IEC 61558-2-12:2024
(Main)Safety of transformers, reactors, power supply units and combinations thereof - Part 2-12: Particular requirements and tests for constant voltage transformers and power supply units for constant voltage
Safety of transformers, reactors, power supply units and combinations thereof - Part 2-12: Particular requirements and tests for constant voltage transformers and power supply units for constant voltage
IEC 61558-2-12:2024 deals with the safety of constant voltage transformers for general applications and power supply units for constant voltage for general applications. Constant voltage transformers incorporating electronic circuits are also covered by this document.
This third edition cancels and replaces the second edition published in 2011. This edition constitutes a technical revision.
This edition includes the following significant technical changes with respect to the previous edition:
a) adjustment of structure and references in accordance with IEC 61558-1:2017;
b) description of constructions moved to IEC 61558-1:2017;
c) new symbol for power supply unit with linearly regulated output voltage.
It has the status of a group safety publication in accordance with IEC Guide 104.
Sécurité des transformateurs, bobines d'inductance, blocs d'alimentation et des combinaisons de ces éléments - Partie 2-12: Exigences particulières et essais pour les transformateurs à tension constante et les blocs d'alimentation pour tension constante
L'IEC 61558-2-12:2024 traite de la sécurité des transformateurs à tension constante pour applications d'ordre général et des blocs d'alimentation pour tension constante pour applications d'ordre général. Les transformateurs à tension constante qui incorporent des circuits électroniques sont également couverts par le présent document.
Cette troisième édition annule et remplace la deuxième édition parue en 2011. Cette édition constitue une révision technique.
Cette édition inclut les modifications techniques majeures suivantes par rapport à l'édition précédente:
a) la structure et les références ont été alignées sur l’IEC 61558-1:2017;
b) la description des constructions a été déplacée dans l’IEC 61558-1:2017;
c) un nouveau symbole a été ajouté pour les blocs d'alimentation dont la régulation de la tension secondaire est linéaire.
Il a le statut de publication groupée de sécurité conformément au Guide 104 de l'IEC.
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IEC 61558-2-12 ®
Edition 3.0 2024-04
REDLINE VERSION
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GROUP ENERGY EFFICIENCY PUBLICATION
Safety of transformers, reactors, power supply units and combination thereof –
Part 2-12: Particular requirements and tests for constant voltage transformers
and power supply units for constant voltage
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IEC 61558-2-12 ®
Edition 3.0 2024-04
REDLINE VERSION
INTERNATIONAL
STANDARD
colour
inside
GROUP ENERGY EFFICIENCY PUBLICATION
Safety of transformers, reactors, power supply units and combination thereof –
Part 2-12: Particular requirements and tests for constant voltage transformers
and power supply units for constant voltage
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 29.180 ISBN 978-2-8322-8741-5
– 2 – IEC 61558-2-12:2024 RLV © IEC 2024
CONTENTS
FOREWORD . 3
INTRODUCTION . 2
1 Scope . 7
2 Normative references . 9
3 Terms and definitions . 9
4 General requirements . 9
5 General notes on tests . 10
6 Ratings . 10
7 Classification . 11
8 Marking and other information . 11
9 Protection against electric shock . 11
10 Change of input voltage setting . 13
11 Output voltage and output current under load . 13
12 No-load output voltage . 14
13 Short-circuit voltage . 15
14 Heating . 15
15 Short-circuit and overload protection . 15
16 Mechanical strength . 16
17 Protection against harmful ingress of dust, solid objects and moisture . 17
18 Insulation resistance, dielectric strength and leakage current . 17
19 Construction . 18
20 Components . 18
21 Internal wiring . 22
22 Supply connection and other external flexible cables or cords . 22
23 Terminals for external conductors . 22
24 Provisions for protective earthing. 22
25 Screws and connections . 22
26 Creepage distances, clearances and distances through insulation . 23
27 Resistance to heat, fire and tracking . 23
28 Resistance to rusting . 23
Annexes . 24
Annex C (normative) .
Annex D (normative) .
Annex L (normative) Routine tests (production test) . 24
Annex R (normative) .
Bibliography . 25
Table 101 – Symbols indicating the kind of transformer . 12
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
SAFETY OF TRANSFORMERS, REACTORS,
POWER SUPPLY UNITS AND COMBINATIONS THEREOF –
Part 2-12: Particular requirements and tests for constant voltage
transformers and power supply units for constant voltage
FOREWORD
1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising
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8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is
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9) IEC draws attention to the possibility that the implementation of this document may involve the use of (a)
patent(s). IEC takes no position concerning the evidence, validity or applicability of any claimed patent rights in
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shall not be held responsible for identifying any or all such patent rights.
This redline version of the official IEC Standard allows the user to identify the changes
made to the previous edition IEC 61558-2-12:2011. A vertical bar appears in the margin
wherever a change has been made. Additions are in green text, deletions are in
strikethrough red text.
– 4 – IEC 61558-2-12:2024 RLV © IEC 2024
IEC 61558-2-12 has been prepared by IEC technical committee 96: Transformers, reactors,
power supply units and combinations thereof. It is an International Standard.
This third edition cancels and replaces the second edition published in 2011. This edition
constitutes a technical revision.
This edition includes the following significant technical changes with respect to the previous
edition:
a) adjustment of structure and references in accordance with IEC 61558-1:2017;
b) description of constructions moved to IEC 61558-1:2017;
c) new symbol for power supply unit with linearly regulated output voltage.
The text of this International Standard is based on the following documents:
Draft Report on voting
96/587/FDIS 96/591/RVD
Full information on the voting for its approval can be found in the report on voting indicated in
the above table.
The language used for the development of this International Standard is English.
This document was drafted in accordance with ISO/IEC Directives, Part 2, and developed in
accordance with ISO/IEC Directives, Part 1 and ISO/IEC Directives, IEC Supplement, available
at www.iec.ch/members_experts/refdocs. The main document types developed by IEC are
described in greater detail at www.iec.ch/standardsdev/publications.
It has the status of a group safety publication in accordance with IEC Guide 104.
This International Standard is to be used in conjunction with IEC 61558-1:2017.
This document supplements or modifies the corresponding clauses in IEC 61558-1:2017, so as
to convert that publication into the IEC standard: Particular requirements and tests for constant
voltage transformers and power supply units for constant voltage.
A list of all parts in the IEC 61558 series published under the general title Safety of
transformers, reactors, power supply units and combinations thereof, can be found on the
IEC website.
Future standards in this series will carry the new general title as cited above. Titles of existing
standards in this series will be updated at the time of the next edition.
Where this document states "addition", "modification" or "replacement", the relevant text of
IEC 61558-1:2017 is to be adopted accordingly.
In this document, the following print types are used:
– requirements proper: in roman type;
– test specifications: in italic type;
– explanatory matter: in smaller roman type:
In the text of this document, the words in bold are defined in Clause 3.
Subclauses, notes, figures and tables additional to those in IEC 61558-1:2017 are numbered
starting from 101; supplementary annexes are entitled AA, BB, etc.
The committee has decided that the contents of this document will remain unchanged until the
stability date indicated on the IEC website under webstore.iec.ch in the data related to the
specific document. At this date, the document will be
• reconfirmed,
• withdrawn, or
• revised.
IMPORTANT – The "colour inside" logo on the cover page of this document indicates
that it contains colours which are considered to be useful for the correct understanding
of its contents. Users should therefore print this document using a colour printer.
– 6 – IEC 61558-2-12:2024 RLV © IEC 2024
INTRODUCTION
IEC TC 96 has a group safety function in accordance with IEC Guide 104 for transformers other
than those intended to supply distribution networks, in particular transformers and power supply
units intended to allow the application of protective measures against electric shock as defined
by TC 64, which is about electrical installations and protection against electric shock, but in
certain cases including the limitation of voltage and horizontal safety function for SELV, in
accordance with IEC 60364-4-41.
The group safety function (GSF) is used because of responsibility for safety extra-low voltage
(SELV) in accordance with IEC 61140:2016, 5.2.6 and IEC 60364-4-41:2005, 414.3.1 or control
circuits in accordance with IEC 60204-1:2016, 7.2.4.
The group safety function is used for each part of IEC 61558-2 because different standards of
the IEC 61558 series can be combined in one construction but in certain cases with no limitation
of rated output power.
For example an auto-transformer in accordance with IEC 61558-2-13 can be designed with a
separate SELV-circuit in accordance with the particular requirements for IEC 61558-2-6 relating
to the general requirements of IEC 61558-1.
SAFETY OF TRANSFORMERS, REACTORS,
POWER SUPPLY UNITS AND COMBINATIONS THEREOF –
Part 2-12: Particular requirements and tests for constant voltage
transformers and power supply units for constant voltage
1 Scope
Replacement:
This part of IEC 61558 deals with the safety of constant voltage transformers for general
applications and power supply units for constant voltage for general applications. Constant
voltage transformers incorporating electronic circuits are also covered by this document.
NOTE 1 Safety includes electrical, thermal and mechanical aspects.
Unless otherwise specified, from here onward, the term transformer covers constant voltage
transformers for general applications and power supply units for constant voltage for
general applications.
This document is applicable to stationary or portable single-phase or polyphase, air-cooled
(natural or forced) independent or associated dry-type:
– constant voltage auto-transformers;
– constant voltage separating transformers;
– constant voltage isolating transformers;
– constant voltage safety isolating transformers.
The windings may can be encapsulated or non-encapsulated.
This standard is applicable to transformers and power supply (linear) with internal operating
frequencies not exceeding 500 Hz.
This standard used in combination with Part 2-16 for switch mode power supply (SMPS) units
is also applicable to power supplies with internal operating frequencies higher than 500 Hz.
Where the two requirements are in conflict, the most severe take precedence.
For power supply units (linear) this document is applicable. For switch mode power supply
units IEC 61558-2-16 is applicable together with this document. Where two requirements are
in conflict, the most severe take precedence.
The rated supply voltage does not exceed 1 000 V AC. The rated supply frequency does not
exceed 500 Hz, the internal operating resonant frequency does not exceed 30 kHz and the
internal operating frequency does not exceed 100 MHz.
The rated output does not exceed:
– 40 kVA for single-phase constant voltage auto-transformers;
– 200 kVA for polyphase constant voltage auto-transformers;
– 25 kVA for single-phase constant voltage separating transformers and constant voltage
isolating transformers;
– 8 – IEC 61558-2-12:2024 RLV © IEC 2024
– 40 kVA for polyphase constant voltage separating transformers and constant voltage
isolating transformers;
– 10 kVA for single-phase constant voltage safety isolating transformers;
– 16 kVA for polyphase constant voltage safety isolating transformers.
This document is applicable to transformers without limitation of the rated output, subject to
an agreement between the purchaser and the manufacturer.
NOTE 2 Transformers intended to supply distribution networks are not included in the scope.
Where applicable to constant voltage auto-transformers
– the no-load output voltage or the rated output voltage does not exceed 1 000 V AC or
1 415 V ripple-free DC, and for independent constant voltage auto-transformers the
no-load output voltage and the rated output voltage exceed 50 V AC or 120 V ripple-free
DC;
– constant voltage auto-transformers covered by this document are used only in
applications where no insulation between circuits is required by the installation rules or by
the end product standard.
Where applicable to constant voltage separating transformers
– the no-load output voltage or the rated output voltage does not exceed 1 000 V AC or
1 415 V ripple-free DC, and for independent constant voltage separating transformers
the no-load output voltage and the rated output voltage exceed 50 V AC or 120 V
ripple-free DC;
– constant voltage separating transformers covered by this document are used only in
applications where double or reinforced insulation between circuits is not required by the
installation rules or by the end product standard.
Where applicable to constant voltage isolating transformers
– the no-load output voltage or the rated output voltage does exceed 50 V AC or 120 V
ripple-free DC and where applicable, does not exceed 500 V AC or 708 V ripple-free DC.
The no-load output voltage and the rated output voltage may can be up to 1 000 V AC
or 1 415 V ripple-free DC for special applications;
– constant voltage isolating transformers covered by this document are used only in
applications where double or reinforced insulation between circuits is required by the
installation rules or by the end product standard.
Where applicable to constant voltage safety isolating transformers
– the no-load output voltage or the rated output voltage does not exceed 50 V AC or 120 V
ripple-free DC;
– constant voltage safety isolating transformers covered by this document are used only
in applications where double or reinforced insulation between circuits is required by the
installation rules or by the end product standard.
This document is not applicable to external circuits and their components intended to be
connected to the input terminals and output terminals of the transformers.
NOTE 3 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.) may be necessary;
– measures to protect the enclosure and the components inside the enclosure against
external influences such as fungus, vermin, termites, solar-radiation, and icing should also
be considered;
– the different conditions for transportation, storage, and operation of the 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.
NOTE 4 Future technological development of transformers may necessitate a need to increase
the upper limit of the frequencies. Until then this document may be used as a guidance
document.
This group safety publication focusing on safety guidance is primarily intended to be used as a
product safety standard for the products mentioned in the scope, but is also intended to be used
by technical committees in the preparation of publications for products similar to those
mentioned in the scope of this group safety publication, in accordance with the principles laid
down in IEC Guide 104 and lSO/lEC Guide 51.
One of the responsibilities of a technical committee is, wherever applicable, to make use of
basic safety publications and/or group safety publications in the preparation of its publications.
2 Normative references
This clause of IEC 61558-1:2017 is applicable except as follows:
Addition
IEC 61558-1:2017, Safety of transformers, reactors, power supply units and combinations
thereof – Part 1: General requirements and tests
IEC 61558-2-16:2021, Safety of transformers, reactors, power supply units and combinations
thereof – Part 16: Particular requirements and tests for switch mode power supply units and
transformers for switch mode power supply units for general applications
3 Terms and definitions
For the purposes of this document, the terms and definitions given in IEC 61558-1 apply, except
as follows:
ISO and IEC maintain terminological databases for use in standardization at the following
addresses:
• IEC Electropedia: available at http://www.electropedia.org/
• ISO Online browsing platform: available at http://www.iso.org/obp
3.1 Transformers
Addition:
3.1.101
constant voltage transformer
transformer intended to limit the influence of the input voltage variations
Note 1 to entry: This type of transformer may can also limit the influence of transients.
3.5 Ratings
Addition
– 10 – IEC 61558-2-12:2024 RLV © IEC 2024
3.1025.101
regulation tolerance
deviation in per cent of the rated output voltage when the constant voltage transformer is
supplied within the rated supply voltage variation
3.1035.102
internal operating resonant frequency
frequency produced within a constant voltage transformer
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:
– 1 000 V AC or 1 415 V ripple-free DC for constant voltage auto-transformers and
constant voltage separating transformers;
– 250 V AC for single-phase portable constant voltage isolating transformers;
– 400 V AC for polyphase portable constant voltage isolating transformers, and
– 500 V AC or 708 V ripple-free DC for constant voltage isolating transformers. For
constant voltage isolating transformers, the rated output voltage may can be up to
1 000 V AC or 1 415 V ripple-free DC to be in accordance with the national wiring rules or
for a special purpose;
– 50 V AC or 120 V ripple-free DC for constant voltage safety isolating transformers;
The rated output voltage shall exceed:
– 50 V AC or 120 V ripple-free DC for independent constant voltage auto-transformers,
constant voltage separating transformers and constant voltage isolating
transformers.
6.102 The rated output shall not exceed:
– 40 kVA for single-phase constant voltage auto-transformers,
– 200 kVA for polyphase constant voltage auto-transformers,
– 25 kVA for single-phase constant voltage separating and isolating transformers,
– 40 kVA for polyphase constant voltage separating and isolating transformers,
– 10 kVA for single-phase constant voltage safety isolating transformers,
– 16 kVA for polyphase constant voltage safety isolating transformers,
except for constant voltage transformers subject to an agreement between the purchaser and
the manufacturer.
6.103 The rated supply frequency shall not exceed 500 Hz.
6.104 The rated value of the output regulation tolerance shall be given at the rated supply
voltage range, the rated output, and the power factor of 1.
6.105 For constant voltage independent transformers the input voltage variation shall not
be less than 10 %.
6.106 The internal operating resonant frequency shall not exceed 30 kHz.
6.107 The internal operating frequency shall not exceed 100 MHz.
Compliance with the requirements of 6.101 to 6.107 is checked by inspection of the marking.
7 Classification
This clause of IEC 61558-1:2017 is applicable.
8 Marking and other information
This clause of IEC 61558-1:2017 is applicable except as follows:
8.1
a)
Replacement of the first sentence by the following:
rated supply voltage(s) and the input voltage variation in %;
b)
Replacement of the first sentence by the following:
rated output voltage(s) and the regulation tolerance of this voltage(s) in %;
h)
Replacement of the first sentence content up to the first semi-colon by the following:
relevant graphical symbols shown in 8.11 Table 101 indicating that indicate the kind of
transformer;
8.11
Addition:
The symbol for linear power supply units shall be used in conjunction with the symbol
indicating the kind of transformer.
– 12 – IEC 61558-2-12:2024 RLV © IEC 2024
Table 101 – Symbols indicating the kind of transformer
Symbol or graphical symbol Explanation or title Identification
Fail-safe constant voltage separating
IEC 60417-6011:2008-02
transformer
Non-short-circuit-proof constant voltage
IEC 60417-6011:2008-02
separating transformer
Short-circuit-proof constant voltage separating
IEC 60417-6011:2008-02
transformer
Fail-safe constant voltage isolating
IEC 60417-6012:2008-09
transformer
Non-short-circuit-proof constant voltage
IEC 60417-6012:2008-09
isolating transformer
Short-circuit-proof constant voltage isolating
IEC 60417-6012:2008-09
transformer
Fail-safe constant voltage safety isolating
IEC 60417-6013:2008-02
transformer
Non-short-circuit-proof constant voltage safety
IEC 60417-6013:2008-02
isolating transformer
Symbol or graphical symbol Explanation or title Identification
Short-circuit-proof constant voltage safety
IEC 60417-6013:2008-02
isolating transformer
Fail-safe constant voltage auto-transformer IEC 60417-6017:2008-02
Non-short-circuit-proof constant voltage
IEC 60417-6017:2008-02
autotransformer
Short-circuit-proof constant voltage
IEC 60417-6017:2008-02
autotransformer
L
Power supply unit, linear IEC 60417-6210:2013-10
9 Protection against electric shock
This clause of IEC 61558-1:2017 is applicable.
10 Change of input voltage setting
This clause of IEC 61558-1:2017 is applicable.
11 Output voltage and output current under load
This clause of IEC 61558-1:2017 is applicable except as follows:
– 14 – IEC 61558-2-12:2024 RLV © IEC 2024
11.1
Replacement:
11.1 When the transformer is connected to the rated supply voltage plus or minus the input
voltage variation declared by the manufacturer, at the rated supply frequency, and loaded
with an impedance resulting in the rated output at the rated output voltage and, for AC, at
the rated power factor, the output voltage shall not differ from the rated value by more than
the regulation tolerance.
Compliance is checked by measuring the output voltage when steady-state conditions are
established. During the test, the transformer is connected to the rated supply voltage, plus
or minus the highest input voltage variation, at the rated supply frequency, and loaded with
an impedance resulting in the rated output at the rated output voltage and the rated power
factor.
For transformers incorporating a rectifier, the output voltage shall be measured at the terminals
of the DC circuit by means of a voltmeter giving the arithmetical mean value, unless the effective
(RMS) value is specifically stated (see 8.1).
For transformers with more than one rated supply voltage, the requirement is applicable for
each of the rated supply voltages.
For transformers with multiple output windings, the loads are applied to every multiple section
simultaneously, unless otherwise declared.
12 No-load output voltage
This clause of IEC 61558-1:2017 is applicable except as follows:
Addition:
The no-load output voltage is measured when the transformer is connected to the rated
supply voltage at the rated supply frequency at ambient temperature.
12.101 The no-load output voltage shall not exceed:
– 1 000 V AC or 1 415 V ripple-free DC for constant voltage auto-transformers and
constant voltage separating transformers;
– 250 V AC for single-phase portable constant voltage isolating transformers;
– 400 V AC for polyphase portable constant voltage isolating transformers, and
– 500 V AC or 708 V ripple-free DC for other constant voltage isolating transformers.
In this case, the no-load output voltage can be up to 1 000 V AC or 1 415 V ripple-free DC
to be in accordance with the national wiring rules or for a special purpose;
– 50 V AC or 120 V ripple-free DC for constant voltage safety isolating transformers.
The no-load output voltage shall exceed:
– 50 V AC or 120 V ripple-free DC for constant voltage independent auto-, separating and
isolating transformers.
For independent 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 difference 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 %.
NOTE 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 shall be is checked by measuring the
no-load output voltage at the ambient temperature when the transformer is connected to the
rated supply voltage plus the highest input voltage variation at the rated supply frequency.
13 Short-circuit voltage
This clause of IEC 61558-1:2017 is applicable.
14 Heating
This clause of IEC 61558-1:2017 is applicable, except as follows:
14.1.1 Temperature-rise test
th
Replacement of the 10th 11 paragraph starting with "Transformers are supplied." by the
following as follows:
The constant voltage transformers are connected to the rated supply voltage and loaded
with an impedance resulting in the rated output, at the rated output voltage and, for AC, at
the rated power factor. The supply voltage is then increased to the value of the highest input
voltage variation declared by the manufacturer. After this voltage increase, no change or
adjustment is made in the circuit. The test is repeated under no-load condition with the highest
or the lowest input voltage variation if this is a more unfavourable condition.
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
nd
Replacement of the 2 paragraph starting with " Compliance is checked." by the following as
follows:
Compliance is checked by inspection and by the following tests, which are carried out
immediately after the test in accordance with 14.1, at the same ambient temperature, and
without changing the position of the constant voltage transformer at the maximum value of
the rated supply voltage designed for the constant voltage transformer.
– 16 – IEC 61558-2-12:2024 RLV © IEC 2024
15.2 Inherently short-circuit proof transformers
Replacement:
Inherently short-circuit-proof constant voltage transformers shall be tested as follows:
Before starting the test, it is necessary to determine the highest output current of the constant
voltage transformer at the maximum value of the supply voltage designed for the constant
voltage transformer. The constant voltage transformer is then loaded with the maximum
output current or the output winding(s) short-circuited, whichever results in the maximum
temperature.
15.3 Non-inherently short-circuit proof transformers
Replacement:
Non-inherently short-circuit-proof constant voltage transformers are tested as follows:
15.3.1 Replacement:
The output windings are short-circuited or overloaded as stated in 15.2. The incorporated
overload protection device shall operate before the temperature exceeds the values shown in
Table 3 5 for any value of the supply voltage between the marked values of rated supply
voltage.
15.5 Fail-safe transformers
15.5.1
Replacement:
Three additional specimens are required, only for the following test. Constant voltage
Transformers used in other tests are not subjected to this test.
Each of the three specimens is mounted as for normal use on a 20 mm thick dull black painted
plywood surface. Each constant voltage transformer is operated at rated supply voltage
plus or minus the input voltage variation declared by the manufacturer,. The output winding
which produced the highest temperature during the test of 14.1 being initially loaded with
1,5 times the rated output current (or, if this is not possible, the maximum value of the output
current obtainable) until steady-state conditions are reached or the constant voltage
transformer fails (whichever occurs first).
If the constant voltage transformer fails, it shall comply, during and after the tests, with the
criteria given in 15.5.2.
If the constant voltage transformer does not fail, the time to reach steady-state conditions is
noted and the chosen output winding is then short-circuited. The test is continued until the
constant voltage transformer fails. Each specimen shall do so within a duration, for this part
of the test, which is no longer than that necessary to attain steady-state conditions, but in any
case it shall not exceed 5 h.
The constant voltage transformer shall fail safely. It shall comply, during and after the test,
with the criteria given in 15.5.2.
16 Mechanical strength
This clause of IEC 61558-1:2017 is applicable.
17 Protection against harmful ingress of dust, solid objects and moisture
This clause of IEC 61558-1:2017 is applicable.
18 Insulation resistance, dielectric strength and leakage current
This clause of IEC 61558-1:2017 is applicable, except as follows:
18.2 Insulation resistance
This subclause of IEC 61558-1 is applicable, except as follows:
Modification for constant voltage auto-transformers:
Table 7: values between each input circuit and all other input circuits, between each output
circuits and all other output circuits are not applicable.
In accordance with Table 13 the values between input circuits and output circuits, between
each input circuit and all other input circuits, between each output circuits and all other
output circuits are not applicable.
18.3 Dielectric strength test
This subclause of IEC 61558-1 is applicable, except as follows:
Modification for constant voltage auto-transformers:
Table 8a: lines 1) and 2) are not applicable.
In accordance with Table 14 the values between input circuits and output circuits are not
applicable.
18.4 Insulation between and within windings
This subclause of IEC 61558-1:2017 is applicable, except as follows:
Addition for constant voltage auto-transformers:
For windings intended to be connected in series or parallel the dielectric strength test for
functional insulation in accordance with Table 14 shall be applied.
18.101
Table 101 – Dielectric strength test voltages for constant voltage auto-transformers
Application of dielectrical strength test voltage Working voltage
V
>50 150 300
Over functional insulation for windings intended to be connected
Working voltage + 500 V
in series or parallel
– 18 – IEC 61558-2-12:2024 RLV © IEC 2024
19 Construction
Replacement of this clause:
NOTE This clause reads slightly differently for each type of constant voltage transformer:
– constant voltage auto-transformers (see 19.1);
– constant voltage separating transformers (see 19.2);
– constant voltage isolating and safety isolating transformers (see 19.3).
19.1 Constant voltage auto-transformers
19.1.1 Plug-connected constant voltage auto-transformers, where the rated input voltage
is higher than the rated output voltage, shall not have any potential to earth at the output
socket higher than the rated output voltage.
This requirement shall be fulfilled by using one of the following methods:
a) Polarized input and output plug and socket-outlet system
In this case, an instruction shall be given for not using such a transformer with a non-polarized
plug and socket-outlet system.
b) Polarity detecting device (for non polarised input and output plug and socket-outlet system)
A polarity detecting device shall only energise the output circuit when the potential to earth at
the poles of the output socket does not exceed the rated output voltage. The contact
separation of the breaking device shall be at least of 3 mm in each pole.
NOTE A magnetic relay is an example of polarity detecting device.
Compliance is checked by the following test:
The auto-transformer is connected to the mains at 1,06 times the rated input voltage under
the most unfavourable condition of load and output voltage. The test is repeated with the polarity
of the input reversed. During the test, the measured potential to earth of each pole shall not
exceed the maximum output voltage under load (1,06 times the rated output voltage taking
into account the permissible deviations of Clause 11).
The contact separation of the device shall be 3 mm minimum in each pole.
Compliance is checked by measurement.
If the polarity detecting device uses a current flowing to the earth for the detection, this current
shall not exceed 0,75 mA and shall only be flowing for the period of measurement until the
polarity is reversed.
Compliance is checked by measurement.
All the tests are repeated under the fault conditions of H.2.3 of Part 1. In this case, the potential
to earth of each pole shall not exceed 1,1 times the maximum output voltage under load for
more than 5 s.
Compliance is checked by measurement.
19.1.2 Protection against direct contact with electrical and moving mechanical parts (contact
path and drive) shall be ensured.
Compliance is checked by inspection.
19.2 Constant voltage separating transformers
19.2.1 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 conductive parts, except by deliberate action.
Compliance is checked by inspection and measurements, taking Clauses 18 and 26 of Part 1
into consideration.
19.2.2 The insulation between the input and output winding(s) shall consist of at least basic
insulation (rated for the working voltage).
In addition, the following applies:
– for class I transformers, the insulation between the input windings and the body, and
between the output windings and the body, shall consist of at least basic insulation (both
basic insulations rated for the working voltage);
– for class II transformers, the insulation between the input windings and the body, and
between the output windings and the body, shall consist of double or reinforced
insulation (both double or reinforced insulations rated for the working voltage).
19.2.3 For constant voltage transformers with intermediate conductive part (e.g. the iron
core) or a resonant circuit not connected to the body and located between the input and output
windings, the insulation between the intermediate conductive part (or a resonant circuit) and
the input windings and between the intermediate conductive part (or a resonant circuit) and
the output windings shall consist of at least basic insulation (rated for the working voltage).
NOTE An intermediate conductive part (or a resonant circuit) 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 following applies:
– for class I transformers, the insulation between the input and output windings via the
intermediate conductive parts shall consist of at least basic insulation (rated for the
working voltage);
– for class II transformers, the insulat
...
IEC 61558-2-12 ®
Edition 3.0 2024-04
EXTENDED VERSION
INTERNATIONAL
STANDARD
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This extended version of IEC 61558-2-12:2024 includes the content of the references made to
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GROUP ENERGY EFFICIENCY PUBLICATION
Safety of transformers, reactors, power supply units and combination thereof –
Part 2-12: Particular requirements and tests for constant voltage transformers
and power supply units for constant voltage
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IEC 61558-2-12 ®
Edition 3.0 2024-04
EXTENDED VERSION
INTERNATIONAL
STANDARD
colour
inside
This extended version of IEC 61558-2-12:2024 includes the content of the references made to
IEC 61558-1:2017
GROUP ENERGY EFFICIENCY PUBLICATION
Safety of transformers, reactors, power supply units and combination thereof –
Part 2-12: Particular requirements and tests for constant voltage transformers
and power supply units for constant voltage
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 29.180 ISBN 978-2-8322-8750-7
– 2 – IEC 61558-2-12:2024 EXV © IEC 2024
CONTENTS
FOREWORD . 9
INTRODUCTION . 12
INTRODUCTION to IEC 61558-2-12 . 14
1 Scope . 15
2 Normative references . 17
3 Terms and definitions . 20
3.1 Transformers . 20
3.2 General terms . 23
3.3 Operations and protections . 25
3.4 Circuits and windings . 27
3.5 Ratings . 27
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 . 35
6 Ratings . 37
7 Classification . 38
8 Marking and other information . 39
9 Protection against electric shock . 47
9.1 General . 47
9.2 Protection against contact with hazardous-live-parts . 47
9.2.1 Determination of hazardous-live-parts . 47
9.2.2 Accessibility to hazardous-live-parts . 48
9.2.3 Accessibility to non hazardous-live-part . 51
9.3 Protection against hazardous electrical discharge . 51
10 Change of input voltage setting . 51
11 Output voltage and output current under load . 52
12 No-load output voltage . 52
13 Short-circuit voltage . 53
14 Heating . 54
14.1 General requirements . 54
14.1.1 Temperature-rise test . 54
14.1.2 Alternative temperature-rise test . 56
14.1.3 Determination of steady-state conditions . 58
14.2 Application of 14.1 or 14.3 according to the insulation system. 60
14.3 Accelerated ageing test for undeclared class of insulation system . 60
14.3.1 General . 60
14.3.2 Heat run . 61
14.3.3 Vibration . 61
14.3.4 Moisture treatment . 61
14.3.5 Measurements . 61
15 Short circuit and overload protection. 62
15.1 General requirements . 62
15.1.1 Short circuit and overload test method . 62
15.1.2 Alternative short circuit and overload test method . 64
15.2 Inherently short-circuit proof transformers . 64
15.3 Non-inherently short-circuit proof transformers. 64
15.4 Non-short-circuit proof transformers . 65
15.5 Fail-safe transformers . 65
16 Mechanical strength . 66
16.1 General . 66
16.2 Stationary transformers . 66
16.3 Portable transformers (except portable transformers with integral pins for
introduction in socket-outlet in the fixed wiring) . 67
16.4 Portable transformers provided with integral pins for introduction in socket-
outlets of the fixed wiring . 67
16.4.1 General requirements . 67
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 . 68
16.5 Additional requirements for transformers to be used in vehicles and railway
applications . 69
16.5.1 Transformers to be used in vehicles and railway applications . 69
16.5.2 Test requirements for the transportation of transformers . 70
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 . 76
18.4 Insulation between and within windings . 78
18.5 Touch current and protective earthing conductor current . 79
18.5.1 General . 79
18.5.2 Touch current . 79
18.5.3 Protective earthing conductor current . 80
19 Construction . 81
19.1 General construction . 81
19.1.1 General . 81
19.1.2 Auto-transformers . 81
19.1.3 Separating transformers . 82
19.1.4 Isolating transformers and safety isolating transformers . 83
19.2 Flammability of materials . 85
19.3 Short-circuit characteristics of portable transformers . 85
19.4 Class II transformer contact prevention of accessible conductive parts . 86
19.5 Class II transformer insulation reassembling after service . 86
19.6 Loosening of wires, screws or similar parts . 86
19.7 Resistor or capacitor connection with accessible conductive parts . 87
19.8 Bridging of separated conductive parts by resistors or capacitors . 87
19.9 Insulating material separating input and output windings . 87
19.10 Accidental contact protection against hazardous-live-parts provided by
isolating coating . 88
– 4 – IEC 61558-2-12:2024 EXV © IEC 2024
19.11 Insulating material of handles, operating levers, knobs and similar parts. 89
19.12 Winding construction . 89
19.13 Fixing of handles, operating levers and similar parts . 93
19.14 Fixing of covers providing protection against electric shock . 93
19.15 Strain on fixed socket-outlets caused by pin-transformers connection . 93
19.16 Portable transformers for use in irregular or harsh conditions . 94
19.17 Drain hole of transformers protected against ingress of water . 94
19.18 Plug connected transformers protected against ingress of water . 94
19.19 Flexible cable or flexible cord connection for class I portable transformers . 94
19.20 SELV- and PELV-circuit separation of live parts . 94
19.21 Protection against contact for FELV-circuit. 95
19.22 Protective earthing regarding class II transformers . 95
19.23 Protective earthing regarding class III transformers . 95
20 Components . 96
21 Internal wiring . 101
22 Supply connection and other external flexible cables or cords . 101
23 Terminals for external conductors . 108
24 Provisions for protective earthing. 109
25 Screws and connections . 111
26 Creepage distances, clearances and distances through insulation . 113
26.1 General . 113
26.2 Creepage distances and clearances . 114
26.2.1 General . 114
26.2.2 Windings covered with adhesive tape . 114
26.2.3 Uncemented insulationing parts . 114
26.2.4 Cemented insulating parts . 114
26.2.5 Enclosed parts (e.g. by impregnation or potting) . 115
26.3 Distance through insulation . 116
27 Resistance to heat, fire and tracking . 127
27.1 General . 127
27.2 Resistance to heat . 127
27.2.1 General . 127
27.2.2 External accessible parts . 127
27.2.3 Internal parts . 128
27.3 Resistance to abnormal heat under fault conditions . 128
27.4 Resistance to fire . 129
27.4.1 General . 129
27.4.2 External accessible parts . 130
27.4.3 Internal parts . 130
27.5 Resistance to tracking . 131
28 Resistance to rusting . 131
Annex A (normative) Measurement of creepage distances and clearances. 132
Annex B (normative) Testing a series of transformers . 136
B.1 General . 136
B.2 Requirements . 136
B.3 Constructional inspection . 137
Annex C (void) . 138
Annex D (void) . 139
Annex E (normative) Glow-wire test . 140
E.1 General . 140
E.2 Severity . 140
E.3 Conditioning . 140
E.4 Test procedure . 140
Annex F (normative) Requirements for manually operated switches which are parts of
transformers assembly . 141
F.1 General . 141
F.2 Switches tested as a separate component . 141
F.3 Switches tested as part of the transformer . 141
Annex G (normative) Tracking test . 144
G.1 General . 144
G.2 Test specimen . 144
G.3 Test apparatus . 144
G.4 Procedure . 144
Annex H (normative) Electronic circuits . 145
H.1 General . 145
H.2 General notes on tests (addition to Clause 5). 145
H.3 Short circuit and overload protection (addition to Clause 15) . 145
H.4 Creepage distances, clearances and distances through insulation (addition
to Clause 26) . 147
Annex I (informative) Dimensions for rectangular cross-section connectors of
transformers, basic dimensions and coordination . 149
Annex J (normative) Measuring network for touch-currents . 151
Annex K (normative) Insulated winding wires . 152
K.1 General . 152
K.2 Type tests . 152
K.2.1 General . 152
K.2.2 Dielectric strength test . 152
K.2.3 Flexibility and adherence . 152
K.2.4 Heat shock . 153
K.2.5 Retention of dielectric strength after bending . 153
K.3 Testing during manufacturing . 154
K.3.1 General . 154
K.3.2 Routine test . 154
K.3.3 Sampling test . 154
Annex L (normative) Routine tests (production tests) . 155
L.1 General . 155
L.2 Protective earthing continuity test . 155
L.3 Checking of no-load output voltage . 155
L.4 Dielectric strength test . 155
L.5 Checking of protective devices mounting . 156
L.6 Visual inspection . 156
L.7 Repetition test after routine dielectric strength test . 156
Annex M (informative) Examples to be used as a guide for 19.1 . 157
M.1 General . 157
M.2 Coil-former . 157
– 6 – IEC 61558-2-12:2024 EXV © IEC 2024
M.2.1 Concentric type . 157
M.2.2 Side-by-side type . 158
M.3 Windings . 158
M.3.1 Without screen . 158
M.3.2 With screen . 159
Annex N (informative) Examples for checking points of dielectric strength test voltages . 160
Annex O (void) . 162
Annex P (informative) Examples for measurement points of creepage distances and
clearances . 163
Annex Q (informative) Explanation of IP numbers for degrees of protection . 166
Q.1 General . 166
Q.2 Degrees of protection against access to hazardous parts and against solid
foreign objects . 166
Q.3 Degrees of protection against ingress of water . 168
Annex R (normative) Explanations of the application of 6.1.2.2.1 of IEC 60664-1:2007 . 169
R.1 Impulse dielectric test . 169
R.2 Example. 169
Annex S (void) . 171
Annex T (void) . 172
Annex U (void) . 173
Annex V (informative) Symbols to be used for thermal cut-outs . 174
V.1 General . 174
V.2 Non-self-resetting thermal cut-out (see 3.3.4) . 174
V.3 Self-resetting thermal cut-out (see 3.3.3) . 174
Annex W (normative) Coated printed circuit boards . 175
W.1 Preamble . 175
W.2 General . 175
W.3 Cold . 175
W.4 Rapid change of temperature . 175
W.5 Additional tests . 175
Bibliography . 176
Index of defined terms . 178
Figure 2 – Mounting box for flush-type transformer . 36
Figure 3 – Test pin (see IEC 61032, test probe 13) . 49
Figure 4 – Standard test finger (see IEC 61032, test probe B) . 50
Figure 5 – Example of back-to-back method – Single phase . 58
Figure 6 – Example of back-to-back method – Three phase . 58
Figure 7 – Amplitude spectrum density for random testing . 70
Figure 8 – Normalised spectrum of shock . 71
Figure 9 – Test voltage sequence . 78
Figure 10 – Test configuration: single-phase equipment on star TN or TT system . 80
Figure 11 – Abrasion resistance test for insulating coated layers . 89
Figure 12 – Flexing test apparatus . 105
Figure 13 – Test arrangement for checking mechanical withstanding of insulating
materials in thin sheet layers . 119
Figure 14 – Ball-pressure apparatus . 127
Figure A.1 – Example 1. 132
Figure A.2 – Example 2. 133
Figure A.3 – Example 3. 133
Figure A.4 – Example 4. 133
Figure A.5 – Example 5. 134
Figure A.6 – Example 6. 134
Figure A.7 – Example 7. 135
Figure A.8 – Example 8. 135
Figure H.1 – Example of an electronic circuit with low-power points . 148
Figure J.1 – Measuring network for touch-current . 151
Figure M.1 – Examples for concentric type constructions . 157
Figure M.2 – Examples for side-by-side type constructions . 158
Figure M.3 – Examples for winding constructions without screen . 158
Figure M.4 – Examples for wrapped winding constructions . 159
Figure M.5 – Examples for winding constructions with screen . 159
Figure N.1 – Transformer of class I construction with metal enclosure . 160
Figure N.2 – Transformer of class II construction with metal enclosure . 161
Figure N.3 – Transformer of class II construction with enclosure of insulating material . 161
Figure P.1 – Transformer of class I construction . 163
Figure P.2 – Transformer of class I construction with earthed metal screen . 164
Figure P.3 – Transformer of class II construction with metal enclosure . 164
Figure P.4 – Transformer of class II construction with enclosure of insulating material . 165
Figure V.1 – Restored by manual operation . 174
Figure V.2 – Restored by disconnection of the supply . 174
Figure V.3 – Thermal link (see 3.3.5) . 174
Figure V.4 – Self-resetting thermal cut-out . 174
Table 1 – Symbols used on equipment or in instructions . 43
Table 101 – Symbols indicating the kind of transformer . 44
Table 2 – Values of maximum temperatures in normal use . 59
Table 3 – Explanation of the maximum winding temperatures required in Table 2 . 60
Table 4 – Test temperature and testing time (in days) per cycle . 61
Table 5 – Maximum values of temperatures under short-circuit or overload conditions . 63
Table 6 – Values of T and k for fuses . 64
Table 7 – Pull force on pins . 68
Table 8 – Conditions for vibration testing (random) . 69
Table 9 – Amplitude spectrum density ASD values for accelerated life testing . 69
Table 10 – Frequency values depending on the weight of the specimen . 70
Table 11 – Excitation values for vibration testing . 70
Table 12 – Solid-object-proof transformer test . 73
Table 13 – Values of insulation resistance . 76
Table 14 – Table of dielectric strength test voltages. 77
– 8 – IEC 61558-2-12:2024 EXV © IEC 2024
Table 15 – Limits for currents . 80
Table 16 – Nominal cross-sectional areas of external flexible cables or cords . 103
Table 17 – Pull and torque to be applied to external flexible cables or cords fixed to
stationary and portable transformers . 107
Table 18 – Torque to be applied to screws and connections . 112
Table 19 – Torque test on glands . 113
Table 20 – Clearances in mm . 120
Table 21 – Creepage distances in mm . 121
Table 22 – Distance through insulation in mm . 122
Table 23 – Creepage distances and clearance between terminals for external
connection . 123
Table 24 – Values of FIW wires with minimum overall diameter and minimum test
voltages according to the total enamel increase . 125
Table A.1 – Width of groove values depending on the pollution degree . 132
Table F.1 – Peak surge current of additional loads. 142
Table I.1 – Dimensions of rectangular copper connectors . 149
Table K.1 – Mandrel diameter . 153
Table K.2 – Oven temperature . 153
Table Q.1 – Degrees of protection against access to hazardous parts indicated by the
first characteristic numeral . 167
Table Q.2 – Degrees of protection against solid foreign objects indicated by the first
characteristic numeral . 167
Table Q.3 – Degrees of protection indicated by the second characteristic numeral . 168
Table R.1 – Impulse test voltage according to 6.1.2.2.1 of IEC 60664-1:2007 . 169
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
SAFETY OF TRANSFORMERS, REACTORS,
POWER SUPPLY UNITS AND COMBINATIONS THEREOF –
Part 2-12: Particular requirements and tests for constant voltage
transformers and power supply units for constant voltage
FOREWORD
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This extended version (EXV) of the official IEC Standard provides the user with the
comprehensive content of the Standard.
made to IEC 61558-1:2017.
The specific content of IEC 61558-2-12:2024 is displayed on a blue background.
– 10 – IEC 61558-2-12:2024 EXV © IEC 2024
IEC 61558-2-12 has been prepared by IEC technical committee 96: Transformers, reactors,
power supply units and combinations thereof. It is an International Standard.
This third edition cancels and replaces the second edition published in 2011. This edition
constitutes a technical revision.
This edition includes the following significant technical changes with respect to the previous
edition:
a) adjustment of structure and references in accordance with IEC 61558-1:2017;
b) description of constructions moved to IEC 61558-1:2017;
c) new symbol for power supply unit with linearly regulated output voltage.
The text of this International Standard is based on the following documents:
Draft Report on voting
96/587/FDIS 96/591/RVD
Full information on the voting for its approval can be found in the report on voting indicated in
the above table.
The language used for the development of this International Standa
...
IEC 61558-2-12 ®
Edition 3.0 2024-04
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
GROUP ENERGY EFFICIENCY PUBLICATION
PUBLICATION GROUPÉE SUR L'EFFICACITÉ ÉNERGÉTIQUE
Safety of transformers, reactors, power supply units and combination thereof –
Part 2-12: Particular requirements and tests for constant voltage transformers
and power supply units for constant voltage
Sécurité des transformateurs, bobines d'inductance, blocs d'alimentation et des
combinaisons de ces éléments –
Partie 2-12: Exigences particulières et essais pour les transformateurs à tension
constante et les blocs d'alimentation pour tension constante
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IEC 61558-2-12 ®
Edition 3.0 2024-04
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
GROUP ENERGY EFFICIENCY PUBLICATION
PUBLICATION GROUPÉE SUR L'EFFICACITÉ ÉNERGÉTIQUE
Safety of transformers, reactors, power supply units and combination thereof –
Part 2-12: Particular requirements and tests for constant voltage transformers
and power supply units for constant voltage
Sécurité des transformateurs, bobines d'inductance, blocs d'alimentation et des
combinaisons de ces éléments –
Partie 2-12: Exigences particulières et essais pour les transformateurs à tension
constante et les blocs d'alimentation pour tension constante
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
INTERNATIONALE
ICS 29.180 ISBN 978-2-8322-8463-6
– 2 – IEC 61558-2-12:2024 © IEC 2024
CONTENTS
FOREWORD . 3
INTRODUCTION . 5
1 Scope . 6
2 Normative references . 8
3 Terms and definitions . 8
4 General requirements . 9
5 General notes on tests . 9
6 Ratings . 9
7 Classification . 10
8 Marking and other information . 10
9 Protection against electric shock . 12
10 Change of input voltage setting . 12
11 Output voltage and output current under load . 12
12 No-load output voltage . 13
13 Short-circuit voltage . 14
14 Heating . 14
15 Short-circuit and overload protection . 14
16 Mechanical strength . 15
17 Protection against harmful ingress of dust, solid objects and moisture . 15
18 Insulation resistance, dielectric strength and leakage current . 16
19 Construction . 16
20 Components . 17
21 Internal wiring . 17
22 Supply connection and other external flexible cables or cords . 17
23 Terminals for external conductors . 17
24 Provisions for protective earthing. 17
25 Screws and connections . 17
26 Creepage distances, clearances and distances through insulation . 17
27 Resistance to heat, fire and tracking . 17
28 Resistance to rusting . 18
Annexes . 19
Annex L (normative) Routine tests (production test) . 19
Bibliography . 20
Table 101 – Symbols indicating the kind of transformer . 11
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
SAFETY OF TRANSFORMERS, REACTORS,
POWER SUPPLY UNITS AND COMBINATIONS THEREOF –
Part 2-12: Particular requirements and tests for constant voltage
transformers and power supply units for constant voltage
FOREWORD
1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising
all national electrotechnical committees (IEC National Committees). The object of IEC is to promote international
co-operation on all questions concerning standardization in the electrical and electronic fields. To this end and
in addition to other activities, IEC publishes International Standards, Technical Specifications, Technical Reports,
Publicly Available Specifications (PAS) and Guides (hereafter referred to as “IEC Publication(s)”). Their
preparation is entrusted to technical committees; any IEC National Committee interested in the subject dealt with
may participate in this preparatory work. International, governmental and non-governmental organizations liaising
with the IEC also participate in this preparation. IEC collaborates closely with the International Organization for
Standardization (ISO) in accordance with conditions determined by agreement between the two organizations.
2) The formal decisions or agreements of IEC on technical matters express, as nearly as possible, an international
consensus of opinion on the relevant subjects since each technical committee has representation from all
interested IEC National Committees.
3) IEC Publications have the form of recommendations for international use and are accepted by IEC National
Committees in that sense. While all reasonable efforts are made to ensure that the technical content of IEC
Publications is accurate, IEC cannot be held responsible for the way in which they are used or for any
misinterpretation by any end user.
4) In order to promote international uniformity, IEC National Committees undertake to apply IEC Publications
transparently to the maximum extent possible in their national and regional publications. Any divergence between
any IEC Publication and the corresponding national or regional publication shall be clearly indicated in the latter.
5) IEC itself does not provide any attestation of conformity. Independent certification bodies provide conformity
assessment services and, in some areas, access to IEC marks of conformity. IEC is not responsible for any
services carried out by independent certification bodies.
6) All users should ensure that they have the latest edition of this publication.
7) No liability shall attach to IEC or its directors, employees, servants or agents including individual experts and
members of its technical committees and IEC National Committees for any personal injury, property damage or
other damage of any nature whatsoever, whether direct or indirect, or for costs (including legal fees) and
expenses arising out of the publication, use of, or reliance upon, this IEC Publication or any other IEC
Publications.
8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is
indispensable for the correct application of this publication.
9) IEC draws attention to the possibility that the implementation of this document may involve the use of (a)
patent(s). IEC takes no position concerning the evidence, validity or applicability of any claimed patent rights in
respect thereof. As of the date of publication of this document, IEC had not received notice of (a) patent(s), which
may be required to implement this document. However, implementers are cautioned that this may not represent
the latest information, which may be obtained from the patent database available at https://patents.iec.ch. IEC
shall not be held responsible for identifying any or all such patent rights.
IEC 61558-2-12 has been prepared by IEC technical committee 96: Transformers, reactors,
power supply units and combinations thereof. It is an International Standard.
This third edition cancels and replaces the second edition published in 2011. This edition
constitutes a technical revision.
This edition includes the following significant technical changes with respect to the previous
edition:
a) adjustment of structure and references in accordance with IEC 61558-1:2017;
b) description of constructions moved to IEC 61558-1:2017;
c) new symbol for power supply unit with linearly regulated output voltage.
– 4 – IEC 61558-2-12:2024 © IEC 2024
The text of this International Standard is based on the following documents:
Draft Report on voting
96/587/FDIS 96/591/RVD
Full information on the voting for its approval can be found in the report on voting indicated in
the above table.
The language used for the development of this International Standard is English.
This document was drafted in accordance with ISO/IEC Directives, Part 2, and developed in
accordance with ISO/IEC Directives, Part 1 and ISO/IEC Directives, IEC Supplement, available
at www.iec.ch/members_experts/refdocs. The main document types developed by IEC are
described in greater detail at www.iec.ch/standardsdev/publications.
It has the status of a group safety publication in accordance with IEC Guide 104.
This International Standard is to be used in conjunction with IEC 61558-1:2017.
This document supplements or modifies the corresponding clauses in IEC 61558-1:2017, so as
to convert that publication into the IEC standard: Particular requirements and tests for constant
voltage transformers and power supply units for constant voltage.
A list of all parts in the IEC 61558 series published under the general title Safety of
transformers, reactors, power supply units and combinations thereof, can be found on the
IEC website.
Future standards in this series will carry the new general title as cited above. Titles of existing
standards in this series will be updated at the time of the next edition.
Where this document states "addition", "modification" or "replacement", the relevant text of
IEC 61558-1:2017 is to be adopted accordingly.
In this document, the following print types are used:
– requirements proper: in roman type;
– test specifications: in italic type;
– explanatory matter: in smaller roman type:
In the text of this document, the words in bold are defined in Clause 3.
Subclauses, notes, figures and tables additional to those in IEC 61558-1:2017 are numbered
starting from 101; supplementary annexes are entitled AA, BB, etc.
The committee has decided that the contents of this document will remain unchanged until the
stability date indicated on the IEC website under webstore.iec.ch in the data related to the
specific document. At this date, the document will be
• reconfirmed,
• withdrawn, or
• revised.
INTRODUCTION
IEC TC 96 has a group safety function in accordance with IEC Guide 104 for transformers other
than those intended to supply distribution networks, in particular transformers and power supply
units intended to allow the application of protective measures against electric shock as defined
by TC 64, which is about electrical installations and protection against electric shock, but in
certain cases including the limitation of voltage and horizontal safety function for SELV, in
accordance with IEC 60364-4-41.
The group safety function (GSF) is used because of responsibility for safety extra-low voltage
(SELV) in accordance with IEC 61140:2016, 5.2.6 and IEC 60364-4-41:2005, 414.3.1 or control
circuits in accordance with IEC 60204-1:2016, 7.2.4.
The group safety function is used for each part of IEC 61558-2 because different standards of
the IEC 61558 series can be combined in one construction but in certain cases with no limitation
of rated output power.
For example an auto-transformer in accordance with IEC 61558-2-13 can be designed with a
separate SELV-circuit in accordance with the particular requirements for IEC 61558-2-6 relating
to the general requirements of IEC 61558-1.
– 6 – IEC 61558-2-12:2024 © IEC 2024
SAFETY OF TRANSFORMERS, REACTORS,
POWER SUPPLY UNITS AND COMBINATIONS THEREOF –
Part 2-12: Particular requirements and tests for constant voltage
transformers and power supply units for constant voltage
1 Scope
Replacement:
This part of IEC 61558 deals with the safety of constant voltage transformers for general
applications and power supply units for constant voltage for general applications. Constant
voltage transformers incorporating electronic circuits are also covered by this document.
NOTE 1 Safety includes electrical, thermal and mechanical aspects.
Unless otherwise specified, from here onward, the term transformer covers constant voltage
transformers for general applications and power supply units for constant voltage for
general applications.
This document is applicable to stationary or portable single-phase or polyphase, air-cooled
(natural or forced) independent or associated dry-type:
– constant voltage auto-transformers;
– constant voltage separating transformers;
– constant voltage isolating transformers;
– constant voltage safety isolating transformers.
The windings can be encapsulated or non-encapsulated.
For power supply units (linear) this document is applicable. For switch mode power supply
units IEC 61558-2-16 is applicable together with this document. Where two requirements are
in conflict, the most severe take precedence.
The rated supply voltage does not exceed 1 000 V AC. The rated supply frequency does not
exceed 500 Hz, the internal operating resonant frequency does not exceed 30 kHz and the
internal operating frequency does not exceed 100 MHz.
The rated output does not exceed:
– 40 kVA for single-phase constant voltage auto-transformers;
– 200 kVA for polyphase constant voltage auto-transformers;
– 25 kVA for single-phase constant voltage separating transformers and constant voltage
isolating transformers;
– 40 kVA for polyphase constant voltage separating transformers and constant voltage
isolating transformers;
– 10 kVA for single-phase constant voltage safety isolating transformers;
– 16 kVA for polyphase constant voltage safety isolating transformers.
This document is applicable to transformers without limitation of the rated output, subject to
an agreement between the purchaser and the manufacturer.
NOTE 2 Transformers intended to supply distribution networks are not included in the scope.
Where applicable to constant voltage auto-transformers
– the no-load output voltage or the rated output voltage does not exceed 1 000 V AC or
1 415 V ripple-free DC, and for independent constant voltage auto-transformers the
no-load output voltage and the rated output voltage exceed 50 V AC or 120 V ripple-free
DC;
– constant voltage auto-transformers covered by this document are used only in
applications where no insulation between circuits is required by the installation rules or by
the end product standard.
Where applicable to constant voltage separating transformers
– the no-load output voltage or the rated output voltage does not exceed 1 000 V AC or
1 415 V ripple-free DC, and for independent constant voltage separating transformers
the no-load output voltage and the rated output voltage exceed 50 V AC or 120 V
ripple-free DC;
– constant voltage separating transformers covered by this document are used only in
applications where double or reinforced insulation between circuits is not required by the
installation rules or by the end product standard.
Where applicable to constant voltage isolating transformers
– the no-load output voltage or the rated output voltage does exceed 50 V AC or 120 V
ripple-free DC and where applicable, does not exceed 500 V AC or 708 V ripple-free DC.
The no-load output voltage and the rated output voltage can be up to 1 000 V AC or
1 415 V ripple-free DC for special applications;
– constant voltage isolating transformers covered by this document are used only in
applications where double or reinforced insulation between circuits is required by the
installation rules or by the end product standard.
Where applicable to constant voltage safety isolating transformers
– the no-load output voltage or the rated output voltage does not exceed 50 V AC or 120 V
ripple-free DC;
– constant voltage safety isolating transformers covered by this document are used only
in applications where double or reinforced insulation between circuits is required by the
installation rules or by the end product standard.
This document is not applicable to external circuits and their components intended to be
connected to the input terminals and output terminals 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
may be applicable to transformers intended for use in special environments.
Future technological development of transformers may necessitate a need to increase the
upper limit of the frequencies. Until then this document may be used as a guidance document.
– 8 – IEC 61558-2-12:2024 © IEC 2024
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 61558-1:2017, Safety of transformers, reactors, power supply units and combinations
thereof – Part 1: General requirements and tests
IEC 61558-2-16:2021, Safety of transformers, reactors, power supply units and combinations
thereof – Part 16: Particular requirements and tests for switch mode power supply units and
transformers for switch mode power supply units for general applications
3 Terms and definitions
For the purposes of this document, the terms and definitions given in IEC 61558-1 apply, except
as follows:
ISO and IEC maintain terminological databases for use in standardization at the following
addresses:
• IEC Electropedia: available at http://www.electropedia.org/
• ISO Online browsing platform: available at http://www.iso.org/obp
3.1 Transformers
Addition
3.1.101
constant voltage transformer
transformer intended to limit the influence of the input voltage variations
Note 1 to entry: This type of transformer can also limit the influence of transients.
3.5 Ratings
Addition
3.5.101
regulation tolerance
deviation in per cent of the rated output voltage when the constant voltage transformer is
supplied within the rated supply voltage variation
3.5.102
internal operating resonant frequency
frequency produced within a constant voltage transformer
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:
– 1 000 V AC or 1 415 V ripple-free DC for constant voltage auto-transformers and
constant voltage separating transformers;
– 250 V AC for single-phase portable constant voltage isolating transformers;
– 400 V AC for polyphase portable constant voltage isolating transformers, and
– 500 V AC or 708 V ripple-free DC for constant voltage isolating transformers. For
constant voltage isolating transformers, the rated output voltage can be up to 1 000 V
AC or 1 415 V ripple-free DC to be in accordance with the national wiring rules or for a
special purpose;
– 50 V AC or 120 V ripple-free DC for constant voltage safety isolating transformers;
The rated output voltage shall exceed:
– 50 V AC or 120 V ripple-free DC for independent constant voltage auto-transformers,
constant voltage separating transformers and constant voltage isolating
transformers.
6.102 The rated output shall not exceed:
– 40 kVA for single-phase constant voltage auto-transformers,
– 200 kVA for polyphase constant voltage auto-transformers,
– 25 kVA for single-phase constant voltage separating and isolating transformers,
– 40 kVA for polyphase constant voltage separating and isolating transformers,
– 10 kVA for single-phase constant voltage safety isolating transformers,
– 16 kVA for polyphase constant voltage safety isolating transformers,
except for constant voltage transformers subject to an agreement between the purchaser and
the manufacturer.
6.103 The rated supply frequency shall not exceed 500 Hz.
6.104 The rated value of the output regulation tolerance shall be given at the rated supply
voltage range, the rated output, and the power factor of 1.
6.105 For independent transformers the input voltage variation shall not be less than 10 %.
6.106 The internal operating resonant frequency shall not exceed 30 kHz.
– 10 – IEC 61558-2-12:2024 © IEC 2024
6.107 The internal operating frequency shall not exceed 100 MHz.
Compliance with the requirements of 6.101 to 6.107 is checked by inspection of the marking.
7 Classification
This clause of IEC 61558-1:2017 is applicable.
8 Marking and other information
This clause of IEC 61558-1:2017 is applicable except as follows:
8.1
a)
Replacement of the first sentence by the following:
rated supply voltage(s) and the input voltage variation in %;
b)
Replacement of the first sentence by the following:
rated output voltage(s) and the regulation tolerance of this voltage(s) in %;
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;
8.11
Addition:
The symbol for linear power supply units shall be used in conjunction with the symbol
indicating the kind of transformer.
Table 101 – Symbols indicating the kind of transformer
Symbol or graphical symbol Explanation or title Identification
Fail-safe constant voltage separating
IEC 60417-6011:2008-02
transformer
Non-short-circuit-proof constant voltage
IEC 60417-6011:2008-02
separating transformer
Short-circuit-proof constant voltage separating
IEC 60417-6011:2008-02
transformer
Fail-safe constant voltage isolating
IEC 60417-6012:2008-09
transformer
Non-short-circuit-proof constant voltage
IEC 60417-6012:2008-09
isolating transformer
Short-circuit-proof constant voltage isolating
IEC 60417-6012:2008-09
transformer
Fail-safe constant voltage safety isolating
IEC 60417-6013:2008-02
transformer
Non-short-circuit-proof constant voltage safety
IEC 60417-6013:2008-02
isolating transformer
– 12 – IEC 61558-2-12:2024 © IEC 2024
Symbol or graphical symbol Explanation or title Identification
Short-circuit-proof constant voltage safety
IEC 60417-6013:2008-02
isolating transformer
Fail-safe constant voltage auto-transformer IEC 60417-6017:2008-02
Non-short-circuit-proof constant voltage
IEC 60417-6017:2008-02
autotransformer
Short-circuit-proof constant voltage
IEC 60417-6017:2008-02
autotransformer
L
Power supply unit, linear IEC 60417-6210:2013-10
9 Protection against electric shock
This clause of IEC 61558-1:2017 is applicable.
10 Change of input voltage setting
This clause of IEC 61558-1:2017 is applicable.
11 Output voltage and output current under load
This clause of IEC 61558-1:2017 is applicable except as follows:
11.1
Replacement:
11.1 When the transformer is connected to the rated supply voltage plus or minus the input
voltage variation declared by the manufacturer, at the rated supply frequency, and loaded
with an impedance resulting in the rated output at the rated output voltage and, for AC, at
the rated power factor, the output voltage shall not differ from the rated value by more than
the regulation tolerance.
Compliance is checked by measuring the output voltage when steady-state conditions are
established. During the test, the transformer is connected to the rated supply voltage, plus
or minus the highest input voltage variation, at the rated supply frequency, and loaded with
an impedance resulting in the rated output at the rated output voltage and the rated power
factor.
For transformers incorporating a rectifier, the output voltage shall be measured at the terminals
of the DC circuit by means of a voltmeter giving the arithmetical mean value, unless the effective
(RMS) value is specifically stated (see 8.1).
For transformers with more than one rated supply voltage, the requirement is applicable for
each of the rated supply voltages.
For transformers with multiple output windings, the loads are applied to every multiple section
simultaneously, unless otherwise declared.
12 No-load output voltage
This clause of IEC 61558-1:2017 is applicable except as follows:
Addition:
The no-load output voltage is measured when the transformer is connected to the rated
supply voltage at the rated supply frequency at ambient temperature.
12.101 The no-load output voltage shall not exceed:
– 1 000 V AC or 1 415 V ripple-free DC for constant voltage auto-transformers and
constant voltage separating transformers;
– 250 V AC for single-phase portable constant voltage isolating transformers;
– 400 V AC for polyphase portable constant voltage isolating transformers, and
– 500 V AC or 708 V ripple-free DC for other constant voltage isolating transformers.
In this case, the no-load output voltage can be up to 1 000 V AC or 1 415 V ripple-free DC
to be in accordance with the national wiring rules or for a special purpose;
– 50 V AC or 120 V ripple-free DC for constant voltage safety isolating transformers.
The no-load output voltage shall exceed:
– 50 V AC or 120 V ripple-free DC for constant voltage independent auto-, separating and
isolating transformers.
For independent 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.
– 14 – IEC 61558-2-12:2024 © IEC 2024
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 %.
The ratio is determined by Formula (1):
UU−
no-load load
×100 (%)
(1)
U
load
where
is the no-load output voltage, expressed in V;
U
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 plus the highest input voltage variation at the rated supply frequency.
13 Short-circuit voltage
This clause of IEC 61558-1:2017 is applicable.
14 Heating
This clause of IEC 61558-1:2017 is applicable, except as follows:
14.1.1 Temperature-rise test
th
Replacement of the 11 paragraph as follows:
The transformers are connected to the rated supply voltage and loaded with an impedance
resulting in the rated output, at the rated output voltage and, for AC, at the rated power
factor. The supply voltage is then increased to the value of the highest input voltage variation
declared by the manufacturer. After this voltage increase, no change or adjustment is made in
the circuit. The test is repeated under no-load condition with the highest or the lowest input
voltage variation if this is a more unfavourable condition.
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
nd
Replacement of the 2 paragraph as follows:
Compliance is checked by inspection and by the following tests, which are carried out
immediately after the test in accordance with 14.1, at the same ambient temperature, and
without changing the position of the transformer at the maximum value of the rated supply
voltage designed for the transformer.
15.2 Inherently short-circuit proof transformers
Replacement:
Inherently short-circuit-proof constant voltage transformers shall be tested as follows:
Before starting the test, it is necessary to determine the highest output current of the
transformer at the maximum value of the supply voltage designed for the transformer. The
transformer is then loaded with the maximum output current or the output winding(s) short-
circuited, whichever results in the maximum temperature.
15.3 Non-inherently short-circuit proof transformers
Replacement:
Non-inherently short-circuit-proof constant voltage transformers are tested as follows:
15.3.1 The output windings are short-circuited or overloaded as stated in 15.2. The
incorporated overload protection device shall operate before the temperature exceeds the
values shown in Table 5 for any value of the supply voltage between the marked values of rated
supply voltage.
15.5 Fail-safe transformers
15.5.1
Replacement:
Three additional specimens are required, only for the following test. Transformers used in
other tests are not subjected to this test.
Each of the three specimens is mounted as for normal use on a 20 mm thick dull black painted
plywood surface. Each transformer is operated at rated supply voltage plus or minus the
input voltage variation declared by the manufacturer. The output winding which produced the
highest temperature during the test of 14.1 being initially loaded with 1,5 times the rated output
current (or, if this is not possible, the maximum value of the output current obtainable) until
steady-state conditions are reached or the transformer fails (whichever occurs first).
If the transformer fails, it shall comply, during and after the tests, with the criteria given in
15.5.2.
If the transformer does not fail, the time to reach steady-state conditions is noted and the
chosen output winding is then short-circuited. The test is continued until the transformer fails.
Each specimen shall do so within a duration, for this part of the test, which is no longer than
that necessary to attain steady-state conditions, but in any case it shall not exceed 5 h.
The transformer shall fail safely. It shall comply, during and after the test, with the criteria
given in 15.5.2.
16 Mechanical strength
This clause of IEC 61558-1:2017 is applicable.
17 Protection against harmful ingress of dust, solid objects and moisture
This clause of IEC 61558-1:2017 is applicable.
– 16 – IEC 61558-2-12:2024 © IEC 2024
18 Insulation resistance, dielectric strength and leakage current
This clause of IEC 61558-1:2017 is applicable, except as follows:
18.2 Insulation resistance
This subclause of IEC 61558-1 is applicable, except as follows:
Modification for constant voltage auto-transformers:
In accordance with Table 13 the values between input circuits and output circuits, between
each input circuit and all other input circuits, between each output circuits and all other
output circuits are not applicable.
18.3 Dielectric strength test
This subclause of IEC 61558-1 is applicable, except as follows:
Modification for constant voltage auto-transformers:
In accordance with Table 14 the values between input circuits and output circuits are not
applicable.
18.4 Insulation between and within windings
This subclause of IEC 61558-1:2017 is applicable, except as follows:
Addition for constant voltage auto-transformers:
For windings intended to be connected in series or parallel the dielectric strength test for
functional insulation in accordance with Table 14 shall be applied.
19 Construction
This clause of IEC 61558-1:2017 is applicable and general requirements for the different
transformer types are defined in the following subclauses of IEC 61558-1:2017:
19.1.2 Auto-transformers
This subclause of IEC 61558-1:2017 is applicable for constant voltage auto-transformers.
Addition:
19.1.2.101 Protection against direct contact with electrical and moving mechanical parts
(contact path and drive) shall be ensured.
Compliance is checked by inspection.
19.1.3 Separating transformers
This subclause of IEC 61558-1:2017 is applicable for constant voltage separating
transformers.
19.1.4 Isolating transformers and safety isolating transformers
This subclause of IEC 61558-1:2017 is applicable for constant voltage isolating transformers
and constant voltage safety isolating transformers.
19.1.4.4
Modification:
NOTE For the purpose of this subclause, the term "windings" does not include internal circuits such as the resonant
circuit.
Addition:
19.1.4.101 Transformers shall not be provided with capacitors which electrically connect
input and output circuits.
20 Components
This clause of IEC 61558-1:2017 is applicable.
21 Internal wiring
This clause of IEC 61558-1:2017 is applicable.
22 Supply connection and other external flexible cables or cords
This clause of IEC 61558-1:2017 is applicable.
23 Terminals for external conductors
This clause of IEC 61558-1:2017 is applicable.
24 Provisions for protective earthing
This clause of IEC 61558-1:2017 is applicable.
25 Screws and connections
This clause of IEC 61558-1:2017 is applicable.
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.
– 18 – IEC 61558-2-12:2024 © IEC 2024
28 Resistance to rusting
This clause of IEC 61558-1:2017 is applicable.
Annexes
The annexes of IEC 61558-1:2017 are applicable, except as follows:
Annex L
(normative)
Routine tests (production test)
This annex of IEC 61558-1:2017 is applicable except as follows:
Addition:
L.101 The output voltage regulation tolerance shall be within the limit declared by the
manufacturer.
Compliance is checked by measurement of the output voltage regulation tolerance at rated
output according to 11.1 but at room temperature of 25 °C ± 10 °C with the transformer in cold
condition.
– 20 – IEC 61558-2-12:2024 © IEC 2024
Bibliography
The Bibliography of IEC 61558-1 is applicable, except as follows:
Addition:
IEC 60204-1:2016, Safety of machinery – Electrical equipment of machines – Part 1: General
requirements
IEC 61140:2016, Protection against electric shock – Common aspects for installation and
equipment
IEC 61558 (all parts), Safety of transformers, reactors, power supply units and combinations
thereof
ISO/IEC GUIDE 51:2014, Safety aspects – Guidelines for their inclusion in standards
____________
– 22 – IEC 61558-2-12:2024 © IEC 2024
SOMMAIRE
AVANT-PROPOS . 23
INTRODUCTION . 26
1 Domaine d'application . 27
2 Références normatives . 29
3 Termes et définitions . 29
4 Exigences générales .
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