IEC 61558-1:2005

Safety of power transformers, power supplies, reactors and similar products - Part 1: General requirements and tests

This International Standard deals with safety aspects of power transformers, power supplies, reactors and similar products such as electrical, thermal and mechanical safety. This standard covers the following types of dry-type transformers, power supplies, including switch mode power supplies, and reactors, the windings of which may be encapsulated or non-encapsulated It has the status of a group safety publication in accordance with IEC Guide 104. The contents of the corrigenda of March 2008, March 2010 and April 2011 have been included in this copy.

Sécurité des transformateurs, alimentations, bobines d'inductance et produits analogues - Partie 1: Exigences générales et essais

La présente Norme internationale traite des aspects relatifs à la sécurité des transformateurs, alimentations, bobines d'inductance, et produits analogues, tels que la sécurité électrique, la sécurité thermique et la sécurité mécanique. La présente norme couvre les transformateurs secs et les alimentations ci-dessous, incluant les alimentations à découpage et bobines d'inductance, dont les enroulements peuvent être enrobés ou non enrobes Elle a le statut de publication groupée de sécurité conformément au guide CEI 104. Le contenu des corrigendas de mars 2008, mars 2010 et abril 2011 a été pris en considération dans cet exemplaire.

General Information

• Status: Published
• Publication Date: 06-Apr-2009
• ICS: 29.180 - Transformers. Reactors
• Technical Committee: TC 96 - Transformers and reactors
• Drafting Committee: MT 1 - TC 96/MT 1
• Current Stage: DELPUB - Deleted Publication
• Start Date: 29-Sep-2017
• Completion Date: 26-Oct-2025

Relations

• Amended By: IEC 61558-1:2005/AMD1:2009 - Amendment 1 - Safety of power transformers, power supplies, reactors and similar products - Part 1: General requirements and tests
• Effective Date: 05-Sep-2023
• Corrected By: IEC 61558-1:2005/COR1:2008 - Corrigendum 1 - Safety of power transformers, power supplies, reactors and similar products - Part 1: General requirements and tests
• Effective Date: 05-Sep-2023
• Corrected By: IEC 61558-1:2005/COR3:2011 - Corrigendum 3 - Safety of power transformers, power supplies, reactors and similar products - Part 1: General requirements and tests
• Effective Date: 05-Sep-2023
• Corrected By: IEC 61558-1:2005/COR2:2010 - Corrigendum 2 - Safety of power transformers, power supplies, reactors and similar products - Part 1: General requirements and tests
• Effective Date: 05-Sep-2023
• Revised: IEC 61558-1:2017 - Safety of transformers, reactors, power supply units and combinations thereof - Part 1: General requirements and tests
• Effective Date: 05-Sep-2023
• Revises: IEC 61558-1:1997/AMD1:1998 - Amendment 1 - Safety of power transformers, power supply units and similar - Part 1: General requirements and tests
• Effective Date: 05-Sep-2023
• Revises: IEC 61558-1:1997/ISH1:2003 - Interpretation sheet 1 - Safety of power transformers, power supply units and similar - Part 1: General requirements and tests
• Effective Date: 05-Sep-2023
• Revises: IEC 61558-1:1997 - Safety of power transformers, power supply units and similar - Part 1: General requirements and tests
• Effective Date: 05-Sep-2023

Standards Content (Sample)

IEC 61558-1 ®
Edition 2.1 2009-04
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
GROUP SAFETY PUBLICATION
PUBLICATION GROUPÉE DE SÉCURITÉ
Safety of power transformers, power supplies, reactors and similar products –
Part 1: General requirements and tests

Sécurité des transformateurs, alimentations, bobines d'inductance et produits
analogues –
Partie 1: Exigences générales et essais
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 la CEI ou du Comité national de la CEI du pays du demandeur.
Si vous avez des questions sur le copyright de la CEI ou si vous désirez obtenir des droits supplémentaires sur cette
publication, utilisez les coordonnées ci-après ou contactez le Comité national de la CEI de votre pays de résidence.

IEC Central Office
3, rue de Varembé
CH-1211 Geneva 20
Switzerland
Email: [e-mail]
Web: www.iec.ch
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 corrigenda or an amendment might have been published.
ƒ Catalogue of IEC publications: www.iec.ch/searchpub
The IEC on-line Catalogue enables you to search by a variety of criteria (reference number, text, technical committee,…).
It also gives information on projects, withdrawn and replaced publications.
ƒ IEC Just Published: www.iec.ch/online_news/justpub
Stay up to date on all new IEC publications. Just Published details twice a month all new publications released. Available
on-line and also by email.
ƒ Electropedia: www.electropedia.org
The world's leading online dictionary of electronic and electrical terms containing more than 20 000 terms and definitions
in English and French, with equivalent terms in additional languages. Also known as the International Electrotechnical
Vocabulary online.
ƒ Customer Service Centre: www.iec.ch/webstore/custserv
If you wish to give us your feedback on this publication or need further assistance, please visit the Customer Service
Centre FAQ or contact us:
Email: [e-mail]
Tel.: [phone]
Fax: [phone]
A propos de la CEI
La Commission Electrotechnique Internationale (CEI) 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 CEI
Le contenu technique des publications de la CEI est constamment revu. Veuillez vous assurer que vous possédez
l’édition la plus récente, un corrigendum ou amendement peut avoir été publié.
ƒ Catalogue des publications de la CEI: www.iec.ch/searchpub/cur_fut-f.htm
Le Catalogue en-ligne de la CEI vous permet d’effectuer des recherches en utilisant différents critères (numéro de référence,
texte, comité d’études,…). Il donne aussi des informations sur les projets et les publications retirées ou remplacées.
ƒ Just Published CEI: www.iec.ch/online_news/justpub
Restez informé sur les nouvelles publications de la CEI. Just Published détaille deux fois par mois les nouvelles
publications parues. Disponible en-ligne et aussi par email.
ƒ Electropedia: www.electropedia.org
Le premier dictionnaire en ligne au monde de termes électroniques et électriques. Il contient plus de 20 000 termes et
définitions en anglais et en français, ainsi que les termes équivalents dans les langues additionnelles. Egalement appelé
Vocabulaire Electrotechnique International en ligne.
ƒ Service Clients: www.iec.ch/webstore/custserv/custserv_entry-f.htm
Si vous désirez nous donner des commentaires sur cette publication ou si vous avez des questions, visitez le FAQ du
Service clients ou contactez-nous:
Email: [e-mail]
Tél.: [phone]
Fax: [phone]
IEC 61558-1 ®
Edition 2.1 2009-04
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
GROUP SAFETY PUBLICATION
PUBLICATION GROUPÉE DE SÉCURITÉ
Safety of power transformers, power supplies, reactors and similar products –
Part 1: General requirements and tests

Sécurité des transformateurs, alimentations, bobines d'inductance et produits
analogues –
Partie 1: Exigences générales et essais

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
PRICE CODE
INTERNATIONALE
CR
CODE PRIX
ICS 29.180 ISBN 978-2-88910-539-7
– 2 – 61558-1 © IEC:2005+A1:2009
CONTENTS
FOREWORD.5
INTRODUCTION.8

1 Scope.11
2 Normative references.13
3 Terms and definitions .16
4 General requirements .29
5 General notes on tests.29
6 Ratings.31
7 Classification .31
8 Marking and other information.33
9 Protection against electric shock.38
10 Change of input voltage setting .41
11 Output voltage and output current under load .42
12 No-load output voltage.42
13 Short-circuit voltage.43
14 Heating.43
15 Short circuit and overload protection .48
16 Mechanical strength.52
17 Protection against harmful ingress of dust, solid objects and moisture.55
18 Insulation resistance, dielectric strength and leakage current .59
19 Construction .63
20 Components .70
21 Internal wiring .76
22 Supply connection and other external flexible cables or cords.76
23 Terminals for external conductors .82
24 Provisions for protective earthing .84
25 Screws and connections .85
26 Creepage distances, clearances and distances through insulation .88
27 Resistance to heat, fire and tracking .97
28 Resistance to rusting .101

Annex A (normative) Measurement of creepage distances and clearances. 109
Annex B (normative) Testing a series of transformers. 113
Annex C (normative) Creepage distances (cr), clearances (cl) and distances through
insulation (dti) Material group II (400 ≤CTI <600) . 115
Annex D (normative) Creepage distances (cr), clearances (cl) and distances through
insulation (dti) Material group I (CTI ≥600) . 118
Annex E (normative) Glow-wire test. 121
Annex F (normative) Requirements for manually operated switches which are parts of
transformers assembly.122

61558-1 © IEC:2005+A1:2009 – 3 –
Annex G (normative) Tracking test . 125
Annex H (normative) Electronic circuits . 126
Annex I (void). 130
Annex J (normative) Measuring network for touch-currents. 131
Annex K (normative) Insulated winding wires for use as multiple layer insulation. 132
Annex L (normative) Routine tests (production tests) . 134
Annex M (informative) Examples to be used as a guide for 19.1 . 136
Annex N (informative) Examples of points of application of test voltages. 139
Annex O (void) . 141
Annex P (informative) Examples of points of measurement of creepage distances
and clearances. 142
Annex Q (informative) Explanation of IP numbers for degrees of protection . 144
Annex R (normative) Explanations of the application of 4.1.1.2.1 of IEC 60664-1
(see 26.2) . 146
Annex S (void) . 147
Annex T (void) . 148
Annex U (informative) Optional t –marking of transformers. 149
w
Annex V (informative) Symbols to be used for thermal cut-outs. 158
Annex W (normative) Coated printed circuit boards . 159

Bibliography . 160
Index of defined terms.161

Figure 0 – IEC 61558 principle .9
Figure 1 – Mounting box for flush-type transformer (see 5.10) . 102
Figure 2 – Standard test finger (see 9.1.2, 15.5.2 and IEC 61032, test probe B). 103
Figure 3 – Test pin (see 9.2 and IEC 61032, test probe 13) . 104
Figure 4 – Abrasion resistance test for insulating coated layers . 104
Figure 5 – Ball-pressure apparatus (see 27.1) . 105
Figure 6 – Test arrangement for checking mechanical withstanding of insulating
materials in thin sheet layers (see 26.3) . 106
Figure 7 – Flexing test apparatus (see 22.9.4) . 107
Figure 8 – Test configuration: single-phase equipment on star TN or TT system . 108
Figure H.1 – Example of an electronic circuit with low-power points (see H.2.2) . 129
Figure J.1 – Measuring network for touch-current . 131
Figure U.1 – Relation between winding temperature and endurance test duration. 156
Figure U.2 – Assessment of claimed value of S . 157

– 4 – 61558-1 © IEC:2005+A1:2009
Table 1 – Values of maximum temperatures in normal use .45
Table 2 – Test temperature and testing time (in days) per cycle.47
Table 3 – Maximum values of temperatures under short-circuit or overload conditions .49
Table 4 – Values of T and k for fuses .50
Table 5 – Pull force on pins .54
Table 6 – Solid-object-proof transformer test .56
Table 7 – Values of insulation resistance.59
Table 8a – Table of dielectric strength test voltages .60
Table 8b – Limits for currents.63
Table 9 – Nominal cross-sectional areas of external flexible cables or cords.78
Table 10 – Pull and torque to be applied to external flexible cables or cords fixed
to stationary and portable transformers .81
Table 11 – Torque to be applied to screws and connections.86
Table 12 – Torque test on glands .88
Table 13 – Creepage distances (cr), clearances (cl) and distances through
insulation (dti) – Material group IIIa (175 ≤ CTI < 400).94
Table C.1 – Creepage distances (cr), clearances (cl) and distances through
insulation (dti) – Material group II (400 ≤CTI <600) . 115
Table D.1 – Creepage distances (cr), clearances (cl) and distances through
insulation (dti) – Material group I (CTI ≥600) . 118
Table F.1 – Peak surge current of the additional load . 123
Table Q.1 – Degrees of protection indicated by the first characteristic numeral . 144
Table Q.2 – Degrees of protection indicated by the second characteristic numeral . 145
Table R.1 – Impulse test voltage according to 4.1.1.2.1 of IEC 60664-1 . 146
Table U.1 – Example of maximum temperatures of windings under short circuit or
overload conditions and at 110 % of rated voltage for transformers subjected to
an endurance test duration of 30 days and a life expectance of 10 years . 151
Table U.2 –Theoretical test temperatures for transformers subjected to an endurance
test duration of 30 days and a life expectancy of 10 years. 153

61558-1 © IEC:2005+A1:2009 – 5 –
INTERNATIONAL ELECTROTECHNICAL COMMISSION
––––––––––
SAFETY OF POWER TRANSFORMERS, POWER SUPPLIES,
REACTORS AND SIMILAR PRODUCTS –

Part 1: General requirements and tests

FOREWORD
1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising
all national electrotechnical committees (IEC National Committees). The object of IEC is to promote
international co-operation on all questions concerning standardization in the electrical and electronic fields. To
this end and in addition to other activities, IEC publishes International Standards, Technical Specifications,
Technical Reports, Publicly Available Specifications (PAS) and Guides (hereafter referred to as “IEC
Publication(s)”). Their preparation is entrusted to technical committees; any IEC National Committee interested
in the subject dealt with may participate in this preparatory work. International, governmental and non-
governmental organizations liaising with the IEC also participate in this preparation. IEC collaborates closely
with the International Organization for Standardization (ISO) in accordance with conditions determined by
agreement between the two organizations.
2) The formal decisions or agreements of IEC on technical matters express, as nearly as possible, an international
consensus of opinion on the relevant subjects since each technical committee has representation from all
interested IEC National Committees.
3) IEC Publications have the form of recommendations for international use and are accepted by IEC National
Committees in that sense. While all reasonable efforts are made to ensure that the technical content of IEC
Publications is accurate, IEC cannot be held responsible for the way in which they are used or for any
misinterpretation by any end user.
4) In order to promote international uniformity, IEC National Committees undertake to apply IEC Publications
transparently to the maximum extent possible in their national and regional publications. Any divergence
between any IEC Publication and the corresponding national or regional publication shall be clearly indicated in
the latter.
5) IEC itself does not provide any attestation of conformity. Independent certification bodies provide conformity
assessment services and, in some areas, access to IEC marks of conformity. IEC is not responsible for any
services carried out by independent certification bodies.
6) All users should ensure that they have the latest edition of this publication.
7) No liability shall attach to IEC or its directors, employees, servants or agents including individual experts and
members of its technical committees and IEC National Committees for any personal injury, property damage or
other damage of any nature whatsoever, whether direct or indirect, or for costs (including legal fees) and
expenses arising out of the publication, use of, or reliance upon, this IEC Publication or any other IEC
Publications.
8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is
indispensable for the correct application of this publication.
9) Attention is drawn to the possibility that some of the elements of this IEC Publication may be the subject of
patent rights. IEC shall not be held responsible for identifying any or all such patent rights.
International Standard IEC 61558-1 has been prepared by IEC technical committee 96: Small
power transformers, reactors and power supply units and similar products
It has the status of a group safety publication in accordance with IEC Guide 104.
This new edition represents a complete revision of the previous edition. The changes were
necessitated by the introduction of new technology and implementation of requirements from
equipment committees.
– 6 – 61558-1  IEC:2005+A1:2009
This consolidated version of IEC 61558-1 consists of the second edition (2005) [documents
96/224/FDIS and 96/228/RVD], its amendment 1 (2009) [documents 96/314/FDIS and
96/320/RVD] and its corrigenda of March 2008, March 2010 and April 2011.
The technical content is therefore identical to the base edition and its amendment and has
been prepared for user convenience.
It bears the edition number 2.1.
A vertical line in the margin shows where the base publication has been modified by
amendment 1.
This publication has been drafted in accordance with the ISO/IEC Directives, Part 2.
This second edition of Part 1 is only to be used in conjunction with parts 2 based on this
edition. The parts 2 contain clauses to supplement or modify the corresponding clauses of this
Part 1 in order to provide the relevant requirements for each type of transformer.
However, individual countries may wish to consider its application, to the extent reasonable, to
transformers not mentioned in the parts 2, and to transformers designed on new principles.
NOTE Annex U contains the optional t system (marking, requirements and tests).
w
IEC 61558 consists of the following parts, under the general title Safety of power transformers,
1)
power supplies, reactors and similar products:
Part 1: General requirements and tests
Part 2-1: Particular requirements for separating transformers for general use
Part 2-2: Particular requirements for control transformers
Part 2-3: Particular requirements for ignition transformers for gas and oil burners
Part 2-4: Particular requirements for isolating transformers for general use
Part 2-5: Particular requirements for shaver transformers and shaver supply units
Part 2-6: Particular requirements for safety isolating transformers for general use
Part 2-7: Particular requirements for transformers for toys
Part 2-8: Particular requirements for bell and chime transformers
Part 2-9: Particular requirements for transformers for class III handlamps for tungsten
filament lamps
Part 2-12: Particular requirements for constant voltage transformers
Part 2-13: Particular requirements for auto-transformers for general use
Part 2-14: Particular requirements for variable transformers (in preparation)
Part 2-15: Particular requirements for isolating transformers for the supply of medical
locations
Part 2-16: Particular requirements for switch mode power supplies and transformers for
switch mode power supplies (in preparation)
Part 2-17: Particular requirements for transformers for switch mode power supplies
Part 2-19: Particular requirements for perturbation attenuation transformers
Part 2-20: Particular requirements for small reactors
___________
1)
Some of the parts of this series published earlier appeared under the general title Safety of power transformers,
power supply units and similar or Safety of power transformers, power supply units and similar devices. Future
editions of these parts will be issued under the new general title indicated above.

61558-1 © IEC:2005+A1:2009 – 7 –
Part 2-23: Particular requirements for transformers for construction sites
Other parts are under consideration.
In this standard, 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 the standard, the words in bold are defined in Clause 3.
The committee has decided that the contents of the base publication and its amendments will
remain unchanged until the maintenance result date indicated on the IEC web site under
"http://webstore.iec.ch" in the data related to the specific publication. At this date,
the publication will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
– 8 – 61558-1 © IEC:2005+A1:2009
INTRODUCTION
This International Standard covers safety requirements for transformers. Where the term
transformer is used, it covers transformers, reactors and power supplies where applicable.
During the development of this standard, to the extent possible, the requirements of IEC 60364
were taken into consideration, so that a transformer may be installed in accordance with the
wiring rules contained in that standard. However, national wiring rules may differ.
This standard recognizes the internationally accepted levels of protection against the possible
electrical, mechanical, and fire hazards caused by transformers operating under normal
conditions in accordance with the manufacturer's instructions. It, also, covers abnormal
conditions which may occur in practice.
A transformer complying with this standard will not necessarily be judged to comply with the
safety principles of this standard if when examined and tested, it is found to have other
features that impair the level of safety covered by these requirements.
A transformer employing materials or having forms of construction differing from those
detailed in this standard may be examined and tested according to the intent of the
requirements, and if found to be substantially equivalent, may be judged to comply with the
safety principles of this standard.
The standard dealing with non-safety aspects of electromagnetic compatibility (EMC) of
transformers is IEC 62041: Power transformers, power supply units, reactors and similar
products – EMC requirements. However, that standard also includes tests which may subject
the transformer to conditions involving the safety aspects.
The objective of Part 1 of IEC 61558 is to provide a set of requirements and tests considered
to be generally applicable to most types of transformers, and which can be called up as
required by the relevant part 2 of IEC 61558. Part 1 is thus not to be regarded as a
specification by itself for any type of transformer, and its provisions apply only to particular
types of transformers to the extent determined by the appropriate part 2. Part 1 of IEC 61558
also contains normative routine tests.
Each part 2 in conjunction with Part 1 contains all the necessary requirements for the
transformer being covered and does not contain references to other parts 2. For
transformers with a protection index IP00 and associated transformers, it is possible to have
circuits corresponding to different parts 2 within the same construction (e.g. SELV output
circuit according to Part 2-6 and 230 V output circuit according to Part 2-4). However, if the
transformer is covered by different parts 2 of IEC 61558, to the extent reasonable, the
relevant part 2 is applied to each function/application separately. If applicable, the effect of one
function on the other is taken into consideration.
If, an appropriate part 2 for a particular transformer or group of transformers does not exist,
the nearest applicable part 2 may be used as a guide to the requirements and tests.
Where the requirements of any of the clauses of a part 2 refer to Part 1 by the phrase "This
clause of Part 1 is applicable", this phrase means all the requirements of that clause of Part 1
are applicable, except those requirements that are, clearly, not applicable to the particular type
of transformer covered by that part 2.
The principle for preparation of the different parts 2 is as follows:

61558-1 © IEC:2005+A1:2009              – 9 –

IEC  1269/05
Figure 0 – IEC 61558 principle

– 10 – 61558-1 © IEC:2005+A1:2009
Relevant clauses of this standard (e.g. clauses dealing with thermal endurance test for
windings) apply also to transformers forming an integral part of an appliance and which cannot
be tested separately.
As an option, the thermal characteristics of transformers can be specified by the rated
maximum operating temperature of the winding (symbol t ) which shall not be exceeded to
w
ensure a minimum lifetime as specified in Annex U. In addition, for transformers subjected to
abnormal conditions as specified in Clause 15, the specified temperature limit shall not be
exceeded when the transformer is built into an appliance or used as an independent
transformer.
61558-1 © IEC:2005+A1:2009 – 11 –
SAFETY OF POWER TRANSFORMERS, POWER SUPPLIES,
REACTORS AND SIMILAR PRODUCTS –

Part 1: General requirements and tests

1 Scope
This International Standard deals with safety aspects of power transformers, power supplies,
reactors and similar products such as electrical, thermal and mechanical safety.
This standard covers the following types of dry-type transformers, power supplies, including
switch mode power supplies, and reactors, the windings of which may be encapsulated or
non-encapsulated :
NOTE 1 The distinction between transformers, power supplies and switch mode power supplies is as follows:
– for transformers, there is no change in frequency .However, transformers (e.g. constant voltage
transformers) may have an internal resonance frequency not exceeding 30 kHz;
– for power supplies, the internal operational frequency and waveform are different from the supply frequency
and waveform, and the internal operational frequency does not exceed 500 Hz (see definition 3.1.19);
– for switch mode power supplies, the internal operational frequency and waveform are different from the
supply frequency and waveform and the internal operational frequency exceeds 500 Hz and does not exceed
100 MHz.
The relevant parts 2 may be found in the introduction of this standard.
a) Stationary or portable, single-phase or poly-phase, air-cooled (natural or forced), isolating
and safety isolating transformers, independent or associated, not forming a part of
distribution networks and with the following characteristics:
– rated supply voltage not exceeding 1 000 V a.c.;
– rated supply frequency not exceeding 500 Hz;
and complying with the following values, unless otherwise specified in the relevant part 2:
• for isolating transformers:
– rated output for single phase transformers, not exceeding 25 kVA, and for poly-
phase transformers not exceeding 40 kVA.
– no-load output voltage and the rated output voltage exceeding 50 V a.c., and not
exceeding 500 V a.c, or 1 000 V a.c. to be in accordance with the National Wiring
Rules or for a special application.
• for safety isolating transformers:
– rated output for single phase transformers not exceeding 10 kVA, and for poly-
phase transformers not exceeding 16 kVA.
– no-load output voltage and the rated output voltage not exceeding 50 V a.c.
between conductors, or between any conductor and protective earth.
NOTE 1 Isolating and safety isolating transformers are used where double or reinforced insulation between
circuits is required by the installation rules or by the appliance specification (for example toys, bells, portable tools,
handlamps).
– 12 – 61558-1 © IEC:2005+A1:2009
b) Stationary or portable, single-phase or polyphase, air-cooled (natural or forced)
separating transformers, auto-transformers, variable transformers and small reactors,
independent or associated, not forming a part of distribution networks and with the
following characteristics:
– rated supply voltage not exceeding 1 000 V a.c.;
– rated supply frequency not exceeding 500 Hz;
and complying with the following values, unless otherwise specified in the relevant part 2:
– no-load output voltage or a rated output voltage for both independent and associated
transformers not exceeding 15 kV a.c., and for independent transformers, a rated
output voltage not less than 50 V a.c.;
– rated output not exceeding the following values:
– 1 kVA for single-phase transformers;
– 2 kVAR for single-phase reactors;
– 5 kVA for poly-phase transformers;
– 10 kVAR for poly-phase reactors.
NOTE 2 Separating transformers are used where double or reinforced insulation between circuits is not
required by the installation rules or by the appliance specification.
NOTE 3 Normally, the transformers of type b) are intended to be associated with the equipment to provide
voltages different from the supply voltage for the functional requirements of the equipment. The protection against
electric shock may be provided or completed by other features of the equipment, such as the body. Parts of output
circuits may be connected to the input circuit or to the protective earth.
c) Stationary or portable, single-phase or polyphase, air-cooled (natural or forced),
independent or associated power supplies and switch mode power supplies
incorporating one or more transformer(s) of type a) or b), not forming a part of distribution
networks and with the following characteristics:
– rated supply voltage not exceeding 1 000 V a.c.;
– rated supply frequency not exceeding 500 Hz;
– internal operational frequency for power supplies not exceeding 500 Hz and for switch
mode power supplies not exceeding 100 MHz;
and with the following values, unless otherwise specified in the relevant part 2:
• for power supplies and switch mode power supplies incorporating isolating
transformers:
– rated output for single- phase or polyphase power supplies or switch mode
power supplies not exceeding 1 kVA;
– no-load output voltage and the rated output voltage exceeding 50 V a.c. or
120 V ripple- free d.c., and not exceeding 500 V a.c. or 708 V ripple- free d.c., or
1 000 V a.c. or 1 415 V ripple- free d.c. to be in accordance with national wiring rules or
for a special application;
• for power supplies and switch mode power supplies incorporating safety isolating
transformers:
– rated output for single- phase or polyphase power supplies and switch mode
power supplies not exceeding 1 kVA;
– no-load output voltage and rated output voltage not exceeding 50 V a.c.or 120 V
ripple- free d.c. between conductors, or between any conductor and protective earth.

61558-1 © IEC:2005+A1:2009 – 13 –
NOTE 4 Power supplies and switch mode power supplies incorporating Isolating and safety
isolating transformers are used where double or reinforced insulation between circuits is required by
the installation rules or by the appliance specification (for example toys, bells, portable tools, handlamps).
• for power supplies and switch mode power supplies incorporating separating
transformers, auto-transformers , and variable transformers:
– rated output for single-phase or polyphase power supplies and switch mode
power supplies not exceeding 1 kVA;
– no-load output voltage and rated output voltage for both, independent and
associated transformers not exceeding 15 kV a.c., and for independent
transformers, a rated output voltage not less than 50 V a.c.;
NOTE 5 Power supplies and switch mode power supplies incorporating separating transformers are
used where double or reinforced insulation between circuits is not required by the installation rules or by
the appliance specification.
d) This standard is also applicable to t -marked transformers with a rated output not
w
exceeding 1 000 VA and where the t -temperature does not exceed 140 °C (t 140).
w w
However, t -marking of transformers is optional.
w
This standard also applies to transformers, power supplies, switch mode power supplies,
and reactors incorporating electronic circuits.
This standard does not apply to external circuits and their components intended to be
connected to the input and output terminals or socket-outlets of the transformers, power
supplies and switch mode power supplies, and reactors.
NOTE 6 Attention is drawn to the following:
– for transformers 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 like
fungus, vermin , termites, solar-radiation, and icing should also be considered;
– the different conditions for transportation, storage, and operation of the transformers should also be
considered;
– additional requirements in accordance with other appropriate standards and national rules may be applicable to
transformers intended for use in special environments, such as tropical environment
NOTE 7 Future technological development of transformers may necessitate a need to increase the upper limit of
the frequencies; until then this standard may be used as a guidance document.

2 Normative references
The following referenced documents are indispensable for the application of this document. For
dated references, only the edition cited applies. For undated references, the latest edition of
the referenced document (including any amendments) applies.
IEC 60065:2001, Safety requirements for mains operated electronic and related apparatus for
household and similar general use
IEC 60068-2-2:1974, Environmental testing – Part 2: Tests – Test B: Dry heat
IEC 60068-2-6, Environmental testing – Part 2: Tests – Test FC: Vibration (sinusoidal)
IEC 60068-2-32, Environmental testing – Part 2: Tests – Test Ed: Free fall

– 14 – 61558-1 © IEC:2005+A1:2009
IEC 60068-2-75, Environmental testing – Part 2: Tests – Test Eh: Hammer tests
IEC 60076-1, Power transformers – Part 1: General
IEC 60083, Plugs and socket-outlets for domestic and similar general use standardized in
member countries of IEC
IEC 60085:1984, Thermal evaluation and classification of electrical insulation
IEC 60112:2003, Method for the determination of the proof and the comparative tracking
indices of solid insulating materials
IEC 60127-3, Miniature fuses – Part 3: Sub-miniature fuse-links
IEC 60216 (all parts), Electrical insulating materials – Properties of thermal endurance
IEC 60227 (all parts), Polyvinyl chloride insulated cables of rated voltages up to and including
450/750 V
IEC 60245 (all parts), Rubber insulated cables – Rated voltages up to and including 450/750 V
IEC 60269 (all parts), Low voltage fuses
IEC 60269-2, Low voltage fuses – Part 2: Supplementary requirements for fuses for use by
authorized persons (fuses mainly for industrial application)
IEC 60269-2-1, Low voltage fuses – Part 2: Supplementary requirements for fuses for use by
authorized persons (fuses mainly for industrial application) – Sections I to VI: Examples of
types of standardized fuses
IEC 60269-3, Low voltage fuses – Part 3: Supplementary requirements for fuses for use by
unskilled persons (fuses mainly for household and similar applications)
IEC 60269-3-1, Low voltage fuses – Part 3: Supplementary requirements for fuses for use by
unskilled persons (fuses mainly for household and similar applications) – Sections I to IV:
examples of types of standardized fuses
IEC 60309 (all parts), Plugs, socket-outlets and couplers for industrial purposes
IEC 60317 (all parts), Specifications for particular types of windings wires
IEC 60320 (all parts), Appliance couplers for household and similar general purposes
IEC 60320-2-3, Appliance couplers for household and similar general purposes – Part 2-3:
Appliance couplers with a degree of protection higher than IPX0
IEC 60384-14, Fixed capacitors for use in electronic equipment – Part 14: Sectional
specification: Fixed capacitors for electromagnetic interference suppression and connection to
the supply mains
2)
IEC 60417-DB:2002 , Graphical symbols for use on equipment
IEC 60449:1973, Voltage bands for electrical installations of buildings
___________
2)
”DB” refers to the IEC on-line database.

61558-1 © IEC:2005+A1:2009 – 15 –
IEC 60454 (all parts), Specification for pressure-sensitive adhesive tapes for electrical
purposes
IEC 60529:1989, Degrees of protection provided by enclosures (IP Code)
IEC 60664-1:1992, Insulation co-ordination for equipment within low voltage systems – Part 1:
Principles, requirements and tests
IEC 60664-3:2003, Insulation co-ordination for equipment within low voltage systems – Part 3:
Use of coating, potting or moulding for protection against pollution
IEC 60691:2002, Thermal-links – Requirements and application guide
IEC 60695-2-10, Fire hazard testing – Part 2-10: Glowing/hot-wire based test methods – Glow-
wire apparatus and common test procedure
IEC 60695-2-11:2000, Fire hazard testing – Part 2-11: Glowing/hot-wire based test methods-
Glow-wire flammability test method for end-products
IEC 60695-10-2, Fire hazard testing – Part 10-2: Abnormal heat – Ball pressure test
IEC 60730 (all parts), Automatic electrical controls for household and similar use
IEC 60730-1:1999, Automatic electrical controls for household and similar use – Part 1:
General requirements
IEC 60851-3:1996, Winding wires – Test methods: Part 3: Mechanical properties
IEC 60851-5:1996, Winding wires – Test methods: Part 5: Electrical properties
IEC 60851-6:1996, Winding wires – Test methods: Part 5: Thermal properties
IEC 60884-1:2002, Plugs and socket-outlets for household and similar purposes – Part 1:
General requirements
IEC 60884-2-4, Plugs and socket-outlets for household and similar purposes – Part 2:
Particular requirements for plugs and socket-outlets for SELV
IEC 60898 (all parts), Electrical accessories – Circuit-breakers for overcurrent protection for
household and similar installations )
IEC 60906-1, IEC System of plugs and socket-outlets for household and similar purposes –
Part 1: Plugs and socket-outlets 16 A 250 V a.c.
IEC 60906-3, IEC System of plugs and socket-outlets for household and similar purposes –
Part 3: SELV plugs and socket-outlets, 16 A 6 V, 12 V, 24 V, 48 V, a.c. and d.c.
IEC 60947-7-1, Low-voltage switchgear and controlgear – Part 7: Ancillary equipment –
Section 1: Terminal blocks for copper conductors
IEC 60990:1990, Methods of measurement of touch current and protective conductor current
___________
3)
IEC 60898-2 is published under the general title Circuit-breakers for overcurrent protection for household and
similar installations (i.e. without the element of “Electrical accessories” in the title).

– 16 – 61558-1 © IEC:2005+A1:2009
IEC 60998-2-1, Connecting devices for low voltage circuits for household and similar purposes –
Part 2-1: Particular requirements for connecting devices as separate entities with screw-type
clamping units
IEC 60998-2-2, Connecting devices for low voltage circuits for household and similar purposes –
Part 2-2: Particular requirements for connecting devices as separate entiti
...

IEC 61558-1
Edition 2.0 2005-09
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
GROUP SAFETY PUBLICATION
PUBLICATION GROUPÉE DE SÉCURITÉ
Safety of power transformers, power supplies, reactors and similar products –
Part 1: General requirements and tests
Sécurité des transformateurs, alimentations, bobines d'inductance et produits
analogues – Partie 1: Exigences générales et essais
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 la CEI ou du Comité national de la CEI du pays du demandeur.
Si vous avez des questions sur le copyright de la CEI ou si vous désirez obtenir des droits supplémentaires sur cette
publication, utilisez les coordonnées ci-après ou contactez le Comité national de la CEI de votre pays de résidence.
IEC Central Office
3, rue de Varembé
CH-1211 Geneva 20
Switzerland
Email: [e-mail]
Web: www.iec.ch
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 corrigenda or an amendment might have been published.
ƒ Catalogue of IEC publications: www.iec.ch/searchpub
The IEC on-line Catalogue enables you to search by a variety of criteria (reference number, text, technical committee,…).
It also gives information on projects, withdrawn and replaced publications.
ƒ IEC Just Published: www.iec.ch/online_news/justpub
Stay up to date on all new IEC publications. Just Published details twice a month all new publications released. Available
on-line and also by email.
ƒ Electropedia: www.electropedia.org
The world's leading online dictionary of electronic and electrical terms containing more than 20 000 terms and definitions
in English and French, with equivalent terms in additional languages. Also known as the International Electrotechnical
Vocabulary online.
ƒ Customer Service Centre: www.iec.ch/webstore/custserv
If you wish to give us your feedback on this publication or need further assistance, please visit the Customer Service
Centre FAQ or contact us:
Email: [e-mail]
Tel.: [phone]
Fax: [phone]
A propos de la CEI
La Commission Electrotechnique Internationale (CEI) 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 CEI
Le contenu technique des publications de la CEI est constamment revu. Veuillez vous assurer que vous possédez
l’édition la plus récente, un corrigendum ou amendement peut avoir été publié.
ƒ Catalogue des publications de la CEI: www.iec.ch/searchpub/cur_fut-f.htm
Le Catalogue en-ligne de la CEI vous permet d’effectuer des recherches en utilisant différents critères (numéro de référence,
texte, comité d’études,…). Il donne aussi des informations sur les projets et les publications retirées ou remplacées.
ƒ Just Published CEI: www.iec.ch/online_news/justpub
Restez informé sur les nouvelles publications de la CEI. Just Published détaille deux fois par mois les nouvelles
publications parues. Disponible en-ligne et aussi par email.
ƒ Electropedia: www.electropedia.org
Le premier dictionnaire en ligne au monde de termes électroniques et électriques. Il contient plus de 20 000 termes et
définitions en anglais et en français, ainsi que les termes équivalents dans les langues additionnelles. Egalement appelé
Vocabulaire Electrotechnique International en ligne.
ƒ Service Clients: www.iec.ch/webstore/custserv/custserv_entry-f.htm
Si vous désirez nous donner des commentaires sur cette publication ou si vous avez des questions, visitez le FAQ du
Service clients ou contactez-nous:
Email: [e-mail]
Tél.: [phone]
Fax: [phone]
IEC 61558-1
Edition 2.0 2005-09
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
GROUP SAFETY PUBLICATION
PUBLICATION GROUPÉE DE SÉCURITÉ
Safety of power transformers, power supplies, reactors and similar products –
Part 1: General requirements and tests
Sécurité des transformateurs, alimentations, bobines d'inductance et produits
analogues – Partie 1: Exigences générales et essais
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
PRICE CODE
INTERNATIONALE
CODE PRIX XH
ICS 29.180 ISBN 2-8318-8170-6
61558-1 ¤ IEC:2005 – 3 – – 2 – 61558-1 © IEC:2005
CONTENTS
FOREWORD.5
INTRODUCTION.8
1 Scope.11
2 Normative references.13
3 Terms and definitions .16
4 General requirements .29
5 General notes on tests.29
6 Ratings.31
7 Classification .31
8 Marking and other information.33
9 Protection against electric shock.38
10 Change of input voltage setting .41
11 Output voltage and output current under load .42
12 No-load output voltage.42
13 Short-circuit voltage.43
14 Heating.43
15 Short circuit and overload protection .48
16 Mechanical strength.52
17 Protection against harmful ingress of dust, solid objects and moisture.55
18 Insulation resistance, dielectric strength and leakage current . . 59
19 Construction .63
20 Components . . 7 0
21 Internal wiring .76
22 Supply connection and other external flexible cables or cords.76
23 Terminals for external conductors .82
24 Provisions for protective earthing .84
25 Screws and connections .85
26 Creepage distances, clearances and distances through insulation .88
27 Resistance to heat, fire and tracking .97
28 Resistance to rusting . 1 0 1
Annex A (normative) Measurement of creepage distances and clearances. 1 0 9
Annex B (normative) Testing a series of transformers.113
Annex C (normative) Creepage distances (cr), clearances (cl) and distances through
insulation (dti) Material group II (400 ≤CTI <600) .115
Annex D (normative) Creepage distances (cr), clearances (cl) and distances through
insulation (dti) Material group I (CTI ≥600) .118
Annex E (normative) Glow-wire test.121
Annex F (normative) Requirements for manually operated switches which are parts of
transformers assembly.122

61558-1 © IEC:200561558-1 ¤ IEC:2005 – 5 – – 3 –
Annex G (normative) Tracking test .125
Annex H (normative) Electronic circuits .126
Annex I (void). 1 3 0
Annex J (normative) Measuring network for touch-currents.131
Annex K (normative) Insulated winding wires for use as multiple layer insulation. 1 3 2
Annex L (normative) Routine tests (production tests) .134
Annex M (informative) Examples to be used as a guide for 19.1 .136
Annex N (informative) Examples of points of application of test voltages.139
Annex O (void) .141
Annex P (informative) Examples of points of measurement of creepage distances and
clearances .142
Annex Q (informative) Explanation of IP numbers for degrees of protection .144
Annex R (normative) Explanations of the application of 4.1.1.2.1 of IEC 60664-1 (see
26.2) .146
Annex S (void) .147
Annex T (void) .148
Annex U (informative) Optional t –marking of transformers.149
w
Annex V (informative) Symbols to be used for thermal cut-outs.158
Annex W (normative) Coated printed circuit boards .159
Bibliography .160
Index of defined terms.161
Figure 0 – IEC 61558 principle .9
Figure 1 – Mounting box for flush-type transformer (see 5.10) . 1 0 2
Figure 2 – Standard test finger (see 9.1.2, 15.5.2 and IEC 61032, test probe B).103
Figure 3 – Test pin (see 9.2 and IEC 61032, test probe 13) .104
Figure 4 – Abrasion resistance test for insulating coated layers . 1 0 4
Figure 5 – Ball-pressure apparatus (see 27.1) .105
Figure 6 – Test arrangement for checking mechanical withstanding of insulating
materials in thin sheet layers (see 26.3) .106
Figure 7 – Flexing test apparatus (see 22.9.4) .107
Figure 8 – Test configuration: single-phase equipment on star TN or TT system .108
Figure H.1 – Example of an electronic circuit with low-power points (see H.2.2) . 1 2 9
Figure J.1 – Measuring network for touch-current . 1 3 1
Figure U.1 – Relation between winding temperature and endurance test duration.156
Figure U.2 – Assessment of claimed value of S .157

61558-1 ¤ IEC:2005 – 7 – – 4 – 61558-1 © IEC:2005
Table 1 – Values of maximum temperatures in normal use .45
Table 2 – Test temperature and testing time (in days) per cycle.47
Table 3 – Maximum values of temperatures under short-circuit or overload conditions .49
Table 4 – Values of T and k for fuses .50
Table 5 – Pull force on pins . . 5 4
Table 6 – Solid-object-proof transformer test . . 5 6
Table 7 – Values of insulation resistance.59
Table 8a – Table of dielectric strength test voltages .60
Table 8b – Limits for currents.63
Table 9 – Nominal cross-sectional areas of external flexible cables or cords.78
Table 10 – Pull and torque to be applied to external flexible cables or cords fixed to
stationary and portable transformers .81
Table 11 – Torque to be applied to screws and connections. . 8 6
Table 12 – Torque test on glands .88
Table 13 – Creepage distances (cr), clearances (cl) and distances through insulation
(dti) – Material group IIIa (175 ≤ CTI < 400) .94
Table C.1 – Creepage distances (cr), clearances (cl) and distances through insulation
(dti) – Material group II (400 ≤CTI <600) . 1 1 5
Table D.1 – Creepage distances (cr), clearances (cl) and distances through insulation
(dti) – Material group I (CTI ≥600).118
Table F.1 – Peak surge current of the additional load .123
Table Q.1 – Degrees of protection indicated by the first characteristic numeral .144
Table Q.2 – Degrees of protection indicated by the second characteristic numeral .145
Table R.1 – Impulse test voltage according to 4.1.1.2.1 of IEC 60664-1 . 1 4 6
Table U.1 – Example of maximum temperatures of windings under short circuit or
overload conditions and at 110 % of rated voltage for transformers subjected to an
endurance test duration of 30 days and a life expectance of 10 years .151
Table U.2 –Theoretical test temperatures for transformers subjected to an endurance
test duration of 30 days and a life expectancy of 10 years. 1 5 3

61558-1 © IEC:2005 – 5 –
INTERNATIONAL ELECTROTECHNICAL COMMISSION
––––––––––
SAFETY OF POWER TRANSFORMERS, POWER SUPPLIES,
REACTORS AND SIMILAR PRODUCTS –

Part 1: General requirements and tests

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.È
4) In order to promote international uniformity, IEC National Committees undertake to apply IEC Publications
transparently to the maximum extent possible in their national and regional publications. Any divergence
between any IEC Publication and the corresponding national or regional publication shall be clearly indicated in
the latter.
5) IEC itself does not provide any attestation of conformity. Independent certification bodies provide conformity
assessment services and, in some areas, access to IEC marks of conformity. IEC is not responsible for any
services carried out by independent certification bodies.
6) All users should ensure that they have the latest edition of this publication.
7) No liability shall attach to IEC or its directors, employees, servants or agents including individual experts and
members of its technical committees and IEC National Committees for any personal injury, property damage or
other damage of any nature whatsoever, whether direct or indirect, or for costs (including legal fees) and
expenses arising out of the publication, use of, or reliance upon, this IEC Publication or any other IEC
Publications.
8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is
indispensable for the correct application of this publication.
9) Attention is drawn to the possibility that some of the elements of this IEC Publication may be the subject of
patent rights. IEC shall not be held responsible for identifying any or all such patent rights.
International Standard IEC 61558-1 has been prepared by IEC technical committee 96: Small
power transformers, reactors and power supply units and similar products
It has the status of a group safety publication in accordance with IEC Guide 104.
This second edition of IEC 61558-1 cancels and replaces the first edition (1997), amendment 1
(1998) and IS 01. This new edition represents a complete revision of the previous edition. The
changes were necessitated by the introduction of new technology and implementation of
requirements from equipment committees.

61558-1 ¤ IEC:2005 – 11 – – 6 – 61558-1 © IEC:2005
The text of this standard is based on the following documents:
FDIS Report on voting
96/224/FDIS 96/228/RVD
Full information on the voting for the approval of this standard can be found in the report on
voting indicated in the above table.
This publication has been drafted in accordance with the ISO/IEC Directives, Part 2.
This second edition of Part 1 is only to be used in conjunction with parts 2 based on this
edition. The parts 2 contain clauses to supplement or modify the corresponding clauses of this
Part 1 in order to provide the relevant requirements for each type of transformer.
However, individual countries may wish to consider its application, to the extent reasonable, to
transformers not mentioned in the parts 2, and to transformers designed on new principles.
NOTE Annex U contains the optional t system (marking, requirements and tests).
w
IEC 61558 consists of the following parts, under the general title Safety of power transformers,
1)
power supplies, reactors and similar products:
Part 1: General requirements and tests
Part 2-1: Particular requirements for separating transformers for general use
Part 2-2: Particular requirements for control transformers
Part 2-3: Particular requirements for ignition transformers for gas and oil burners
Part 2-4: Particular requirements for isolating transformers for general use
Part 2-5: Particular requirements for shaver transformers and shaver supply units
Part 2-6: Particular requirements for safety isolating transformers for general use
Part 2-7: Particular requirements for transformers for toys
Part 2-8: Particular requirements for bell and chime transformers
Part 2-9: Particular requirements for transformers for class III handlamps for tungsten
filament lamps
Part 2-12: Particular requirements for constant voltage transformers
Part 2-13: Particular requirements for auto-transformers for general use
Part 2-14: Particular requirements for variable transformers (in preparation)
Part 2-15: Particular requirements for isolating transformers for the supply of medical
locations
Part 2-16: Particular requirements for switch mode power supplies and transformers for
switch mode power supplies (in preparation)
___________
1)
Some of the parts of this series published earlier appeared under the general title Safety of power transformers,
power supply units and similar or Safety of power transformers, power supply units and similar devices. Future
editions of these parts will be issued under the new general title indicated above.

61558-1  IEC:2005 – 7 –
Part 2-17: Particular requirements for transformers for switch mode power supplies
Part 2-19: Particular requirements for perturbation attenuation transformers
Part 2-20: Particular requirements for small reactors
Part 2-23: Particular requirements for transformers for construction sites
Other parts are under consideration.
In this standard, 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 the standard, the words in bold are defined in Clause 3.
The committee has decided that the contents of this publication will remain unchanged until the
maintenance result date indicated on the IEC web site under "http://webstore.iec.ch" in the data
related to the specific publication. At this date, the publication will be
• reconfirmed;
• withdrawn;
• replaced by a revised edition, or
• amended.
The contents of the corrigenda of March 2008, March 2010 and April 2011 have been
included in this copy.
61558-1 ¤ IEC:2005 – 15 – – 8 – 61558-1 © IEC:2005
INTRODUCTION
This International Standard covers safety requirements for transformers. Where the term
transformer is used, it covers transformers, reactors and power supplies where applicable.
During the development of this standard, to the extent possible, the requirements of IEC 60364
were taken into consideration, so that a transformer may be installed in accordance with the
wiring rules contained in that standard. However, national wiring rules may differ.
This standard recognizes the internationally accepted levels of protection against the possible
electrical, mechanical, and fire hazards caused by transformers operating under normal
conditions in accordance with the manufacturer's instructions. It, also, covers abnormal
conditions which may occur in practice.
A transformer complying with this standard will not necessarily be judged to comply with the
safety principles of this standard if when examined and tested, it is found to have other
features that impair the level of safety covered by these requirements.
A transformer employing materials or having forms of construction differing from those
detailed in this standard may be examined and tested according to the intent of the
requirements, and if found to be substantially equivalent, may be judged to comply with the
safety principles of this standard.
The standard dealing with non-safety aspects of electromagnetic compatibility (EMC) of
transformers is IEC 62041: Power transformers, power supply units, reactors and similar
products – EMC requirements. However, that standard also includes tests which may subject
the transformer to conditions involving the safety aspects.
The objective of Part 1 of IEC 61558 is to provide a set of requirements and tests considered
to be generally applicable to most types of transformers, and which can be called up as
required by the relevant part 2 of IEC 61558. Part 1 is thus not to be regarded as a
specification by itself for any type of transformer, and its provisions apply only to particular
types of transformers to the extent determined by the appropriate part 2. Part 1 of IEC 61558
also contains normative routine tests.
Each part 2 in conjunction with Part 1 contains all the necessary requirements for the
transformer being covered and does not contain references to other parts 2. For
transformers with a protection index IP00 and associated transformers, it is possible to have
circuits corresponding to different parts 2 within the same construction (e.g. SELV output
circuit according to Part 2-6 and 230 V output circuit according to Part 2-4). However, if the
transformer is covered by different parts 2 of IEC 61558, to the extent reasonable, the
relevant part 2 is applied to each function/application separately. If applicable, the effect of one
function on the other is taken into consideration.
If, an appropriate part 2 for a particular transformer or group of transformers does not exist,
the nearest applicable part 2 may be used as a guide to the requirements and tests.
Where the requirements of any of the clauses of a part 2 refer to Part 1 by the phrase "This
clause of Part 1 is applicable", this phrase means all the requirements of that clause of Part 1
are applicable, except those requirements that are, clearly, not applicable to the particular type
of transformer covered by that part 2.
The principle for preparation of the different parts 2 is as follows:

61558-1 ¤ IEC:2005                   – 17 –
61558-1 © IEC:2005 – 9 –
IEC  1269/05
Figure 0 – IEC 61558 principle

61558-1 ¤ IEC:2005 – 19 – – 10 – 61558-1 © IEC:2005
Relevant clauses of this standard (e.g. clauses dealing with thermal endurance test for
windings) apply also to transformers forming an integral part of an appliance and which cannot
be tested separately.
As an option, the thermal characteristics of transformers can be specified by the rated
maximum operating temperature of the winding (symbol t ) which shall not be exceeded to
w
ensure a minimum lifetime as specified in Annex U. In addition, for transformers subjected to
abnormal conditions as specified in Clause 15, the specified temperature limit shall not be
exceeded when the transformer is built into an appliance or used as an independent
transformer.
61558-1 © IEC:200561558-1 ¤ IEC:2005 – 21 – – 11 –
SAFETY OF POWER TRANSFORMERS, POWER SUPPLIES,
REACTORS AND SIMILAR PRODUCTS –
Part 1: General requirements and tests
1 Scope
This International Standard deals with safety aspects of power transformers, power supplies,
reactors and similar products such as electrical, thermal and mechanical safety.
This standard covers the following types of dry-type transformers, power supplies, including
switch mode power supplies, and reactors, the windings of which may be encapsulated or
non-encapsulated :
NOTE 1 The distinction between transformers, power supplies and switch mode power supplies is as follows:
– for transformers, there is no change in frequency .However, transformers (e.g. constant voltage
transformers) may have an internal resonance frequency not exceeding 30 kHz;
– for power supplies, the internal operational frequency and waveform are different from the supply frequency
and waveform, and the internal operational frequency does not exceed 500 Hz (see definition 3.1.19);
– for switch mode power supplies, the internal operational frequency and waveform are different from the
supply frequency and waveform and the internal operational frequency exceeds 500 Hz and does not exceed
100 MHz.
The relevant parts 2 may be found in the introduction of this standard.
a) Stationary or portable, single-phase or poly-phase, air-cooled (natural or forced), isolating
and safety isolating transformers, independent or associated, not forming a part of
distribution networks and with the following characteristics:
– rated supply voltage not exceeding 1 000 V a.c.;
– rated supply frequency not exceeding 500 Hz;
and complying with the following values, unless otherwise specified in the relevant part 2:
• for isolating transformers:
– rated output for single phase transformers, not exceeding 25 kVA, and for poly-
phase transformers not exceeding 40 kVA.
– no-load output voltage and the rated output voltage exceeding 50 V a.c., and not
exceeding 500 V a.c, or 1 000 V a.c. to be in accordance with the National Wiring
Rules or for a special application.
• for safety isolating transformers:
– rated output for single phase transformers not exceeding 10 kVA, and for poly-
phase transformers not exceeding 16 kVA.
– no-load output voltage and the rated output voltage not exceeding 50 V a.c.
between conductors, or between any conductor and protective earth.
NOTE 1 Isolating and safety isolating transformers are used where double or reinforced insulation between
circuits is required by the installation rules or by the appliance specification (for example toys, bells, portable tools,
handlamps).
61558-1 ¤ IEC:2005 – 23 – – 12 – 61558-1 © IEC:2005
b) Stationary or portable, single-phase or polyphase, air-cooled (natural or forced)
separating transformers, auto-transformers, variable transformers and small reactors,
independent or associated, not forming a part of distribution networks and with the
following characteristics:
– rated supply voltage not exceeding 1 000 V a.c.;
– rated supply frequency not exceeding 500 Hz;
and complying with the following values, unless otherwise specified in the relevant part 2:
– no-load output voltage or a rated output voltage for both independent and associated
transformers not exceeding 15 kV a.c., and for independent transformers, a rated
output voltage not less than 50 V a.c.;
– rated output not exceeding the following values:
– 1 kVA for single-phase transformers;
– 2 kVAR for single-phase reactors;
– 5 kVA for poly-phase transformers;
– 10 kVAR for poly-phase reactors.
NOTE 2 Separating transformers are used where double or reinforced insulation between circuits is not
required by the installation rules or by the appliance specification.
NOTE 3 Normally, the transformers of type b) are intended to be associated with the equipment to provide
voltages different from the supply voltage for the functional requirements of the equipment. The protection against
electric shock may be provided or completed by other features of the equipment, such as the body. Parts of output
circuits may be connected to the input circuit or to the protective earth.
c) Stationary or portable, single-phase or polyphase, air-cooled (natural or forced),
independent or associated power supplies and switch mode power supplies
incorporating one or more transformer(s) of type a) or b), not forming a part of distribution
networks and with the following characteristics:
– rated supply voltage not exceeding 1 000 V a.c.;
– rated supply frequency not exceeding 500 Hz;
– internal operational frequency for power supplies not exceeding 500 Hz and for switch
mode power supplies not exceeding 100 MHz;
and with the following values, unless otherwise specified in the relevant part 2:
• for power supplies and switch mode power supplies incorporating isolating
transformers:
– rated output for single- phase or polyphase power supplies or switch mode
power supplies not exceeding 1 kVA;
– no-load output voltage and the rated output voltage exceeding 50 V a.c. or
120 V ripple- free d.c., and not exceeding 500 V a.c. or 708 V ripple- free d.c., or
1 000 V a.c. or 1 415 V ripple- free d.c. to be in accordance with national wiring rules or
for a special application;
• for power supplies and switch mode power supplies incorporating safety isolating
transformers:
– rated output for single- phase or polyphase power supplies and switch mode
power supplies not exceeding 1 kVA;
– no-load output voltage and rated output voltage not exceeding 50 V a.c.or 120 V
ripple- free d.c. between conductors, or between any conductor and protective earth.

61558-1 © IEC:200561558-1 ¤ IEC:2005 – 25 – – 13 –
NOTE 4 Power supplies and switch mode power supplies incorporating Isolating and safety
isolating transformers are used where double or reinforced insulation between circuits is required by
the installation rules or by the appliance specification (for example toys, bells, portable tools, handlamps).
• for power supplies and switch mode power supplies incorporating separating
transformers, auto-transformers , and variable transformers:
– rated output for single-phase or polyphase power supplies and switch mode
power supplies not exceeding 1 kVA;
– no-load output voltage and rated output voltage for both, independent and
associated transformers not exceeding 15 kV a.c., and for independent
transformers, a rated output voltage not less than 50 V a.c.;
NOTE 5 Power supplies and switch mode power supplies incorporating separating transformers are
used where double or reinforced insulation between circuits is not required by the installation rules or by
the appliance specification.
d) This standard is also applicable to t -marked transformers with a rated output not
w
exceeding 1 000 VA and where the t -temperature does not exceed 140 °C (t 140).
w w
However, t -marking of transformers is optional.
w
This standard also applies to transformers, power supplies, switch mode power supplies,
and reactors incorporating electronic circuits.
This standard does not apply to external circuits and their components intended to be
connected to the input and output terminals or socket-outlets of the transformers, power
supplies and switch mode power supplies, and reactors.
NOTE 6 Attention is drawn to the following:
– for transformers 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 like
fungus, vermin , termites, solar-radiation, and icing should also be considered;
– the different conditions for transportation, storage, and operation of the transformers should also be
considered;
– additional requirements in accordance with other appropriate standards and national rules may be applicable to
transformers intended for use in special environments, such as tropical environment
NOTE 7 Future technological development of transformers may necessitate a need to increase the upper limit of
the frequencies; until then this standard may be used as a guidance document.
2 Normative references
The following referenced documents are indispensable for the application of this document. For
dated references, only the edition cited applies. For undated references, the latest edition of
the referenced document (including any amendments) applies.
IEC 60065:2001, Safety requirements for mains operated electronic and related apparatus for
household and similar general use
IEC 60068-2-2:1974, Environmental testing – Part 2: Tests – Test B: Dry heat
IEC 60068-2-6, Environmental testing – Part 2: Tests – Test FC: Vibration (sinusoidal)
IEC 60068-2-32, Environmental testing – Part 2: Tests – Test Ed: Free fall

61558-1 ¤ IEC:2005 – 27 – – 14 – 61558-1 © IEC:2005
IEC 60068-2-75, Environmental testing – Part 2: Tests – Test Eh: Hammer tests
IEC 60076-1, Power transformers – Part 1: General
IEC 60083, Plugs and socket-outlets for domestic and similar general use standardized in
member countries of IEC
IEC 60085:1984, Thermal evaluation and classification of electrical insulation
IEC 60112:2003, Method for the determination of the proof and the comparative tracking
indices of solid insulating materials
IEC 60127-3, Miniature fuses – Part 3: Sub-miniature fuse-links
IEC 60216 (all parts), Electrical insulating materials – Properties of thermal endurance
IEC 60227 (all parts), Polyvinyl chloride insulated cables of rated voltages up to and including
450/750 V
IEC 60245 (all parts), Rubber insulated cables – Rated voltages up to and including 450/750 V
IEC 60269 (all parts), Low voltage fuses
IEC 60269-2, Low voltage fuses – Part 2: Supplementary requirements for fuses for use by
authorized persons (fuses mainly for industrial application)
IEC 60269-2-1, Low voltage fuses – Part 2: Supplementary requirements for fuses for use by
authorized persons (fuses mainly for industrial application) – Sections I to VI: Examples of
types of standardized fuses
IEC 60269-3, Low voltage fuses – Part 3: Supplementary requirements for fuses for use by
unskilled persons (fuses mainly for household and similar applications)
IEC 60269-3-1, Low voltage fuses – Part 3: Supplementary requirements for fuses for use by
unskilled persons (fuses mainly for household and similar applications) – Sections I to IV:
examples of types of standardized fuses
IEC 60309 (all parts), Plugs, socket-outlets and couplers for industrial purposes
IEC 60317 (all parts), Specifications for particular types of windings wires
IEC 60320 (all parts), Appliance couplers for household and similar general purposes
IEC 60320-2-3, Appliance couplers for household and similar general purposes – Part 2-3:
Appliance couplers with a degree of protection higher than IPX0
IEC 60384-14, Fixed capacitors for use in electronic equipment – Part 14: Sectional
specification: Fixed capacitors for electromagnetic interference suppression and connection to
the supply mains
2)
, Graphical symbols for use on equipment
IEC 60417-DB:2002
IEC 60449:1973, Voltage bands for electrical installations of buildings
___________
2)
”DB” refers to the IEC on-line database.

61558-1 © IEC:200561558-1 ¤ IEC:2005 – 29 – – 15 –
IEC 60454 (all parts), Specification for pressure-sensitive adhesive tapes for electrical
purposes
IEC 60529:1989, Degrees of protection provided by enclosures (IP Code)
IEC 60664-1:1992, Insulation co-ordination for equipment within low voltage systems – Part 1:
Principles, requirements and tests
IEC 60664-3:2003, Insulation co-ordination for equipment within low voltage systems – Part 3:
Use of coating, potting or moulding for protection against pollution
IEC 60691:2002, Thermal-links – Requirements and application guide
IEC 60695-2-10, Fire hazard testing – Part 2-10: Glowing/hot-wire based test methods – Glow-
wire apparatus and common test procedure
IEC 60695-2-11:2000, Fire hazard testing – Part 2-11: Glowing/hot-wire based test methods-
Glow-wire flammability test method for end-products
IEC 60695-10-2, Fire hazard testing – Part 10-2: Abnormal heat – Ball pressure test
IEC 60730 (all parts), Automatic electrical controls for household and similar use
IEC 60730-1:1999, Automatic electrical controls for household and similar use – Part 1:
General requirements
IEC 60851-3:1996, Winding wires – Test methods: Part 3: Mechanical properties
IEC 60851-5:1996, Winding wires – Test methods: Part 5: Electrical properties
IEC 60851-6:1996, Winding wires – Test methods: Part 5: Thermal properties
IEC 60884-1:2002, Plugs and socket-outlets for household and similar purposes – Part 1:
General requirements
IEC 60884-2-4, Plugs and socket-outlets for household and similar purposes – Part 2:
Particular requirements for plugs and socket-outlets for SELV
IEC 60898 (all parts), Electrical accessories – Circuit-breakers for overcurrent protection for
household and similar installations )
IEC 60906-1, IEC System of plugs and socket-outlets for household and similar purposes –
Part 1: Plugs and socket-outlets 16 A 250 V a.c.
IEC 60906-3, IEC System of plugs and socket-outlets for household and similar purposes –
Part 3: SELV plugs and socket-outlets, 16 A 6 V, 12 V, 24 V, 48 V, a.c. and d.c.
IEC 60947-7-1, Low-voltage switchgear and controlgear – Part 7: Ancillary equipment –
Section 1: Terminal blocks for copper conductors
IEC 60990:1990, Methods of measurement of touch current and protective conductor current
___________
3)
IEC 60898-2 is published under the general title Circuit-breakers for overcurrent protection for household and
similar installations (i.e. without the element of “Electrical accessories” in the title).

61558-1 ¤ IEC:2005 – 31 – – 16 – 61558-1 © IEC:2005
IEC 60998-2-1, Connecting devices for low voltage circuits for household and similar purposes –
Part 2-1: Particular requirements for connecting devices as separate entities with screw-type
clamping units
IEC 60998-2-2, Connecting devices for low voltage circuits for household and similar purposes –
Part 2-2: Particular requirements for connecting devices as separate entities with screwless-
type clamping units
IEC 60999-1, Connecting devices – Safety requirements for screw-type and screwless-type
clamping units for electrical copper con
...