IEC 61558-2-14:2012

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

IEC 61558-2-14:2012 deals with 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 standard. This first edition cancels and replaces the chapter IV of the IEC 60989 published in 1991. It is a technical revision. This edition includes the following significant technical changes with respect to the previous edition:
a) update of the existing text;
b) complete editorial review.
This part has the status of a group safety publication in accordance with IEC Guide 104:2010. The preparation of safety publications and the use of basic safety publications and group safety publications. The attention of National Committees is drawn to the fact that equipment manufacturers and testing organizations may need a transitional period following publication of a new, amended or revised IEC publication in which to make products in accordance with the new requirements and to equip themselves for conducting new or revised tests. It is the recommendation of the committee that the content of this publication be adopted for implementation nationally not earlier than 12 months from the date of publication.
This publication is to be read in conjunction with IEC 61558-1:2005.

Sécurité des transformateurs, bobines d'inductance, blocs d'alimentation et des combinaisons de ces éléments - Partie 2-14: Exigences particulières et essais pour les transformateurs variables et les blocs d'alimentation incorporant des transformateurs variables

La CEI 61558-2-14:2012 traite de la sécurité des transformateurs variables pour applications générales et des blocs d'alimentation incorporant des transformateurs variables pour applications générales. Les transformateurs incorporant des circuits électroniques sont également couverts par la présente norme. Cette première édition annule et remplace le chapitre IV de la CEI 60989 parue en 1991. Elle constitue une révision technique. Cette édition inclut les modifications techniques majeures suivantes par rapport à l'édition précédente:
a) mise à jour du texte existant;
b) revue éditoriale complète.
La présente partie a le statut de publication groupée de sécurité conformément au guide CEI 104:2010. The preparation of safety publications and the use of basic safety publications and group safety publications (disponible en anglais seulement). L'attention des Comités Nationaux est attirée sur le fait que les fabricants d'appareils et les organismes d'essai peuvent avoir besoin d'une période transitoire après la publication d'une nouvelle publication CEI, ou d'une publication amendée ou révisée, pour fabriquer des produits conformes aux nouvelles exigences et pour adapter leurs équipements aux nouveaux essais ou aux essais révisés. Le comité recommande que le contenu de cette publication soit entériné au niveau national au plus tôt 12 mois après la date de publication.
Cette publication doit être lue conjointement avec la CEI 61558-1:2005.

General Information

• Status: Published
• Publication Date: 21-Nov-2012
• ICS: 29.180 - Transformers. Reactors
• Technical Committee: TC 96 - Transformers and reactors
• Current Stage: DELPUB - Deleted Publication
• Start Date: 02-May-2022
• Completion Date: 31-Mar-2021

Relations

• Revised: IEC 61558-2-14:2022 - 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
• Effective Date: 05-Sep-2023

Overview

IEC 61558-2-14:2012 is an international standard published by the International Electrotechnical Commission (IEC) that addresses the safety requirements and testing methods for variable transformers and power supply units incorporating variable transformers used in general applications. This standard covers transformers with rated voltages up to 1000 V AC and frequencies up to 500 Hz, including those integrated with electronic circuits. It ensures electrical, thermal, mechanical, and chemical safety aspects to protect users and equipment. IEC 61558-2-14:2012 replaces the earlier Chapter IV of IEC 60989 (1991) and provides updated, technically revised guidelines with an editorial review for clarity and comprehensiveness.

This standard serves as a group safety publication under IEC Guide 104:2010 and should be used in conjunction with IEC 61558-1:2005, which outlines the general requirements for safety of transformers, reactors, power supply units, and combinations thereof.

Key Topics

• Scope and Applicability
  Applies to stationary or portable, single or polyphase, air-cooled (natural or forced) variable transformers, including variable auto-transformers, separating transformers, isolating transformers, and safety isolating transformers, as well as power supply units incorporating these transformers. It excludes transformers governed by IEC 60076-11.

• Safety Requirements
  Covers comprehensive safety criteria including protection against electric shock, mechanical strength, prevention of harmful ingress of dust and moisture, and insulation requirements aimed at safeguarding operational integrity and user safety.

• Performance Testing
  Defines rigorous test protocols such as verification of output voltage and current under load, no-load output voltage, short-circuit voltage, heating tests, short-circuit and overload protection assessments, and dielectric strength tests to validate transformer safety and durability.

• Marking and Information
  Specifies requirements for clear marking, including rated voltage, current, frequency, and other essential information to ensure safe and correct usage.

• Construction and Components
  Details constructional requirements for windings (encapsulated or non-encapsulated), internal wiring, terminals, screws, connections, and provisions for protective earthing to guarantee the mechanical and electrical robustness of transformers.

• Environmental and Durability Considerations
  Includes protection measures against rusting, fire resistance, tracking resistance, and mechanical strength to extend the lifespan and reliability of variable transformers and related power supplies.

Applications

IEC 61558-2-14:2012 is critical for manufacturers, testing laboratories, and regulatory bodies involved in the design, production, certification, and quality control of:

• Variable transformers used in laboratories, industrial machinery controls, audio equipment, voltage regulation, and testing devices.
• Power supply units incorporating variable transformers that require precise voltage adjustments for specialized electronic and electrical applications.
• Transformers integrated into systems that demand safety compliance with rigorous international standards to facilitate global market access.
• Equipment requiring assurance of safety against electrical hazards, mechanical failures, and environmental factors in residential, commercial, and industrial settings.

Adopting this standard ensures enhanced product safety, compliance with international regulations, and fosters consumer trust by minimizing risks associated with electrical and thermal faults.

Related Standards

• IEC 61558-1:2005 – General safety requirements for transformers, reactors, power supply units, and their combinations.
• IEC 61558-2-16 – Particular safety requirements for switch mode power supply units, applicable when power supplies exceed 500 Hz.
• IEC 60076-11 – Power transformers safety, excluded from IEC 61558-2-14 scope but relevant for power transformer applications.
• IEC Guide 104:2010 – Guidelines on the preparation of safety publications to ensure uniformity and acceptance worldwide.

For comprehensive compliance, IEC 61558-2-14:2012 should be considered alongside these standards to cover all aspects of transformer safety, testing, and certification procedures effectively.

---

By following IEC 61558-2-14, manufacturers, designers, and safety compliance engineers can ensure their variable transformers and associated power supply units meet internationally recognized safety benchmarks, reducing risks and supporting sustainable electrical product development globally.

Standards Content (Sample)

IEC 61558-2-14 ®
Edition 1.0 2012-11
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
GROUP SAFETY PUBLICATION
PUBLICATION GROUPÉE DE SÉCURITÉ
Safety of transformers, reactors, power supply units and combination thereof –
Part 2-14: Particular requirements and tests for variable transformers and power
supply units incorporating variable transformers

Sécurité des transformateurs, bobines d’inductance, blocs d’alimentation et des
combinaisons de ces éléments –
Partie 2-14: Exigences particulières et essais pour les transformateurs variables
et les blocs d’alimentation incorporant des transformateurs variables

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IEC 61558-2-14 ®
Edition 1.0 2012-11
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
GROUP SAFETY PUBLICATION
PUBLICATION GROUPÉE DE SÉCURITÉ

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

Part 2-14: Particular requirements and tests for variable transformers and power

supply units incorporating variable transformers

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

combinaisons de ces éléments –

Partie 2-14: Exigences particulières et essais pour les transformateurs variables

et les blocs d’alimentation incorporant des transformateurs variables

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
PRICE CODE
INTERNATIONALE
CODE PRIX T
ICS 29.180 ISBN 978-2-83220-499-3

– 2 – 61558-2-14 © IEC:2012
CONTENTS
FOREWORD . 3
1 Scope . 6
2 Normative references . 8
3 Terms and definitions . 8
4 General requirements . 9
5 General notes on tests . 9
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 . 12
12 No-load output voltage . 12
13 Short-circuit voltage . 14
14 Heating . 15
15 Short circuit and overload protection . 15
16 Mechanical strength . 15
17 Protection against harmful ingress of dust, solid objects and moisture . 16
18 Insulation resistance, dielectric strength and leakage current . 16
19 Construction . 16
20 Components . 20
21 Internal wirings . 20
22 Supply connection and other external flexible cables or cords . 20
23 Terminals for external conductors . 20
24 Provision for protective earthing . 20
25 Screws and connections . 21
26 Creepage distances, clearances and distances through insulation . 21
27 Resistance to heat, fire and tracking . 21
28 Resistance to rusting . 21
Annexes . 22
Bibliography . 23

Table 101 – Output voltages difference for auto transformers, separating and safety
isolating transformers . 14
Table 102 – Output voltages difference for isolating transformers . 14
Table 103 – Maximum permitted temperatures of the winding . 15

61558-2-14 © IEC:2012 – 3 –
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
SAFETY OF TRANSFORMERS, REACTORS,
POWER SUPPLY UNITS AND COMBINATION THEREOF –

Part 2-14: Particular requirements and tests for variable transformers
and power supply units incorporating variable 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
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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 61558-2-14 has been prepared by technical committee 96:
Transformers, reactors, power supply units and combination thereof.
This first edition cancels and replaces the chapter IV of the IEC 60989 published in 1991. It is a
technical revision.
This edition includes the following significant technical changes with respect to the previous
edition:
a) update of the existing text;
b) complete editorial review.
– 4 – 61558-2-14 © IEC:2012
The text of this standard is based on the following documents:
FDIS Report on voting
96/395/FDIS 96/398/RVD
Full information on the voting for the approval of this standard can be found in the report on
voting indicated in the above table.
This publication has been drafted in accordance with the ISO/IEC Directives, Part 2.
This part has the status of a group safety publication in accordance with IEC Guide 104:2010,
The preparation of safety publications and the use of basic safety publications and group
safety publications.
This part is intended to be used in conjunction with the latest edition of IEC 61558-1 and its
amendments. It is based on the second edition (2005) of that standard and its Amendment 1
(2009).
This part supplements or modifies the corresponding clauses in IEC 61558-1, so as to convert
that publication into the IEC standard: Particular requirements and tests for variable
transformers and power supply units incorporating variable transformers.
A list of all parts of the IEC 61558 series, under the general title: Safety of transformers,
reactors, power supply units and combination 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 a particular subclause of Part 1 is not mentioned in this part, that subclause applies as
far as is reasonable. Where this part states "addition", "modification" or "replacement", the
relevant text of Part 1 is to be adapted accordingly.
In this part, 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 part, the words in bold are defined in Clause 3.
Subclauses, notes, figures and tables additional to those in Part 1 are numbered starting from
101; supplementary annexes are entitled AA, BB, etc.
The committee has decided that the contents of this publication will remain unchanged until the
stability date indicated on the IEC web site under "http://webstore.iec.ch" in the data related to
the specific publication. At this date, the publication will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
NOTE The attention of National Committees is drawn to the fact that equipment manufacturers and testing
organizations may need a transitional period following publication of a new, amended or revised IEC publication in
which to make products in accordance with the new requirements and to equip themselves for conducting new or
revised tests.
61558-2-14 © IEC:2012 – 5 –
It is the recommendation of the committee that the content of this publication be adopted for implementation
nationally not earlier than 12 months from the date of publication.

– 6 – 61558-2-14 © IEC:2012
SAFETY OF TRANSFORMERS, REACTORS,
POWER SUPPLY UNITS AND COMBINATION THEREOF –

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

1 Scope
Replacement:
This part of IEC 61558 deals with 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 standard.
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.
The rated supply voltage does not exceed 1 000 V a.c., and the rated supply frequency
does not exceed 500 Hz.
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
This part does not apply to transformers covered by IEC 60076-11.
This part is applicable to stationary or portable, single-phase or polyphase, air-cooled (natural
or forced) independent or associated 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 be encapsulated or non-encapsulated.
The rated output does not exceed:
– 40 kVA for single-phase variable auto-transformers and power supply units
incorporating single-phase variable auto-transformers;

61558-2-14 © IEC:2012 – 7 –
– 200 kVA for poly-phase variable auto-transformers and power supply units
incorporating poly-phase variable auto-transformers;
– 1 kVA for single-phase variable separating transformers and power supply units
incorporating single-phase variable separating transformers;
– 5 kVA for poly-phase 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 poly-phase 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 poly-phase variable safety isolating transformers and power supply units
incorporating poly-phase variable safety isolating transformers.
This part is applicable to transformers without limitation of the rated output subject to an
agreement between the purchaser and the manufacturer.
NOTE 2 Transformers intended to supply distribution networks are not included in the scope.
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 a.c. or
1 415 V ripple free d.c.;
– for independent auto-transformers the rated output voltage does exceed 50 V a.c or
120 V ripple-free d.c. but not exceed 250 V a.c. .
NOTE 3 Normally, the variable auto-transformers and power supply units are intended to be associated
with the equipment to provide voltages different from the supply voltage for the functional reasons. The
protection against electric shock can be provided by other features of the equipment, such as the body.
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 transformers and associated power supply units and may have a rated output
voltage less than 50 V a.c.
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 a.c. or
1 415 V ripple free d.c.;
– for portable separating transormers the rated output voltage does exceed 50 V a.c or
120 V ripple-free d.c.;
– covered by this part may 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 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. 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 earth.
NOTE 5 Variable separating transformers and power supply units incorporating variable separating
transformers intended to be used by technically skilled or trained personal are considered as associated
transformers and associated power supply units and can have a rated output voltage less than 50 V a.c. or 120
V ripple-free d.c.
For variable isolating transformers and power supply units incorporating variable
isolating transformers:
– 8 – 61558-2-14 © IEC:2012
– the no-load output voltage or the rated output voltage does not exceed 500 V a.c. or
708 V ripple free d.c. The no-load output voltage and the rated output voltage may be
up to 1 000 V a.c. or 1 415 V ripple free d.c. for special applications or in accordance with
national wiring rules;
– for independent isolating transformers the rated output voltage does not exceed
250 V a.c.; .
– 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 a.c. or
120 V ripple-free d.c.;
– are used where double or reinforced insulation between circuits is required by the
installation rules or by the end product standard.
This part 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:
– 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 part may be used as a guidance document.
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)
3 Terms and definitions
This clause of Part 1 is applicable, except as follows:
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

61558-2-14 © IEC:2012 – 9 –
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 poly-phase 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.
If the current collector may not stay permanently in the same position it has to be marked on
the transformer.
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.

– 10 – 61558-2-14 © IEC:2012
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 a.c. or 1 415 V ripple-free d.c. for variable auto- and separating transformers;
– 500 V a.c. or 708 V ripple-free d.c for variable isolating transformers; the rated output
voltage may exceed these limits in order to be in accordance with the national wiring rules,
however, it shall not exceed 1 000 V a.c. or 1 415 V ripple free d.c.;
– 250 V a.c. for portable auto-transformers, portable separating transformers and
independent isolating transformers;
– 50 V a.c. or 120 V ripple-free d.c. for variable safety isolating transformers.
This standard is also applicable for variable transformers of a rated output voltage of more
than 1 000 V a.c. or 1 415 d.c. 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 a.c. or 120 V ripple-free d.c. for variable independent auto- and independent
separating transformers.
6.102 The rated output shall not exceed the following,
– 40 kVA for single-phase variable auto-transformers;
– 200 kVA for poly-phase variable auto-transformers;
– 1 kVA for single-phase variable separating transformers;
– 5 kVA for poly-phase variable separating transformers;
– 25 kVA for single-phase variable isolating transformers;
– 40 kVA for poly-phase variable isolating transformers;
– 10 kVA for single-phase variable safety isolating transformers;
– 16 kVA for poly-phase 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 and internal operational frequencies shall not exceed 500 Hz.
6.104 The rated supply voltage shall not exceed 1 000 V a.c.
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:

61558-2-14 © IEC:2012 – 11 –
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
r.m.s. value, this shall be stated.
NOTE An r.m.s. value is distinguished from an arithmetic mean value by the use of r.m.s. 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;
8.11 Addition:
Symbol or Explanation or title Identification
graphical IEC 60417
symbol
Fail-safe separating variable transformer 6014-1

Non-short-circuit proof separating variable transformer 6014-2

Short-circuit proof separating variable transformer (inherently or
6014-3
non-inherently)
Fail-safe isolating variable transformer 6015-1

Non-short-circuit proof isolating variable transformer 6015-2

Short-circuit proof isolating variable transformer (inherently or
6015-3
non-inherently)
Fail-safe safety isolating variable transformer 6016-1

Non-short-circuit proof safety isolating variable transformer 6016-2

Short-circuit proof safety isolating variable transformer (inherently
6016-3
or non-inherently)
Fail-safe variable auto-transformer 6018-1

Non-short-circuit proof variable auto-transformer 6018-2

Short-circuit proof variable auto-transformer (inherently or non-
6018-3
inherently)
– 12 – 61558-2-14 © IEC:2012
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 auto- or separating
transformers, intended to be used only by technically skilled or trained personal).
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 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 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.

61558-2-14 © IEC:2012 – 13 –
12.101 The no-load output voltage shall not exceed:
– 1 000 V a.c. or 1 415 V ripple-free d.c for auto- and separating transformers;
– 500 V a.c. or 708 V ripple-free d.c for isolating transformers. The no-load output
voltage and the rated output voltage may be up to 1 000 V a.c. or 1 415 V ripple free d.c.
for special applications;
NOTE The no-load output voltage and the rated output voltage can be up to 1 000 V a.c. or 1 415 V ripple
free d.c. in accordance with national wiring rules.
– 50 V a.c. or 120 V ripple-free d.c for safety isolating transformers.
For independent 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 a.c. for variable independent auto- and variable independent separating
transformers or 120 V ripple-free d.c.;
– variable 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 transformers and associated power supply units and may have a
rated output voltage less than 50 V a.c.
12.102 The difference between the no-load output voltage and the output voltage under
load shall not be excessive.
The difference is expressed as a percentage of the latter voltage calculated according to the
following formula:
U – U
no-load
load
× 100 %
U
load
where
U is the no-load output voltage, and
no-load
U is the output voltage under load,
load
It is measured when the current collector is placed in the most unfavourable position.

– 14 – 61558-2-14 © IEC:2012
Table 101 – Output voltages difference for auto transformers,
separating 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
As for transformer types of a rated output power of more than 630 VA, the given ratio of non-
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.
It is measured when the current collector stays in the maximum end position.
Table 102 – Output voltages difference for isolating transformers
Rated output Ratio between no-load output voltage and output
voltage under load
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 checked by measuring the
no-load output voltage at 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 shall not exceed the values shown in Table 101 and 102.
13 Short-circuit voltage
This clause of Part 1 is not applicable.
Replacement:
61558-2-14 © IEC:2012 – 15 –
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 the
ambient temperature.
14 Heating
This clause of Part 1 is applicable except as follows:
th
14.1 Modification of the 10 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,
no change is made in the circuit.
In addition, for 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 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 103.
Table 103 – 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 of the first paragraph as follows:
Non-short circuit proof transformers are tested as indicated in 15.3 with the current
collector placed in the most unfavourable position.
16 Mechanical strength
This clause of Part 1 is applicable except as follows:
Additional subclause:
– 16 – 61558-2-14 © IEC:2012
16.101 Test of 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 ± 2 cm/s. In case of motor driven current collector the speed shall be the highest speed
provided bx the motor.
NOTE A cycle is a forward and backward movement.
After the test, the variable transformer (including all parts of the drive) shall still meet all
requirements specified in this part.
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.

61558-2-14 © IEC:2012 – 17 –
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 pole
shall not exceed the maximum output voltage under load (1,1 times the rated output voltage
taking into account the permissible deviations of Clause 11).
Compliance is checked by measurement.
If the polarity detecting device uses a current flowing to the earth for the detection, this current
shall not exceed 0,75 mA and shall only be flowing for the period of measurement until the
polarity is reversed.
Compliance is checked by measurement.
All the tests are repeated under the fault conditions of H.2.3 of Part 1. In this case the potential
to earth of each pole shall not exceed 1,1 times the maximum output voltage under load for
more than 5 s.
Compliance is checked by measurement.
19.1.1.2 Protection against direct contact with electrical and moving mechanical parts
(contact path and drive) shall be ensured.
Compliance is checked by inspection.
19.1.2 Variable separating transformers
19.1.2.1 The input and output circuits shall be electrically separated from each other, and
the construction shall be such that there is no possibility of any connection between these
circuits, either directly or indirectly, via other conductive parts, except by deliberate action.
Compliance is checked by inspection and measurements, taking Clauses 18 and 26 into
consideration.
19.1.2.2 The insulation between the input and output winding(s) shall consist of at least
basic insulation (rated for the working voltage).
In addition, the following applies:
– for class I transformers, the insulation between the input windings and the body, and
between the output windings and the body, shall consist of 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).

– 18 – 61558-2-14 © IEC:2012
19.1.2.3 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 and 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 t
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