IEC 61558-2-7:2023

IEC 61558-2-7 EXV ®
Edition 3.0 2023-06
EXTENDED VERSION
INTERNATIONAL
STANDARD
colour
inside
This extended version of IEC 61558-2-7:2023 includes the content of the references made to
IEC 61558-1:2017
GROUP SAFETY PUBLICATION
Safety of transformers, reactors, power supply units and combinations thereof –
Part 2-7: Particular requirements and tests for transformers and power supply
units for toys
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized in any form
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IEC 61558-2-7 EXV ®
Edition 3.0 2023-06
EXTENDED VERSION
INTERNATIONAL
STANDARD
colour
inside
This extended version of IEC 61558-2-7:2023 includes the content of the references made to
IEC 61558-1:2017
GROUP SAFETY PUBLICATION
Safety of transformers, reactors, power supply units and combinations thereof –
Part 2-7: Particular requirements and tests for transformers and power supply
units for toys
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 29.180 ISBN 978-2-8322-7168-1
– 2 – IEC 61558-2-7:2023 EXV  IEC 2023

CONTENTS
FOREWORD . 9
INTRODUCTION TO IEC 61558-1:2017 . 12
INTRODUCTION . 15
1 Scope . 16
2 Normative references . 17
3 Terms and definitions . 20
3.1 Transformers . 20
3.2 General terms . 24
3.3 Operations and protections . 25
3.4 Circuits and windings . 27
3.5 Ratings . 28
3.6 No-load values . 30
3.7 Insulation . 30
3.8 Touch current and protective earthing conductor current . 34
4 General requirements . 34
5 General notes on tests . 34
6 Ratings . 37
7 Classification . 37
8 Marking and other information . 38
9 Protection against electric shock . 44
9.1 General . 44
9.2 Protection against contact with hazardous-live-parts . 45
9.2.1 Determination of hazardous-live-parts . 45
9.2.2 Accessibility to hazardous-live-parts . 45
9.2.3 Accessibility to non hazardous-live-part . 48
9.3 Protection against hazardous electrical discharge . 48
10 Change of input voltage setting . 49
11 Output voltage and output current under load . 49
12 No-load output voltage . 50
13 Short-circuit voltage . 51
14 Heating . 51
14.1 General requirements . 51
14.1.1 Temperature-rise test . 51
14.1.2 Alternative temperature-rise test . 53
14.1.3 Determination of steady-state conditions . 56
14.2 Application of 14.1 or 14.3 according to the insulation system. 58
14.3 Accelerated ageing test for undeclared class of insulation system . 59
14.3.1 General . 59
14.3.2 Heat run . 59
14.3.3 Vibration . 59
14.3.4 Moisture treatment . 60
14.3.5 Measurements . 60
15 Short circuit and overload protection. 60
15.1 General requirements . 60
15.1.1 Short circuit and overload test method . 60

15.1.2 Alternative short circuit and overload test method . 62
15.2 Inherently short-circuit proof transformers . 62
15.3 Non-inherently short-circuit proof transformers. 62
15.4 Non-short-circuit proof transformers . 64
15.5 Fail-safe transformers . 64
16 Mechanical strength . 65
16.1 General . 65
16.2 Stationary transformers . 66
16.3 Portable transformers (except portable transformers with integral pins for
introduction in socket-outlet in the fixed wiring) . 66
16.4 Portable transformers provided with integral pins for introduction in socket-
outlets of the fixed wiring . 66
16.4.1 General requirements . 66
16.4.2 Portable transformers provided with integral pins according to EN
50075 (IEC plug type C) for introduction in socket-outlets of the fixed
wiring . 67
16.5 Additional requirements for transformers to be used in vehicles and railway
applications . 68
16.5.1 Transformers to be used in vehicles and railway applications . 68
16.5.2 Test requirements for the transportation of transformers . 69
17 Protection against harmful ingress of dust, solid objects and moisture . 71
17.1 Degrees of protection provided by enclosures (IP code) . 71
17.1.1 General requirements . 71
17.1.2 Tests on transformers with enclosure . 72
17.2 Humidity treatment . 74
18 Insulation resistance, dielectric strength and leakage current . 75
18.1 General . 75
18.2 Insulation resistance . 75
18.3 Dielectric strength test . 75
18.4 Insulation between and within windings . 77
18.5 Touch current and protective earthing conductor current . 77
18.5.1 General . 77
18.5.2 Touch current . 78
18.5.3 Protective earthing conductor current . 79
19 Construction . 80
19.1 General construction . 80
19.2 Flammability of materials . 80
19.3 Short-circuit characteristics of portable transformers . 80
19.4 Class II transformer contact prevention of accessible conductive parts . 80
19.5 Class II transformer insulation reassembling after service . 81
19.6 Loosening of wires, screws or similar parts . 81
19.7 Resistor or capacitor connection with accessible conductive parts . 81
19.8 Bridging of separated conductive parts by resistors or capacitors . 82
19.9 Insulating material separating input and output windings . 82
19.10 Accidental contact protection against hazardous-live-parts provided by
isolating coating . 83
19.11 Insulating material of handles, operating levers, knobs and similar parts. 84
19.12 Winding construction . 84
19.13 Fixing of handles, operating levers and similar parts . 88
19.14 Fixing of covers providing protection against electric shock . 88

– 4 – IEC 61558-2-7:2023 EXV  IEC 2023

19.15 Strain on fixed socket-outlets caused by pin-transformers connection . 88
19.16 Portable transformers for use in irregular or harsh conditions . 88
19.17 Drain hole of transformers protected against ingress of water . 88
19.18 Plug connected transformers protected against ingress of water . 88
19.19 Flexible cable or flexible cord connection for class I portable transformers . 88
19.20 SELV- and PELV-circuit separation of live parts . 89
19.21 Protection against contact for FELV-circuit. 89
19.22 Protective earthing regarding class II transformers . 90
19.23 Protective earthing regarding class III transformers . 90
20 Components . 91
21 Internal wiring . 97
22 Supply connection and other external flexible cables or cords . 97
23 Terminals for external conductors . 104
24 Provisions for protective earthing. 106
25 Screws and connections . 106
26 Creepage distances, clearances and distances through insulation . 109
26.1 General . 109
26.2 Creepage distances and clearances . 109
26.2.1 General . 109
26.2.2 Windings covered with adhesive tape . 109
26.2.3 Uncemented insulationing parts . 109
26.2.4 Cemented insulating parts . 110
26.2.5 Enclosed parts (e.g. by impregnation or potting) . 110
26.3 Distance through insulation . 112
27 Resistance to heat, fire and tracking . 122
27.1 General . 122
27.2 Resistance to heat . 122
27.2.1 General . 122
27.2.2 External accessible parts . 122
27.2.3 Internal parts . 123
27.3 Resistance to abnormal heat under fault conditions . 123
27.4 Resistance to fire . 124
27.4.1 General . 124
27.4.2 External accessible parts . 125
27.4.3 Internal parts . 125
27.5 Resistance to tracking . 126
28 Resistance to rusting . 126
Annex A (normative) Measurement of creepage distances and clearances. 127
Annex B (normative) Testing a series of transformers . 131
B.1 General . 131
B.2 Requirements . 131
B.3 Constructional inspection . 132
Annex C (void) . 133
Annex D (void) . 134
Annex E (normative) Glow-wire test . 135
E.1 General . 135
E.2 Severity . 135

E.3 Conditioning . 135
E.4 Test procedure . 135
Annex F (normative) Requirements for manually operated switches which are parts of
transformers assembly . 136
F.1 General . 136
F.2 Switches tested as a separate component . 136
F.3 Switches tested as part of the transformer . 136
Annex G (normative) Tracking test . 139
G.1 General . 139
G.2 Test specimen . 139
G.3 Test apparatus . 139
G.4 Procedure . 139
Annex H (normative) Electronic circuits . 140
H.1 General . 140
H.2 General notes on tests (addition to Clause 5). 140
H.3 Short circuit and overload protection (addition to Clause 15) . 140
H.4 Creepage distances, clearances and distances through insulation (addition
to Clause 26) . 142
Annex I (informative) Dimensions for rectangular cross-section connectors of
transformers, basic dimensions and coordination . 144
Annex J (normative) Measuring network for touch-currents . 147
Annex K (normative) Insulated winding wires . 148
K.1 General . 148
K.2 Type tests . 148
K.2.1 General . 148
K.2.2 Dielectric strength test . 148
K.2.3 Flexibility and adherence . 148
K.2.4 Heat shock . 149
K.2.5 Retention of dielectric strength after bending . 149
K.3 Testing during manufacturing . 150
K.3.1 General . 150
K.3.2 Routine test . 150
K.3.3 Sampling test . 150
Annex L (normative) Routine tests (production tests) . 151
L.1 General . 151
L.2 Protective earthing continuity test . 151
L.3 Checking of no-load output voltage . 151
L.4 Dielectric strength test . 151
L.5 Checking of protective devices mounting . 152
L.6 Visual inspection . 152
L.7 Repetition test after routine dielectric strength test . 152
Annex M (informative) Examples to be used as a guide for 19.1 . 153
M.1 General . 153
M.2 Coil-former . 153
M.2.1 Concentric type . 153
M.2.2 Side-by-side type . 154
M.3 Windings . 154
M.3.1 Without screen . 154

– 6 – IEC 61558-2-7:2023 EXV  IEC 2023

M.3.2 With screen . 155
Annex N (informative) Examples for checking points of dielectric strength test voltages . 156
Annex O (void) . 158
Annex P (informative) Examples for measurement points of creepage distances and
clearances . 159
Annex Q (informative) Explanation of IP numbers for degrees of protection . 162
Q.1 General . 162
Q.2 Degrees of protection against access to hazardous parts and against solid
foreign objects . 162
Q.3 Degrees of protection against ingress of water . 164
Annex R (normative) Explanations of the application of 6.1.2.2.1 of IEC 60664-1:2007 . 165
R.1 Impulse dielectric test . 165
R.2 Example. 165
Annex S (void) . 167
Annex T (void) . 168
Annex U (void) . 169
Annex V (informative) Symbols to be used for thermal cut-outs . 170
V.1 General . 170
V.2 Non-self-resetting thermal cut-out (see 3.3.4) . 170
V.3 Self-resetting thermal cut-out (see 3.3.3) . 170
Annex W (normative) Coated printed circuit boards . 171
W.1 Preamble . 171
W.2 General . 171
W.3 Cold . 171
W.4 Rapid change of temperature . 171
W.5 Additional tests . 171
Bibliography . 172
Index of defined terms . 174

Figure 1 – IEC 61558 principle . 13
Figure 2 – Mounting box for flush-type transformer . 36
Figure 3 – Test pin (see IEC 61032, test probe 13) . 46
Figure 4 – Standard test finger (see IEC 61032, test probe B) . 47
Figure 101 – Small test finger . 48
Figure 5 – Example of back-to-back method – Single phase . 55
Figure 6 – Example of back-to-back method – Three phase . 56
Figure 102 – Arrangement for impact test for transformers (see 16.101) . 65
Figure 7 – Amplitude spectrum density for random testing . 69
Figure 8 – Normalised spectrum of shock . 70
Figure 9 – Test voltage sequence . 77
Figure 10 – Test configuration: single-phase equipment on star TN or TT system . 79
Figure 11 – Abrasion resistance test for insulating coated layers . 83
Figure 12 – Flexing test apparatus . 102
Figure 13 – Test arrangement for checking mechanical withstanding of insulating
materials in thin sheet layers . 114
Figure 14 – Ball-pressure apparatus . 122

Figure A.1 – Example 1. 127
Figure A.2 – Example 2. 128
Figure A.3 – Example 3. 128
Figure A.4 – Example 4. 128
Figure A.5 – Example 5. 129
Figure A.6 – Example 6. 129
Figure A.7 – Example 7. 130
Figure A.8 – Example 8. 130
Figure H.1 – Example of an electronic circuit with low-power points . 143
Figure J.1 – Measuring network for touch-current . 147
Figure M.1 – Examples for concentric type constructions . 153
Figure M.2 – Examples for side-by-side type constructions . 154
Figure M.3 – Examples for winding constructions without screen . 154
Figure M.4 – Examples for wrapped winding constructions . 155
Figure M.5 – Examples for winding constructions with screen . 155
Figure N.1 – Transformer of class I construction with metal enclosure . 156
Figure N.2 – Transformer of class II construction with metal enclosure . 157
Figure N.3 – Transformer of class II construction with enclosure of insulating material . 157
Figure P.1 – Transformer of class I construction . 159
Figure P.2 – Transformer of class I construction with earthed metal screen . 160
Figure P.3 – Transformer of class II construction with metal enclosure . 160
Figure P.4 – Transformer of class II construction with enclosure of insulating material . 161
Figure V.1 – Restored by manual operation . 170
Figure V.2 – Restored by disconnection of the supply . 170
Figure V.3 – Thermal link (see 3.3.5) . 170
Figure V.4 – Self-resetting thermal cut-out . 170

Table 1 – Symbols used on equipment or in instructions . 41
Table 101 – Symbols indicating the kind of transformer . 43
Table 2 – Values of maximum temperatures in normal use . 51
Table 2 – Values of maximum temperatures in normal use . 57
Table 3 – Explanation of the maximum winding temperatures required in Table 2 . 58
Table 4 – Test temperature and testing time (in days) per cycle . 59
Table 5 – Maximum values of temperatures under short-circuit or overload conditions . 61
Table 5 – Maximum values of temperatures under short-circuit or overload conditions . 62
Table 6 – Values of T and k for fuses . 63
Table 7 – Pull force on pins . 67
Table 8 – Conditions for vibration testing (random) . 68
Table 9 – Amplitude spectrum density ASD values for accelerated life testing . 68
Table 10 – Frequency values depending on the weight of the specimen . 69
Table 11 – Excitation values for vibration testing . 69
Table 12 – Solid-object-proof transformer test . 72
Table 13 – Values of insulation resistance . 75

– 8 – IEC 61558-2-7:2023 EXV  IEC 2023

Table 14 – Table of dielectric strength test voltages. 76
Table 15 – Limits for currents . 79
Table 16 – Nominal cross-sectional areas of external flexible cables or cords . 99
Table 17 – Pull and torque to be applied to external flexible cables or cords fixed to
stationary and portable transformers . 103
Table 18 – Torque to be applied to screws and connections . 107
Table 19 – Torque test on glands . 108
Table 20 – Clearances in mm . 115
Table 21 – Creepage distances in mm . 116
Table 22 – Distance through insulation in mm . 117
Table 23 – Creepage distances and clearance between terminals for external
connection . 118
Table 24 – Values of FIW wires with minimum overall diameter and minimum test
voltages according to the total enamel increase . 120
Table A.1 – Width of groove values depending on the pollution degree . 127
Table F.1 – Peak surge current of additional loads. 137
Table I.1 – Dimensions of rectangular copper connectors . 145
Table K.1 – Mandrel diameter . 149
Table K.2 – Oven temperature . 149
Table Q.1 – Degrees of protection against access to hazardous parts indicated by the
first characteristic numeral . 163
Table Q.2 – Degrees of protection against solid foreign objects indicated by the first
characteristic numeral . 163
Table Q.3 – Degrees of protection indicated by the second characteristic numeral . 164
Table R.1 – Impulse test voltage according to 6.1.2.2.1 of IEC 60664-1:2007 . 165

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

Part 2-7: Particular requirements and tests for
transformers and power supply units for toys

FOREWORD
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to IEC 61558-1:2017.
The specific content of IEC 61558-2-7:2023 is displayed on a blue background.

– 10 – IEC 61558-2-7:2023 EXV  IEC 2023

IEC 61558-2-7 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 2007. 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) new symbol for power supply unit with linearly regulated output voltage.
The text of this International Standard is based on the following documents:
Draft Report on voting
96/579/FDIS 96/581/RVD
Full information on the voting for its approval can be found in the report on voting indicated in
the above table.
The language used for the development of this International Standard is English.
This document was drafted in accordance with ISO/IEC Directives, Part 2, and developed in
accordance with ISO/IEC Directives, Part 1 and ISO/IEC Directives, IEC Supplement, available
at www.iec.ch/members_experts/refdocs. The main document types developed by IEC are
described in greater detail at www.iec.ch/publications.
It has the status of a group safety publication in accordance with IEC Guide 104.
This International Standard is to be used in conjunction with IEC 61558-1:2017.
This document supplements or modifies the correspon
...

IEC 61558-2-7 ®
Edition 3.0 2023-06
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
GROUP SAFETY PUBLICATION
PUBLICATION GROUPÉE DE SÉCURITÉ
Safety of transformers, reactors, power supply units and combinations thereof –
Part 2-7: Particular requirements and tests for transformers and power supply
units for toys
Sécurité des transformateurs, bobines d'inductance, blocs d'alimentation et des
combinaisons de ces éléments –
Partie 2-7: Exigences particulières et essais pour les transformateurs et blocs
d'alimentation pour jouets
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IEC 61558-2-7 ®
Edition 3.0 2023-06
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
GROUP SAFETY PUBLICATION
PUBLICATION GROUPÉE DE SÉCURITÉ

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

Part 2-7: Particular requirements and tests for transformers and power supply

units for toys
Sécurité des transformateurs, bobines d'inductance, blocs d'alimentation et des

combinaisons de ces éléments –

Partie 2-7: Exigences particulières et essais pour les transformateurs et blocs

d'alimentation pour jouets
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
INTERNATIONALE
ICS 29.180 ISBN 978-2-8322-7089-9

– 2 – IEC 61558-2-7:2023  IEC 2023
CONTENTS
FOREWORD . 3
INTRODUCTION . 5
1 Scope . 6
2 Normative references . 7
3 Terms and definitions . 7
4 General requirements . 8
5 General notes on tests . 8
6 Ratings . 8
7 Classification . 8
8 Marking and other information . 9
9 Protection against electric shock . 10
10 Change of input voltage setting . 11
11 Output voltage and output current under load . 11
12 No-load output voltage . 12
13 Short-circuit voltage . 12
14 Heating . 12
15 Short circuit and overload protection. 13
16 Mechanical strength . 14
17 Protection against harmful ingress of dust, solid objects and moisture . 15
18 Insulation resistance, dielectric strength and leakage current . 15
19 Construction . 15
20 Components . 17
21 Internal wiring . 18
22 Supply connection and other external flexible cable or cords . 18
23 Terminals for external conductors . 19
24 Provisions for protective earthing. 19
25 Screws and connections . 19
26 Creepage distances, clearances and distances through insulation . 19
27 Resistance to heat, fire and tracking . 19
28 Resistance to rusting . 19
Annexes . 20
Bibliography . 21

Figure 101 – Small test finger . 11
Figure 102 – Arrangement for impact test for transformers (see 16.101) . 14

Table 101 – Symbols indicating the kind of transformer . 10
Table 2 – Values of maximum temperatures in normal use . 13
Table 5 – Maximum values of temperatures under short-circuit or overload conditions . 13

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

Part 2-7: Particular requirements and tests for
transformers and power supply units for toys

FOREWORD
1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising
all national electrotechnical committees (IEC National Committees). The object of IEC is to promote international
co-operation on all questions concerning standardization in the electrical and electronic fields. To this end and
in addition to other activities, IEC publishes International Standards, Technical Specifications, Technical Reports,
Publicly Available Specifications (PAS) and Guides (hereafter referred to as “IEC Publication(s)”). Their
preparation is entrusted to technical committees; any IEC National Committee interested in the subject dealt with
may participate in this preparatory work. International, governmental and non-governmental organizations liaising
with the IEC also participate in this preparation. IEC collaborates closely with the International Organization for
Standardization (ISO) in accordance with conditions determined by agreement between the two organizations.
2) The formal decisions or agreements of IEC on technical matters express, as nearly as possible, an international
consensus of opinion on the relevant subjects since each technical committee has representation from all
interested IEC National Committees.
3) IEC Publications have the form of recommendations for international use and are accepted by IEC National
Committees in that sense. While all reasonable efforts are made to ensure that the technical content of IEC
Publications is accurate, IEC cannot be held responsible for the way in which they are used or for any
misinterpretation by any end user.
4) In order to promote international uniformity, IEC National Committees undertake to apply IEC Publications
transparently to the maximum extent possible in their national and regional publications. Any divergence between
any IEC Publication and the corresponding national or regional publication shall be clearly indicated in the latter.
5) IEC itself does not provide any attestation of conformity. Independent certification bodies provide conformity
assessment services and, in some areas, access to IEC marks of conformity. IEC is not responsible for any
services carried out by independent certification bodies.
6) All users should ensure that they have the latest edition of this publication.
7) No liability shall attach to IEC or its directors, employees, servants or agents including individual experts and
members of its technical committees and IEC National Committees for any personal injury, property damage or
other damage of any nature whatsoever, whether direct or indirect, or for costs (including legal fees) and
expenses arising out of the publication, use of, or reliance upon, this IEC Publication or any other IEC
Publications.
8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is
indispensable for the correct application of this publication.
9) Attention is drawn to the possibility that some of the elements of this IEC Publication may be the subject of patent
rights. IEC shall not be held responsible for identifying any or all such patent rights.
IEC 61558-2-7 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 2007. 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) new symbol for power supply unit with linearly regulated output voltage.

– 4 – IEC 61558-2-7:2023  IEC 2023
The text of this International Standard is based on the following documents:
Draft Report on voting
96/579/FDIS 96/581/RVD
Full information on the voting for its approval can be found in the report on voting indicated in
the above table.
The language used for the development of this International Standard is English.
This document was drafted in accordance with ISO/IEC Directives, Part 2, and developed in
accordance with ISO/IEC Directives, Part 1 and ISO/IEC Directives, IEC Supplement, available
at www.iec.ch/members_experts/refdocs. The main document types developed by IEC are
described in greater detail at www.iec.ch/publications.
It has the status of a group safety publication in accordance with IEC Guide 104.
This International Standard is to be used in conjunction with IEC 61558-1:2017.
This document supplements or modifies the corresponding clauses in IEC 61558-1:2017, so as
to convert that publication into the IEC standard: Particular requirements and tests for
transformers and power supply units for toys.
A list of all parts in the IEC 61558 series published under the general title Safety of
transformers, reactors, power supply units and combinations thereof, can be found on the
IEC website.
Future standards in this series will carry the new general title as cited above. Titles of existing
standards in this series will be updated at the time of the next edition.
Where this document states "addition", "modification" or "replacement", the relevant text of
IEC 61558-1:2017 is to be adopted accordingly.
In this document, the following print types are used:
• requirements proper: in roman type;
• test specifications: in italic type;
• explanatory matter: in smaller roman type:
In the text of this document, the words in bold are defined in Clause 3.
Subclauses, notes, figures and tables additional to those in IEC 61558-1:2017 are numbered
starting from 101; supplementary annexes are entitled AA, BB, etc.
The committee has decided that the contents of this document will remain unchanged until the
stability date indicated on the IEC website under webstore.iec.ch in the data related to the
specific document. At this date, the document will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
INTRODUCTION
IEC TC 96 has a group safety function in accordance with IEC Guide 104 for transformers other
than those intended to supply distribution networks, in particular transformers and power supply
units intended to allow the application of protective measures against electric shock as defined
by TC 64, but in certain cases including the limitation of voltage and horizontal safety function
for SELV, in accordance with IEC 60364-4-41.
The group safety function (GSF) is used because of responsibility for safety extra-low voltage
(SELV) in accordance with IEC 61140:2016, 5.2.6 and IEC 60364-4-41:2005, 414.3.1 or control
circuits in accordance with IEC 60204-1:2016, 7.2.4.
The group safety function is used for each part of IEC 61558-2 because different standards of
the IEC 61558 series can be combined in one construction but in certain cases with no limitation
of rated output power.
For example, an auto-transformer in accordance with IEC 61558-2-13 can be designed with a
separate SELV-circuit in accordance with the particular requirements for IEC 61558-2-6 relating
to the general requirements of IEC 61558-1.

– 6 – IEC 61558-2-7:2023  IEC 2023
SAFETY OF TRANSFORMERS, REACTORS,
POWER SUPPLY UNITS AND COMBINATIONS THEREOF –

Part 2-7: Particular requirements and tests for
transformers and power supply units for toys

1 Scope
Replacement:
This part of IEC 61558 deals with the safety of transformers for toys and power supply units
incorporating transformers for toys. Transformers for toys 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 transformers for
toys and power supply units incorporating transformers for toys.
This document is applicable to stationary and portable single-phase, air-cooled (natural or
forced) dry-type transformers. The windings can be encapsulated or non-encapsulated.
This document is applicable to independent transformers and transformers for specific use.
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 takes precedence.
The rated supply voltage does not exceed 250 V AC. The rated supply frequency and the
internal operating frequencies do not exceed 500 Hz.
The rated output does not exceed 200 VA and a rated output current does not exceed 10 A.
The no-load output voltage does not exceed 33 V AC or 46 V ripple-free DC, and the rated
output voltage does not exceed 24 V AC or 33 V ripple-free DC.
In general, this document does not take into consideration children playing with the
transformers.
This document is not applicable to external circuits and their components intended to be
connected to the input and output terminals or socket-outlets of the transformers.
Attention is drawn to the following if necessary:
• for transformers intended to be used in vehicles, on board ships, and aircraft, additional
requirements (from other applicable standards, national rules, etc.);
• measures to protect the enclosure and the components inside the enclosure against
external influences such as fungus, vermin, termites, solar-radiation, and icing;
• the different conditions for transportation, storage, and operation of the transformers;
• additional requirements in accordance with other appropriate standards and national rules
can be applicable to transformers intended for use in special environments;

• for transformers for toys intended to be used as a battery charger for use with children
additional requirements can apply.
Future technological development of transformers can necessitate a need to increase the
upper limit of the frequencies. Until then this document can be used as a guidance document.
This group safety publication focusing on safety guidance is primarily intended to be used as a
product safety standard for the products mentioned in the scope, but is also intended to be used
by technical committees in the preparation of publications for products similar to those
mentioned in the scope of this group safety publication, in accordance with the principles laid
down in IEC Guide 104 and lSO/lEC Guide 51.
One of the responsibilities of a technical committee is, wherever applicable, to make use of
basic safety publications and/or group safety publications in the preparation of its publications.
2 Normative references
This clause of IEC 61558-1:2017 is applicable except as follows:
Addition:
IEC TR 60083, Plugs and socket-outlets for domestic and similar general use standardized in
member countries of IEC
IEC 60227-1:2007, Polyvinyl chloride insulated cables of rated voltages up to and including
450/750 V – Part 1: General requirements
IEC 60245-1:2003, Rubber insulated cables – Rated voltages up to and including 450/750 V –
Part 1: General requirements
IEC 61558-1:2017, Safety of transformers, reactors, power supply units and combinations
thereof – Part 1: General requirements and tests
IEC 61558-2-16, Safety of transformers, reactors, power 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
3 Terms and definitions
For the purposes of this document, the terms and definitions given in IEC 61558-1:2017 apply,
except as follows:
ISO and IEC maintain terminological databases for use in standardization at the following
addresses:
• IEC Electropedia: available at https://www.electropedia.org/
• ISO Online browsing platform: available at http://www.iso.org/obp
Addition:
3.1.101
transformer for toys
independent safety isolating transformer designed to supply toys not fixed to, or
incorporated in, toys and having a rated output voltage not exceeding 24 V AC

– 8 – IEC 61558-2-7:2023  IEC 2023
3.1.102
power supply unit for toys
power supply unit incorporating a transformer for toys not fixed to, or incorporated in, toys
and having a rated output voltage not exceeding 24 V AC or 33 V ripple-free DC
4 General requirements
This clause of IEC 61558-1:2017 is applicable.
5 General notes on tests
This clause of IEC 61558-1:2017 is applicable.
6 Ratings
This clause of IEC 61558-1:2017 is applicable except as follows:
Addition:
6.101 The rated output voltage shall not exceed 24 V AC or 33 V ripple-free DC.
6.102 The rated output shall not exceed 200 VA.
6.103 The rated supply frequency shall not exceed 500 Hz.
6.104 There shall be only one rated supply voltage not exceeding 250 V AC.
6.105 The rated output current shall not exceed 10 A.
Compliance with the requirements of 6.101 to 6.105 is checked by inspection of the marking.
7 Classification
This clause of IEC 61558-1:2017 is applicable, except as follows:
7.1
Replacement:
According to their protection against electric shock:
− class II transformers.
7.2
Replacement:
According to short-circuit protection or protection against abnormal conditions:
• inherently short-circuit proof transformers;
• non-inherently short-circuit-proof transformers;
• fail-safe transformers.
7.4
Replacement:
According to their mobility:
• portable transformers;
• stationary transformers.
7.5
Replacement:
According to their duty type:
• continuous operation.
7.8
Replacement:
According to their transient overvoltage condition:
• overvoltage category II.
8 Marking and other information
This clause of IEC 61558-1:2017 is applicable, except as follows:
8.1
h)
Replacement of the content up to the first semi-colon by the following:
relevant graphical symbols shown in Table 101 that indicate the kind of transformer.
m)
Replacement:
transformers suitable for outdoor use shall be marked with the appropriate degree of protection
(IP code);
8.11
Addition:
The symbol for linear power supply units shall be used in conjunction with the symbol
indicating the kind of transformer.

– 10 – IEC 61558-2-7:2023  IEC 2023
Table 101 – Symbols indicating the kind of transformer
Symbol or graphical symbol Explanation or title Identification
Safety isolating tranformers for toys
(Inherently short-circuit proof transformers, non-
inherently short-circuit proof transformers or fail-
IEC 60417-5219:2006-12
safe transformers)
To indicate a fail-safe function, the letter F may be

used adjacent of the graphical symbol.
L
Power supply unit, linear IEC 60417-6210:2013-10

Addition:
8.101
The instructions for use shall include the following statement or equivalent:
Instructions to parents: ”Transformers and power supply units for toys are not intended to be
used as toys, and the use of these products by children shall be under the full supervision of
parents.”
8.102
The instructions for use of transformers using power supply cords with the degree of protection
IP65 shall include the following statement or equivalent:
Instructions to parents: ”This transformer or power supply unit for toys is not intended for
permanent outdoor usage and for instance rain conditions shall be avoided.”
9 Protection against electric shock
This clause of IEC 61558-1:2017 is applicable except as follows:
9.2.2 Accessibility to hazardous-live-parts
Modification:
The standard test finger of Figure 4 is replaced by the small test finger of Figure 101.
Addition:
It shall not be possible to gain access to live parts of the input circuit or to the metal parts
separated from live parts by basic insulation only, even after removal of the covers that can
be removed with the aid of a tool.

Dimensions in millimetres
where
Material is metal
Tolerances on dimensions are ±0,125 mm
Both joints shall permit movement in the same plane and the same direction through an angle of 90° with a 0° to 10°
tolerance
Figure 101 – Small test finger
10 Change of input voltage setting
This clause of IEC 61558-1:2017 is applicable, except as follows:
Replacement:
Transformers shall have only one rated supply voltage or one rated supply voltage range.
Compliance is checked by inspection.
11 Output voltage and output current under load
This clause of IEC 61558-1:2017 is applicable except as follows:
11.1
Modification:
When the transformer is connected to the rated supply voltage, at the rated supply
frequency and loaded with an impedance resulting in the rated output at the rated output
voltage and, for an AC rated power factor, the output voltage shall not differ from the rated
value by more than 10 % for AC or 15 % for DC.
This requirement is applicable to all the output windings and their tappings.

– 12 – IEC 61558-2-7:2023  IEC 2023
12 No-load output voltage
This clause of IEC 61558-1:2017 is applicable, except as follows:
Addition:
12.101 The no-load output voltage shall not exceed 33 V AC or 46 V ripple-free DC. For toy
transformers, this output voltage limitation applies even when output windings not intended
for interconnection are connected in series.
12.102 The difference between the no-load output voltage and the output voltage under load
shall not be excessive.
The ratio between the no-load output voltage measured in Clause 12 and the output voltage
under load measured during the test of Clause 11, expressed as a percentage of the latter
voltage, shall not exceed 10 % for AC or 15 % for DC.
The ratio is determined by Formula (1):
UU−
no-load load
×100 %
( ) (1)
U
load
where
U is the no-load output voltage, expressed in V;
no-load
U is the output voltage under load, expressed in V.
load
Compliance with the requirements of 12.101 and 12.102 is checked by measuring the no-load
output voltage at the ambient temperature when the transformer is connected to the rated
supply voltage at the rated supply frequency.
13 Short-circuit voltage
This clause of IEC 61558-1:2017 is not applicable.
14 Heating
This clause of IEC 61558-1:2017 is applicable, except as follows:
Modification:
Replace the requirements for external enclosures of Table 2 of stationary transformers by
the following:
Table 2 – Values of maximum temperatures in normal use
Temperature
Parts
°C
External enclosures (which can be touched with the small test finger of
Figure 101), handles and the like, if made of
− metal;
− other material. 71
External enclosures (which cannot be touched with the small test finger of
Figure 101). 85
15 Short circuit and overload protection
This clause of IEC 61558-1:2017 is applicable, except as follows:
15.1.1 Short circuit and overload test method
Addition:
Transformers shall be of either short-circuit-proof or fail-safe construction. Short-circuit-
proof transformers shall withstand overloads that can occur during normal use. They shall not
incorporate fuses.
If the short-circuit output current exceeds 20 A, a non-self-resetting overload protective device
shall be incorporated.
Non-self-resetting overload protective devices, if any, shall be incorporated in the input circuit.
Replace the requirements for external enclosures of Table 5 by the following:
Table 5 – Maximum values of temperatures
under short-circuit or overload conditions
Maximum temperature
Parts
°C
External enclosures (which can be touched with the small test finger of
Figure 101), if made of
− metal;
− other material. 71
Addition:
15.3.101 The transformer having a short-circuit output current exceeding 20 A shall be
connected to the rated supply voltage in the cold condition (i.e., as received and in the normal
room ambient), and each output circuit or winding shall be short-circuited, one at a time, while
the other windings or output circuits are open-circuited.
Only the output circuits with a short-circuit current exceeding 20 A shall be short-circuited in
the case of more than one output current.
The overload protective device shall operate within 1 s.

– 14 – IEC 61558-2-7:2023  IEC 2023
15.5.2 Modification of the first dash as follows:
– the temperature of any part of the enclosure of the fail-safe transformer that can be
touched with the small test finger of Figure 101 shall not exceed
• 58 °C if made of metal;
• 71 °C if made of other material.
16 Mechanical strength
This clause of IEC 61558-1:2017 is applicable, except as follows:
16.1 General
Replacement of the second paragraph as follows:
Compliance is checked by the test of 16.2 for stationary transformers and by the tests of 16.2,
16.3, 16.4, and 16.101, as appropriate, for portable transformers.
Dimensions in millimetres
Figure 102 – Arrangement for impact test for transformers (see 16.101)
Addition:
16.101 In addition, transformers are subjected to the following test:
The transformer is dropped against a steel bar mounted on a solid wall of brick, stone, concrete
or the like, as shown in Figure 102.
The bar is of 40 mm × 40 mm × 5 mm right-angle section with the corner rounded to a radius of
5 mm. It is mounted in contact with the wall, or, if necessary, in contact with a steel packing
block which is in contact with the wall.

The transformer is suspended by its flexible cable or cord so that it rests against the corner of
the bar, the point of suspension being 1 m above the bar. It is then drawn away from the bar in
a plane perpendicular to the wall until it has risen through a height of 400 mm.
The transformer is allowed to fall against the bar. For transformers shaped as a cube or
parallelogram, one blow is applied to each of the six sides of the transformer; for transformers
shaped differently, one blow is applied to each similarly exposed side.
The steel packing block is only necessary if the shape of the transformer is such that, without
it, the transformer does not hit the bar.
In addition, the transformer is allowed to fall freely from a height of 400 mm onto a steel plate,
at least 5 mm thick, placed on a flat concrete base.
The number of falls is 10 times with the transformer cable mounted as in normal use, and the
orientation of the transformer is different for each fall.
After the test, the transformer shall show no damage within the meaning of this document. In
particular, live parts shall not become accessible.
17 Protection against harmful ingress of dust, solid objects and moisture
This clause of IEC 61558-1:2017 is applicable.
18 Insulation resistance, dielectric strength and leakage current
This clause of IEC 61558-1:2017 is applicable, except as follows:
Addition:
18.101 The touch current shall in no operating condition exceed the values of Table 15.
NOTE Certain transformer types can have high initial touch current when first switched on, which does not
decrease rapidly in a low-load condition.
19 Construction
This clause of IEC 61558-1:2017 is applicable, except as follows:
19.1 General construction
Replacement:
The input and output circuits shall be electrically separated from each other and the
construction shall be such that there is no possibility of any connection between these circuits,
either directly or indirectly, via other metal parts, except by deliberate action.
Compliance is checked by inspection and measurements, taking Clause 18 and Clause 26 into
consideration.
19.1.101 The insulation between the input and output winding(s) shall consist of double
or reinforced insulation. In addition, the insulation between the input windings and the
body, and between the output windings and the body shall consist of double or reinforced
insulation.
– 16 – IEC 61558-2-7:2023  IEC 2023
19.1.102 For transformers with intermediate conductive parts (for example, the iron core),
not connected to the body and located between the input and output windings, the insulation
between the intermediate conductive part and the input windings or between the
intermediate conductive part and the output windings shall consist of at least basic
insulation.
NOTE An intermediate conductive part, not separated from the input or output windings or the body by at least
basic insulation, is considered to be connected to the relevant part(s).
In addition, the insulation between the input and output windings, via the intermediate
conductive part, shall consist of double or reinforced insulation; the insulation between the
input windings and the body, and between the output windings and the body, via the
intermediate conductive part, shall consist of double or reinforced insulation.
Addition:
19.101 Transformers shall comply with the requirements for degree of protection IP4X or
higher with the exception of output terminals.
Transformers for outdoor use shall have a degree of protection of IP65 / IP67 or higher.
Compliance is checked by the tests of Clause 17.
19.102 There shall be no connections between the output circuit and the protective earth.
19.103 There shall be no connections between the output circuit and the body.
Compliance is checked by inspection.
19.104 The input and output terminals for the connection of external wiring shall be so located
that the distance measured between the points of introduction of the conductors into these
terminals is not less than 25 mm. If a barrier is used to obtain this distance, the measurement
shall be made over and around the barrier and it shall be of insulating material and be
permanently fixed to the transformer.
Compliance is checked by inspection and by measurement disregarding intermediate
conductive parts.
19.105 Transformers shall be class II.
19.106 Transformers shall not be fixed to or incorporated in toys.
Compliance is checked by inspection.
19.107 Transformers with AC terminals in the output circuit shall be designed such that
when
– the output circuits of two or more transformers are connected together, and
– the input circuit of at least one of the transformers is connected to the mains supply, and
– the input circuit of at least one of the transformers is not connected to the mains supply,
the voltage across the bare pins of the plug of the transformers not connected to the mains
supply shall not exceed 33 V AC.
Compliance is checked by measurement of the voltage between the pins of the plug when the
output circuit is supplied by the rated output voltage(s).

20 Components
This clause of IEC 61558-1:2017 is applicable, except as follows:
20.5
Addition:
Transformers shall not be provided with switches connected to the flexible supply cables or
cords.
20.6
Addition:
Socket-outlets in the output circuit of the transformers and plugs accepted by those socket-
outlets shall not be interchangeable with plugs and socket outlets listed in IEC TR 60083. This
requirement is not applicable to socket-outlets with corresponding plugs which are too large to
be introduced into the mains socket outlets or that are too small so they can only be loosely
inserted and do not stay firmly in place in the socket outlet aperture while in contact with the
supply mains.
Socket-outlets for connectors such as jack types, USB types, RCA phono types with a diameter
or diagonal measurement between 3,75 mm and 5,25 mm and length greater than 7 mm are
considered to fail this requirement.
Compliance is checked by inspection.
20.8.1
Modification:
For non-self-resetting thermal cut-outs and non-self-resetting overload protective devices,
the number of cycles of operation is increased from 300 to 1 000.
Addition:
20.101 It shall be possible to reset the non-self-resetting thermal cut-outs and non-self-
resetting overload protective devices without removing their covers.
Compliance is checked by short-circuiting the output terminals and connecting the transformer
to the rated supply voltage until the device operates. If more than one set of output terminals
are provided, each set shall be tested separately.
It shall not be possible to maintain the thermal cut-out or the overload protective device in the
"ON" position by operating the resetting means.
After removal of the short circuit, it shall be possible to put the overload protective device in the
"ON" position without removing any covers. If necessary, after cooling.
20.102 Control devices, if any, shall be in the output circuit and shall operate reliably.
Compliance is checked by inspection and by the following test:

– 18 – IEC 61558-2-7:2023  IEC 2023
The control is operated 5 000 times. Each time from one extreme end of the range to the other
at a uniform rate of approximately 30 cycles per minute with the transformer connected to the
rated supply voltage and loaded with the rated output current at unity power factor.
During this test, no interruption of the current shall occur. After the test, the temperatures of
the transformer windings shall not exceed the values specified in 14.2, and the no-load input
current shall not alter by a short-circuit placed between the turns of the windings of the output
circuit.
20.103 The operating means of control devices, if any, shall not be affixed to the transformers
with the exception of transformers for toy railway applications.
NOTE In Denmark, the exception of 20.103 is not applicable.
21 Internal wiring
This clause of IEC 61558-1:2017 is applicable.
22 Supply connection and other external flexible cable or cords
This clause of IEC 61558-1:2017 is applicable, except as follows:
22.5
Modification:
Power supply cords of transformers complying with the requirements for degree of protection
IP4X or IP65 shall not be lighter than ordinary tough rubber sheathed cord (code designation
60245 IEC 53 of IEC 60245-1) or ordinary polyvinyl chloride sheathed flexible cord (code
designation 60227 IEC 53 of IEC 60227-1).
Power supply cords of transformers with the degree of protection of IP67 shall not be lighter
than ordinary polychloroprene sheathed cord (code designation 60245 IEC 57 of IEC 60245-1).
22.6
Replacement:
Appliance couplers are not allowed in the input circuits of transformers.
22.7
Modification:
For transformers having a mass greater than 500 g excluding the cable or cord, the cross-
sectional area of the supply cable or cord shall be at least 1 mm².
22.9
Modification:
Power supply cords can be connected to the transformers by type Y and type Z
attachments. Type X attachment is not allowed.

23 Terminals for external conductors
This clause of IEC 61558-1:2017 is applicable.
24 Provisions for protective earthing
This clause of IEC 61558-1:2017 is not applicable.
25 Screws and connections
This clause of IEC 61558-1:2017 is applicable.
26 Creepage distances, clearances and distances through insulation
This clause of IEC 61558-1:2017 is applicable.
27 Resistance to heat, fire and tracking
This clause of IEC 61558-1:2017 is applicable.
28 Resistance to rusting
This clause of IEC 61558-1:2017 is applicable.

– 20 – IEC 61558-2-7:2023  IEC 2023
Annexes
The annexes of IEC 61558-1:2017 are applicable.

Bibliography
The Bibliography of IEC 61558-1:2017 is applicable, except as follows:
Addition:
IEC 61558 (all parts), Safety of transformers, reactors, power supply units and combinations
thereof
IEC 61558-2-6, Safety of transformers, reactors, power supply units and combinations thereof
– Part 2-6: Particular requirements and tests for safety isolating transformers and power supply
units incorporating safety isolating transformers for general applications
IEC 61558-2-13, Safety of transformers, reactors, power supply units and combinations thereof
– Part 2-13: Particular requirements and tests for auto-transformers and power supply units
incorporating auto-transformers for general applications
IEC 60204-1:2016, Safety of machinery – Electrical equipment of machines – Part 1: Gene
...