EN IEC 61558-2-2:2025

• Abstract:

  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 distribution 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 may be provided or completed by other features of the equipment, such as the body. Parts of output circuits may be connected to the input circuits or to protective earthing. 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.); - measures to protect the enclosure and the components inside the enclosure against external influences such as fungus, vermin, termites, solar-radiation, and icing; - the different conditions for transportation, storage, and operation of the transformers; - additional requirements in accordance with other appropriate standards and national rules may be applicable to transformers intended for use in special environments. Future technological development of transformers may necessitate a need to increase the upper limit of the frequencies. Until then this document may be used as a guidance document. 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.

• Status: Published
• Publication Date: 13-Mar-2025
• ICS: 29.180 - Transformers. Reactors
• Technical Committee: CLC/SR 96 - Small power transformers, reactors, power supply units and similar products
• Drafting Committee: IEC/TC 96 - IEC_TC_96
• Current Stage: 9093 - Decision to confirm - Review Enquiry
• Start Date: 05-Jan-2026
• Completion Date: 25-Aug-2026
• Directive: Harmonized Standard2014/35/EU - Directive 2014/35/EU of the European Parliament and of the Council of 26 February 2014 on the harmonisation of the laws of the Member States relating to the making available on the market of electrical equipment designed for use within certain voltage limits
• Mandate: M/511 - Mandate to CEN, CENELEC and ETSI relating to harmonised standards in the field of the Low Voltage Directive
• Ref Project: SIST EN IEC 61558-2-2:2025 - 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

• Replaces: EN 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: 24-Jan-2023
• Refers: EN IEC 61558-1:2019 - Safety of transformers, reactors, power supply units and combinations thereof - Part 1: General requirements and tests
• Effective Date: 03-Feb-2026
• Refers: EN IEC 61558-2-16:2025 - 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
• Effective Date: 03-Feb-2026
• Referred By: EN IEC 61204-7:2018 - Low-voltage switch mode power supplies - Part 7: Safety requirements
• Effective Date: 03-Feb-2026
• Referred By: EN IEC 60204-32:2025 - Safety of machinery - Electrical equipment of machines - Part 32: Requirements for hoisting machines
• Effective Date: 03-Feb-2026
• Referred By: EN 60598-1:2015 - Luminaires - Part 1: General requirements and tests
• Effective Date: 03-Feb-2026
• Referred By: CLC/TR 62453-51-20:2019 - Field device tool (FDT) interface specification - Part 51-20: Communication implementation for common object model - IEC 61784 CPF 2
• Effective Date: 03-Feb-2026

Overview

EN IEC 61558-2-2:2025 is a key European and International Standard developed by CLC and IEC, providing specific safety requirements and test methods for control transformers and power supply units incorporating control transformers. Covering stationary or portable, single-phase or polyphase, air-cooled dry-type transformers, the standard applies to both encapsulated and non-encapsulated designs operating at rated supply voltages up to 1,000 V AC and frequencies up to 500 Hz. It addresses products up to 25 kVA (single-phase) and 40 kVA (polyphase), but can cover higher outputs if agreed between purchaser and manufacturer. Safety aspects addressed by this standard encompass electrical, thermal, and mechanical criteria to ensure reliable operation and protection for users and equipment.

Key Topics

• Scope and Applicability
  EN IEC 61558-2-2:2025 applies to transformers and power supply units with integrated control transformers, covering devices for control circuits, signaling, and interlocking. Transformers covered may include integrated electronic circuits and are typically used to provide alternative voltages for industrial or equipment functional needs.

• Exclusions

  • Does not cover transformers for distribution networks (see IEC 60076-11 for those)
  • Excludes certain switch mode power supply units (see EN IEC 61558-2-16 in combination)
  • Not applicable for equipment requiring double or reinforced insulation between circuits

• Electrical Safety

  • Maximum rated supply voltage: 1,000 V AC
  • Maximum no-load or rated output voltage: 1,000 V AC or 1,415 V ripple-free DC
  • For independent transformers, minimum no-load output voltage: 50 V AC or 120 V DC
  • Protection against electric shock primarily managed by associated equipment or the equipment body

• Construction and Markings

  • Clearly defined requirements for markings, including rated and instantaneous output in VA
  • Safety covers mechanical strength, ingress protection, and insulation
  • Specific tests for short-circuit and overload conditions
  • Enhanced requirements for insulation distances and dielectric strength to handle surges due to inductive loads

• Environmental Considerations

  • Guidance includes factors for protection against dust, moisture, pests, solar radiation, and icing
  • Acknowledges special requirements for applications in vehicles, ships, aircraft, or harsh environments

Applications

Control transformers and power supply units with integrated control transformers are widely used in:

• Industrial Automation and Control Panels: Providing safe, stable voltages for relays, contactors, and signaling circuits.
• Machinery and Manufacturing Equipment: Supplying control and interlock voltages, or adapting supply voltages for machine tools and robots.
• Building Automation: Powering control equipment in HVAC, elevators, and access systems.
• Test and Measurement Devices: Supplying isolated, regulated voltages for laboratory and quality assurance equipment.
• Custom Power Supply Assemblies: When equipment function requires voltages different from the main supply, or for devices built to specific customer requirements.

The standard ensures that these transformers deliver consistent performance while mitigating risks related to electric shock, overheating, short-circuits, or mechanical failure.

Related Standards

For comprehensive compliance and optimized equipment safety, related standards should be considered:

• EN IEC 61558-1:2019 - General requirements for safety of transformers, reactors, and power supply units
• EN IEC 61558-2-16:2025 - Requirements for switch mode power supply units and transformers
• IEC 60204-1:2018 - Safety of machinery - Electrical equipment of machines
• IEC 60076-11:2018 - Power transformers - Dry-type transformers (not applicable to control transformers in EN IEC 61558-2-2)
• EN IEC 61558-2-13:2025 - Requirements for auto transformers and power supply units incorporating auto transformers

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Implementing EN IEC 61558-2-2:2025 helps manufacturers, engineers, and specifiers assure the safety and reliability of control transformers, supporting compliance with European directives, improving product quality, and reducing operational risks. This standard is essential for anyone involved in the design, production, or certification of electrical control equipment in industrial and commercial environments.

SLOVENSKI STANDARD
01-maj-2025
Varnost transformatorjev, dušilk, napajalnikov in kombinacij teh elementov - 2-2.
del: Posebne zahteve in preskusi za kontrolne transformatorje in napajalnike s
kontrolnimi transformatorji
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
Sicherheit von Transformatoren, Drosseln, Netzgeräten und entsprechenden
Kombinationen – Teil 2-2: Besondere Anforderungen und Prüfungen für
Steuertransformatoren und Netzgeräten, die Steuertransformatoren enthalten
Sécurité des transformateurs, alimentations, bobines d'inductance et produits analogues
- Partie 2-2: Règles particulières et essais pour les transformateurs de commande et les
alimentations incorporant les transformateurs de commande
Ta slovenski standard je istoveten z: EN IEC 61558-2-2:2025
ICS:
29.180 Transformatorji. Dušilke Transformers. Reactors
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EUROPEAN STANDARD EN IEC 61558-2-2

NORME EUROPÉENNE
EUROPÄISCHE NORM March 2025
ICS 29.180 Supersedes EN 61558-2-2:2007
English Version
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)
Sécurité des transformateurs, bobines d'inductance, blocs Sicherheit von Transformatoren, Drosseln, Netzgeräten und
d'alimentation et combinaisons de ces éléments - Partie 2- entsprechenden Kombinationen - Teil 2-2: Besondere
2: Exigences particulières et essais pour les Anforderungen und Prüfungen für Steuertransformatoren
transformateurs de commande et les blocs d'alimentation und Netzgeräten, die Steuertransformatoren enthalten
qui incorporent des transformateurs de commande (IEC 61558-2-2:2022)
(IEC 61558-2-2:2022)
This European Standard was approved by CENELEC on 2024-10-16. CENELEC members are bound to comply with the CEN/CENELEC
Internal Regulations which stipulate the conditions for giving this European Standard the status of a national standard without any alteration.
Up-to-date lists and bibliographical references concerning such national standards may be obtained on application to the CEN-CENELEC
Management Centre or to any CENELEC member.
This European Standard exists in three official versions (English, French, German). A version in any other language made by translation
under the responsibility of a CENELEC member into its own language and notified to the CEN-CENELEC Management Centre has the
same status as the official versions.
CENELEC members are the national electrotechnical committees of Austria, Belgium, Bulgaria, Croatia, Cyprus, the Czech Republic,
Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, the
Netherlands, Norway, Poland, Portugal, Republic of North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland,
Türkiye and the United Kingdom.

European Committee for Electrotechnical Standardization
Comité Européen de Normalisation Electrotechnique
Europäisches Komitee für Elektrotechnische Normung
CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels
© 2025 CENELEC All rights of exploitation in any form and by any means reserved worldwide for CENELEC Members.
Ref. No. EN IEC 61558-2-2:2025 E

European foreword
The text of document 96/548/FDIS, future edition 3 of IEC 61558-2-2, prepared by TC 96
"Transformers, reactors, power supply units, and combinations thereof" was submitted to the IEC-
CENELEC parallel vote and approved by CENELEC as EN IEC 61558-2-2:2025.
The following dates are fixed:
• latest date by which the document has to be implemented at national (dop) 2026-03-31
level by publication of an identical national standard or by endorsement
• latest date by which the national standards conflicting with the (dow) 2028-03-31
document have to be withdrawn
This document supersedes EN 61558-2-2:2007 and all of its amendments and corrigenda (if any).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. CENELEC shall not be held responsible for identifying any or all such patent rights.
This document is read in conjunction with EN IEC 61558-1:2019.
Any feedback and questions on this document should be directed to the users’ national committee. A
complete listing of these bodies can be found on the CENELEC website.
Endorsement notice
The text of the International Standard IEC 61558-2-2:2022 was approved by CENELEC as a
European Standard without any modification.
In the official version, for Bibliography, the following notes have to be added for the standard indicated:
IEC 60076-11:2018 NOTE Approved as EN IEC 60076-11:2018 (not modified)
IEC 60204-1:2016 NOTE Approved as EN 60204-1:2018
IEC 61558 series NOTE Approved as EN 61558 series
IEC 61558-2-13:2022 NOTE Approved as EN IEC 61558-2-13:2025 (not modified)
Annex ZA
(normative)
Normative references to international publications
with their corresponding European publications
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any amendments)
applies.
NOTE 1  Where an International Publication has been modified by common modifications, indicated by (mod),
the relevant EN/HD applies.
NOTE 2  Up-to-date information on the latest versions of the European Standards listed in this annex is available
here: www.cencenelec.eu.
Annex ZA of EN IEC 61558-1 is applicable, except as follows:
Add:
Publication Year Title EN/HD Year
IEC 61558-1 2017 Safety of transformers, reactors, power EN IEC 61558-1 2019
supply units and combinations thereof -
Part 1: General requirements and tests
IEC 61558-2-16 2021 Safety of transformers, reactors, power EN IEC 61558-2-16 2025
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

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

IEC 61558-2-2:2022  IEC 2022 – 3 –
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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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.
IEC 61558-2-2:2022  IEC 2022 – 5 –
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 6020
...