ρ ρρ ρρ
20
χ χχ χχ
20
=1/ρ ρρ ρρ
20
coefficient α αα αα
20
[mm2
Ω ΩΩ ΩΩ/m] [m/mm2
Ω ΩΩ ΩΩ] [K-1]
Aluminium 0.0287 34.84 3.8⋅10-3
Brass, CuZn 40 ≤ 0.067 ≥ 15 2⋅10-3
Constantan 0.50 2 -3⋅10-4
Copper 0.0175 57.14 3.95⋅10-3
Gold 0.023 43.5 3.8⋅10-3
Iron wire 0.1 to 0,15 10 to 6.7 4.5⋅10-3
Lead 0.208 4.81 3.9⋅10
-3
Magnesium 0.043 23.26 4.1⋅10
-3
Manganin 0.43 2.33 4⋅10
-6
Mercury 0.941 1.06 9.2⋅10
-4
Ni Cr 8020 1 1 2.5⋅10
-4
Nickeline 0.43 2.33 2.3⋅10
-4
Silver 0.016 62.5 3.8⋅10
-3
Zinc 0.06 16.7 4.2⋅10
-3
Resistivity values, conductivity and temperature coefficient at
20 °C of the main electrical materials
Main electrotechnical formulas
Impedance
jX
L
-jX
C
R
+
+
–
jB
C
-jB
L
G
+
+
–
Y
G U B
Z
R X
U
resistance of a conductor at temperature ϑ
conductance of a conductor at temperature ϑ
resistivity of a conductor at temperature ϑ
capacitive reactance
inductive reactance
impedance
module impedance
phase impedance
conductance
capacitive susceptance
inductive susceptance
admittance
module admittance
phase admittance
R
θ
=ρ
θ
⋅
S
G
θ
=
1
R
θ
= χ
θ
⋅
S
ρ
ϑ
=ρ
20 [1 + α
20
(ϑ – 20)]
= - X
C
=
-1
ω ⋅ C
1
2 ⋅ π ⋅ f ⋅ C
X
L
= ω ⋅ L = 2 ⋅ π ⋅ f ⋅ L
Z
= R + jX
Y
= G
2
+ B
2
ϕ = arctan
R
X
G
=
1
R
B
C
=
-1
X
C
= ω ⋅ C = 2 ⋅ π ⋅ f ⋅ C
B
L
=
-1
X
L
= –
1
ω ⋅ L
= –
1
2 ⋅ π ⋅ f ⋅ L
Y
= G – jB
Z
= R
2
+ X
2
ϕ = arctan
B
G
235 234 ABB SACE - Electrical devices
Annex E: Main physical quantities and
electrotechnical formulas
ABB SACE - Electrical devices
Annex E: Main physical quantities and
electrotechnical formulas
Annex E: main physical quantities Annex E: main physical quantities
Indipendences in series
Admittances in parallel
Z =
1
Z
1
+
1
Z
2
+
1
Z
3
+ …
1
Indipendences in parallel
Admittances in series
Z
2
Z
3
Z
1
Y
1
Y
2
Y
3
Z
1
Z
2
Z
3 Z
1
+ Z
2
+ Z
3
+ … Z =
Y =
1
Y
1
+
1
Y
2
+
1
Y
3
+ …
1
Y
2
Y
3
Y
1
Y
1
+ Y
2
+ Y
3
+ … Y =
Delta-star and star-delta transformations
Z
12
2
Z
23
0
Z
2
Z
1
Z
3
Z
13
1
3
∆→Y
Z
1
=
Z
12
⋅ Z
13
Z
12
+ Z
13
+ Z
23
Z
2
=
Z
12
⋅ Z
23
Z
12
+ Z
13
+ Z
23
Z
3
=
Z
23
⋅ Z
13
Z
12
+ Z
13
+ Z
23
Z
12
= Z
1
+ Z
2
+
Z
1
⋅ Z
2
Z
3
Y→∆
Z
23
= Z
2
+ Z
3
+
Z
2
⋅ Z
3
Z
1
Z
13
= Z
3
+ Z
1
+
Z
3
⋅ Z
1
Z
2
Transformers
Two-winding transformer
rated current
short-circuit power
short-circuit current
longitudinal impedance
longitudinal resistance
longitudinal reactance
S
k
=
S
r
u
k
%
⋅ 100
I
k
=
S
k
3 ⋅ U
r
=
I
r
u
k
%
⋅ 100
I
r
=
S
r
3 ⋅ U
r
u
k
% S
r U
2
r
Z
T
=
100
u
k
%
⋅
S
r
=
100
⋅
3 ⋅ I
2
r
U
2
r
R
T
=
100
p
k
%
⋅
S
r
=
100
⋅
3 ⋅ I
2
r
p
k
% S
r
X
T
= Z
T
2
– R
T
2
Three-winding transformer
Z
1
Z
2
Z
3
2 3
1
Z
12
=
u
12
100
⋅
U
r
S
r12
2
Z
13
=
u
13
100
⋅
U
r
S
r13
2
Z
23
=
u
23
100
⋅
U
r
S
r23
2
Z
1
=
1
2
(Z
12
+ Z
13
– Z
23
)
Z
2
=
1
2
(Z
12
+ Z
23
– Z
13
)
Z
3
=
1
2
(Z
13
+ Z
23
– Z
12
)
Caption
ρ
20
resistivity at 20 °C
total length of conductor
S cross section of conductor
α
20
temperature coefficient of conductor at 20 °C
θ temperature of conductor
ρθ resistivity against the conductor temperature
ω angular frequency
f frequency
r resistance of conductor per length unit
x reactance of conductor per length unit
u
k
%short-circuit percentage voltage of the transformer
S
r
rated apparent power of the transformer
U
r
rated voltage of the transformer
p
k
%percentage impedance losses of the transformer under short-circuit
conditions
power loss
single-phase three-phase continuous
∆u =
∆U
U
r
⋅ 100
P = U ⋅ I ⋅ cosϕ P = U ⋅ I
Q = U ⋅ I ⋅ sinϕ
S = 3 ⋅ U ⋅ I = P
2
+ Q
2
S = U ⋅ I = P
2
+ Q
2
P = 3 ⋅ U ⋅ I ⋅ cosϕ
Q = 3 ⋅ U ⋅ I ⋅ sinϕ
cosϕ =
P
S
voltage drop
percentage
voltage drop
active power
reactive power
apparent power
power factor
∆u =
∆U
U
r
⋅ 100 ∆u =
∆U
U
r
⋅ 100
–
–
– cosϕ =
P
S
∆P = 2 ⋅ ⋅ r ⋅ I
2
∆P = 3 ⋅ ⋅ r ⋅ I
2
∆P = 2 ⋅ ⋅ r ⋅ I
2
∆U = 2 ⋅ I ⋅ ⋅ (r ⋅ cosϕ x ⋅ sinϕ) 3 ⋅ I ⋅ ⋅ (r ⋅ cosϕ x ⋅ sinϕ) ∆U = ∆U = 2 ⋅ I ⋅ ⋅ r
Voltage drop and power
Annex E: Main physical quantities and
electrotechnical formulas
236 ABB SACE - Electrical devices
Annex E: Main physical quantities and
electrotechnical formulas
Annex E: main physical quantities
E
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Electrical installation handbook
Volum e 2
1SD C 010001D 0202
ABB SACE
Electrical devices
ABB SACE S.p.A.
An ABB Group Company
L.V. Breakers
Via Baioni, 35
24123 Bergamo - Italy
Tel.: +39 035.395.111 - Telefax: +39 035.395.306-433
http://www.abb.com
D ue to possible developm ents of standards as w ell as of
m aterials, the characteristics and dim ensions specified in
this docum ent m ay only be considered binding after
confirm ation by AB B SAC E. 1
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