IEC 61558-2-20:2022

Safety of transformers, reactors, power supply units and combinations thereof - Part 2-20: Particular requirements and tests for small reactors

IEC 61558-2-20:2022 deals with the safety of small reactors for general applications. Small reactors incorporating electronic circuits are also covered by this document. This third edition cancels and replaces the second edition published in 2010. This edition constitutes a technical revision. This edition includes the following significant technical changes with respect to the previous edition:
- adjustment of structure and references in accordance with IEC 61558-1:2017.
- additional Annex AA with references for characteristic parameter measurements.
- additional Annex BB for associated reactors with frequencies above 500 Hz.
- additional Annex CC for partial discharge.
It has the status of a group safety publication in accordance with IEC Guide 104.

Sécurité des transformateurs, bobines d'inductance, blocs d'alimentation et des combinaisons de ces éléments - Partie 2-20 : Règles particulières et essais pour les petites bobines d'inductance

L'IEC 61558-2-20:2022 traite de la sécurité des petites bobines d'inductance pour applications d'ordre général. Les petites bobines d'inductance qui incorporent des circuits électroniques sont également couvertes par le présent document. Cette troisième édition annule et remplace la deuxième édition parue en 2010. Cette édition constitue une révision technique. Cette édition inclut les modifications techniques majeures suivantes par rapport à l'édition précédente:
- la structure et les références ont été alignées sur l'IEC 61558-1:2017;
- l'Annexe AA a été ajoutée et contient des références pour les mesurages des paramètres caractéristiques;
- l'Annexe BB a été ajoutée pour les bobines d'inductance associées dont les fréquences sont supérieures à 500 Hz;
- l'Annexe CC a été ajoutée pour l'essai de décharge partielle.
Il a le statut de publication groupée de sécurité conformément au l'IEC Guide 104.

General Information

• Status: Published
• Publication Date: 05-Dec-2022
• ICS: 29.180 - Transformers. Reactors
• Technical Committee: TC 96 - Transformers and reactors
• Drafting Committee: MT 1 - TC 96/MT 1
• Current Stage: PPUB - Publication issued
• Start Date: 06-Dec-2022
• Completion Date: 30-Dec-2022

Relations

• Revises: IEC 61558-2-20:2010 - Safety of transformers, reactors, power supply units and combinations thereof - Part 2-20: Particular requirements and tests for small reactors
• Effective Date: 05-Sep-2023

Overview

IEC 61558-2-20:2022 - Safety of transformers, reactors, power supply units and combinations thereof - Part 2-20: Particular requirements and tests for small reactors - is the third edition (2022) of this IEC standard. It updates and replaces the 2010 edition and is a technical revision aligned with IEC 61558-1:2017. The standard is a group safety publication under IEC Guide 104 and covers stationary or portable, single‑phase or polyphase, dry‑type small reactors (encapsulated or non‑encapsulated), including those incorporating electronic circuits.

Key application limits given in the standard:

• Rated supply voltage ≤ 1 000 V AC or 1 500 V ripple‑free DC
• Rated/internal operating frequency ≤ 1 100 MHz
• Rated power ≤ 25 kVAR (single‑phase) or 50 kVAR (poly‑phase)
• Additional provisions for reactors with fundamental frequencies > 500 Hz (Annex BB)

Key topics and requirements

IEC 61558-2-20 defines particular safety and test requirements that supplement IEC 61558-1:2017. Major technical topics include:

• General requirements and classification for small reactors
• Marking and user information (nameplate, symbols)
• Protection against electric shock and earthing provisions
• Electrical performance tests: voltage drop, no‑load output voltage, short‑circuit voltage
• Thermal and heating tests and overload/short‑circuit protection
• Insulation and dielectric tests: insulation resistance, dielectric strength, leakage current
• Partial discharge testing (new Annex CC) for assessing insulation integrity
• Mechanical strength and resistance to ingress (dust, moisture)
• Construction, internal wiring, terminals, screws and connections
• Creepage, clearance, resistance to heat/fire/tracking
• Annex AA: characteristic parameter measurement references
• Annex BB: specific requirements for associated reactors operating above 500 Hz

Practical applications and who uses this standard

This standard is used by:

• Design engineers and manufacturers of small dry‑type reactors and inductive components to ensure safe design and compliance.
• Test laboratories and certification bodies performing type and routine safety testing.
• Safety and compliance managers, procurement teams, and OEMs integrating reactors into equipment or power supplies.
• Regulatory authorities and installers who reference safety requirements for installations and equipment approvals.

Adopting IEC 61558-2-20 helps reduce electrical and fire risks, ensures consistent testing practices (including partial discharge and high‑frequency considerations), and aligns product documentation and markings with international safety norms.

Related standards

• IEC 61558-1:2017 (general requirements for transformers, reactors, PSUs) - this part supplements/modifies it.
• Other referenced IEC documents for high‑voltage, ballast, or EMI components (see normative references in the standard).

Keywords: IEC 61558-2-20, small reactors, safety standard, dry‑type reactor, partial discharge, high‑frequency reactors, IEC 61558-1, reactor testing, transformer safety.

Standards Content (Sample)

IEC 61558-2-20 ®
Edition 3.0 2022-12
REDLINE VERSION
INTERNATIONAL
STANDARD
colour
inside
GROUP SAFETY PUBLICATION
Safety of transformers, reactors, power supply units and combinations thereof –
Part 2-20: Particular requirements and tests for small reactors
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized in any form
or by any means, electronic or mechanical, including photocopying and microfilm, without permission in writing from
either IEC or IEC's member National Committee in the country of the requester. If you have any questions about IEC
copyright or have an enquiry about obtaining additional rights to this publication, please contact the address below or
your local IEC member National Committee for further information.

IEC Secretariat Tel.: [phone]
3, rue de Varembé [e-mail]
CH-1211 Geneva 20 www.iec.ch
Switzerland
About the IEC
The International Electrotechnical Commission (IEC) is the leading global organization that prepares and publishes
International Standards for all electrical, electronic and related technologies.

About IEC publications
The technical content of IEC publications is kept under constant review by the IEC. Please make sure that you have the
latest edition, a corrigendum or an amendment might have been published.

IEC publications search - webstore.iec.ch/advsearchform IEC Products & Services Portal - products.iec.ch
The advanced search enables to find IEC publications by a Discover our powerful search engine and read freely all the
variety of criteria (reference number, text, technical publications previews. With a subscription you will always
committee, …). It also gives information on projects, replaced have access to up to date content tailored to your needs.
and withdrawn publications.
Electropedia - www.electropedia.org
IEC Just Published - webstore.iec.ch/justpublished
The world's leading online dictionary on electrotechnology,
Stay up to date on all new IEC publications. Just Published
containing more than 22 300 terminological entries in English
details all new publications released. Available online and
and French, with equivalent terms in 19 additional languages.
once a month by email.
Also known as the International Electrotechnical Vocabulary

(IEV) online.
IEC Customer Service Centre - webstore.iec.ch/csc

If you wish to give us your feedback on this publication or
need further assistance, please contact the Customer Service
Centre: [e-mail].
IEC 61558-2-20 ®
Edition 3.0 2022-12
REDLINE VERSION
INTERNATIONAL
STANDARD
colour
inside
GROUP SAFETY PUBLICATION
Safety of transformers, reactors, power supply units and combinations thereof –
Part 2-20: Particular requirements and tests for small reactors
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 29.180 ISBN 978-2-8322-6233-7

– 2 – IEC 61558-2-20:2022 RLV © IEC 2022
CONTENTS
FOREWORD . 3
INTRODUCTION . 2
1 Scope . 7
2 Normative references . 8
3 Terms and definitions . 8
4 General requirements . 11
5 General notes on tests . 11
6 Ratings . 11
7 Classification . 11
8 Marking and other information . 12
9 Protection against electric shock . 15
10 Change of voltage setting . 15
11 Voltage drop . 15
12 No-load output voltage . 15
13 Short-circuit voltage . 16
14 Heating . 16
15 Short-circuit and overload protection . 16
16 Mechanical strength . 18
17 Protection against harmful ingress of dust, solid objects and moisture . 18
18 Insulation resistance, dielectric strength and leakage current . 18
19 Construction . 18
20 Components . 19
21 Internal wiring . 19
22 Supply connection and other external flexible cable or cords . 19
23 Terminals for external conductors . 19
24 Provisions for protective earthing. 19
25 Screws and connections . 19
26 Creepage distances, clearances and distances through insulation . 20
27 Resistance to heat, fire and tracking . 20
28 Resistance to rusting . 20
Annexes . 21
Annex AA (informative) Characteristic parameter measurements . 21
Annex BB (normative) Particular requirements for associated reactors with
frequencies > 500 Hz . 21
Annex CC (normative) Partial discharge (PD) test . 23
Bibliography . 24

Table 101 – Symbols indicating the kind of transformer . 14

INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
SAFETY OF TRANSFORMERS, REACTORS,
POWER SUPPLY UNITS AND COMBINATIONS THEREOF –

Part 2-20: Particular requirements and tests for small reactors

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.
This redline version of the official IEC Standard allows the user to identify the changes made to
the previous edition IEC 61558-2-20:2010. A vertical bar appears in the margin wherever a change
has been made. Additions are in green text, deletions are in strikethrough red text.

– 4 – IEC 61558-2-20:2022 RLV © IEC 2022
IEC 61558-2-20 has been prepared by IEC technical committee 96: Transformers, reactors,
power supply units and combinations thereof. It is an International Standard.
This third edition cancels and replaces the second edition published in 2010. This edition
constitutes a technical revision.
This edition includes the following significant technical changes with respect to the previous
edition:
a) Adjustment of structure and references in accordance with IEC 61558-1:2017.
b) Additional Annex AA with references for characteristic parameter measurements.
c) Additional Annex BB for associated reactors with frequencies above 500 Hz.
d) Additional Annex CC for partial discharge.
The text of this International Standard is based on the following documents:
Draft Report on voting
96/556/FDIS 96/564/RVD
Full information on the voting for its approval can be found in the report on voting indicated in
the above table.
The language used for the development of this International Standard is English.
This document was drafted in accordance with ISO/IEC Directives, Part 2, and developed in
accordance with ISO/IEC Directives, Part 1 and ISO/IEC Directives, IEC Supplement, available
at www.iec.ch/members_experts/refdocs. The main document types developed by IEC are
described in greater detail at www.iec.ch/publications.
It has the status of a group safety publication in accordance with IEC Guide 104.
This International Standard is to be used in conjunction with IEC 61558-1:2017.
This document supplements or modifies the corresponding clauses in IEC 61558-1:2017, so as
to convert that publication into the IEC standard: Particular requirements and tests for small
reactors.
A list of all parts in the IEC 61558 series published under the general title Safety of transformers,
reactors, power supply units and combinations thereof, can be found on the IEC website.
Future standards in this series will carry the new general title as cited above. Titles of existing
standards in this series will be updated at the time of the next edition.
Where this document states "addition", "modification" or "replacement", the relevant text of
IEC 61558-1:2017 is to be adopted accordingly.
In this document, the following print types are used:
– requirements proper: in roman type;
– test specifications: in italic type;
– explanatory matter: in smaller roman type.
In the text of this document, the words in bold are defined in Clause 3.

Subclauses, notes, figures and tables additional to those in IEC 61558-1:2017 are numbered
starting from 101; supplementary annexes are entitled AA, BB, etc.
The committee has decided that the contents of this document will remain unchanged until the
stability date indicated on the IEC website under 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.
IMPORTANT – The "colour inside" logo on the cover page of this document indicates that it
contains colours which are considered to be useful for the correct understanding of its
contents. Users should therefore print this document using a colour printer.

– 6 – IEC 61558-2-20:2022 RLV © IEC 2022
INTRODUCTION
IEC TC 96 has a group safety function in accordance with IEC Guide 104 for transformers other
than those intended to supply distribution networks, in particular transformers and power supply
units intended to allow the application of protective measures against electric shock as defined
by TC 64, but in certain cases including the limitation of voltage and horizontal safety function
for SELV, in accordance with IEC 60364-4-41.
The group safety function (GSF) is used because of responsibility for safety extra-low voltage
(SELV) in accordance with IEC 61140:2016, 5.2.6 and IEC 60364-4-41:2005, 414.3.1 or control
circuits in accordance with IEC 60204-1:2016, 7.2.4.
The group safety function is used for each part of IEC 61558-2 because different standards of
the IEC 61558 series can be combined in one construction but in certain cases with no limitation
of rated output power.
For example an auto-transformer in accordance with IEC 61558-2-13 can be designed with a
separate SELV-circuit in accordance with the particular requirements for IEC 61558-2-6 relating
to the general requirements of IEC 61558-1.

SAFETY OF TRANSFORMERS, REACTORS,
POWER SUPPLY UNITS AND COMBINATIONS THEREOF –

Part 2-20: Particular requirements and tests for small reactors

1 Scope
Replacement
This part of IEC 61558 deals with the safety of small reactors for general applications. Small
reactors incorporating electronic circuits are also covered by this document.
NOTE 1 Safety includes electrical, thermal and mechanical aspects.
Unless otherwise specified, from here onward, the term transformer or reactor covers small
reactors.
This document is applicable to stationary or portable, single-phase or polyphase, air-cooled
(natural or forced) general purpose reactors including alternating current, premagnetised and
current compensated independent or associated dry-type reactors. The windings can be
encapsulated or non-encapsulated.
The rated supply voltage does not exceed 1 000 V AC or 1 500 V ripple-free DC, the rated
supply frequency and the internal operational operating frequencies do not exceed 1
100 MHz.
This document can be used for reactors with a fundamental frequency above 500 Hz (see
Annex BB).
The rated power does not exceed:
– 25 kVAR AC (25 kW DC) for single-phase reactors,
– 50 kVAR AC (50 kW DC) for poly-phase reactors.
This document is applicable to reactors without limitation of the rated power subject to an
agreement between the purchaser and the manufacturer.
This part is applicable to dry-type reactors. The windings may be encapsulated or non-
encapsulated.
This document does not apply to:
– reactors covered by IEC 60289 IEC 60076-6 for rated voltages above 1 000 V;
– ballast for tubular fluorescent covered by IEC 61347-2-8;
– ballast for discharge lamps (excluding tubular fluorescent lamps) covered by IEC 61347‑2‑9.
– fixed inductors for electromagnetic interference suppression covered by IEC 60938 series
NOTE 2 For reactors filled with liquid dielectric or pulverised material such as sand, additional requirements are
under consideration.
NOTE 3 Normally, reactors are intended to be associated with equipment for functional requirements of the
equipment or requirements by the installation rules or by other appliance specifications. The protection against
electric shock may be provided or completed by other parts or features of the equipment, such as the body.
NOTE 4 Reactors for particular applications will in the future be covered by complementary normative annexes.

– 8 – IEC 61558-2-20:2022 RLV © IEC 2022
NOTE 3 Attention is drawn to the following if necessary:
– for reactors intended to be used in vehicles, on board ships, and aircraft, additional
requirements (from other applicable standards, national rules, etc.) may be necessary;
– measures to protect the enclosure and the components inside the enclosure against
external influences such as fungus, vermin, termites, solar-radiation, and icing should also
be considered;
– the different conditions for transportation, storage, and operation of the reactors should
also be considered;
– additional requirements in accordance with other appropriate standards and national rules
may be applicable to reactors intended for use in special environments, such as tropical
environment.
NOTE 4 Normally, reactors are intended to be associated with equipment for functional requirements of the
equipment or requirements by the installation rules or by other appliance specifications.
NOTE 5 Reactors incorporating electronic circuits and components are also covered by this standard.
NOTE 6 The protection against electric shock may be provided (or completed) by other parts or features of the
equipment, such as the body.
NOTE 7 Reactors for particular applications will in the future be covered by complementary normative annexes.
NOTE 8 Future technological development of reactors may necessitate a need to increase the
upper limit of the frequencies. Until then, this document may be used as a guidance document.
This group safety publication focusing on safety guidance is primarily intended to be used as a
product safety standard for the products mentioned in the scope, but is also intended to be used
by technical committees in the preparation of publications for products similar to those
mentioned in the scope of this group safety publication, in accordance with the principles laid
down in IEC Guide 104 and lSO/lEC Guide 51.
One of the responsibilities of a technical committee is, wherever applicable, to make use of
basic safety publications and/or group safety publications in the preparation of its publications.
2 Normative references
This clause of IEC 61558-1:2017 is applicable, except as follows:
Addition
IEC 60076-6:2007, Power transformers – Part 6: Reactors
IEC 61558-1:20052017, Safety of power transformers, power supplies, reactors and similar
products transformers, reactors, power supply units and combinations thereof – Part 1: General
requirements and tests
IEC 61558-2-16:2021, Safety of transformers, reactors, power supply units and combinations
thereof – Part 16: Particular requirements and tests for switch mode power supply units and
transformers for switch mode power supply units for general applications
3 Terms and definitions
This clause of Part 1 is applicable, except as follows:
For the purposes of this document, the terms and definitions given in IEC 61558-1:2017 apply.

ISO and IEC maintain terminology databases for use in standardization at the following
addresses:
• IEC Electropedia: available at https://www.electropedia.org/
• ISO Online browsing platform: available at https://www.iso.org/obp
Modification
Where IEC 61558-1:2017 is applicable, the word "transformer", if used, shall be replaced by
"reactor".
3.1 Transformers
This subclause of IEC 61558-1:2017 is applicable, except as follows:
Addition
3.1.101
reactor
arrangement comprising one or more windings with an impedance depending on the frequency,
working in accordance with the principle of self-induction whereby a magnetising current
generates a magnetic field through a magnetically effective core or through air
NOTE Reactors with toroidal core are also included in this definition.
3.1.102101
alternating current reactor
reactor in which the magnetising current generates an alternating magnetic field, changing its
polarity depending on the frequency
3.1.103102
premagnetised reactor
reactor in which the magnetising direct current generates a magnetic field of only one polarity,
while a superimposed alternating current alters the direct magnetic field depending on its
strength and the frequency
3.1.104103
current compensated reactor
reactor with at least two windings on a common core, where the magnetising currents are in
opposite directions in order to reduce the magnetic flux
Replacement
3.1.1059
overload proof reactor
reactor in which the temperature does not exceed the specified limits when the reactor is
overloaded and continues to meet all requirements of this document after the removal of the
overload
3.1.1059.1
non-inherently overload proof reactor
overload proof reactor equipped with a protective device which opens the circuit, or reduces
the current in the circuit when the reactor is overloaded, and which continues to meet all
requirements of this document after the removal of the overload and resetting or replacing of
the protective device
Note 1 to entry: Examples of protective devices are fuses, overload releases, thermal fuses, thermal links,
thermal cut-outs, PTC resistors, and automatic circuit-breakers.

– 10 – IEC 61558-2-20:2022 RLV © IEC 2022
Note 2 to entry: In case of protection by a device which cannot be replaced nor re-set, the wording "continues to
meet all requirements of this document after removal of the overload" does not imply that the reactor continues to
operate.
3.1.1059.2
inherently overload proof reactor
overload proof reactor not equipped with a device to protect the reactor and in which the
temperature in the case of overload, by construction, does not exceed the specified limits and
which continues to operate and meet all the requirements of this document after the removal of
the overload
3.1.10610
non-overload proof reactor
reactor which is intended to be protected against excessive temperature by means of a
protective device not provided with the reactor and which continues to meet all the
requirements of this document after the removal of the overload and resetting or replacing of
the protective device
3.1.10711
fail-safe reactor
reactor which, after abnormal use, permanently fails to function by an interruption of the failing
circuit but presents no danger to the user or surroundings
3.4 Circuits and windings
This subclause of Part 1 is not applicable.
3.5 Ratings
This subclause of IEC 61558-1:2017 is applicable, except as follows:
Replacement
3.5.4
rated current
rated current, assigned to the reactor by the manufacturer including harmonics, if any, which
influence the heating of the reactor
Addition
3.5.101
rated power
sum of the products of the rated voltage drop and the rated current at the rated frequency
for the different windings
3.5.102
rated inductance
inductance of the reactor designed by the manufacturer for the specified operating condition
of the reactor
Note 1 to entry: The specific operating conditions of DC reactors are determined by the DC component and the
superimposed AC component.
3.5.103
rated resistance
DC resistance of a winding of a reactor designed by the manufacturer for the specified
operating conditions of the reactor

3.5.104
rated voltage drop
voltage across a winding of the reactor at the rated current and the rated frequency assigned
by the manufacturer
3.6 No-load values
This subclause of IEC 61558-1:2017 is not applicable.
3.7 Insulation
This subclause of Part 1 is applicable.
4 General requirements
This clause of IEC 61558-1:2017 is applicable.
5 General notes on tests
This clause of IEC 61558-1:2017 is applicable.
6 Ratings
This clause of IEC 61558-1:2017 is applicable, except as follows:
Replacement:
Addition
6.101 The rated supply voltage shall not exceed 1 000 V AC or 1 500 V ripple-free DC.
6.102 The rated power shall not exceed 25 kVAR AC (25 kW DC) for single-phase reactors
and 50 kVAR AC (50 kW DC) for poly-phase reactors, except for reactors subject to an
agreement between the purchaser and the manufacturer.
6.103 The rated supply frequency and the internal operational operating frequencies does
shall not exceed 100 MHz.
6.104 The values of rated inductance and rated resistance shall be given at the rated
ambient temperature, under no load conditions, and the tolerance shall be declared by the
manufacturer.
Compliance with the requirements of 6.1 to 6.4 6.101 to 6.104 is checked by inspection of the
marking.
NOTE 1 Measurements for characteristic parameters are described in Annex AA.
NOTE 2 See Annex BB for reactors with a fundamental frequency above 500 Hz.
7 Classification
This clause of IEC 61558-1:2017 is applicable, except as follows:
7.1
– 12 – IEC 61558-2-20:2022 RLV © IEC 2022
Replacement
Reactors are classified according to their protection against electric shock:
– class I reactors;
– class II reactors;
– class III reactors.
NOTE Incorporated reactors are not classified; their degree of protection against electric shock is determined by
the way in which the reactors are incorporated.
7.2
Replacement
Reactors are classified according to the protection against abnormal use:
– inherently overload proof reactors;
– non-inherently overload proof reactors;
– non-overload proof reactors;
– fail-safe reactors.
8 Marking and other information
This clause of IEC 61558-1:2017 is applicable, except as follows:
8.1
Replacement
Reactors shall be marked with the following parameters:
a) rated supply voltage in volts (V);
b) rated supply frequency (ies) in hertz (Hz);
c) rated voltage drop in volts (V) only for AC reactors;
d) rated power in volt-amperes reactive VAR or kilovolt-amperes reactive kVAR for AC, in
watts (W) or kilowatts (kW) for DC;
e) rated current and harmonics, if any, in amperes (A) or milliamperes (mA);
f) symbol or abbreviation DC for nature of direct current, if applicable;
g) symbol or abbreviation AC for nature of alternating current, if applicable;
h) rated inductance of the winding(s) in henries (H) or millihenries (mH) for reactors
followed by the appropriate tolerance;
NOTE 1 Only one of the values c), d) or h) needs to be marked, as the others can be calculated
from the given values.
i) the reactor shall be marked with one of the graphical symbols shown in 8.11;
j) rated resistance of the winding(s) in ohms (Ω) or milliohms (mΩ) followed by the
appropriate tolerance;
NOTE 2 The marking j) may can be given in the literature instead of being marked.
NOTE A description for characteristic parameter measurements is described in Annex AA.
k) model or type references;
l) name or trademark of the manufacturer or responsible supplier vendor;
m) indication of the protection index IP, if other than IP00;
n) rated maximum ambient temperature t , if other than 25 °C;
a
NOTE 3 It is recommended that the values of t are given in steps of 5 °C for t ≤ 50 °C and in
a a
steps of 10 °C for t > 50 °C.
a
o) rated minimum ambient temperature t , if lower than +10 °C and if a temperature
amin
sensitive device is used;
NOTE 4 It is recommended that the values of t are given in steps of 5 °C.
amin
p) duty cycle, if any, unless the operating time is limited by the construction of the reactor
or corresponds to the operating conditions. The marking of short-time duty cycle or
intermittent duty cycle shall correspond to normal use. The operating time for reactors
with short-time duty shall be expressed in seconds (s) or minutes (min); the operating
time and the resting time of reactors with intermittent duty cycle shall be expressed
in seconds (s) or minutes (min), separated by an oblique stroke;
q) symbol for overvoltage category, if other than OVC II;
r) switching frequency (ies) of the supplying frequency inverter;
s) reactors to be used with forced air cooling where the fan is not a part of the reactor
shall be marked with “AF” followed by the air speed, expressed in m/s;
t) symbol for class II construction, for class II reactors only;
u) symbol for class III construction, for class III reactors only;
NOTE 5 Additional markings are allowed provide they do not give rise to if there is no
misunderstanding.
All markings except those under i) and j) may be illustrated as QR Code according to
ISO/IEC 18004.
v) symbol indicating the maximum altitude of installation, if higher than 2 000 m.
8.4
Replacement
Reactors with tapped or multiple windings shall be clearly marked in accordance with 8.1.
8.5
Replacement
Reactors which are declared to be overload proof reactors and comply with the requirements
for such reactors shall be marked with the symbol for overload proof reactors.
Non-inherently overload proof reactors with incorporated fuses and non-overload proof
reactors designed to be protected by fuses shall, in addition, be marked with the rated current
(amperes or milliamperes) of the protecting fuse-link, followed or preceded by the symbol for
the time current characteristics of the fuse in accordance with the relevant standard, if
applicable.
Non-inherently overload proof reactors with incorporated replaceable protective devices
other than fuses and non-overload proof reactor designed to be protected with protective
devices other than fuses shall, in addition, be marked with the manufacturer’s model or type
reference of the device, and/or ratings of the device.

– 14 – IEC 61558-2-20:2022 RLV © IEC 2022
NOTE Overload proof reactors with non-replaceable devices need no additional marking
regarding the protective device.
The marking shall be sufficient to ensure correct replacement of the protective device.
When replaceable protective devices other than fuses are used, appropriate information about
their replacement shall be provided in an instruction sheet or the equivalent accompanying the
reactor.
Reactors declared to be fail-safe reactors and comply with the requirements for such reactors
shall be marked with the symbol for fail-safe reactors.
8.11
Addition
Table 101 – Symbols indicating the kind of transformer
Symbol or graphical Explanation or title Identification
symbol
a
H Henry –
a
Ohm –
Ω
Fail-safe reactor IEC 60417-5950 (2002-10)
or
Non-overload proof reactor IEC 60417-5951 (2002-10)
or
Overload proof reactor (inherently or non- IEC 60417-5952 (2002-10)
inherently)
or
a
Multiples or submultiples are allowed.

Symbol or graphical symbol Explanation or title Identification
Fail-safe reactor IEC 60417-5950:2002-10

Non-overload proof reactor IEC 60417-5951:2002-10

Overload proof reactor
IEC 60417-5952:2002-10
(inherently or non-inherently)

9 Protection against electric shock
This clause of IEC 61558-1:2017 is applicable.
10 Change of input voltage setting
Replacement of the entire clause by the following:
10 Change of voltage setting
Reactors with more than one rated supply voltage or more than one rated voltage drop shall
be so constructed that the voltage setting cannot be changed without the aid of a tool.
Reactors which can be set to different rated supply voltages and rated voltage drops shall
be so constructed that the indication of the voltage to which the reactor is set for is discernible
on the reactor when it is ready for use.
Compliance is checked by inspection.
NOTE As an example, the requirement concerning the voltage setting is met if a tool is needed to remove a cover
before the voltage setting can be changed.
11 Output voltage and output current under load
Replacement of the entire clause by the following:
11 Voltage drop
11.1 The voltage drop shall not differ by more than 25 % of the rated value.
For premagnetised reactors and reactors with additional components such as capacitors,
rectifiers, etc., the voltage drop shall not differ by more than 30 % of the rated value.
Compliance is checked by measuring or calculating the voltage drop when steady-state
conditions are established, the reactor being at the rated supply frequency and the rated
supply current.
This requirement is valid for each rated voltage drop for reactors with multiple rated voltage
drops.
For reactors with several windings, each winding group is loaded simultaneously if not stated
otherwise.
NOTE The deviation is checked if the rated voltage drop is marked according to 8.1.
11.2 Void.
12 No-load output voltage
This clause of IEC 61558-1:2017 is not applicable.

– 16 – IEC 61558-2-20:2022 RLV © IEC 2022
13 Short-circuit voltage
This clause of IEC 61558-1:2017 is not applicable.
14 Heating
This clause of IEC 61558-1:2017 is applicable, except as follows:
14.1 Modification:
Replace the 10th paragraph starting by "Transformers are supplied." by the following:
The reactor is supplied at rated supply frequency by a current equal to 1,1 times the rated
supply current. After this current increase, no change is made in the supply circuit.
Replace the 16th paragraph starting by "For transformers with more than one input or output
winding." by the following:
For reactors with tapped windings, the results to be considered are those showing the highest
temperatures.
14.1.1 Temperature-rise test
Replacement
th
Replace the 11 paragraph as follows:
The reactor is supplied at rated supply frequency by a current equal to 1,1 times the rated
current. After this current increase, no change is made in the supply circuit.
th
Replace the 18 paragraph as follows:
For reactors with tapped windings, the results to be considered are those showing the highest
temperatures.
Addition
NOTE The temperature-rise test can be performed with the specific voltage- and current waveform of the application
to consider a high content of harmonics which is subject to an agreement between the purchaser and the
manufacturer.
15 Short-circuit and overload protection
This clause of IEC 61558-1:2017 is applicable, except as follows:
15.1 General
Replace the first paragraph starting with "Transformers shall not become." by the following:
15.1.1 Short circuit and overload test method
Replacement
st
Replace the 1 paragraph as follows:

Reactors shall not become unsafe due to overloads which may occur in normal use.
Compliance is checked by inspection and by the following tests carried out immediately after
the test of 14.1 at the same ambient temperature, at the same current, and without changing
the position of the reactor:
– for inherently overload proof reactors, by the test of 15.2;
– for non-inherently overload proof reactors, by the test of 15.3;
– for non-overload proof reactors, by the test of 15.4;
– for fail-safe reactors, by the test of 15.5.
15.2 Inherently short-circuit proof transformers
Replacement
15.2 Inherently overload proof reactors
Inherently overload proof reactors are tested at 1,06 times the rated supply voltage until
steady-state conditions are reached.
15.3 Non-inherently short-circuit proof transformers
Modification:
Replacement
15.3 Non-inherently overload proof reactors are tested as follows:
15.3.1 This subclause of IEC 61558-1:2017 is not applicable.
15.4 Non-short-circuit proof transformers
Replacement
15.4 Non-overload proof reactors
Non-overload proof reactors are tested as indicated in 15.3. The protective device specified
by the manufacturer is connected to the relevant circuit.
Associated non-overload proof reactors are tested under the most unfavourable conditions
of normal use with the correct protective device specified by the manufacturer connected to the
circuit, and in the most unfavourable load conditions for the type of equipment or circuit for
which the reactor is designed for.
NOTE Examples of load conditions are the following: continuous, short-time or intermittent duty.
15.5 Fail-safe transformers
Replacement
15.5 Fail-safe reactors
15.5.1 Three additional new samples are used specifically for the following test:
Each of the three specimens is mounted as in normal use on a 20 mm thick dull black painted
plywood surface. Each reactor is operated at 1,5 times the rated supply current under
1,06 times the rated supply voltage until steady-state conditions are reached or the reactor
fails (whichever occurs first).

– 18 – IEC 61558-2-20:2022 RLV © IEC 2022
If the reactor fails, it shall comply, during and after the tests, with the criteria in 15.5.2.
If the reactor does not fail, the time to reach steady state conditions shall be recorded. Then,
the current is increased in steps of 50 % of the rated supply current each 10 min until the
reactor fails. Each specimen shall be tested within a time duration for this part of the test no
longer than the time necessary to obtain steady-state conditions. This time shall not exceed 5 h.
The reactor shall fail safely and comply, during and after the tests, with the criteria in 15.5.2.
If the reactor does not fail, it is not considered as a fail-safe reactor.
15.5.2 The subclause 15.5.2 of Part 1 is applicable.
16 Mechanical strength
This clause of IEC 61558-1:2017 is applicable.
17 Protection against harmful ingress of dust, solid objects and moisture
This clause of IEC 61558-1:2017 is applicable.
18 Insulation resistance, dielectric strength and leakage current
This clause of IEC 61558-1:2017 is applicable.
19 Construction
This clause of IEC 61558-1:2017 is applicable, except as follows:
19.1 General construction
This subclause of IEC 61558-1:2017 is not applicable.
Addition
19.12.101 Reactors shall withstand higher currents without displacement or deformation of
core, winding and connections.
Compliance is checked by the following test:
The reactor for AC shall be connected directly to a sinusoidal supply voltage at the rated
supply frequency. The reactor for DC shall be connected directly to a half-rectified sinusoidal
voltage at the rated supply frequency. The circuit shall be protected by a fuse rated 15 times
the rated supply current of the reactor. The voltage is adjusted within 2 s until 15 times the
rated supply current occurs, but not exceeding 1,06 of the rated supply voltage. To avoid
thermal overload, the test shall be terminated after 2 s under full load.
NOTE The supply conductors are allowed to can be fixed.
After the test, a visual inspection shall be conducted to ascertain that the electrical connections
have not become loose, the creepage distances and clearances are not reduced to smaller
values than those stated in Clause 26, and no deformation reducing the protection according to
Clause 9 is observed. In case of doubt, measurements are made after dismantling the reactor
if necessary.
20 Components
This clause of IEC 61558-1:2017 is applicable, except as follows:
20.78.3
Replacement
In this standard, A PTC resistor of the indirect heating type is considered to be a non-self-
resetting thermal cut-out.
Compliance is checked by the following test:
The reactor shall operate for 48 h (two days) at 1,1 times of the rated supply voltage and the
rated supply frequency. The output shall be under 1,5 times of the rated current.
The PTC shall operate and stay in high impedance position until the supply is switched off.
If the PTC does not operate, the current is increased by steps in 10 % of the rated current in
15 min max. 5 times of the rated current.
After 48 h, the reactor shall be allowed to cool down to approximately ambient temperature.
This test shall be repeated 5 times at the maximum ambient temperature declared for the
reactor.
At the end of the test, the reactor shall withstand the test of Clause 18, shall show no damage
and shall operate correctly in the sense of this standard.
NOTE Consider high voltages and arcing which can occur after interruptions especially in DC circuits.
21 Internal wiring
This clause of IEC 61558-1:2017 is applicable.
22 Supply connection and other external flexible cable or cords
This clause of IEC 61558-1:2017 is applicable.
23 Terminals for external conductors
This clause of IEC 61558-1:2017 is applicable.
24 Provisions for protective earthing
This clause of IEC 61558-1:2017 is applicable.
25 Screws and connections
This clause of IEC 61558-1:2017 is applicable.

– 20 – IEC 61558-2-20:2022 RLV © IEC 2022
26 Creepage distances, clearances and distances through insulation
This clause of IEC 61558-1:2017 is applicable.
NOTE For values for frequencies above 30 kHz the values in IEC 61558-2-16 is applicable. See Annex BB for a
reactors above 500 Hz.
27 Resistance to heat, fire and tracking
This clause of IEC 61558-1:2017 is applicable, except as follows:
27.23 This subclause of IEC 61558-1:2017 is not applicable.
28 Resistance to rusting
This clause of IEC 61558-1:2017 is applicable.

Annexes
Annexes A to V W of IEC 61558-1:2017 are applicable.
...

IEC 61558-2-20 ®
Edition 3.0 2022-12
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
GROUP SAFETY PUBLICATION
PUBLICATION GROUPÉE DE SÉCURITÉ
Safety of transformers, reactors, power supply units and combinations thereof –
Part 2-20: Particular requirements and tests for small reactors

Sécurité des transformateurs, bobines d'inductance, blocs d'alimentation et
combinaisons de ces éléments –
Partie 2-20: Exigences particulières et essais pour les petites bobines
d'inductance
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized in any form
or by any means, electronic or mechanical, including photocopying and microfilm, without permission in writing from
either IEC or IEC's member National Committee in the country of the requester. If you have any questions about IEC
copyright or have an enquiry about obtaining additional rights to this publication, please contact the address below or
your local IEC member National Committee for further information.

Droits de reproduction réservés. Sauf indication contraire, aucune partie de cette publication ne peut être reproduite
ni utilisée sous quelque forme que ce soit et par aucun procédé, électronique ou mécanique, y compris la photocopie
et les microfilms, sans l'accord écrit de l'IEC ou du Comité national de l'IEC du pays du demandeur. Si vous avez des
questions sur le copyright de l'IEC ou si vous désirez obtenir des droits supplémentaires sur cette publication, utilisez
les coordonnées ci-après ou contactez le Comité national de l'IEC de votre pays de résidence.

IEC Secretariat Tel.: [phone]
3, rue de Varembé [e-mail]
CH-1211 Geneva 20 www.iec.ch
Switzerland
About the IEC
The International Electrotechnical Commission (IEC) is the leading global organization that prepares and publishes
International Standards for all electrical, electronic and related technologies.

About IEC publications
The technical content of IEC publications is kept under constant review by the IEC. Please make sure that you have the
latest edition, a corrigendum or an amendment might have been published.

IEC publications search - webstore.iec.ch/advsearchform IEC Products & Services Portal - products.iec.ch
The advanced search enables to find IEC publications by a Discover our powerful search engine and read freely all the
variety of criteria (reference number, text, technical publications previews. With a subscription you will always
committee, …). It also gives information on projects, replaced have access to up to date content tailored to your needs.
and withdrawn publications.
Electropedia - www.electropedia.org
IEC Just Published - webstore.iec.ch/justpublished
The world's leading online dictionary on electrotechnology,
Stay up to date on all new IEC publications. Just Published
containing more than 22 300 terminological entries in English
details all new publications released. Available online and
and French, with equivalent terms in 19 additional languages.
once a month by email.
Also known as the International Electrotechnical Vocabulary

(IEV) online.
IEC Customer Service Centre - webstore.iec.ch/csc
If you wish to give us your feedback on this publication or
need further assistance, please contact the Customer Service
Centre: [e-mail].
A propos de l'IEC
La Commission Electrotechnique Internationale (IEC) est la première organisation mondiale qui élabore et publie des
Normes internationales pour tout ce qui a trait à l'électricité, à l'électronique et aux technologies apparentées.

A propos des publications IEC
Le contenu technique des publications IEC est constamment revu. Veuillez vous assurer que vous possédez l’édition la
plus récente, un corrigendum ou amendement peut avoir été publié.

Recherche de publications IEC - IEC Products & Services Portal - products.iec.ch
webstore.iec.ch/advsearchform Découvrez notre puissant moteur de recherche et consultez
La recherche avancée permet de trouver des publications IEC gratuitement tous les aperçus des publications. Avec un
en utilisant différents critères (numéro de référence, texte, abonnement, vous aurez toujours accès à un contenu à jour
comité d’études, …). Elle donne aussi des informations sur adapté à vos besoins.
les projets et les publications remplacées ou retirées.

Electropedia - www.electropedia.org
IEC Just Published - webstore.iec.ch/justpublished
Le premier dictionnaire d'électrotechnologie en ligne au
Restez informé sur les nouvelles publications IEC. Just
monde, avec plus de 22 300 articles terminologiques en
Published détaille les nouvelles publications parues.
anglais et en français, ainsi que les termes équivalents dans
Disponible en ligne et une fois par mois par email.
19 langues additionnelles. Egalement appelé Vocabulaire

Electrotechnique International (IEV) en ligne.
Service Clients - webstore.iec.ch/csc

Si vous désirez nous donner des commentaires sur cette
publication ou si vous avez des questions contactez-nous:
[e-mail].
IEC 61558-2-20 ®
Edition 3.0 2022-12
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
GROUP SAFETY PUBLICATION
PUBLICATION GROUPÉE DE SÉCURITÉ

Safety of transformers, reactors, power supply units and combinations thereof –

Part 2-20: Particular requirements and tests for small reactors

Sécurité des transformateurs, bobines d'inductance, blocs d'alimentation et

combinaisons de ces éléments –

Partie 2-20: Exigences particulières et essais pour les petites bobines

d'inductance
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
INTERNATIONALE
ICS 29.180 ISBN 978-2-8322-6118-7

– 2 – IEC 61558-2-20:2022 © IEC 2022
CONTENTS
FOREWORD . 3
INTRODUCTION . 5
1 Scope . 6
2 Normative references . 7
3 Terms and definitions . 7
4 General requirements . 9
5 General notes on tests . 9
6 Ratings . 10
7 Classification . 10
8 Marking and other information . 11
9 Protection against electric shock . 13
10 Change of voltage setting . 13
11 Voltage drop . 14
12 No-load output voltage . 14
13 Short-circuit voltage . 14
14 Heating . 14
15 Short-circuit and overload protection . 15
16 Mechanical strength . 16
17 Protection against harmful ingress of dust, solid objects and moisture . 16
18 Insulation resistance, dielectric strength and leakage current . 16
19 Construction . 16
20 Components . 17
21 Internal wiring . 17
22 Supply connection and other external flexible cable or cords . 17
23 Terminals for external conductors . 18
24 Provisions for protective earthing. 18
25 Screws and connections . 18
26 Creepage distances, clearances and distances through insulation . 18
27 Resistance to heat, fire and tracking . 18
28 Resistance to rusting . 18
Annexes . 19
Annex AA (informative) Characteristic parameter measurements . 19
Annex BB (normative) Particular requirements for associated reactors with
frequencies > 500 Hz . 19
Annex CC (normative) Partial discharge (PD) test . 21
Bibliography . 22

Table 101 – Symbols indicating the kind of transformer . 13

INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
SAFETY OF TRANSFORMERS, REACTORS,
POWER SUPPLY UNITS AND COMBINATIONS THEREOF –

Part 2-20: Particular requirements and tests for small reactors

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.
IEC 61558-2-20 has been prepared by IEC technical committee 96: Transformers, reactors,
power supply units and combinations thereof. It is an International Standard.
This third edition cancels and replaces the second edition published in 2010. This edition
constitutes a technical revision.
This edition includes the following significant technical changes with respect to the previous
edition:
a) Adjustment of structure and references in accordance with IEC 61558-1:2017.
b) Additional Annex AA with references for characteristic parameter measurements.
c) Additional Annex BB for associated reactors with frequencies above 500 Hz.
d) Additional Annex CC for partial discharge.

– 4 – IEC 61558-2-20:2022 © IEC 2022
The text of this International Standard is based on the following documents:
Draft Report on voting
96/556/FDIS 96/564/RVD
Full information on the voting for its approval can be found in the report on voting indicated in
the above table.
The language used for the development of this International Standard is English.
This document was drafted in accordance with ISO/IEC Directives, Part 2, and developed in
accordance with ISO/IEC Directives, Part 1 and ISO/IEC Directives, IEC Supplement, available
at www.iec.ch/members_experts/refdocs. The main document types developed by IEC are
described in greater detail at www.iec.ch/publications.
It has the status of a group safety publication in accordance with IEC Guide 104.
This International Standard is to be used in conjunction with IEC 61558-1:2017.
This document supplements or modifies the corresponding clauses in IEC 61558-1:2017, so as
to convert that publication into the IEC standard: Particular requirements and tests for small
reactors.
A list of all parts in the IEC 61558 series published under the general title Safety of transformers,
reactors, power supply units and combinations thereof, can be found on the IEC website.
Future standards in this series will carry the new general title as cited above. Titles of existing
standards in this series will be updated at the time of the next edition.
Where this document states "addition", "modification" or "replacement", the relevant text of
IEC 61558-1:2017 is to be adopted accordingly.
In this document, the following print types are used:
– requirements proper: in roman type;
– test specifications: in italic type;
– explanatory matter: in smaller roman type.
In the text of this document, the words in bold are defined in Clause 3.
Subclauses, notes, figures and tables additional to those in IEC 61558-1:2017 are numbered
starting from 101; supplementary annexes are entitled AA, BB, etc.
The committee has decided that the contents of this document will remain unchanged until the
stability date indicated on the IEC website under 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.
INTRODUCTION
IEC TC 96 has a group safety function in accordance with IEC Guide 104 for transformers other
than those intended to supply distribution networks, in particular transformers and power supply
units intended to allow the application of protective measures against electric shock as defined
by TC 64, but in certain cases including the limitation of voltage and horizontal safety function
for SELV, in accordance with IEC 60364-4-41.
The group safety function (GSF) is used because of responsibility for safety extra-low voltage
(SELV) in accordance with IEC 61140:2016, 5.2.6 and IEC 60364-4-41:2005, 414.3.1 or control
circuits in accordance with IEC 60204-1:2016, 7.2.4.
The group safety function is used for each part of IEC 61558-2 because different standards of
the IEC 61558 series can be combined in one construction but in certain cases with no limitation
of rated output power.
For example an auto-transformer in accordance with IEC 61558-2-13 can be designed with a
separate SELV-circuit in accordance with the particular requirements for IEC 61558-2-6 relating
to the general requirements of IEC 61558-1.

– 6 – IEC 61558-2-20:2022 © IEC 2022
SAFETY OF TRANSFORMERS, REACTORS,
POWER SUPPLY UNITS AND COMBINATIONS THEREOF –

Part 2-20: Particular requirements and tests for small reactors

1 Scope
Replacement
This part of IEC 61558 deals with the safety of small reactors for general applications. Small
reactors incorporating electronic circuits are also covered by this document.
NOTE 1 Safety includes electrical, thermal and mechanical aspects.
Unless otherwise specified, from here onward, the term transformer or reactor covers small
reactors.
This document is applicable to stationary or portable, single-phase or polyphase, air-cooled
(natural or forced) general purpose reactors including alternating current, premagnetised and
current compensated independent or associated dry-type reactors. The windings can be
encapsulated or non-encapsulated.
The rated supply voltage does not exceed 1 000 V AC or 1 500 V ripple-free DC, the rated
supply frequency and the internal operating frequencies do not exceed 100 MHz.
This document can be used for reactors with a fundamental frequency above 500 Hz (see
Annex BB).
The rated power does not exceed:
– 25 kVAR AC (25 kW DC) for single-phase reactors,
– 50 kVAR AC (50 kW DC) for poly-phase reactors.
This document is applicable to reactors without limitation of the rated power subject to an
agreement between the purchaser and the manufacturer.
This document does not apply to:
– reactors covered by IEC 60076-6 for rated voltages above 1 000 V;
– ballast for tubular fluorescent covered by IEC 61347-2-8;
– ballast for discharge lamps (excluding tubular fluorescent lamps) covered by IEC 61347‑2‑9.
– fixed inductors for electromagnetic interference suppression covered by IEC 60938 series
NOTE 2 For reactors filled with liquid dielectric or pulverised material such as sand, additional requirements are
under consideration.
NOTE 3 Normally, reactors are intended to be associated with equipment for functional requirements of the
equipment or requirements by the installation rules or by other appliance specifications. The protection against
electric shock may be provided or completed by other parts or features of the equipment, such as the body.
NOTE 4 Reactors for particular applications will in the future be covered by complementary normative annexes.
Attention is drawn to the following if necessary:
– for reactors intended to be used in vehicles, on board ships, and aircraft, additional
requirements (from other applicable standards, national rules, etc.);

– measures to protect the enclosure and the components inside the enclosure against
external influences such as fungus, vermin, termites, solar-radiation, and icing;
– the different conditions for transportation, storage, and operation of the reactors;
– additional requirements in accordance with other appropriate standards and national rules
may be applicable to reactors intended for use in special environments.
Future technological development of reactors may necessitate a need to increase the upper
limit of the frequencies. Until then, this document may be used as a guidance document.
This group safety publication focusing on safety guidance is primarily intended to be used as a
product safety standard for the products mentioned in the scope, but is also intended to be used
by technical committees in the preparation of publications for products similar to those
mentioned in the scope of this group safety publication, in accordance with the principles laid
down in IEC Guide 104 and lSO/lEC Guide 51.
One of the responsibilities of a technical committee is, wherever applicable, to make use of
basic safety publications and/or group safety publications in the preparation of its publications.
2 Normative references
This clause of IEC 61558-1:2017 is applicable, except as follows:
Addition
IEC 60076-6:2007, Power transformers – Part 6: Reactors
IEC 61558-1:2017, Safety of transformers, reactors, power supply units and combinations
thereof – Part 1: General requirements and tests
IEC 61558-2-16:2021, Safety of transformers, reactors, power supply units and combinations
thereof – Part 16: Particular requirements and tests for switch mode power supply units and
transformers for switch mode power supply units for general applications
3 Terms and definitions
For the purposes of this document, the terms and definitions given in IEC 61558-1:2017 apply.
ISO and IEC maintain terminology databases for use in standardization at the following
addresses:
• IEC Electropedia: available at https://www.electropedia.org/
• ISO Online browsing platform: available at https://www.iso.org/obp
Modification
Where IEC 61558-1:2017 is applicable, the word "transformer", if used, shall be replaced by
"reactor".
– 8 – IEC 61558-2-20:2022 © IEC 2022
3.1 Transformers
This subclause of IEC 61558-1:2017 is applicable, except as follows:
Addition
3.1.101
alternating current reactor
reactor in which the magnetising current generates an alternating magnetic field, changing its
polarity depending on the frequency
3.1.102
premagnetised reactor
reactor in which the magnetising direct current generates a magnetic field of only one polarity,
while a superimposed alternating current alters the direct magnetic field depending on its
strength and the frequency
3.1.103
current compensated reactor
reactor with at least two windings on a common core, where the magnetising currents are in
opposite directions in order to reduce the magnetic flux
Replacement
3.1.9
overload proof reactor
reactor in which the temperature does not exceed the specified limits when the reactor is
overloaded and continues to meet all requirements of this document after the removal of the
overload
3.1.9.1
non-inherently overload proof reactor
overload proof reactor equipped with a protective device which opens the circuit, or reduces
the current in the circuit when the reactor is overloaded, and which continues to meet all
requirements of this document after the removal of the overload and resetting or replacing of
the protective device
Note 1 to entry: Examples of protective devices are fuses, overload releases, thermal fuses, thermal links,
thermal cut-outs, PTC resistors, and automatic circuit-breakers.
Note 2 to entry: In case of protection by a device which cannot be replaced nor re-set, the wording "continues to
meet all requirements of this document after removal of the overload" does not imply that the reactor continues to
operate.
3.1.9.2
inherently overload proof reactor
overload proof reactor not equipped with a device to protect the reactor and in which the
temperature in the case of overload, by construction, does not exceed the specified limits and
which continues to operate and meet all the requirements of this document after the removal of
the overload
3.1.10
non-overload proof reactor
reactor which is intended to be protected against excessive temperature by means of a
protective device not provided with the reactor and which continues to meet all the
requirements of this document after the removal of the overload and resetting or replacing of
the protective device
3.1.11
fail-safe reactor
reactor which, after abnormal use, permanently fails to function by an interruption of the failing
circuit but presents no danger to the user or surroundings
3.5 Ratings
This subclause of IEC 61558-1:2017 is applicable, except as follows:
Replacement
3.5.4
rated current
rated current, assigned to the reactor by the manufacturer including harmonics, if any, which
influence the heating of the reactor
Addition
3.5.101
rated power
sum of the products of the rated voltage drop and the rated current at the rated frequency
for the different windings
3.5.102
rated inductance
inductance of the reactor designed by the manufacturer for the specified operating condition
of the reactor
Note 1 to entry: The specific operating conditions of DC reactors are determined by the DC component and the
superimposed AC component.
3.5.103
rated resistance
DC resistance of a winding of a reactor designed by the manufacturer for the specified
operating conditions of the reactor
3.5.104
rated voltage drop
voltage across a winding of the reactor at the rated current and the rated frequency assigned
by the manufacturer
3.6 No-load values
This subclause of IEC 61558-1:2017 is not applicable.
4 General requirements
This clause of IEC 61558-1:2017 is applicable.
5 General notes on tests
This clause of IEC 61558-1:2017 is applicable.

– 10 – IEC 61558-2-20:2022 © IEC 2022
6 Ratings
This clause of IEC 61558-1:2017 is applicable, except as follows:
Addition
6.101 The rated supply voltage shall not exceed 1 000 V AC or 1 500 V ripple-free DC.
6.102 The rated power shall not exceed 25 kVAR AC (25 kW DC) for single-phase reactors
and 50 kVAR AC (50 kW DC) for poly-phase reactors.
Reactors without limitation of the rated output shall be subject to agreement between the
purchaser and the manufacturer.
6.103 The rated supply frequency and the internal operating frequencies shall not exceed
100 MHz.
6.104 The values of rated inductance and rated resistance shall be given at the rated
ambient temperature, under no load conditions, and the tolerance shall be declared by the
manufacturer.
Compliance with the requirements of 6.101 to 6.104 is checked by inspection of the marking.
NOTE 1 Measurements for characteristic parameters are described in Annex AA.
NOTE 2 See Annex BB for reactors with a fundamental frequency above 500 Hz.
7 Classification
This clause of IEC 61558-1:2017 is applicable, except as follows:
7.1
Replacement
Reactors are classified according to their protection against electric shock:
– class I reactors;
– class II reactors;
– class III reactors.
NOTE Incorporated reactors are not classified; their degree of protection against electric shock is determined by
the way in which the reactors are incorporated.
7.2
Replacement
Reactors are classified according to the protection against abnormal use:
– inherently overload proof reactors;
– non-inherently overload proof reactors;
– non-overload proof reactors;
– fail-safe reactors.
8 Marking and other information
This clause of IEC 61558-1:2017 is applicable, except as follows:
8.1
Replacement
Reactors shall be marked with the following parameters:
a) rated supply voltage in volts (V);
b) rated supply frequency (ies) in hertz (Hz);
c) rated voltage drop in volts (V) only for AC reactors;
d) rated power in volt-amperes reactive VAR or kilovolt-amperes reactive kVAR for AC, in
watts (W) or kilowatts (kW) for DC;
e) rated current and harmonics, if any, in amperes (A) or milliamperes (mA);
f) symbol or abbreviation DC for nature of direct current, if applicable;
g) symbol or abbreviation AC for nature of alternating current, if applicable;
h) rated inductance of the winding(s) in henries (H) or millihenries (mH) for reactors
followed by the appropriate tolerance;
Only one of the values c), d) or h) needs to be marked.
i) the reactor shall be marked with one of the graphical symbols shown in 8.11;
j) rated resistance of the winding(s) in ohms (Ω) or milliohms (mΩ) followed by the
appropriate tolerance;
The marking j) can be given in the literature instead of being marked.
NOTE A description for characteristic parameter measurements is described in Annex AA.
k) model or type references;
l) name or trademark of the manufacturer or responsible vendor;
m) indication of the protection index IP, if other than IP00;
n) rated maximum ambient temperature t , if other than 25 °C;
a
It is recommended that the values of t are given in steps of 5 °C for t ≤ 50 °C and in steps of
a a
10 °C for t > 50 °C.
a
o) rated minimum ambient temperature t , if lower than +10 °C and if a temperature
amin
sensitive device is used;
It is recommended that the values of t are given in steps of 5 °C.
amin
p) duty cycle, if any, unless the operating time is limited by the construction of the reactor
or corresponds to the operating conditions. The marking of short-time duty cycle or
intermittent duty cycle shall correspond to normal use. The operating time for reactors
with short-time duty shall be expressed in seconds (s) or minutes (min); the operating
time and the resting time of reactors with intermittent duty cycle shall be expressed
in seconds (s) or minutes (min), separated by an oblique stroke;
q) symbol for overvoltage category, if other than OVC II;
r) switching frequency (ies) of the supplying frequency inverter;
s) reactors to be used with forced air cooling where the fan is not a part of the reactor
shall be marked with “AF” followed by the air speed, expressed in m/s;

– 12 – IEC 61558-2-20:2022 © IEC 2022
t) symbol for class II construction, for class II reactors only;
u) symbol for class III construction, for class III reactors only;
Additional markings are allowed if there is no misunderstanding.
All markings except those under i) and j) may be illustrated as QR Code according to
ISO/IEC 18004.
v) symbol indicating the maximum altitude of installation, if higher than 2 000 m.
8.4
Replacement
Reactors with tapped or multiple windings shall be clearly marked in accordance with 8.1.
8.5
Replacement
Reactors which are declared to be overload proof reactors and comply with the requirements
for such reactors shall be marked with the symbol for overload proof reactors.
Non-inherently overload proof reactors with incorporated fuses and non-overload proof
reactors designed to be protected by fuses shall, in addition, be marked with the rated current
(amperes or milliamperes) of the protecting fuse-link, followed or preceded by the symbol for
the time current characteristics of the fuse in accordance with the relevant standard, if
applicable.
Non-inherently overload proof reactors with incorporated replaceable protective devices
other than fuses and non-overload proof reactor designed to be protected with protective
devices other than fuses shall, in addition, be marked with the manufacturer’s model or type
reference of the device, and/or ratings of the device.
Overload proof reactors with non-replaceable devices need no additional marking regarding
the protective device.
The marking shall be sufficient to ensure correct replacement of the protective device.
When replaceable protective devices other than fuses are used, appropriate information about
their replacement shall be provided in an instruction sheet or the equivalent accompanying the
reactor.
Reactors declared to be fail-safe reactors and comply with the requirements for such reactors
shall be marked with the symbol for fail-safe reactors.

8.11
Addition
Table 101 – Symbols indicating the kind of transformer
Symbol or graphical symbol Explanation or title Identification
Fail-safe reactor IEC 60417-5950:2002-10

Non-overload proof reactor IEC 60417-5951:2002-10

Overload proof reactor
IEC 60417-5952:2002-10
(inherently or non-inherently)

9 Protection against electric shock
This clause of IEC 61558-1:2017 is applicable.
10 Change of input voltage setting
Replacement of the entire clause by the following:
10 Change of voltage setting
Reactors with more than one rated supply voltage or more than one rated voltage drop shall
be so constructed that the voltage setting cannot be changed without the aid of a tool.
Reactors which can be set to different rated supply voltages and rated voltage drops shall
be so constructed that the indication of the voltage to which the reactor is set for is discernible
on the reactor when it is ready for use.
Compliance is checked by inspection.
NOTE As an example, the requirement concerning the voltage setting is met if a tool is needed to remove a cover
before the voltage setting can be changed.

– 14 – IEC 61558-2-20:2022 © IEC 2022
11 Output voltage and output current under load
Replacement of the entire clause by the following:
11 Voltage drop
11.1 The voltage drop shall not differ by more than 25 % of the rated value.
For premagnetised reactors and reactors with additional components such as capacitors,
rectifiers, etc., the voltage drop shall not differ by more than 30 % of the rated value.
Compliance is checked by measuring or calculating the voltage drop when steady-state
conditions are established, the reactor being at the rated supply frequency and the rated
current.
This requirement is valid for each rated voltage drop for reactors with multiple rated voltage
drops.
For reactors with several windings, each winding group is loaded simultaneously if not stated
otherwise.
NOTE The deviation is checked if the rated voltage drop is marked according to 8.1.
11.2 Void.
12 No-load output voltage
This clause of IEC 61558-1:2017 is not applicable.
13 Short-circuit voltage
This clause of IEC 61558-1:2017 is not applicable.
14 Heating
This clause of IEC 61558-1:2017 is applicable, except as follows:
14.1.1 Temperature-rise test
Replacement
th
paragraph as follows:
Replace the 11
The reactor is supplied at rated supply frequency by a current equal to 1,1 times the rated
current. After this current increase, no change is made in the supply circuit.
th
Replace the 18 paragraph as follows:
For reactors with tapped windings, the results to be considered are those showing the highest
temperatures.
Addition
NOTE The temperature-rise test can be performed with the specific voltage- and current waveform of the application
to consider a high content of harmonics which is subject to an agreement between the purchaser and the
manufacturer.
15 Short-circuit and overload protection
This clause of IEC 61558-1:2017 is applicable, except as follows:
15.1.1 Short circuit and overload test method
Replacement
st
paragraph as follows:
Replace the 1
Reactors shall not become unsafe due to overloads which may occur in normal use.
Compliance is checked by inspection and by the following tests carried out immediately after
the test of 14.1 at the same ambient temperature, at the same current, and without changing
the position of the reactor:
– for inherently overload proof reactors, by the test of 15.2;
– for non-inherently overload proof reactors, by the test of 15.3;
– for non-overload proof reactors, by the test of 15.4;
– for fail-safe reactors, by the test of 15.5.
15.2 Inherently short-circuit proof transformers
Replacement
15.2 Inherently overload proof reactors
Inherently overload proof reactors are tested at 1,06 times the rated supply voltage until
steady-state conditions are reached.
15.3 Non-inherently short-circuit proof transformers
Replacement
15.3 Non-inherently overload proof reactors
15.3.1 This subclause of IEC 61558-1:2017 is not applicable.
15.4 Non-short-circuit proof transformers
Replacement
15.4 Non-overload proof reactors
Non-overload proof reactors are tested as indicated in 15.3. The protective device specified
by the manufacturer is connected to the relevant circuit.
Associated non-overload proof reactors are tested under the most unfavourable conditions
of normal use with the correct protective device specified by the manufacturer connected to the
circuit, and in the most unfavourable load conditions for the type of equipment or circuit for
which the reactor is designed for.

– 16 – IEC 61558-2-20:2022 © IEC 2022
NOTE Examples of load conditions are the following: continuous, short-time or intermittent duty.
15.5 Fail-safe transformers
Replacement
15.5 Fail-safe reactors
15.5.1 Three additional new samples are used specifically for the following test:
Each of the three specimens is mounted as in normal use on a 20 mm thick dull black painted
plywood surface. Each reactor is operated at 1,5 times the rated current under 1,06 times the
rated supply voltage until steady-state conditions are reached or the reactor fails (whichever
occurs first).
If the reactor fails, it shall comply, during and after the tests, with the criteria in 15.5.2.
If the reactor does not fail, the time to reach steady state conditions shall be recorded. Then,
the current is increased in steps of 50 % of the rated current each 10 min until the reactor
fails. Each specimen shall be tested within a time duration for this part of the test no longer
than the time necessary to obtain steady-state conditions. This time shall not exceed 5 h.
The reactor shall fail safely and comply, during and after the tests, with the criteria in 15.5.2.
If the reactor does not fail, it is not considered as a fail-safe reactor.
16 Mechanical strength
This clause of IEC 61558-1:2017 is applicable.
17 Protection against harmful ingress of dust, solid objects and moisture
This clause of IEC 61558-1:2017 is applicable.
18 Insulation resistance, dielectric strength and leakage current
This clause of IEC 61558-1:2017 is applicable.
19 Construction
This clause of IEC 61558-1:2017 is applicable, except as follows:
19.1 General construction
This subclause of IEC 61558-1:2017 is not applicable.
Addition
19.12.101 Reactors shall withstand higher currents without displacement or deformation of
core, winding and connections.
Compliance is checked by the following test:

The reactor for AC shall be connected directly to a sinusoidal supply voltage at the rated
supply frequency. The reactor for DC shall be connected directly to a half-rectified sinusoidal
voltage at the rated supply frequency. The circuit shall be protected by a fuse rated 15 times
the rated current of the reactor. The voltage is adjusted within 2 s until 15 times the rated
current occurs, but not exceeding 1,06 of the rated supply voltage. To avoid thermal overload,
the test shall be terminated after 2 s under full load.
The supply conductors can be fixed.
After the test, a visual inspection shall be conducted to ascertain that the electrical connections
have not become loose, the creepage distances and clearances are not reduced to smaller
values than those stated in Clause 26, and no deformation reducing the protection according to
Clause 9 is observed. In case of doubt, measurements are made after dismantling the reactor
if necessary.
20 Components
This clause of IEC 61558-1:2017 is applicable, except as follows:
20.8.3
Replacement
A PTC resistor of the indirect heating type is considered to be a non-self-resetting thermal
cut-out.
Compliance is checked by the following test:
The reactor shall operate for 48 h (two days) at 1,1 times of the rated supply voltage and the
rated supply frequency. The output shall be under 1,5 times of the rated current.
The PTC shall operate and stay in high impedance position until the supply is switched off.
If the PTC does not operate, the current is increased by steps in 10 % of the rated current in
15 min max. 5 times of the rated current.
After 48 h, the reactor shall be allowed to cool down to approximately ambient temperature.
This test shall be repeated 5 times at the maximum ambient temperature declared for the
reactor.
At the end of the test, the reactor shall withstand the test of Clause 18, shall show no damage
and shall operate correctly in the sense of this standard.
NOTE Consider high voltages and arcing which can occur after interruptions especially in DC circuits.
21 Internal wiring
This clause of IEC 61558-1:2017 is applicable.
22 Supply connection and other external flexible cable or cords
This clause of IEC 61558-1:2017 is applicable.

– 18 – IEC 61558-2-20:2022 © IEC 2022
23 Terminals for external conductors
This clause of IEC 61558-1:2017 is applicable.
24 Provisions for protective earthing
This clause of IEC 61558-1:2017 is applicable.
25 Screws and connections
This clause of IEC 61558-1:2017 is applicable.
26 Creepage distances, clearances and distances through insulation
This clause of IEC 61558-1:2017 is applicable.
NOTE See Annex BB for a reactors above 500 Hz.
27 Resistance to heat, fire and tracking
This clause of IEC 61558-1:2017 is applicable, except as follows:
27.3 This subclause of IEC 61558-1:2017 is not applicable.
28 Resistance to rusting
This clause of IEC 61558-1:2017 is applicable.

Annexes
Annexes A to W of IEC 61558-1:2017 are applicable.

Addition
Annex AA
(informative)
Characteristic parameter measurements
A detailed description for characteristic parameter measurements can be found in
IEC 60076-6:2007 for instance in 7.8.5, 9.10.5, 11.8.5, 12.8.5, Clause B.3 or Clause B.4.

Addition
Annex BB
(normative)
Particular requirements for associated
reactors with frequencies > 500 Hz
BB.0 General
This annex is applicable for separate testing of associated reactors with a fundamental
frequency > 500 Hz and the high frequency requirements of BB.4
...