IEC 61558-2-14:2022

IEC 61558-2-14 ®
Edition 2.0 2022-05
REDLINE VERSION
INTERNATIONAL
STANDARD
colour
inside
GROUP SAFETY PUBLICATION
Safety of transformers, reactors, power supply units and combinations thereof –
Part 2-14: Particular requirements and tests for variable transformers and power
supply units incorporating variable transformers for general applications

All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized in any form
or by any means, electronic or mechanical, including photocopying and microfilm, without permission in writing from
either IEC or IEC's member National Committee in the country of the requester. If you have any questions about IEC
copyright or have an enquiry about obtaining additional rights to this publication, please contact the address below or
your local IEC member National Committee for further information.

IEC Secretariat Tel.: +41 22 919 02 11
3, rue de Varembé info@iec.ch
CH-1211 Geneva 20 www.iec.ch
Switzerland
About the IEC
The International Electrotechnical Commission (IEC) is the leading global organization that prepares and publishes
International Standards for all electrical, electronic and related technologies.

About IEC publications
The technical content of IEC publications is kept under constant review by the IEC. Please make sure that you have the
latest edition, a corrigendum or an amendment might have been published.

IEC publications search - webstore.iec.ch/advsearchform IEC Products & Services Portal - products.iec.ch
The advanced search enables to find IEC publications by a Discover our powerful search engine and read freely all the
variety of criteria (reference number, text, technical publications previews. With a subscription you will always
committee, …). It also gives information on projects, replaced have access to up to date content tailored to your needs.
and withdrawn publications.
Electropedia - www.electropedia.org
IEC Just Published - webstore.iec.ch/justpublished
The world's leading online dictionary on electrotechnology,
Stay up to date on all new IEC publications. Just Published
containing more than 22 300 terminological entries in English
details all new publications released. Available online and
and French, with equivalent terms in 19 additional languages.
once a month by email.
Also known as the International Electrotechnical Vocabulary

(IEV) online.
IEC Customer Service Centre - webstore.iec.ch/csc

If you wish to give us your feedback on this publication or
need further assistance, please contact the Customer Service
Centre: sales@iec.ch.
IEC 61558-2-14 ®
Edition 2.0 2022-05
REDLINE VERSION
INTERNATIONAL
STANDARD
colour
inside
GROUP SAFETY PUBLICATION
Safety of transformers, reactors, power supply units and combinations thereof –
Part 2-14: Particular requirements and tests for variable transformers and power
supply units incorporating variable transformers for general applications
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 29.180 ISBN 978-2-8322-5038-9
– 2 – IEC 61558-2-14:2022 RLV  IEC 2022
CONTENTS
FOREWORD . 3
INTRODUCTION . 6
1 Scope . 7
2 Normative references . 9
3 Terms and definitions . 9
4 General requirements . 10
5 General notes on tests . 11
6 Ratings . 11
7 Classification . 12
8 Marking and other information . 12
9 Protection against electric shock . 14
10 Change of input voltage setting . 14
11 Output voltage and output current under load . 14
12 No-load output voltage . 14
13 Short-circuit voltage . 16
14 Heating . 17
15 Short-circuit and overload protection . 17
16 Mechanical strength . 17
17 Protection against harmful ingress of dust, solid objects and moisture . 18
18 Insulation resistance, dielectric strength and leakage current . 18
19 Construction . 18
20 Components . 22
21 Internal wirings . 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 . 22
27 Resistance to heat, fire and tracking . 22
28 Resistance to rusting . 22
Annexes . 23
Bibliography . 24

Table 101 – Symbols indicating the kind of transformer . 12
Table 101 102 – Output voltages difference ratio for auto-transformers,
separating transformers and safety isolating transformers . 16
Table 102 103 – Output voltages difference ratio for isolating transformers . 16
Table 103 104 – Maximum permitted temperatures of the winding . 17

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

Part 2-14: Particular requirements and tests for variable
transformers and power supply units incorporating
variable transformers for general applications

FOREWORD
1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising
all national electrotechnical committees (IEC National Committees). The object of IEC is to promote international
co-operation on all questions concerning standardization in the electrical and electronic fields. To this end and
in addition to other activities, IEC publishes International Standards, Technical Specifications, Technical Reports,
Publicly Available Specifications (PAS) and Guides (hereafter referred to as “IEC Publication(s)”). Their
preparation is entrusted to technical committees; any IEC National Committee interested in the subject dealt with
may participate in this preparatory work. International, governmental and non-governmental organizations liaising
with the IEC also participate in this preparation. IEC collaborates closely with the International Organization for
Standardization (ISO) in accordance with conditions determined by agreement between the two organizations.
2) The formal decisions or agreements of IEC on technical matters express, as nearly as possible, an international
consensus of opinion on the relevant subjects since each technical committee has representation from all
interested IEC National Committees.
3) IEC Publications have the form of recommendations for international use and are accepted by IEC National
Committees in that sense. While all reasonable efforts are made to ensure that the technical content of IEC
Publications is accurate, IEC cannot be held responsible for the way in which they are used or for any
misinterpretation by any end user.
4) In order to promote international uniformity, IEC National Committees undertake to apply IEC Publications
transparently to the maximum extent possible in their national and regional publications. Any divergence between
any IEC Publication and the corresponding national or regional publication shall be clearly indicated in the latter.
5) IEC itself does not provide any attestation of conformity. Independent certification bodies provide conformity
assessment services and, in some areas, access to IEC marks of conformity. IEC is not responsible for any
services carried out by independent certification bodies.
6) All users should ensure that they have the latest edition of this publication.
7) No liability shall attach to IEC or its directors, employees, servants or agents including individual experts and
members of its technical committees and IEC National Committees for any personal injury, property damage or
other damage of any nature whatsoever, whether direct or indirect, or for costs (including legal fees) and
expenses arising out of the publication, use of, or reliance upon, this IEC Publication or any other IEC
Publications.
8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is
indispensable for the correct application of this publication.
9) Attention is drawn to the possibility that some of the elements of this IEC Publication may be the subject of patent
rights. IEC shall not be held responsible for identifying any or all such patent rights.
This redline version of the official IEC Standard allows the user to identify the changes made to
the previous edition IEC 61558-2-14:2012. 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 61558-2-14:2022 RLV  IEC 2022
IEC 61558-2-14 has been prepared by IEC technical committee 96: Transformers, reactors,
power supply units and combinations thereof. It is an International standard.
This second edition cancels and replaces the first edition published in 2012. 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 symbols for power supply units with linearly regulated output voltages and required
current collector position changes.
The text of this International standard is based on the following documents:
Draft Report on voting
96/507/CDV 96/528/RVC
Full information on the voting for its approval can be found in the report on voting indicated in
the above table.
The language used for the development of this International Standard is English.
This document was drafted in accordance with ISO/IEC Directives, Part 2, and developed in
accordance with ISO/IEC Directives, Part 1 and ISO/IEC Directives, IEC Supplement, available
at www.iec.ch/members_experts/refdocs. The main document types developed by IEC are
described in greater detail at www.iec.ch/publications.
It has the status of a group safety publication in accordance with IEC Guide 104.
This International Standard is to be used in conjunction with IEC 61558-1:2017.
NOTE When "Part 1" is mentioned in this standard, it refers to 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 variable
transformers and power supply units incorporating variable transformers for general
applications.
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 adapted accordingly.
In this document, the following print types are used:
• requirements proper: in roman type;
• test specifications: in italic type;
• explanatory matter: in smaller roman type.
In the text of this document, the words in bold are defined in Clause 3.
Subclauses, notes, figures and tables additional to those in IEC 61558-1:2017 are numbered
starting from 101; supplementary annexes are entitled AA, BB, etc.

The committee has decided that the contents of this document will remain unchanged until the
stability date indicated on the IEC website under webstore.iec.ch in the data related to the
specific document. At this date, the document will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
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 61558-2-14:2022 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 limitation of voltage and horizontal safety
function for SELV in accordance with IEC 60364-4-41.
The group safety function (GSF) is necessary because of responsibility e.g. 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 needed 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 2-14: Particular requirements and tests for variable
transformers and power supply units incorporating
variable transformers for general applications

1 Scope
Replacement
This part of IEC 61558 deals with the safety of variable transformers for general applications
and power supply units incorporating variable transformers for general applications.
Transformers incorporating electronic circuits are also covered by this document.
NOTE 1 Safety includes electrical, thermal, mechanical and chemical aspects.
Unless otherwise specified, from here onward, the term transformer covers variable
transformers for general applications and power supply units incorporating variable
transformers for general applications.
This standard is applicable to transformers and power supply units (linear) with internal
operational frequencies not exceeding 500 Hz.
This standard used in combination with Part 2-16 for switch mode power supply units (SMPS)
is also applicable to power supplies with internal operational 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.
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 variable dry-type transformers:
– variable auto-transformers and power supply units incorporating variable auto-
transformers;
– variable separating transformers and power supply units incorporating variable
separating transformers;
– variable isolating transformers and power supply units incorporating variable isolating
transformers;
– variable safety isolating transformers and power supply units incorporating variable
safety isolating transformers.
The windings may 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 operational frequencies do not exceed 500 Hz.
The rated output does not exceed:
– 40 kVA for single-phase variable auto-transformers and power supply units incorporating
single-phase variable auto-transformers;
– 200 kVA for polyphase variable auto-transformers and power supply units incorporating
poly-phase variable auto-transformers;

– 8 – IEC 61558-2-14:2022 RLV  IEC 2022
– 1 kVA for single-phase variable separating transformers and power supply units
incorporating single-phase variable separating transformers;
– 5 kVA for polyphase variable separating transformers and power supply units
incorporating poly-phase variable separating transformers;
– 25 kVA for single-phase variable isolating transformers and power supply units
incorporating single-phase variable isolating transformers;
– 40 kVA for polyphase variable isolating transformers and power supply units
incorporating poly-phase variable isolating transformers;
– 10 kVA for single-phase variable safety isolating transformers and power supply units
incorporating single-phase variable safety isolating transformers;
– 16 kVA for polyphase variable safety isolating transformers and power supply units
incorporating poly-phase variable safety isolating transformers.
This document is applicable to variable 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.
For variable auto-transformers and power supply units incorporating variable 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;
– for independent variable auto-transformers the rated output voltage does exceed
50 V AC or 120 V ripple-free DC but does not exceed 250 V AC.
NOTE 3 Normally, variable auto-transformers and power supply units are intended to be associated with
equipment to provide voltages different from the supply voltage for the functional reasons requirements of the
equipment. The protection against electric shock can be provided or completed by other features of the equipment,
such as the body.
NOTE 4 Variable auto-transformers and power supply units incorporating variable auto-transformers intended
to be used by technically skilled or trained personnel are considered as associated variable transformers and
associated power supply units may can have a rated output voltage less than 50 V AC.
For variable separating transformers and power supply units incorporating variable
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;
– for portable variable separating transformers the rated output voltage does exceed
50 V AC or 120 V ripple-free DC;
– covered by this part may are only be used where double or reinforced insulation between
circuits is not required by the installation rules or by the end product standard.
NOTE 4 5 Normally, variable separating transformers and power supply units are intended to be associated
with equipment to provide voltages different from the supply voltage for the functional reasons 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 protective earthing.
NOTE 5 6 Variable separating transformers and power supply units incorporating variable separating
transformers intended to be used by technically skilled or trained personnel are considered as associated variable
transformers and associated power supply units and can have a rated output voltage less than 50 V AC or 120 V
ripple-free DC.
For variable isolating transformers and power supply units incorporating variable isolating
transformers:
– the no-load output voltage or the rated output voltage 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 or in accordance with
national wiring the installation rules;

– for independent variable isolating transformers the rated output voltage does not
exceed 250 V AC;
– are used where double or reinforced insulation between circuits is required by the
installation rules or by the end product standard.
For variable safety isolating transformers and power supply units incorporating 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;
– are used 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 6 Attention is drawn to the following, if necessary:
– additional requirements for transformers intended to be used in vehicles, on board ships,
and aircraft, additional requirements (from other applicable standards, national rules, etc.
can 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 are also
considered;
– the different conditions for transportation, storage, and operation of the transformers are
also be considered;
– additional requirements in accordance with other appropriate standards and national rules
can be applicable to transformers intended for use in special environments, such as
tropical environment.
Future technological development of transformers 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 TCs 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 TC is, wherever applicable, to make use of BSPs and/or GSPs
in the preparation of its publications.
2 Normative references
This clause of Part 1 is applicable except as follows:
Addition
IEC 61558-1:2005, Safety of power transformers, power supplies, reactors and similar products
– Part 1: General requirements and tests
Amendment 1 (2009)
IEC 61558-1:2017, Safety of transformers, reactors, power supply units and combinations
thereof – Part 1: General requirements and tests
3 Terms and definitions
This clause of Part 1 is applicable, except as follows:

– 10 – IEC 61558-2-14:2022 RLV  IEC 2022
For the purposes of this document, the terms and definitions given in Part 1 apply except as
follows:
ISO and IEC maintain terminology 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
variable transformer
transformer having unlimited numbers of transformation ratios and adjustable by means of a
movable current collector positioned along a continuous path of locally exposed winding turns
3.1.102
variable auto-transformer
variable transformer in which input and output voltages are derived from a common winding
3.2 General terms
Addition
3.2.101
current collector
assembly of moving contact parts which serve to transmit current from a point on the contact
path to the tapping point at the bushings or terminals
3.2.102
drive
mechanical assembly used for moving the current collector
3.2.103
fixed winding
winding or part of the winding with no means for varying the transformation ratio
3.2.104
variable winding
winding or part of the winding with a contact path used for varying the transformation ratio
3.5 Ratings
Modification
3.5.5 is not applicable.
Addition
3.5.101
rated output voltage range
output voltage range (for polyphase transformer and power supply units, the phase-to-phase
voltage) at rated supply voltage, rated supply frequency, rated output current, and rated
power factor assigned to the transformer or power supply unit by the manufacturer
4 General requirements
This clause of Part 1 is applicable except as follows:

Addition
If the current collector may not cannot stay permanently in the same position it has to shall
be marked on the variable transformer with the symbol IEC 60417-6263:2014-03 (see 8.11)
placed adjacent to the supply information (e.g. on the rating plate).
5 General notes on tests
This clause of Part 1 is applicable except as follows:
5.3
Addition
The test of 16.101 shall be conducted before all other tests.
6 Ratings
This clause of Part 1 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 variable auto-transformers and variable
separating transformers;
– 500 V AC or 708 V ripple-free DC for variable isolating transformers; the rated output
voltage may can exceed these limits in order to be in accordance with the national wiring
installation rules, however, it shall not exceed 1 000 V AC or 1 415 V ripple-free DC;
– 250 V AC for portable variable auto-transformers, portable variable separating
transformers and independent variable isolating transformers;
– 50 V AC or 120 V ripple-free DC for variable safety isolating transformers.
This document is also applicable to variable transformers of a rated output voltage of more
than 1 000 V AC or 1 415 V ripple-free DC. Such transformers, however, are classified as
special transformers and are subject to agreement between purchaser and manufacturer. Such
special variable transformers have no limitation in terms of their rated output voltage.
The rated output voltage shall exceed:
– 50 V AC or 120 V ripple-free DC for variable independent variable auto-transformers and
independent variable separating transformers.
6.102 The rated output shall not exceed:
– 40 kVA for single-phase variable auto-transformers;
– 200 kVA for polyphase variable auto-transformers;
– 1 kVA for single-phase variable separating transformers;
– 5 kVA for polyphase variable separating transformers;
– 25 kVA for single-phase variable isolating transformers;
– 40 kVA for polyphase variable isolating transformers;
– 10 kVA for single-phase variable safety isolating transformers;
– 16 kVA for polyphase variable safety isolating transformers.
Transformers without limitation of the rated output shall be subject to agreement between the
purchaser and the manufacturer.
6.103 The rated supply frequency and internal operational frequencies shall not exceed
500 Hz.
– 12 – IEC 61558-2-14:2022 RLV  IEC 2022
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 Part 1 is applicable.
8 Marking and other information
This clause of Part 1 is applicable except as follows:
8.1 b)
Replacement
rated output voltage range in volts or kilovolts;
For transformers incorporating a rectifier, the rated output voltage range after the rectifier
shall be marked with the arithmetic mean value. If, however, the output voltage is given as an
RMS value, this shall be stated.
NOTE An RMS value is distinguished from an arithmetic mean value by the use of RMS in the marking.
8.1 h)
Replacement of the first sentence by the following:
Relevant graphical symbols shown in 8.11 indicating the kind of transformers;
Replacement
Replace 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 Explanation or title Identification
graphical IEC 60417
symbol
Fail-safe variable separating variable transformer 6014-1
IEC 60417-6014:2008-02
Non-short-circuit proof variable separating variable 6014-2
transformer
IEC 60417-6014:2008-02
Short-circuit proof variable separating variable transformer
6014-3
(inherently or non-inherently)
IEC 60417-6014:2008-02
Fail-safe variable isolating variable transformer 6015-1
IEC 60417-6015:2008-02
Non-short-circuit proof variable isolating variable 6015-2
transformer
IEC 60417-6015:2008-02
Short-circuit proof variable isolating variable transformer 6015-3
(inherently or non-inherently)
IEC 60417-6015:2008-02
Fail-safe safety variable isolating variable transformer 6016-1
IEC 60417-6016:2008-02
Non-short-circuit proof variable safety isolating variable 6016-2
transformer
IEC 60417-6016:2008-02
Short-circuit proof variable safety isolating variable 6016-3
transformer (inherently or non-inherently)
IEC 60417-6016:2008-02
Fail-safe variable auto-transformer 6018-1
IEC 60417-6018:2008-02
Non-short-circuit proof variable auto-transformer 6018-2
IEC 60417-6018:2008-02
– 14 – IEC 61558-2-14:2022 RLV  IEC 2022
Short-circuit proof variable auto-transformer (inherently or 6018-3
non-inherently)
IEC 60417-6018:2008-02
Power supply unit, linear IEC 60417-6210:2013-10
L
Current collector position change IEC 60417-6263:2014-03

Addition
8.101 An instruction sheet showing the method of operation, use and maintenance shall be
supplied with each transformer (e.g. in case of variable associated variable auto-
transformers or associated variable separating transformers, intended to be used only by
technically skilled or trained personnel).
If the variable transformer is not short-circuit proof, the information shall be given in the
instruction sheet for use.
The overload protection and short-circuit protective devices in the primary circuit of a variable
transformer cannot provide adequate overload protection in the secondary circuit. It is,
therefore, always necessary to provide secondary circuit protection.
8.102 The short-circuit voltage at a certain position of the current collector shall be marked,
when it is subject to an agreement between purchaser and manufacturer.
9 Protection against electric shock
This clause of Part 1 is applicable.
10 Change of input voltage setting
This clause of Part 1 is applicable.
11 Output voltage and output current under load
This clause of Part 1 is applicable except as follows:
Addition
11.101 When the transformer is connected to the rated supply voltage, at the rated supply
frequency, and loaded with the rated output current, at the rated power factor, the maximum
output voltage shall not differ from the rated value by more than 10 % at the highest output
voltage.
The output voltage is measured when the transformer is connected to the rated supply
voltage, at the rated supply frequency, and loaded with the rated output current, at the
rated power factor and with the current collector in a position which will produce the highest
voltage drop in steady state condition. In case of a variable auto-transformer, the
measurement is made with the current collector in the middle of the input winding.
The current collector should be placed in the most unfavourable position when tappings or
elevated voltage are included in the construction.
12 No-load output voltage
This clause of Part 1 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 variable auto-transformers and variable
separating transformers;
– 500 V AC or 708 V ripple-free DC for variable isolating transformers. 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;
NOTE 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 in accordance with national wiring the installation rules.
– 50 V AC or 120 V ripple-free DC for variable safety isolating transformers.
For independent variable transformers, this output voltage limitation applies even when
output windings, not intended for interconnection, are connected in series.
The no-load output voltage shall exceed 50 V AC or 120 V ripple-free DC for variable
independent variable auto-transformers and variable independent variable separating
transformers or 120 V ripple-free d.c.
Independent variable auto-transformers and independent auto- and variable independent
separating transformers and power supply units intended to be used by technically skilled or
trained personnel are considered as associated variable transformers and associated power
supply units and may can have a rated output voltage less than 50 V AC.
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 the values shown in Table 102 and Table 103.
The difference is expressed as a percentage of the latter voltage calculated according to the
following formula:
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
The output voltages are measured when the current collector is placed in the most
unfavourable position.
– 16 – IEC 61558-2-14:2022 RLV  IEC 2022
Table 101 102 – Output voltages difference ratio for auto-transformers,
separating transformers and safety isolating transformers
Type of transformer Ratio between no-load output voltage and output
Rated output voltage under load
VA %
Inherently short-circuit proof transformers:
- up to and including 63 100
- over 63 up to and including 630 50
- over 630 20
Other transformers:
- up to and including 10 100
- over 10 up to and including 25 50
- over 25 up to and including 63 20
- over 63 up to and including 250 15
- over 250 up to and including 630 10
- over 630 5
For transformer types of a rated output power of more than 630 VA, the given ratio of no-
load output voltage to on-load output voltage can exceed 5 %. Such transformers, however,
are classified as special transformers and are subject to agreement between purchaser and
manufacturer.
The output voltage is measured when the current collector stays in the maximum end
position.
Table 102 103 – Output voltages difference ratio for isolating transformers
Type of transformer Ratio between no-load output voltage and output
voltage under load
Rated output
VA %
- up to and including 63 20
- over 63 up to and including 250 15
- over 250 up to and including 630 10
- over 630 5
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 at the rated supply frequency with the current collector in the
same position as that used in the measurement of 11.101.
The difference ratio shall not exceed the values shown in Table 102 and Table 103.
13 Short-circuit voltage
This clause of Part 1 is not applicable.
Replacement
If there is a short-circuit voltage marking corresponding to a certain position of the current
collector, the measured short-circuit voltage shall not deviate from the marked short-circuit
voltage by more than 20 %.
Compliance is checked by measuring the short-circuit voltage of the transformer at ambient
temperature.
14 Heating
This clause of Part 1 is applicable except as follows:
th
14.1.1 Modification of the 10 paragraph as follows:
Replacement
th
Replace the 11 paragraph as follows:
Transformers are supplied at the rated supply voltage and loaded with an impedance
producing the rated output current, at the rated power factor and with the current collector
repositioned to produce maximum output voltage (maximum voltage drop) within the range.
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. The output current is not adjusted for independent variable transformers. After this
configuration, no change is made in the circuit.
In addition, for variable auto-transformers, the test is repeated, except the current collector
is placed in the middle position of the input winding.
Addition
14.101 The temperature of the winding at the winding/current collector contact point in its
most unfavourable position is measured by the use of thermocouples or other suitable means
and shall not exceed the values shown in Table 104.
Table 103 104 – Maximum permitted temperatures of the winding
Insulation class of winding A E B F H
Temperatures °C 105 120 130 155 180

15 Short-circuit and overload protection
This clause of Part 1 is applicable except as follows:
15.4 Non-short-circuit proof transformers
Replacement
Replace the first paragraph as follows:
Non-short-circuit proof transformers are tested as indicated in 15.3 of Part 1 with the current
collector placed in the most unfavourable position.
16 Mechanical strength
This clause of Part 1 is applicable except as follows:
Addition
16.101 Test of the drive
The transformer is loaded with an impedance producing the rated output current when the
current collector is set at the maximum output voltage setting within the range. The current
collector is moved over the entire length of the winding for 50 000 cycles at a speed of
10 cm/s ± 2 cm/s. In the case of a motor driven current collector the speed shall be the highest
speed provided by the motor.
NOTE A cycle is a forward and backward movement.

– 18 – IEC 61558-2-14:2022 RLV  IEC 2022
After the test, the variable transformer (including all parts of the drive) shall still meet all the
requirements specified in this document.
17 Protection against harmful ingress of dust, solid objects and moisture
This clause of Part 1 is applicable.
18 Insulation resistance, dielectric strength and leakage current
This clause of Part 1 is applicable except as follows:
18.4 Insulation between and within windings
Addition
During the test of insulation between winding it is allowed to isolate the current collector from
the windings.
19 Construction
This clause of Part 1 is applicable except as follows:
Replacement of 19.1:
19.1 General
NOTE To reflect different transformer types, this subclause is separated into the following three parts.
19.1.1 Variable auto-transformers
19.1.2 Variable separating transformers
19.1.3 Variable isolating and safety isolating transformers
19.1.1 Variable auto-transformers
19.1.1.1 Plug connected 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:
19.1.1.1.1 Polarised 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-polarised
plug and socket-outlet system.
19.1.1.1.2 Polarity detecting device (for non polarised input and output plug and socket-outlet
system)
A polarity detecting device shall only energize 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 supply at 1,1 times the rated input voltage
under the most unfavorable 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 p
...