IEC 61558-2-2:2022

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

IEC 61558-2-2:2022 deals with the safety of control transformers and power supply units incorporating control transformers. Transformers incorporating electronic circuits are also covered by this document. 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:
- adjustment of structure and references in accordance with IEC 61558-1:2017;
- new general symbol for control transformers;
- 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 combinaisons de ces éléments - Partie 2-2: Exigences particulières et essais pour les transformateurs de commande et les blocs d'alimentation qui incorporent des transformateurs de commande

L'IEC 61558-2-2:2022 traite de la sécurité des transformateurs de commande et des blocs d'alimentation qui incorporent des transformateurs de commande. Les transformateurs qui incorporent des circuits électroniques sont également couverts par le présent document. Cette troisième édition annule et remplace la deuxième édition parue en 2007. Cette édition constitue une révision technique. Cette édition inclut les modifications techniques majeures suivantes par rapport à l'édition précédente:
- la structure et les références ont été alignées sur l'IEC 61558-1:2017;
- un nouveau symbole général a été ajouté pour les transformateurs de commande;
- 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.

General Information

• Status: Published
• Publication Date: 18-Oct-2022
• ICS: 29.180 - Transformers. Reactors
• Technical Committee: TC 96 - Transformers and reactors
• Drafting Committee: MT 1 - TC 96/MT 1
• Current Stage: PPUB - Publication issued
• Start Date: 19-Oct-2022
• Completion Date: 04-Nov-2022

Relations

• Revises: IEC 61558-2-2:2007 - Safety of power transformers, power supplies, reactors and similar products - Part 2-2: Particular requirements and tests for control transformers and power supplies incorporating control transformers
• Effective Date: 05-Sep-2023

Overview

IEC 61558-2-2:2022 - "Safety of transformers, reactors, power supply units and combinations thereof - Part 2-2" - defines particular safety requirements and tests for control transformers and power supply units incorporating control transformers. This third edition (2022) replaces the 2007 edition, constitutes a technical revision and is published as a group safety publication (IEC Guide 104). It applies mainly to dry-type, air-cooled control transformers (including those with electronic circuits) used for control and safety extra-low-voltage (SELV) applications.

Key topics and requirements

The standard supplements IEC 61558-1:2017 and covers practical safety and test topics, including:

• Scope and classification - applicability to stationary/portable, single- or poly-phase devices; dry-type constructions; limits on voltages and frequencies.
• Rated limits - rated supply voltage ≤ 1 000 V AC and rated/internal frequency ≤ 500 Hz; no‑load or rated output voltage ≤ 1 000 V AC (or 1 415 V ripple‑free DC). Typical rated thermal output limits: 25 kVA (single-phase) and 40 kVA (polyphase), unless otherwise agreed.
• Electrical safety - protection against electric shock, insulation, creepage/clearance distances, dielectric strength, leakage current.
• Performance tests - output voltage/current under load, no-load voltage, short‑circuit voltage, short‑circuit and overload protection.
• Thermal and mechanical tests - heating, mechanical strength, resistance to fire/tracking and rusting.
• Construction and components - internal wiring, terminals, earthing provisions, components selection and marking.
• Ingress protection - protection against dust, solid objects and moisture.
• Specific symbols and markings - introduction of a new general symbol for control transformers and a new symbol for power supplies with linearly regulated outputs.
• Coordination with switch‑mode supplies - linear power supply units are covered here; switch‑mode power supplies are addressed by IEC 61558-2-16 in conjunction with this part - where requirements conflict, the more stringent applies.

Applications and who uses this standard

IEC 61558-2-2:2022 is used by:

• Transformer and power-supply manufacturers designing and marking control transformers and linear control PSUs.
• Product design and safety engineers ensuring compliance with electrical, thermal and mechanical safety requirements.
• Test laboratories and certification bodies performing safety and type tests.
• Procurement and compliance teams specifying safe control transformers for industrial control panels, machine tools, building automation, and SELV control circuits.
• Electrical installers and maintenance teams referencing safe limits and markings.

Related standards

• IEC 61558-1:2017 (general requirements)
• IEC 61558-2-16 (switch‑mode power supplies)
• IEC 60076-11 (other transformer types - excluded)
• SELV and control-circuit references: IEC 61140, IEC 60364-4-41, IEC 60204-1

This standard is essential for ensuring the safety, marking, testing and correct selection of control transformers and associated power supply units in industrial and control applications.

Standards Content (Sample)

IEC 61558-2-2 ®
Edition 3.0 2022-10
REDLINE VERSION
INTERNATIONAL
STANDARD
colour
inside
GROUP SAFETY PUBLICATION
Safety of power transformers, power supplies, reactors, power supply units and
similar products combinations thereof –
Part 2-2: Particular requirements and tests for control transformers and power
supplies supply units incorporating control transformers

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IEC 61558-2-2 ®
Edition 3.0 2022-10
REDLINE VERSION
INTERNATIONAL
STANDARD
colour
inside
GROUP SAFETY PUBLICATION
Safety of power transformers, power supplies, reactors, power supply units and
similar products combinations thereof –
Part 2-2: Particular requirements and tests for control transformers and power
supplies supply units incorporating control transformers
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 29.180 ISBN 978-2-8322-5919-1
– 2 – IEC 61558-2-2:2022 RLV  IEC 2022
CONTENTS
FOREWORD . 3
INTRODUCTION . 2
1 Scope . 7
2 Normative references . 7
3 Terms and definitions . 9
4 General requirements . 10
5 General notes on tests . 10
6 Ratings . 10
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 . 13
12 No-load output voltage . 13
13 Short-circuit voltage . 14
14 Heating . 14
15 Short-circuit and overload protection . 14
16 Mechanical strength . 14
17 Protection against harmful ingress of dust, solid objects and moisture . 14
18 Insulation resistance, dielectric strength and leakage current . 14
19 Construction . 15
20 Components . 16
21 Internal wiring . 16
22 Supply connection and other external flexible cables or cords . 16
23 Terminals for external conductors . 16
24 Provisions for protective earthing. 16
25 Screws and connections . 16
26 Creepage distances, clearances and distances through insulation . 16
27 Resistance to heat, fire and tracking . 17
28 Resistance to rusting . 17
Annexes . 18
Bibliography . 19

Table 101 – Symbols indicating the kind of transformer . 11

INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
SAFETY OF POWER TRANSFORMERS, POWER SUPPLIES,
REACTORS, POWER SUPPLY UNITS AND SIMILAR PRODUCTS
COMBINATIONS THEREOF –
Part 2-2: Particular requirements and tests for control transformers
and power supplies supply units incorporating control transformers

FOREWORD
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This redline version of the official IEC Standard allows the user to identify the changes made to
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has been made. Additions are in green text, deletions are in strikethrough red text.

– 4 – IEC 61558-2-2:2022 RLV  IEC 2022
International standard IEC 61558-2-2 has been prepared by IEC technical committee 96:
Transformers, reactors, power supply units and combinations thereof.
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 general symbol for control transformers;
c) new symbol for power supply unit with linearly regulated output voltage.
The text of this document is based on the following documents:
Draft Report on voting
96/548/FDIS 96/554/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 document 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 document 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 control
transformers and power supply units incorporating control transformers.
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 www.webstore.iec.ch in the data related to the
specific document. At this date, the document will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
IMPORTANT – The "colour inside" logo on the cover page of this document indicates that it
contains colours which are considered to be useful for the correct understanding of its
contents. Users should therefore print this document using a colour printer.

– 6 – IEC 61558-2-2:2022 RLV  IEC 2022
INTRODUCTION
IEC TC 96 has a group safety function in accordance with IEC Guide 104 for transformers other
than those intended to supply distribution networks, in particular transformers and power supply
units intended to allow the application of protective measures against electric shock as defined
by TC 64, but in certain cases including the limitation of voltage and horizontal safety function
for SELV, in accordance with IEC 60364-4-41.
The group safety function (GSF) is used because of responsibility for example 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 the IEC 61558-2 series 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 POWER TRANSFORMERS, POWER SUPPLIES,
REACTORS, POWER SUPPLY UNITS AND SIMILAR PRODUCTS
COMBINATIONS THEREOF –
Part 2-2: Particular requirements and tests for control transformers
and power supplies supply units incorporating control transformers

1 Scope
Replacement:
This part of IEC 61558 deals with the safety aspects of control transformers and power
supplies supply units incorporating control transformers. Transformers incorporating
electronic circuits are also covered by this document.
NOTE 1 Safety includes electrical, thermal and mechanical safety aspects.
This Part 2-2 is applicable to control transformers and power supplies incorporating both
control transformers and electronic circuits. This Part 2-2 is not applicable to external
circuits and their components intended to be connected to the input terminals, output terminals
or socket-outlets of the transformer and power supplies.
Unless otherwise specified, from here onward, the term transformer covers control
transformers and power supply units incorporating control transformers.
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.
This document does not apply to transformers covered by IEC 60076-11.
This Part 2-2 applies to stationary or portable, single-phase or poly-phase, air-cooled (natural
or forced), independent or associated control transformers and power supplies
incorporating a control transformer, having a rated supply voltage not exceeding 1 000 V
a.c. and rated supply and internal operating frequency not exceeding 500 Hz.
This document is applicable to stationary or portable, single-phase or polyphase, air-cooled
(natural or forced) independent or associated dry-type transformers. The windings can be
encapsulated or non-encapsulated.
The rated supply voltage does not exceed 1 000 V AC and the rated supply frequency and
the internal operating frequencies do not exceed 500 Hz.
The rated thermal output does not exceed:
• 25 kVA for single-phase control transformers and power supplies incorporating control
transformers,
• 40 kVA for polyphase control transformers and power supplies incorporating control
transformers.
This document is applicable to control transformers and power supplies incorporating
control transformers without limitation of the rated thermal output, subject to an agreement
between the purchaser and the manufacturer.

– 8 – IEC 61558-2-2:2022 RLV  IEC 2022
This Part 2-2 is applicable to dry-type transformers. The windings may be encapsulated or
non-encapsulated.
NOTE 2 Transformers intended to supply networks are not included in the scope.
The no-load output voltage or the rated output voltage does not exceed 1 000 V AC or
1 415 V ripple-free DC. For independent control transformers and independent power
supplies incorporating control transformers, the no-load output voltage and / or the rated
output voltage is not less than 50 V AC or 120 V ripple-free DC.
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 Control Transformers covered by this document are only used in applications where double or reinforced
insulation between circuits is not required by the installation rules or by the end product standard.
NOTE 4 Normally the control transformers and power supplies incorporating control transformers are intended
to be used with equipment to provide voltages different from the supply voltage for the functional requirements of the
equipment. The protection against electric shock may can be provided (or completed) by other features of the
equipment, such as the body. Parts of output circuits may can be connected to the input circuits or to protective
earthing.
This Part 2-2 is applicable to control transformers and power supplies incorporating control
transformers associated with specific equipment, to the extent decided upon by the relevant
IEC technical committees.
NOTE 2 Attention is drawn to the following, if necessary:
• for control transformers and power supplies incorporating control transformers
intended to be used in vehicles, on board ships, and on board 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 control
transformers and power supplies incorporating control transformers should also be
considered;
• additional requirements in accordance with other appropriate standards and national rules
may can be applicable to control transformers and power supplies incorporating control
transformers intended for use in special environments, such as tropical environments.
NOTE 3 Future technological development of control transformers and power supplies
incorporating control transformers may can necessitate a need to increase the upper limit of
the frequencies. Until then this document may 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 60076-11, Power transformers – Part 11: Dry-type transformers
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 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
This clause of Part 1 is applicable except as follows:
Replacement of the third paragraph:
When the term transformer is used from here forward, it covers control transformers and
power supplies incorporating control transformer(s) where applicable.
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 http://www.electropedia.org/
• ISO Online browsing platform: available at http://www.iso.org/obp
Addition:
3.1.101
control transformer
transformer intended to supply power to control circuits (e.g. controlling, signalling,
interlocking, etc.)
3.5.101
rated thermal output
product of the rated output voltage and the rated output current, or for polyphase
transformers, the appropriate factor (e. g. for three-phase transformers 3 ) times the product
of the rated output voltage and the rated output current delivered in continuous operation
loaded at power factor 1
Note 1 to entry: If the transformer has more than one output winding or/and tapped output winding (or both),
the rated output denotes the sum of the products of rated output voltage and rated output current for output
circuits intended to be loaded simultaneously.
3.5.102
admissible instantaneous output
product of the rated output voltage and the rated instantaneous output current, or for
polyphase transformers, the appropriate factor (e. g. for three-phase transformers 3 ) times
the product of the rated output voltage and the rated instantaneous output current delivered
at power factor 0,5
Note 1 to entry: If the transformer has more than one output winding or/and tapped output winding (or both),
the rated output denotes the sum of the products of rated output voltage and rated instantaneous output current
for output circuits intended to be loaded simultaneously.

– 10 – IEC 61558-2-2:2022 RLV  IEC 2022
3.5.103
rated instantaneous output current
output current for the specific operating conditions at the rated output voltage and the rated
supply frequency at power factor 0,5 assigned to the transformer by the manufacturer
4 General requirements
This clause of IEC 61558-1:2017 is applicable.
5 General notes on tests
This clause of IEC 61558-1:2017 is applicable.
6 Ratings
This clause of IEC 61558-1:2017 is applicable except as follows:
Replacement Addition:
6.101 The rated output voltage shall not exceed 1 000 V AC or 1 415 V ripple-free DC and
for independent transformers shall exceed 50 V AC or 120 V ripple-free DC.
For independent transformers, this output voltage limitation applies even when output
windings, not intended for interconnection, are connected in series.
6.102 The rated thermal output shall not exceed:
• 25 kVA for single-phase transformers except,
• 40 kVA for polyphase transformers except for transformers subject to an agreement
between the purchaser and the manufacturer.
Transformers without limitation of the rated thermal output shall be subject to agreement
between the purchaser and the manufacturer.
6.103 The rated supply frequency and the internal operating frequencies shall not
exceed 500 Hz.
6.104 The rated supply voltage shall not exceed 1 000 V AC.
Compliance with the requirements of 6.101 to 6.104 is checked by inspection of the marking.
7 Classification
This clause of IEC 61558-1:2017 is applicable except as follows:
7.8
Replacement
Control transformers shall be classified for overvoltage category III.

8 Marking and other information
This clause of IEC 61558-1:2017 is applicable except as follows:
8.1 c)
Replacement:
the transformers shall be marked with the rated thermal output and the admissible
instantaneous output in volt-ampere, separated by an oblique stroke (e.g. 100/300 VA);
d)
Replacement:
Item d) is not applicable.
h)
Replacement:
the transformers shall be marked with one of the graphical symbols shown in 8.11.
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:
Symbol or graphical symbol Explanation or title Identification
Fail-safe control transformer
Non-short-circuit proof control transformer

Short-circuit proof control transformer

(inherently or non-inherently)

The symbol for linear power supply units shall be used in conjunction with the symbol
indicating the kind of transformer.

– 12 – IEC 61558-2-2:2022 RLV  IEC 2022
Table 101 – Symbols indicating the kind of transformer
Symbol or graphical symbol Explanation or title Identification
Fail-safe control transformer IEC 60417-6036:2010-08

Non-short-circuit-proof control transformer IEC 60417-6037:2010-08

Short-circuit-proof control transformer IEC 60417-6038:2010-08
(inherently or non-inherently)

Power supply unit, linear IEC 60417-6210:2013-10
L
Addition:
8.101 If transformers are provided with input tappings to allow adjustments to the supply
voltage, these tappings shall be marked with the value or the variation (e.g. +5 V or –5 V) of
the input voltage corresponding to the tapping.
NOTE If control transformers are provided with input tappings to allow adjustments to the supply voltage, tappings
in steps of 5 % are preferred.
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:
When the transformer is connected to the rated supply voltage, at rated supply frequency,
and loaded with an impedance at power factor 1 resulting in the rated thermal output at the
rated output voltage, the output voltage shall not differ from the rated value by more
than ±5 %.
Compliance is checked by measuring the output voltage when steady-state conditions are
established.
Immediately after the transformer is loaded with an impedance resulting in the admissible
instantaneous output at the rated output voltage at power factor 0,5 (inductive), the output
voltage measured shall not be less than 95 % of the measured voltage at the rated thermal
output.
NOTE The output voltage measurement for the admissible instantaneous output should be
carried out within 50 ms after applying this overload to minimise the effects of supplementary
heating of the transformer.
For transformers with more than one rated supply voltage, the requirement is applicable for
each of the rated supply voltages.
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 1 000 V AC or 1 415 V ripple-free DC
and for independent transformers shall exceed 50 V AC or 120 V ripple-free DC.
For independent transformers, this output voltage limitation applies even when output
windings, not intended for interconnection, are connected in series.
NOTE The requirement for series connection does not apply to associated or IP 00 transformers.
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 %.

– 14 – IEC 61558-2-2:2022 RLV  IEC 2022
NOTE The ratio is defined 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 when at the ambient temperature, when the transformer being is connected
to the rated supply voltage at the rated supply frequency and at the rated thermal output.
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
Replacement of the tenth eleventh paragraph:
Transformers are supplied at the rated supply voltage and loaded with an impedance
producing the rated thermal output, at the rated output voltage and, for AC current, at the
rated power factor. The value of the output current is measured when steady state is
established. Then the supply voltage is increased by 10 % and the output current is adjusted to
the same value measured before previously. The output current is not adjusted for independent
transformers. After this increase of the supply voltage, no change is made in the circuit. The
test is repeated under no-load condition, if this is a more unfavourable situation.
15 Short-circuit and overload protection
This clause of IEC 61558-1:2017 is applicable.
16 Mechanical strength
This clause of IEC 61558-1:2017 is applicable.
17 Protection against harmful ingress of dust, solid objects and moisture
This clause of IEC 61558-1:2017 is applicable.
18 Insulation resistance, dielectric strength and leakage current
This clause of IEC 61558-1:2017 is applicable except as follows:

18.3 Dielectric strength test
Add the following paragraph and note before Table 8a:
For transformers, the values of test voltages for basic insulation (boxes 1) and 3) in Table
8a) are multiplied by a factor of 1,4.
Addition:
The required values of the dielectric strength test voltages for basic insulation of Table 14
shall be multiplied by a factor of 1,4.
NOTE Basic insulation has been increased because transformers are subjected to surge voltages due to the
inductive nature of their loads.
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, through via other conductive parts, except by deliberate action.
Compliance is checked by inspection and measurements, taking Clause 18 and Clause 26 into
consideration.
19.1.1 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 requirements apply:
• for class I transformers, the insulation between the input windings and the body, and
between the output windings and the body, shall consist of 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).
19.1.2 For transformers with intermediate conductive parts (e.g. the iron core) not
connected to the body and located between the input and output windings, the insulation
between the intermediate conductive parts and the input windings or between the
intermediate conductive parts and the output windings shall consist of at least basic
insulation (rated for the working voltage).
NOTE An intermediate conductive part not separated from the input or output windings or the body by at least
a basic insulation is considered to be connected to the relevant part(s).
In addition, the following requirements apply:
– 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);
– 16 – IEC 61558-2-2:2022 RLV  IEC 2022
– for class II transformers, the insulation between the input windings and the body, and
between the output windings and the body via the intermediate conductive parts shall
consist of double or reinforced insulation (rated for the working voltage).
Addition:
19.101 There shall be no connections between the output circuits and the protective earth
unless allowed by the relevant equipment standard for associated transformers.
19.102 There shall be no connections between the output circuits and the body unless
allowed by the relevant equipment standard for associated transformers.
Compliance is checked by inspection.
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 except as follows:
26.1 General
Replacement of the first paragraph:
Creepage distances, clearances and distances through insulation shall not be less than
the values shown in Table 13, the values for basic insulation (boxes 1, 3 and 5) being
multiplied by a factor of 1,4.
The required values of creepage distances and clearances for basic insulation in
accordance with Table 20 and Table 21 shall be multiplied by a factor of 1,4.

NOTE 101 Basic insulation has been increased because transformers are subjected to surge voltages due to the
inductive nature of their loads.
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.

– 18 – IEC 61558-2-2:2022 RLV  IEC 2022
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 60076-11:2018, Power transformers – Part 11: Dry-type transformers
IEC 60204-1:2016, Safety of machinery – Electrical equipment of machines – Part 1: General
requirements
IEC 61558 (all parts), Safety of transformers, reactors, power supply units and combinations
thereof
IEC 61558-2-13:2022, 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
ISO/IEC Guide 51:2014, Safety aspects – Guidelines for their inclusion in standards
IEC Guide 104:2019, The preparation of safety publications and the use of basic safety
publications and group safety publications

____________
IEC 61558-2-2 ®
Edition 3.0 2022-10
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
GROUP SAFETY PUBLICATION
PUBLICATION GROUPÉE DE SÉCURITÉ
Safety of transformers, reactors, power supply units and combinations thereof –
Part 2-2: Particular requirements and tests for control transformers and power
supply units incorporating control transformers

Sécurité des transformateurs, bobines d'inductance, blocs d'alimentation et
combinaisons de ces éléments –
Partie 2-2: Exigences particulières et essais pour les transformateurs de
commande et les blocs d'alimentation qui incorporent des transformateurs de
commande
– 2 – IEC 61558-2-2:2022  IEC 2022
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 . 9
8 Marking and other information . 9
9 Protection against electric shock . 10
10 Change of input voltage setting . 10
11 Output voltage and output current under load . 11
12 No-load output voltage . 11
13 Short-circuit voltage . 12
14 Heating . 12
15 Short-circuit and overload protection . 12
16 Mechanical strength . 12
17 Protection against harmful ingress of dust, solid objects and moisture . 12
18 Insulation resistance, dielectric strength and leakage current . 12
19 Construction . 13
20 Components . 14
21 Internal wiring . 14
22 Supply connection and other external flexible cables or cords . 14
23 Terminals for external conductors . 14
24 Provisions for protective earthing. 14
25 Screws and connections . 14
26 Creepage distances, clearances and distances through insulation . 14
27 Resistance to heat, fire and tracking . 14
28 Resistance to rusting . 14
Annexes . 15
Bibliography . 16

Table 101 – Symbols indicating the kind of transformer . 10

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

Part 2-2: Particular requirements and tests for control transformers
and power supply units incorporating control transformers

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 C
...

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Edition 3.0 2022-10
EXTENDED VERSION
INTERNATIONAL
STANDARD
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GROUP SAFETY PUBLICATION
Safety of transformers, reactors, power supply units and combinations thereof –
Part 2-2: Particular requirements and tests for control transformers and power
supply units incorporating control transformers
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IEC 61558-2-2 EXV ®
Edition 3.0 2022-10
EXTENDED VERSION
INTERNATIONAL
STANDARD
colour
inside
This extended version of IEC 61558-2-2:2022 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 2-2: Particular requirements and tests for control transformers and power
supply units incorporating control transformers
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 29.180 ISBN 978-2-8322-5932-0
– 2 – IEC 61558-2-2:2022 EXV © IEC 2022
CONTENTS
FOREWORD .9
INTRODUCTION TO IEC 61558-1:2017 . 12
INTRODUCTION . 15
1 Scope . 16
2 Normative references . 17
3 Terms and definitions . 20
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 . 45
9.1 General . 45
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 . 46
9.2.3 Accessibility to non hazardous-live-part . 49
9.3 Protection against hazardous electrical discharge . 49
10 Change of input voltage setting . 49
11 Output voltage and output current under load . 50
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 . 54
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 . 63
15.5 Fail-safe transformers . 63

16 Mechanical strength . 64
16.1 General . 64
16.2 Stationary transformers. 64
16.3 Portable transformers (except portable transformers with integral pins for
introduction in socket-outlet in the fixed wiring) . 65
16.4 Portable transformers provided with integral pins for introduction in socket-
outlets of the fixed wiring . 65
16.4.1 General requirements . 65
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 . 66
16.5 Additional requirements for transformers to be used in vehicles and railway
applications . 67
16.5.1 Transformers to be used in vehicles and railway applications . 67
16.5.2 Test requirements for the transportation of transformers . 68
17 Protection against harmful ingress of dust, solid objects and moisture . 69
17.1 Degrees of protection provided by enclosures (IP code) . 69
17.1.1 General requirements . 69
17.1.2 Tests on transformers with enclosure . 70
17.2 Humidity treatment . 72
18 Insulation resistance, dielectric strength and leakage current . 73
18.1 General . 73
18.2 Insulation resistance . 73
18.3 Dielectric strength test . 74
18.4 Insulation between and within windings . 76
18.5 Touch current and protective earthing conductor current . 76
18.5.1 General . 76
18.5.2 Touch current . 77
18.5.3 Protective earthing conductor current . 78
19 Construction . 78
19.1 General construction . 78
19.1.3 Separating transformers . 79
19.1.4 Isolating transformers and safety isolating transformers . 80
19.2 Flammability of materials . 82
19.3 Short-circuit characteristics of portable transformers . 82
19.4 Class II transformer contact prevention of accessible conductive parts . 83
19.5 Class II transformer insulation reassembling after service . 83
19.6 Loosening of wires, screws or similar parts . 83
19.7 Resistor or capacitor connection with accessible conductive parts . 84
19.8 Bridging of separated conductive parts by resistors or capacitors . 84
19.9 Insulating material separating input and output windings . 84
19.10 Accidental contact protection against hazardous-live-parts provided by
isolating coating . 85
19.11 Insulating material of handles, operating levers, knobs and similar parts . 86
19.12 Winding construction . 86
19.13 Fixing of handles, operating levers and similar parts . 90
19.14 Fixing of covers providing protection against electric shock . 90
19.15 Strain on fixed socket-outlets caused by pin-transformers connection. 90
19.16 Portable transformers for use in irregular or harsh conditions . 91

– 4 – IEC 61558-2-2:2022 EXV © IEC 2022
19.17 Drain hole of transformers protected against ingress of water . 91
19.18 Plug connected transformers protected against ingress of water . 91
19.19 Flexible cable or flexible cord connection for class I portable transformers . 91
19.20 SELV- and PELV-circuit separation of live parts. 91
19.21 Protection against contact for FELV-circuit . 92
19.22 Protective earthing regarding class II transformers . 92
19.23 Protective earthing regarding class III transformers . 92
20 Components . 93
21 Internal wiring . 98
22 Supply connection and other external flexible cables or cords . 98
23 Terminals for external conductors . 104
24 Provisions for protective earthing . 106
25 Screws and connections . 107
26 Creepage distances, clearances and distances through insulation . 110
26.1 General . 110
26.2 Creepage distances and clearances . 111
26.2.1 General . 111
26.2.2 Windings covered with adhesive tape . 111
26.2.3 Uncemented insulationing parts . 111
26.2.4 Cemented insulating parts . 111
26.2.5 Enclosed parts (e.g. by impregnation or potting) . 112
26.3 Distance through insulation . 113
27 Resistance to heat, fire and tracking . 124
27.1 General . 124
27.2 Resistance to heat . 124
27.2.1 General . 124
27.2.2 External accessible parts . 124
27.2.3 Internal parts . 125
27.3 Resistance to abnormal heat under fault conditions . 125
27.4 Resistance to fire. 126
27.4.1 General . 126
27.4.2 External accessible parts . 127
27.4.3 Internal parts . 127
27.5 Resistance to tracking . 128
28 Resistance to rusting. 128

Annex A (normative) Measurement of creepage distances and clearances . 129
Annex B (normative) Testing a series of transformers . 133
B.1 General . 133
B.2 Requirements . 133
B.3 Constructional inspection . 134
Annex C (void) . 135
Annex D (void) . 136
Annex E (normative) Glow-wire test . 137
E.1 General . 137
E.2 Severity . 137
E.3 Conditioning . 137

E.4 Test procedure . 137
Annex F (normative) Requirements for manually operated switches which are parts of
transformers assembly . 138
F.1 General . 138
F.2 Switches tested as a separate component . 138
F.3 Switches tested as part of the transformer . 138
Annex G (normative) Tracking test . 141
G.1 General . 141
G.2 Test specimen . 141
G.3 Test apparatus . 141
G.4 Procedure . 141
Annex H (normative) Electronic circuits . 142
H.1 General . 142
H.2 General notes on tests (addition to Clause 5) . 142
H.3 Short circuit and overload protection (addition to Clause 15) . 142
H.4 Creepage distances, clearances and distances through insulation (addition
to Clause 26) . 144
Annex I (informative) Dimensions for rectangular cross-section connectors of
transformers, basic dimensions and coordination . 146
Annex J (normative) Measuring network for touch-currents . 149
Annex K (normative) Insulated winding wires . 150
K.1 General . 150
K.2 Type tests . 150
K.2.1 General . 150
K.2.2 Dielectric strength test . 150
K.2.3 Flexibility and adherence . 150
K.2.4 Heat shock . 151
K.2.5 Retention of dielectric strength after bending . 151
K.3 Testing during manufacturing . 152
K.3.1 General . 152
K.3.2 Routine test . 152
K.3.3 Sampling test . 152
Annex L (normative) Routine tests (production tests) . 153
L.1 General . 153
L.2 Protective earthing continuity test. 153
L.3 Checking of no-load output voltage . 153
L.4 Dielectric strength test . 153
L.5 Checking of protective devices mounting . 154
L.6 Visual inspection . 154
L.7 Repetition test after routine dielectric strength test . 154
Annex M (informative) Examples to be used as a guide for 19.1 . 155
M.1 General . 155
M.2 Coil-former . 155
M.2.1 Concentric type . 155
M.2.2 Side-by-side type. 156
M.3 Windings . 156
M.3.1 Without screen . 156
M.3.2 With screen . 157

– 6 – IEC 61558-2-2:2022 EXV © IEC 2022
Annex N (informative) Examples for checking points of dielectric strength test voltages. 158
Annex O (void) . 160
Annex P (informative) Examples for measurement points of creepage distances and
clearances . 161
Annex Q (informative) Explanation of IP numbers for degrees of protection . 164
Q.1 General . 164
Q.2 Degrees of protection against access to hazardous parts and against solid
foreign objects . 164
Q.3 Degrees of protection against ingress of water . 166
Annex R (normative) Explanations of the application of 6.1.2.2.1 of IEC 60664-1:2007 . 167
R.1 Impulse dielectric test . 167
R.2 Example . 167
Annex S (void) . 169
Annex T (void) . 170
Annex U (void) . 171
Annex V (informative) Symbols to be used for thermal cut-outs . 172
V.1 General . 172
V.2 Non-self-resetting thermal cut-out (see 3.3.4) . 172
V.3 Self-resetting thermal cut-out (see 3.3.3) . 172
Annex W (normative) Coated printed circuit boards . 173
W.1 Preamble. 173
W.2 General . 173
W.3 Cold . 173
W.4 Rapid change of temperature . 173
W.5 Additional tests . 173
Bibliography . 174
Index of defined terms . 176

Figure 1 – IEC 61558 principle . 13
Figure 2 – Mounting box for flush-type transformer . 37
Figure 3 – Test pin (see IEC 61032, test probe 13). 47
Figure 4 – Standard test finger (see IEC 61032, test probe B) . 48
Figure 5 – Example of back-to-back method – Single phase . 55
Figure 6 – Example of back-to-back method – Three phase . 56
Figure 7 – Amplitude spectrum density for random testing . 68
Figure 8 – Normalised spectrum of shock . 69
Figure 9 – Test voltage sequence . 76
Figure 10 – Test configuration: single-phase equipment on star TN or TT system . 78
Figure 11 – Abrasion resistance test for insulating coated layers . 86
Figure 12 – Flexing test apparatus . 102
Figure 13 – Test arrangement for checking mechanical withstanding of insulating
materials in thin sheet layers . 116
Figure 14 – Ball-pressure apparatus . 124
Figure A.1 – Example 1 . 129
Figure A.2 – Example 2 . 130
Figure A.3 – Example 3 . 130

Figure A.4 – Example 4 . 130
Figure A.5 – Example 5 . 131
Figure A.6 – Example 6 . 131
Figure A.7 – Example 7 . 132
Figure A.8 – Example 8 . 132
Figure H.1 – Example of an electronic circuit with low-power points . 145
Figure J.1 – Measuring network for touch-current . 149
Figure M.1 – Examples for concentric type constructions . 155
Figure M.2 – Examples for side-by-side type constructions . 156
Figure M.3 – Examples for winding constructions without screen . 156
Figure M.4 – Examples for wrapped winding constructions . 157
Figure M.5 – Examples for winding constructions with screen . 157
Figure N.1 – Transformer of class I construction with metal enclosure . 158
Figure N.2 – Transformer of class II construction with metal enclosure . 159
Figure N.3 – Transformer of class II construction with enclosure of insulating material . 159
Figure P.1 – Transformer of class I construction . 161
Figure P.2 – Transformer of class I construction with earthed metal screen . 162
Figure P.3 – Transformer of class II construction with metal enclosure . 162
Figure P.4 – Transformer of class II construction with enclosure of insulating material . 163
Figure V.1 – Restored by manual operation. 172
Figure V.2 – Restored by disconnection of the supply . 172
Figure V.3 – Thermal link (see 3.3.5) . 172
Figure V.4 – Self-resetting thermal cut-out . 172

Table 1 – Symbols used on equipment or in instructions . 42
Table 101 – Symbols indicating the kind of transformer . 43
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 6 – Values of T and k for fuses . 62
Table 7 – Pull force on pins . 66
Table 8 – Conditions for vibration testing (random) . 67
Table 9 – Amplitude spectrum density ASD values for accelerated life testing . 67
Table 10 – Frequency values depending on the weight of the specimen . 68
Table 11 – Excitation values for vibration testing . 68
Table 12 – Solid-object-proof transformer test . 71
Table 13 – Values of insulation resistance . 74
Table 14 – Table of dielectric strength test voltages . 75
Table 15 – Limits for currents . 78
Table 16 – Nominal cross-sectional areas of external flexible cables or cords . 100
Table 17 – Pull and torque to be applied to external flexible cables or cords fixed to
stationary and portable transformers . 104

– 8 – IEC 61558-2-2:2022 EXV © IEC 2022
Table 18 – Torque to be applied to screws and connections . 108
Table 19 – Torque test on glands. 110
Table 20 – Clearances in mm . 117
Table 21 – Creepage distances in mm . 118
Table 22 – Distance through insulation in mm . 119
Table 23 – Creepage distances and clearance between terminals for external connection . 120
Table 24 – Values of FIW wires with minimum overall disameter and minimum test
voltages according to the total enamel increase . 122
Table A.1 – Width of groove values depending on the pollution degree . 129
Table F.1 – Peak surge current of additional loads . 139
Table I.1 – Dimensions of rectangular copper connectors . 147
Table K.1 – Mandrel diameter . 151
Table K.2 – Oven temperature . 151
Table Q.1 – Degrees of protection against access to hazardous parts indicated by the
first characteristic numeral . 165
Table Q.2 – Degrees of protection against solid foreign objects indicated by the first
characteristic numeral . 165
Table Q.3 – Degrees of protection indicated by the second characteristic numeral . 166
Table R.1 – Impulse test voltage according to 6.1.2.2.1 of IEC 60664-1:2007 . 167

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

Part 2-2: Particular requirements and tests for control transformers
and power supply units incorporating control transformers

FOREWORD
1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising
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This extended version (EXV) of the official IEC Standard provides the user with a
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Particular subclauses of IEC 61558-1:2017 are displayed in the content on a blue
background.
– 10 – IEC 61558-2-2:2022 EXV © IEC 2022
International standard IEC 61558-2-2 has been prepared by IEC technical committee 96:
Transformers, reactors, power supply units and combinations thereof.
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:
adjustment of structure and references in accordance with IEC 61558-1:2017;
new general symbol for control transformers;
new symbol for power supply unit with linearly regulated output voltage.
The text of this document is based on the following documents:
Draft Report on voting
96/548/FDIS 96/554/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 document 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 document 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 control
transformers and power supply units incorporating control transformers.
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 www.webstore.iec.ch in the data related to the
specific document. At this date, the document will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
IMPORTANT – The 'colour inside' logo on the cover page of this publication indicates that it
contains colours which are considered to be useful for the corre
...

IEC 61558-2-2 ®
Edition 3.0 2022-10
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
GROUP SAFETY PUBLICATION
PUBLICATION GROUPÉE DE SÉCURITÉ
Safety of transformers, reactors, power supply units and combinations thereof –
Part 2-2: Particular requirements and tests for control transformers and power
supply units incorporating control transformers

Sécurité des transformateurs, bobines d'inductance, blocs d'alimentation et
combinaisons de ces éléments –
Partie 2-2: Exigences particulières et essais pour les transformateurs de
commande et les blocs d'alimentation qui incorporent des transformateurs de
commande
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IEC 61558-2-2 ®
Edition 3.0 2022-10
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
GROUP SAFETY PUBLICATION
PUBLICATION GROUPÉE DE SÉCURITÉ

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

Part 2-2: Particular requirements and tests for control transformers and power

supply units incorporating control transformers

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

combinaisons de ces éléments –

Partie 2-2: Exigences particulières et essais pour les transformateurs de

commande et les blocs d'alimentation qui incorporent des transformateurs de

commande
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
INTERNATIONALE
ICS 29.180 ISBN 978-2-8322-5809-5

– 2 – IEC 61558-2-2:2022  IEC 2022
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 . 9
8 Marking and other information . 9
9 Protection against electric shock . 10
10 Change of input voltage setting . 10
11 Output voltage and output current under load . 11
12 No-load output voltage . 11
13 Short-circuit voltage . 12
14 Heating . 12
15 Short-circuit and overload protection . 12
16 Mechanical strength . 12
17 Protection against harmful ingress of dust, solid objects and moisture . 12
18 Insulation resistance, dielectric strength and leakage current . 12
19 Construction . 13
20 Components . 14
21 Internal wiring . 14
22 Supply connection and other external flexible cables or cords . 14
23 Terminals for external conductors . 14
24 Provisions for protective earthing. 14
25 Screws and connections . 14
26 Creepage distances, clearances and distances through insulation . 14
27 Resistance to heat, fire and tracking . 14
28 Resistance to rusting . 14
Annexes . 15
Bibliography . 16

Table 101 – Symbols indicating the kind of transformer . 10

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

Part 2-2: Particular requirements and tests for control transformers
and power supply units incorporating control transformers

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
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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
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3) IEC Publications have the form of recommendations for international use and are accepted by IEC National
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Publications is accurate, IEC cannot be held responsible for the way in which they are used or for any
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4) In order to promote international uniformity, IEC National Committees undertake to apply IEC Publications
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any IEC Publication and the corresponding national or regional publication shall be clearly indicated in the latter.
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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
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8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is
indispensable for the correct application of this publication.
9) Attention is drawn to the possibility that some of the elements of this IEC Publication may be the subject of patent
rights. IEC shall not be held responsible for identifying any or all such patent rights.
International standard IEC 61558-2-2 has been prepared by IEC technical committee 96:
Transformers, reactors, power supply units and combinations thereof.
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 general symbol for control transformers;
c) new symbol for power supply unit with linearly regulated output voltage.

– 4 – IEC 61558-2-2:2022  IEC 2022
The text of this document is based on the following documents:
Draft Report on voting
96/548/FDIS 96/554/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 document 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 document 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 control
transformers and power supply units incorporating control transformers.
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 www.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 example 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 the IEC 61558-2 series 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 61558-2-2:2022  IEC 2022
SAFETY OF TRANSFORMERS, REACTORS,
POWER SUPPLY UNITS AND COMBINATIONS THEREOF –

Part 2-2: Particular requirements and tests for control transformers
and power supply units incorporating control transformers

1 Scope
Replacement:
This part of IEC 61558 deals with the safety of control transformers and power supply units
incorporating control transformers. 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 control
transformers and power supply units incorporating control transformers.
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.
This document does not apply to transformers covered by IEC 60076-11.
This document is applicable to stationary or portable, single-phase or polyphase, air-cooled
(natural or forced) independent or associated dry-type transformers. The windings can be
encapsulated or non-encapsulated.
The rated supply voltage does not exceed 1 000 V AC and the rated supply frequency and
the internal operating frequencies do not exceed 500 Hz.
The rated thermal output does not exceed:
• 25 kVA for single-phase transformers,
• 40 kVA for polyphase transformers.
This document is applicable to transformers without limitation of the rated thermal output,
subject to an agreement between the purchaser and the manufacturer.
NOTE 2 Transformers intended to supply networks are not included in the scope.
The no-load output voltage or the rated output voltage does not exceed 1 000 V AC or
1 415 V ripple-free DC. For independent transformers the no-load output voltage and / or
the rated output voltage is not less than 50 V AC or 120 V ripple-free DC.
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 Transformers covered by this document are only used in applications where double or reinforced
insulation between circuits is not required by the installation rules or by the end product standard.

NOTE 4 Normally the control transformers are intended to be used with equipment to provide voltages different
from the supply voltage for the functional requirements of the equipment. The protection against electric shock can
be provided or completed by other features of the equipment, such as the body. Parts of output circuits can be
connected to the input circuits or to protective earthing.
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.
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 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 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 http://www.electropedia.org/
• ISO Online browsing platform: available at http://www.iso.org/obp
Addition:
3.1.101
control transformer
transformer intended to supply power to control circuits (e.g. controlling, signalling,
interlocking, etc.)
– 8 – IEC 61558-2-2:2022  IEC 2022
3.5.101
rated thermal output
product of the rated output voltage and the rated output current, or for polyphase
transformers, the appropriate factor (e. g. for three-phase transformers 3 ) times the product
of the rated output voltage and the rated output current delivered in continuous operation
loaded at power factor 1
Note 1 to entry: If the transformer has more than one output winding or tapped output winding (or both), the
rated output denotes the sum of the products of rated output voltage and rated output current for output circuits
intended to be loaded simultaneously.
3.5.102
admissible instantaneous output
product of the rated output voltage and the rated instantaneous output current, or for
polyphase transformers, the appropriate factor (e. g. for three-phase transformers 3 ) times
the product of the rated output voltage and the rated instantaneous output current delivered
at power factor 0,5
Note 1 to entry: If the transformer has more than one output winding or tapped output winding (or both), the
rated output denotes the sum of the products of rated output voltage and rated instantaneous output current for
output circuits intended to be loaded simultaneously.
3.5.103
rated instantaneous output current
output current for the specific operating conditions at the rated output voltage and the rated
supply frequency at power factor 0,5 assigned to the transformer by the manufacturer
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 and
for independent transformers shall exceed 50 V AC or 120 V ripple-free DC.
For independent transformers, this output voltage limitation applies even when output
windings, not intended for interconnection, are connected in series.
6.102 The rated thermal output shall not exceed:
• 25 kVA for single-phase transformers,
• 40 kVA for polyphase transformers.
Transformers without limitation of the rated thermal output shall be subject to agreement
between the purchaser and the manufacturer.

6.103 The rated supply frequency and the internal operating frequencies shall not
exceed 500 Hz.
6.104 The rated supply voltage shall not exceed 1 000 V AC.
Compliance with the requirements of 6.101 to 6.104 is checked by inspection of the marking.
7 Classification
This clause of IEC 61558-1:2017 is applicable except as follows:
7.8
Replacement
Control transformers shall be classified for overvoltage category III.
8 Marking and other information
This clause of IEC 61558-1:2017 is applicable except as follows:
8.1 c)
Replacement:
the transformers shall be marked with the rated thermal output and the admissible
instantaneous output in volt-ampere, separated by an oblique stroke (e.g. 100/300 VA);
d)
Replacement:
Item d) is not applicable.
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.

– 10 – IEC 61558-2-2:2022  IEC 2022
Table 101 – Symbols indicating the kind of transformer
Symbol or graphical symbol Explanation or title Identification
Fail-safe control transformer IEC 60417-6036:2010-08

Non-short-circuit-proof control transformer IEC 60417-6037:2010-08

Short-circuit-proof control transformer IEC 60417-6038:2010-08
(inherently or non-inherently)

Power supply unit, linear IEC 60417-6210:2013-10
L
Addition:
8.101 If transformers are provided with input tappings to allow adjustments to the supply
voltage, these tappings shall be marked with the value or the variation (e.g. +5 V or –5 V) of
the input voltage corresponding to the tapping.
NOTE If control transformers are provided with input tappings to allow adjustments to the supply voltage, tappings
in steps of 5 % are preferred.
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:
When the transformer is connected to the rated supply voltage, at rated supply frequency,
and loaded with an impedance at power factor 1 resulting in the rated thermal output at the
rated output voltage, the output voltage shall not differ from the rated value by more
than ±5 %.
Compliance is checked by measuring the output voltage when steady-state conditions are
established.
Immediately after the transformer is loaded with an impedance resulting in the admissible
instantaneous output at the rated output voltage at power factor 0,5 (inductive), the output
voltage measured shall not be less than 95 % of the measured voltage at the rated thermal
output.
The output voltage measurement for the admissible instantaneous output should be carried
out within 50 ms after applying this overload to minimise the effects of supplementary heating
of the transformer.
For transformers with more than one rated supply voltage, the requirement is applicable for
each of the rated supply voltages.
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 1 000 V AC or 1 415 V ripple-free DC
and for independent transformers shall exceed 50 V AC or 120 V ripple-free DC.
For independent transformers, this output voltage limitation applies even when output
windings, not intended for interconnection, are connected in series.
NOTE The requirement for series connection does not apply to associated or IP 00 transformers.
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 %.

– 12 – IEC 61558-2-2:2022  IEC 2022
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 and at the rated thermal output.
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
Replacement of the eleventh paragraph:
Transformers are supplied at the rated supply voltage and loaded with an impedance
producing the rated thermal output, at the rated output voltage and, for AC current, at the
rated power factor. The value of the output current is measured when steady state is
established. Then the supply voltage is increased by 10 % and the output current is adjusted to
the same value measured previously. The output current is not adjusted for independent
transformers. After this increase of the supply voltage, no change is made in the circuit. The
test is repeated under no-load condition, if this is a more unfavourable situation.
15 Short-circuit and overload protection
This clause of IEC 61558-1:2017 is applicable.
16 Mechanical strength
This clause of IEC 61558-1:2017 is applicable.
17 Protection against harmful ingress of dust, solid objects and moisture
This clause of IEC 61558-1:2017 is applicable.
18 Insulation resistance, dielectric strength and leakage current
This clause of IEC 61558-1:2017 is applicable except as follows:

18.3 Dielectric strength test
Addition:
The required values of the dielectric strength test voltages for basic insulation of Table 14
shall be multiplied by a factor of 1,4.
NOTE Basic insulation has been increased because transformers are subjected to surge voltages due to the
inductive nature of their loads.
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 conductive parts, except by deliberate action.
Compliance is checked by inspection and measurements, taking Clause 18 and Clause 26 into
consideration.
19.1.1 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 requirements apply:
• for class I transformers, the insulation between the input windings and the body, and
between the output windings and the body, shall consist of 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).
19.1.2 For transformers with intermediate conductive parts (e.g. the iron core) not
connected to the body and located between the input and output windings, the insulation
between the intermediate conductive parts and the input windings or between the
intermediate conductive parts and the output windings shall consist of at least basic
insulation (rated for the working voltage).
NOTE An intermediate conductive part not separated from the input or output windings or the body by at least
a basic insulation is considered to be connected to the relevant part(s).
In addition, the following requirements apply:
– 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 insulation between the input windings and the body, and
between the output windings and the body via the intermediate conductive parts shall
consist of double or reinforced insulation (rated for the working voltage).
Addition:
19.101 There shall be no connections between the output circuits and the protective earth
unless allowed by the relevant equipment standard for associated transformers.

– 14 – IEC 61558-2-2:2022  IEC 2022
19.102 There shall be no connections between the output circuits and the body unless
allowed by the relevant equipment standard for associated transformers.
Compliance is checked by inspection.
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 except as follows:
26.1 General
Replacement of the first paragraph:
The required values of creepage distances and clearances for basic insulation in
accordance with Table 20 and Table 21 shall be multiplied by a factor of 1,4.
NOTE Basic insulation has been increased because transformers are subjected to surge voltages due to the
inductive nature of their loads.
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.

Annexes
The annexes of IEC 61558-1:2017 are applicable.

– 16 – IEC 61558-2-2:2022  IEC 2022
Bibliography
The bibliography of IEC 61558-1:2017 is applicable, except as follows:
Addition:
IEC 60076-11:2018, Power transformers – Part 11: Dry-type transformers
IEC 60204-1:2016, Safety of machinery – Electrical equipment of machines – Part 1: General
requirements
IEC 61558 (all parts), Safety of transformers, reactors, power supply units and combinations
thereof
IEC 61558-2-13:2022, 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
ISO/IEC Guide 51:2014, Safety aspects – Guidelines for their inclusion in standards
IEC Guide 104:2019, The preparation of safety publications and the use of basic safety
publications and group safety publications

____________
– 18 – IEC 61558-2-2:2022  IEC 2022
SOMMAIRE
AVANT-PROPOS . 19
INTRODUCTION . 22
1 Domaine d'application . 23
2 Références normatives . 24
3 Termes et définitions . 25
4 Exigences générales . 25
5 Généralités sur les essais. 25
6 Caractéristiques assignées . 26
7 Classification . 26
8 Marquage et indications . 26
9 Protection contre les chocs électriques . 28
10 Changement de la tension primaire d'alimentation . 28
11 Tension secondaire et courant secondaire en charge . 28
12 Tension secondaire à vide . 28
13 Tension de court-circuit . 29
14 Echauffements. 29
15 Protection contre les courts-circuits et les surcharges . 29
16 Résistance mécanique . 29
17 Protection contre les effets nuisibles dus à la pénétration de poussière, d'objets
solides et de l'humidité . 29
18 Résistance d'isolement, rigidité diélectrique et courant de fuite . 30
19 Construction . 30
20 Composants . 31
21 Conducteurs internes. 31
22 Raccordement à l'alimentation et câbles souples externes . 31
23 Bornes pour conducteurs externes . 31
24 Dispositions en vue de la mise à la terre de protection . 31
25 Vis et connexions . 31
26 Lignes de fuite, distances d'isolement et distances à travers l'isolation . 31
27 Résistance à la chaleur, au feu et aux courants de cheminement . 32
28 Protection contre la rouille . 32
Annexes . 33
Bibliographie . 34

Tableau 101 – Symboles qui indiquent le type de transformateur . 27

COMMISSION ÉLECTROTECHNIQUE INTERNATIONALE
____________
SÉCURITÉ DES TRANSFORMATEURS, BOBINES D'INDUCTANCE,
BLOCS D'ALIMENTATION ET COMBINAISONS DE CES ÉLÉMENTS –

Partie 2-2: Exigences particulières et essais pour les transformateurs
de commande et les blocs d'alimentation qui incorporent
des transformateurs de commande

AVANT-PROPOS
1) La Commission Electrotechnique Internationale (IEC) est une organisation mondiale de normalisation composée
de l'ensemble des comités électrotechniques nationaux (Comités nationaux de l'IEC). L'IEC a pour objet de
favoriser la coopération internationale pour toutes les questions de normalisation dans les domaines de
l'électricité et de l'électronique. A cet effet, l'IEC – entre autres activités – publie des Normes internationales,
des Spécifications techniques, des Rapports techniques, des Spécifications accessibles au public (PAS) et des
Guides (ci-après dénommés "Publication(s) de l'IEC"). Leur élaboration est confiée à des comités d'études, aux
travaux desquels tout Comité national intéressé par le sujet traité peut participer. Les organisations
internationales, gouvernementales et non gouvernementales, en liaison avec l'IEC, participent également aux
travaux. L'IEC collabore étroitement avec l'Organisation Internationale de Normalisation (ISO), selon des
conditions fixées par accord entre les deux organisations.
2) Les décisions ou accords officiels de l'IEC concernant les questions techniques représentent, dans la mesure du
possible, un accord international sur les sujets étudiés, étant donné que les Comités nationaux de l'IEC intéressés
sont représentés dans chaque comité d'études.
3) Les Publications de l'IEC se présentent sous la forme de recommandations internationales et sont agréées
comme telles par les Comités nationaux de l'IEC. Tous les efforts raisonnables sont entrepris afin que
l'IEC s'assure de l'exactitude du contenu technique de ses publications; l'IEC ne peut pas être tenue responsable
de l'éventuelle mauvaise utilisation ou interprétation qui en est faite par un quelconque utilisateur final.
4) Dans le but d'encourager l'uniformité internationale, les Comités nationaux de l'IEC s'engagent, dans toute la
mesure possible, à appliquer de façon transparente les Publications de l'IEC dans leurs publications nationales
et régionales. Toutes divergences entre toutes Publications de l'IEC et toutes publications nationales ou
régionales correspon
...