EN IEC 61558-2-12:2025

SLOVENSKI STANDARD
01-maj-2025
Nadomešča:
SIST EN 61558-2-12:2011
Varnost transformatorjev, dušilk, napajalnikov in kombinacij teh elementov - 2-12.
del: Posebne zahteve in preskusi za transformatorje s konstantno napetostjo in
napajalnike s konstantno napetostjo
Safety of transformers, reactors, power supply units and combination thereof - Part 2-12:
Particular requirements and tests for constant voltage transformers and power supply
units for constant voltage
Sicherheit von Transformatoren, Drosseln, Netzgeräten und entsprechenden
Kombinationen - Teil 2-12: Besondere Anforderungen und Prüfungen für magnetische
Spannungskonstanthalter und Netzgeräte, die Spannungskonstanthalter enthalten
Sécurité des transformateurs, bobines d'inductance, blocs d'alimentation et des
combinaisons de ces éléments - Partie 2-12: Exigences particulières et essais pour les
transformateurs à tension constante et les blocs d'alimentation pour tension constante
Ta slovenski standard je istoveten z: EN IEC 61558-2-12:2025
ICS:
29.180 Transformatorji. Dušilke Transformers. Reactors
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EUROPEAN STANDARD EN IEC 61558-2-12

NORME EUROPÉENNE
EUROPÄISCHE NORM March 2025
ICS 29.180 Supersedes EN 61558-2-12:2011
English Version
Safety of transformers, reactors, power supply units and
combination thereof - Part 2-12: Particular requirements and
tests for constant voltage transformers and power supply units
for constant voltage
(IEC 61558-2-12:2024)
Sécurité des transformateurs, bobines d'inductance, blocs Sicherheit von Transformatoren, Drosseln, Netzgeräten und
d'alimentation et des combinaisons de ces éléments - entsprechenden Kombinationen - Teil 2-12: Besondere
Partie 2-12: Exigences particulières et essais pour les Anforderungen und Prüfungen für magnetische
transformateurs à tension constante et les blocs Spannungskonstanthalter und Netzgeräte, die
d'alimentation pour tension constante Spannungskonstanthalter enthalten
(IEC 61558-2-12:2024) (IEC 61558-2-12:2024)
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 61558-2-12:2025 E

European foreword
The text of document 96/587/FDIS, future edition 3 of IEC 61558-2-12, prepared by TC 96
"Transformers, reactors, power supply units, and combinations thereof" was submitted to the IEC-
CENELEC parallel vote and approved by CENELEC as EN IEC 61558-2-12:2025.
The following dates are fixed:
• latest date by which the document has to be implemented at national (dop) 2026-03-31
level by publication of an identical national standard or by endorsement
• latest date by which the national standards conflicting with the (dow) 2028-03-31
document have to be withdrawn
This document supersedes EN 61558-2-12:2011 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 is read in conjunction with EN IEC 61558-1:2019.
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 61558-2-12:2024 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 60204-1:2016 NOTE Approved as EN 60204-1:2018
IEC 61140:2016 NOTE Approved as EN 61140:2016 (not modified)
IEC 61558 series NOTE Approved as EN 61558 series
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.
Annex ZA of EN IEC 61558-1:2019 is applicable, except as follows:
Add:
Publication Year Title EN/HD Year
IEC 61558-1 2017 Safety of transformers, reactors, power EN IEC 61558-1 2019
supply units and combinations thereof -
Part 1: General requirements and tests
IEC 61558-2-16 2021 Safety of transformers, reactors, power EN IEC 61558-2-16 2025
supply units and combinations thereof -
Part 2-16: Particular requirements and
tests for switch mode power supply units
and transformers for switch mode power
supply units for general applications

IEC 61558-2-12 ®
Edition 3.0 2024-04
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
GROUP ENERGY EFFICIENCY PUBLICATION

PUBLICATION GROUPÉE SUR L'EFFICACITÉ ÉNERGÉTIQUE

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

Part 2-12: Particular requirements and tests for constant voltage transformers

and power supply units for constant voltage

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

combinaisons de ces éléments –

Partie 2-12: Exigences particulières et essais pour les transformateurs à tension

constante et les blocs d'alimentation pour tension constante

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
INTERNATIONALE
ICS 29.180  ISBN 978-2-8322-8463-6

– 2 – IEC 61558-2-12:2024 © IEC 2024
CONTENTS
FOREWORD . 3
INTRODUCTION . 5
1 Scope . 6
2 Normative references . 8
3 Terms and definitions . 8
4 General requirements . 9
5 General notes on tests . 9
6 Ratings . 9
7 Classification . 10
8 Marking and other information . 10
9 Protection against electric shock . 12
10 Change of input voltage setting . 12
11 Output voltage and output current under load . 12
12 No-load output voltage . 13
13 Short-circuit voltage . 14
14 Heating . 14
15 Short-circuit and overload protection . 14
16 Mechanical strength . 15
17 Protection against harmful ingress of dust, solid objects and moisture . 15
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 cables or cords . 17
23 Terminals for external conductors . 17
24 Provisions for protective earthing. 17
25 Screws and connections . 17
26 Creepage distances, clearances and distances through insulation . 17
27 Resistance to heat, fire and tracking . 17
28 Resistance to rusting . 18
Annexes . 19
Annex L (normative) Routine tests (production test) . 19
Bibliography . 20

Table 101 – Symbols indicating the kind of transformer . 11

IEC 61558-2-12:2024 © IEC 2024 – 3 –
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
SAFETY OF TRANSFORMERS, REACTORS,
POWER SUPPLY UNITS AND COMBINATIONS THEREOF –

Part 2-12: Particular requirements and tests for constant voltage
transformers and power supply units for constant voltage

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) IEC draws attention to the possibility that the implementation of this document may involve the use of (a)
patent(s). IEC takes no position concerning the evidence, validity or applicability of any claimed patent rights in
respect thereof. As of the date of publication of this document, IEC had not received notice of (a) patent(s), which
may be required to implement this document. However, implementers are cautioned that this may not represent
the latest information, which may be obtained from the patent database available at https://patents.iec.ch. IEC
shall not be held responsible for identifying any or all such patent rights.
IEC 61558-2-12 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 2011. 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) description of constructions moved to IEC 61558-1:2017;
c) new symbol for power supply unit with linearly regulated output voltage.

– 4 – IEC 61558-2-12:2024 © IEC 2024
The text of this International Standard is based on the following documents:
Draft Report on voting
96/587/FDIS 96/591/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/standardsdev/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 constant
voltage transformers and power supply units for constant voltage.
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, or
• revised.
IEC 61558-2-12:2024 © IEC 2024 – 5 –
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, which is about electrical installations and protection against electric shock, 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 61558-2-12:2024 © IEC 2024
SAFETY OF TRANSFORMERS, REACTORS,
POWER SUPPLY UNITS AND COMBINATIONS THEREOF –

Part 2-12: Particular requirements and tests for constant voltage
transformers and power supply units for constant voltage

1 Scope
Replacement:
This part of IEC 61558 deals with the safety of constant voltage transformers for general
applications and power supply units for constant voltage for general applications. Constant
voltage transformers 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 covers constant voltage
transformers for general applications and power supply units for constant voltage for
general applications.
This document is applicable to stationary or portable single-phase or polyphase, air-cooled
(natural or forced) independent or associated dry-type:
– constant voltage auto-transformers;
– constant voltage separating transformers;
– constant voltage isolating transformers;
– constant voltage safety isolating transformers.
The windings can be encapsulated or non-encapsulated.
For power supply units (linear) this document is applicable. For switch mode power supply
units IEC 61558-2-16 is applicable together with this document. Where two requirements are
in conflict, the most severe take precedence.
The rated supply voltage does not exceed 1 000 V AC. The rated supply frequency does not
exceed 500 Hz, the internal operating resonant frequency does not exceed 30 kHz and the
internal operating frequency does not exceed 100 MHz.
The rated output does not exceed:
– 40 kVA for single-phase constant voltage auto-transformers;
– 200 kVA for polyphase constant voltage auto-transformers;
– 25 kVA for single-p
...