EN IEC 61921:2025
(Main)Power capacitors - Low-voltage power factor correction banks
Power capacitors - Low-voltage power factor correction banks
NEW!IEC 61921:2017 is available as IEC 61921:2017 RLV which contains the International Standard and its Redline version, showing all changes of the technical content compared to the previous edition.IEC 61921:2017 is applicable to low-voltage AC shunt capacitor banks intended to be used for power factor correction purposes, possibly equipped with a built-in switchgear and controlgear apparatus capable of connecting to or disconnecting from the mains part(s) of the bank with the aim to correct its power factor. Low-voltage power factor correction banks if not otherwise indicated hereinafter and where applicable comply with the requirements of IEC 61439-1 and IEC 61439-2. This second edition cancels and replaces the first edition published in 2003. It constitutes a technical revision. This edition includes the following significant technical changes with respect to the previous edition: numerous changes regarding verification methods to align with IEC 61439-1; modification of marking; add routine verification of rated output; new Annex D with guidance on methods for temperature rise verification; update of normative references; general editorial review. Keywords: low-voltage AC shunt capacitor banks
Leistungskondensatoren - Kondensatorbatterien zur Korrektur des Niederspannungsleistungsfaktors
Condensateurs de puissance - Batteries de compensation du facteur de puissance basse tension
NEW!IEC 61921:2017 est disponible sous forme de IEC 61921:2017 RLV qui contient la Norme internationale et sa version Redline, illustrant les modifications du contenu technique depuis l'édition précédente.L'IEC 61921:2017 s’applique aux batteries de condensateurs shunt à basse tension en courant alternatif destinées à être utilisées pour la compensation du facteur de puissance, ces batteries comportant éventuellement des appareillages de connexion et de commande intégrés capables de mettre sous tension ou hors tension une ou des fractions de l’ensemble afin de compenser le facteur de puissance du réseau. Sauf indication contraire dans la présente norme et le cas échéant, les batteries de compensation du facteur de puissance basse tension satisfont aux exigences de l'IEC 61439‑1 et de l'IEC 61439-2. Cette deuxième édition annule et remplace la première édition parue en 2003. Cette édition constitue une révision technique. Cette édition inclut les modifications techniques majeures suivantes par rapport à l'édition précédente: nombreuses modifications concernant l'alignement des méthodes de vérification sur l'IEC 61439-1; modification de marquage; ajout d'une vérification individuelle systématique de la puissance assignée; nouvelle Annexe D avec préconisations portant sur les méthodes de vérification de l'échauffement; actualisation des références normatives; révision rédactionnelle générale. Mots clés: condensateurs shunt à basse tension en courant alternatif
Močnostni kondenzatorji - Nizkonapetostne baterije za korekcijo močnostnega faktorja (IEC 61921:2017)
Ta mednarodni standard se uporablja za nizkonapetostne vzporedne kondenzatorske baterije za izmenični tok, namenjene za korekcijo močnostnega faktorja, po možnosti opremljene z vgrajeno stikalno in krmilno napravo, ki jo je mogoče priklopiti na omrežne dele baterije oziroma odklopiti z njih z namenom korekcije močnostnega faktorja.
Če v nadaljevanju dokumenta ni navedeno drugače in kjer je to primerno, nizkonapetostne baterije za korekcijo močnostnega faktorja izpolnjujejo zahteve standardov IEC 61439-1 in IEC 61439-2.
General Information
Relations
Standards Content (Sample)
SLOVENSKI STANDARD
01-oktober-2025
Nadomešča:
SIST EN 61921:2003
Močnostni kondenzatorji - Nizkonapetostne baterije za korekcijo močnostnega
faktorja (IEC 61921:2017)
Power capacitors - Low-voltage power factor correction banks (IEC 61921:2017)
Kondensatorbatterien zur Korrektur des Niederspannungsleistungsfaktors (IEC
61921:2017)
Condensateurs de puissance - Batteries de compensation du facteur de puissance
basse tension (IEC 61921:2017)
Ta slovenski standard je istoveten z: EN IEC 61921:2025
ICS:
31.060.70 Močnostni kondenzatorji Power capacitors
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.
EUROPEAN STANDARD EN IEC 61921
NORME EUROPÉENNE
EUROPÄISCHE NORM August 2025
ICS 31.060.70 Supersedes EN 61921:2003
English Version
Power capacitors - Low-voltage power factor correction banks
(IEC 61921:2017)
Condensateurs de puissance - Batteries de compensation Leistungskondensatoren - Kondensatorbatterien zur
du facteur de puissance basse tension Korrektur des Niederspannungsleistungsfaktors
(IEC 61921:2017) (IEC 61921:2017)
This European Standard was approved by CENELEC on 2024-10-16. CENELEC members are bound to comply with the CEN/CENELEC
Internal Regulations which stipulate the conditions for giving this European Standard the status of a national standard without any alteration.
Up-to-date lists and bibliographical references concerning such national standards may be obtained on application to the CEN-CENELEC
Management Centre or to any CENELEC member.
This European Standard exists in three official versions (English, French, German). A version in any other language made by translation
under the responsibility of a CENELEC member into its own language and notified to the CEN-CENELEC Management Centre has the
same status as the official versions.
CENELEC members are the national electrotechnical committees of Austria, Belgium, Bulgaria, Croatia, Cyprus, the Czech Republic,
Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, the
Netherlands, Norway, Poland, Portugal, Republic of North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland,
Türkiye and the United Kingdom.
European Committee for Electrotechnical Standardization
Comité Européen de Normalisation Electrotechnique
Europäisches Komitee für Elektrotechnische Normung
CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels
© 2025 CENELEC All rights of exploitation in any form and by any means reserved worldwide for CENELEC Members.
Ref. No. EN IEC 61921:2025 E
European foreword
The text of document 33/607/FDIS, future edition 2 of IEC 61921, prepared by TC 33 "Power
capacitors and their applications" was submitted to the IEC-CENELEC parallel vote and approved by
CENELEC as EN IEC 61921:2025.
The following dates are fixed:
• latest date by which the document has to be implemented at national (dop) 2026-08-31
level by publication of an identical national standard or by endorsement
• latest date by which the national standards conflicting with the (dow) 2028-08-31
document have to be withdrawn
This document supersedes EN 61921:2003 and all of its amendments and corrigenda (if any).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. CENELEC shall not be held responsible for identifying any or all such patent rights.
This document has been prepared under a standardization request addressed to CENELEC by the
European Commission. The Standing Committee of the EFTA States subsequently approves these
requests for its Member States.
Any feedback and questions on this document should be directed to the users’ national committee. A
complete listing of these bodies can be found on the CENELEC website.
Endorsement notice
The text of the International Standard IEC 61921:2017 was approved by CENELEC as a European
Standard without any modification.
In the official version, for Bibliography, the following notes have to be added for the standard indicated:
IEC 60060-1:2010 NOTE Approved as EN 60060-1:2010 (not modified)
IEC 60831-2:2014 NOTE Approved as EN 60831-2:2014 (not modified)
IEC 60931-2:1995 NOTE Approved as EN 60931-2:1996 (not modified)
IEC 60931-3:1996 NOTE Approved as EN 60931-3:1996 (not modified)
IEC 61000-2-2:2002 NOTE Approved as EN 61000-2-2:2002 (not modified)
Annex ZA
(normative)
Normative references to international publications
with their corresponding European publications
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any amendments)
applies.
NOTE 1 Where an International Publication has been modified by common modifications, indicated by (mod),
the relevant EN/HD applies.
NOTE 2 Up-to-date information on the latest versions of the European Standards listed in this annex is available
here: www.cencenelec.eu.
Publication Year Title EN/HD Year
IEC 61439-1 2011 Low-voltage switchgear and controlgear - -
assemblies - Part 1: General rules
IEC 61439-2 2011 Low-voltage switchgear and controlgear - -
assemblies - Part 2: Power switchgear and
controlgear assemblies
IEC 60831-1 2014 Shunt power capacitors of the self-healing type for EN 60831-1 2014
a.c. systems having a rated voltage up to and
including 1 000 V - Part 1: General - Performance,
testing and rating - Safety requirements - Guide for
installation and operation
IEC 60931-1 1996 Shunt power capacitors of the non-self-healing EN 60931-1 1996
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
IEC 61642 1997 Industrial a.c. networks affected by harmonics - EN 61642 1997
Application of filters and shunt capacitors
IEC 61921 ®
Edition 2.0 2017-06
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Power capacitors – Low-voltage power factor correction banks
Condensateurs de puissance – Batteries de compensation du facteur de
puissance basse tension
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
INTERNATIONALE
ICS 31.060.70 ISBN 978-2-8322-4423-4
– 2 – IEC 61921:2017 © IEC 2017
CONTENTS
FOREWORD . 4
1 Scope . 6
2 Normative references . 6
3 Terms and definitions . 6
4 Marking of a capacitor bank . 7
5 Service conditions . 8
6 Guide for design, installation, operation and safety . 8
6.1 General . 8
6.2 Design . 8
6.2.1 Choice of rated voltage . 8
6.2.2 Switching and overload protection . 9
6.3 Installation and operation . 10
6.3.1 Electrical environment . 10
6.3.2 Secondary effects of the capacitor bank . 10
6.3.3 Overvoltages . 10
6.3.4 Overload currents . 10
6.4 Safety . 11
6.4.1 Discharging devices. 11
6.4.2 Discharging after disconnection . 11
6.4.3 Fire hazard in case of failure . 12
6.4.4 Human and property damage . 12
6.4.5 Busbar . 12
6.4.6 Connection of systems. 12
7 Design verification . 12
7.1 General . 12
7.2 Strength of material and parts . 12
7.3 Verification of degree of protection of enclosures . 12
7.4 Verification of clearances and creepage distances . 12
7.5 Protection against electric shock and integrity of protective circuits . 13
7.6 Incorporation of switching devices and components . 13
7.7 Internal electrical circuits and connections . 13
7.8 Terminals for external conductors . 13
7.9 Verification of dielectric properties . 13
7.10 Verification of temperature-rise limits . 13
7.11 Verification of short-circuit withstand strength . 13
7.12 Electromagnetic compatibility . 13
7.13 Verification of mechanical operation. 14
8 Routine verification . 14
8.1 General . 14
8.2 Degree of protection of enclosures. 14
8.3 Clearances and creepage distances . 14
8.4 Protection against electric shock and integrity of protective circuits . 14
8.5 Incorporation of built-in components . 14
8.6 Internal electrical circuits and connections . 14
8.7 Terminals for external conductors . 14
IEC 61921:2017 © IEC 2017 – 3 –
8.8 Mechanical operation . 14
8.9 Dielectric properties . 14
8.10 Wiring, operational performance and function, including verification of rated
output . 15
Annex A (normative) Minimum and maximum cross-sections of copper conductors
suitable for connections . 16
Annex B (informative) Formulae for capacitors and installations . 17
B.1 Computation of the output of three-phase capacitors from three single-phase
capacitance measurements . 17
B.2 Resonance frequency . 17
B.3 Voltage rise . 17
B.4 Inrush transient current . 18
B.4.1 Switching in of a single capacitor . 18
B.4.2 Switching of capacitors in parallel with energized capacitor(s) . 18
B.4.3 Discharge resistance in single-phase units or in one-phase or
polyphase units . 18
Annex C (informative) Definition of similar designs for capacitor bank . 19
Annex D (informative) Methods for connecting additional capacitors for performing
temperature rise test . 20
Bibliography . 21
Figure D.1 – Configurations for temperature rise test . 20
– 4 – IEC 61921:2017 © IEC 2017
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
POWER CAPACITORS –
LOW-VOLTAGE POWER FACTOR CORRECTION BANKS
FOREWORD
1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising
all national electrotechnical committees (IEC National Committees). The object of IEC is to promote
international co-operation on all questions concerning standardization in the electrical and electronic fields. To
this end and in addition to other activities, IEC publishes International Standards, Technical Specifications,
Technical Reports, Publicly Available Specifications (PAS) and Guides (hereafter referred to as “IEC
Publication(s)”). Their preparation is entrusted to technical committees; any IEC National Committee interested
in the subject dealt with may participate in this preparatory work. International, governmental and non-
governmental organizations liaising with the IEC also participate in this preparation. IEC collaborates closely
with the International Organization for Standardization (ISO) in accordance with conditions determined by
agreement between the two organizations.
2) The formal decisions or agreements of IEC on technical matters express, as nearly as possible, an international
consensus of opinion on the relevant subjects since each technical committee has representation from all
interested IEC National Committees.
3) IEC Publications have the form of recommendations for international use and are accepted by IEC National
Committees in that sense. While all reasonable efforts are made to ensure that the technical content of IEC
Publications is accurate, IEC cannot be held responsible for the way in which they are used or for any
misinterpretation by any end user.
4) In order to promote international uniformity, IEC National Committees undertake to apply IEC Publications
transparently to the maximum extent possible in their national and regional publications. Any divergence
between any IEC Publication and the corresponding national or regional publication shall be clearly indicated in
the latter.
5) IEC itself does not provide any attestation of conformity. Independent certification bodies provide conformity
assessment services and, in some areas, access to IEC marks of conformity. IEC is not responsible for any
services carried out by independent certification bodies.
6) All users should ensure that they have the latest edition of this publication.
7) No liability shall attach to IEC or its directors, employees, servants or agents including individual experts and
members of its technical committees and IEC National Committees for any personal injury, property damage or
other damage of any nature whatsoever, whether direct or indirect, or for costs (including legal fees) and
expenses arising out of the publication, use of, or reliance upon, this IEC Publication or any other IEC
Publications.
8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is
indispensable for the correct application of this publication.
9) Attention is drawn to the possibility that some of the elements of this IEC Publication may be the subject of
patent rights. IEC shall not be held responsible for identifying any or all such patent rights.
International Standard IEC 61921 has been prepared by IEC technical committee 33: Power
capacitors and their applications.
This second edition cancels and replaces the first edition published in 2003. It constitutes a
technical revision.
This edition includes the following significant technical changes with respect to the previous
edition:
• numerous changes regarding verification methods to align with IEC 61439-1;
• modification of marking;
• add routine verification of rated output;
• new Annex D with guidance on methods for temperature rise verification;
• update of normative references;
• general editorial review.
IEC 61921:2017 © IEC 2017 – 5 –
The text of this International Standard is based on the following documents:
FDIS Report on voting
33/607/FDIS 33/611/RVD
Full information on the voting for the approval of this International Standard can be found in
the report on voting indicated in the above table.
This document has been drafted in accordance with the ISO/IEC Directives, Part 2.
The committee has decided that the contents of this document will remain unchanged until the
stability date indicated on the IEC website under "http://webstore.iec.ch" in the data related to
the specific document. At this date, the document will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
– 6 – IEC 61921:2017 © IEC 2017
POWER CAPACITORS –
LOW-VOLTAGE POWER FACTOR CORRECTION BANKS
1 Scope
This International Standard is applicable to low-voltage AC shunt capacitor banks intended to
be used for power factor correction purposes, possibly equipped with a built-in switchgear and
controlgear apparatus capable of connecting to or disconnecting from the mains part(s) of the
bank with the aim to correct its power factor.
Low-voltage power factor correction banks if not otherwise indicated hereinafter and where
applicable comply with the requirements of IEC 61439-1 and IEC 61439-2.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their
content constitutes requirements of this document. For dated references, only the edition
cited applies. For undated references, the latest edition of the referenced document (including
any amendments) applies.
IEC 61439-1:2011, Low-voltage switchgear and controlgear assemblies – Part 1: General
rules
IEC 61439-2:2011, Low-voltage switchgear and controlgear assemblies – Part 2: Power
switchgear and controlgear assemblies
IEC 60831-1:2014, Shunt power capacitors of the self-healing type for AC systems having a
rated voltage up to and including 1 000 V – Part 1: General – Performance, testing and rating
– Safety requirements – Guide for installation and operation
IEC 60931-1:1996, Shunt power capacitors of the non-self-healing type for AC 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
IEC 61642:1997, Industrial AC networks affected by harmonics – Application of filters and
shunt capacitors
3 Terms and definitions
For the purposes of this document, the terms and definitions given in IEC 61439-1,
IEC 61439-2, IEC 60831-1 and IEC 60931-1 and the following apply.
ISO and IEC maintain terminological databases for use in standardization at the following
addresses:
• IEC Electropedia: available at http://www.electropedia.org/
• ISO Online browsing platform: available at http://www.iso.org/obp
3.1
Low-voltage AC capacitor bank or power factor correction bank
Combination of one or more low-voltage capacitor units together with associated switching
devices and control, measuring, signalling, protective, regulating equipment, etc., completely
IEC 61921:2017 © IEC 2017 – 7 –
assembled under the responsibility of the assembly manufacturer with all the internal
electrical and mechanical interconnections and structural parts
Note 1 to entry: The capacitor bank can be fixed, manually switched or automatically controlled through the use of
a power factor controller.
Note 2 to entry: The components of switchgear and controlgear of the automatic bank may be electromechanical
or electronic.
3.2
step of capacitor bank
combination of one or more capacitor units switched together through a single switch with
possible detuned reactors, connecting wires, and associated switchgear and controlgear
apparatus
3.3
automatic reactive power controller
device designed to calculate the reactive power absorbed by the load connected to the power
line and to control the switching on and off of the steps of the automatic bank, in order to
compensate for the reactive power
Note 1 to entry: The reactive power is normally calculated at the fundamental frequency.
Note 2 to entry: The controller may be “built-in” or “free-standing”.
Note 3 to entry: The controller generally performs functions of measurement / monitoring of power, controlling (of
capacitor steps) and protection (of capacitor bank).
3.4
transient inrush current I
t
transient overcurrent of high amplitude and frequency that may occur when a capacitor is
switched on, the amplitude and frequency being determined by factors such as the short-
circuit impedance of the supply, the amount of energized capacitance switched in parallel and
the instant of the switching
3.5
rated reactive power Q (of a capacitor bank)
N
total reactive power of a capacitor bank at the rated frequency and voltage, calculated by the
total impedance of the bank including reactors, if any
3.6
maximum permissible current
value of current declared by the manufacturer which can be present continuously in the
capacitor bank, used for installation and protection settings
4 Marking of a capacitor bank
The following minimum information shall be given by the manufacturer on a rating plate to be
fixed on the capacitor bank.
1) Manufacturer’s name or trademark.
2) Identification number or type designation.
3) Date of manufacture, in clear or code form.
4) Rated reactive power, Q in kilovars (kvar).
N
5) Rated voltage, U in volts (V).
N
in hertz (Hz).
6) Rated frequency, f
N
7) Reference to the IEC 61921 standard and its year of publication.
– 8 – IEC 61921:2017 © IEC 2017
The following information must also be given by the manufacturer, on the rating plate or on
instruction sheet.
8) Rating of steps, in kvar.
9) Value of series reactor if any (or reactance ratio in % or tuning frequency).
10) Minimum and maximum ambient temperatures in degrees Celsius (°C).
11) Degree of protection of enclosure.
12) Location type: indoor or outdoor.
13) Rated short time withstand current (I ).
cw
14) Rated conditional short-circuit current (I ), if applicable.
cc
15) Maximum permissible current.
16) Rated insulation voltage(U ).
i
17) Rated impulse withstand voltage (U ).
imp
5 Service conditions
See relevant clauses of IEC 61439-1 and IEC 61439-2.
6 Guide for de
...
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