IEC 61558-2-1:2021

Safety of transformers, reactors, power supply units and combinations thereof - Part 2-1: Particular requirements and tests for separating transformers and power supply units incorporating separating transformers for general applications

IEC 61558-2-1:2021 deals with the safety of separating transformers for general applications and power supply units incorporating separating transformers for general applications. Transformers incorporating electronic circuits are also covered by this document.
This third edition cancels and replaces the second edition published in 2007. This edition constitutes a technical revision.
This edition includes the following significant technical changes with respect to the previous edition:
a) Adjustment of structure and references in accordance with IEC 61558-1:2017;
b) Description of constructions moved to IEC 61558-1:2017;
c) New symbol for power supply unit with linearly regulated output voltage.
It has the status of a group safety publication in accordance with IEC Guide 104.
This International Standard is to be used in conjunction with IEC 61558-1:2017.

Sécurité des transformateurs, bobines d'inductance, blocs d'alimentation et des combinaisons de ces éléments – Partie 2-1: Exigences particulières et essais pour les transformateurs d'isolement à enroulements séparés et les blocs d'alimentation incorporant des transformateurs d'isolement à enroulements séparés pour applications d'ordre général

IEC 61558-2-1:2021 La présente partie de l'IEC 61558 traite de la sécurité des transformateurs d'isolement à enroulements séparés pour applications d'ordre général et des blocs d'alimentation incorporant des transformateurs d'isolement à enroulements séparés pour applications d'ordre général. Les transformateurs incorporant des circuits électroniques sont également couverts par le présent document.

General Information

• Status: Published
• Publication Date: 20-Apr-2021
• ICS: 29.180 - Transformers. Reactors
• Technical Committee: TC 96 - Transformers and reactors
• Drafting Committee: MT 1 - TC 96/MT 1
• Current Stage: PPUB - Publication issued
• Start Date: 21-Apr-2021
• Completion Date: 14-May-2021

Relations

• Revises: IEC 61558-2-1:2007 - Safety of power transformers, power supplies, reactors and similar products - Part 2-1: Particular requirements and tests for separating transformers and power supplies incorporating separating transformers for general applications
• Effective Date: 05-Sep-2023

Overview

IEC 61558-2-1:2021 - Edition 3.0 - is the International Electrotechnical Commission (IEC) product safety standard for separating transformers and power supply units incorporating separating transformers for general applications. This third edition cancels and replaces the 2007 edition and constitutes a technical revision. It is a group safety publication (IEC Guide 104) and is intended to be used in conjunction with IEC 61558-1:2017.

Key scope points:

• Covers stationary or portable, single- or polyphase, dry-type, air-cooled separating transformers and linear power supply units (including transformers incorporating electronic circuits).
• Rated supply voltage ≤ 1 000 V AC; frequencies (supply and internal) ≤ 500 Hz.
• Rated output limits: up to 1 kVA for single-phase and 5 kVA for polyphase (unless otherwise agreed).
• No-load/rated output voltages limited to ≤ 1 000 V AC or 1 415 V ripple-free DC; independent transformers not less than 50 V AC or 120 V ripple-free DC.
• Not applicable to switch-mode power supply units (see IEC 61558-2-16), transformers for distribution networks (IEC 60076-11), or certain transport environments without additional rules.

This edition includes structural alignment with IEC 61558-1:2017, relocates construction descriptions to Part 1, and adds a new symbol for linearly regulated power supply units.

Key Topics and Requirements

The standard supplements IEC 61558-1 with particular requirements and test criteria for separating transformers and related power supply units:

• Electrical safety: protection against electric shock, insulation resistance, dielectric strength, leakage current.
• Thermal safety: heating limits, temperature rise tests, resistance to heat and fire.
• Short-circuit and overload: tests and protective measures.
• Mechanical safety: mechanical strength, internal wiring, components, terminals and connectors.
• Ingress and environmental protection: protection against dust, solid objects, moisture; resistance to rusting; suitability for intended environments.
• Creepage and clearance: distances through and across insulation, tracking resistance.
• Marking and documentation: ratings, classification, symbols (including the new symbol for linear regulation), and instructions.
• Test specifications and classification tables detail required test methods and symbol definitions.

Applications and Who Uses It

IEC 61558-2-1 is primarily used by:

• Transformer and linear power supply manufacturers for product design and safety compliance.
• Compliance engineers and test laboratories performing type testing and certification.
• Product safety officers, OEMs and system integrators who select transformers or incorporate separating transformers into equipment.
• Procurement and regulatory teams ensuring equipment meets international safety requirements.

Typical applications include medical-adjacent equipment (where SELV/functional isolation is needed), industrial control panels, instrumentation, and general-purpose isolation transformers used to provide safety or functional separation.

Related Standards

• IEC 61558-1:2017 - General requirements (use in conjunction)
• IEC 61558-2-16 - Particular requirements for switch-mode power supply units
• IEC 60076-11 - Power transformers (excluded from this part)
• Safety and installation references: IEC 61140, IEC 60364-4-41, IEC 60204-1

For manufacturers and safety assessors, IEC 61558-2-1:2021 is the authoritative reference for designing, testing and certifying separating transformers and linear power supplies for general applications.

Standards Content (Sample)

IEC 61558-2-1 ®
Edition 3.0 2021-04
INTERNATIONAL
STANDARD
GROUP SAFETY PUBLICATION
Safety of transformers, reactors, power supply units and combinations thereof –
Part 2-1: Particular requirements and tests for separating transformers and
power supply units incorporating separating transformers for general
applications
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IEC 61558-2-1 ®
Edition 3.0 2021-04
INTERNATIONAL
STANDARD
GROUP SAFETY PUBLICATION
Safety of transformers, reactors, power supply units and combinations thereof –

Part 2-1: Particular requirements and tests for separating transformers and

power supply units incorporating separating transformers for general

applications
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 29.180 ISBN 978-2-8322-9696-7

– 2 – IEC 61558-2-1:2021 © IEC 2021
CONTENTS
FOREWORD . 3
INTRODUCTION . 5
1 Scope . 6
2 Normative references . 7
3 Terms and definitions . 7
4 General requirements . 7
5 General notes on tests . 7
6 Ratings . 8
7 Classification . 8
8 Marking and other information . 8
9 Protection against electric shock . 9
10 Change of input voltage setting . 9
11 Output voltage and output current under load . 9
12 No-load output voltage . 9
13 Short-circuit voltage . 10
14 Heating . 10
15 Short-circuit and overload protection . 10
16 Mechanical strength . 11
17 Protection against harmful ingress of dust, solid objects and moisture . 11
18 Insulation resistance, dielectric strength and leakage current . 11
19 Construction . 11
20 Components . 11
21 Internal wiring . 11
22 Supply connection and other external flexible cable or cords . 11
23 Terminals for external conductors . 11
24 Provisions for protective earthing. 11
25 Screws and connections . 11
26 Creepage distances, clearances and distances through insulation . 11
27 Resistance to heat, fire and tracking . 11
28 Resistance to rusting . 12
Annexes . 13
Bibliography . 14

Table 101 – Symbols indicating the kind of transformer . 9
Table 102 – Output voltage ratio . 10

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

Part 2-1: Particular requirements and tests for separating
transformers and power supply units incorporating separating
transformers for general applications

FOREWORD
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International standard IEC 61558-2-1 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) Description of constructions moved to IEC 61558-1:2017;
c) New symbol for power supply unit with linearly regulated output voltage.

– 4 – IEC 61558-2-1:2021 © IEC 2021
The text of this International Standard is based on the following documents:
Draft Report on voting
96/499/FDIS 96/510/RVD
Full information on the voting for its approval can be found in the report on voting indicated in
the above table.
The language used for the development of this International Standard is English.
This document was drafted in accordance with ISO/IEC Directives, Part 2, and developed in
accordance with ISO/IEC Directives, Part 1 and ISO/IEC Directives, IEC Supplement,
available at www.iec.ch/members_experts/refdocs. The main document types developed by
IEC are described in greater detail at www.iec.ch/standardsdev/publications.
It has the status of a group safety publication in accordance with IEC Guide 104.
This International Standard is to be used in conjunction with IEC 61558-1:2017.
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
separating transformers and power supply units incorporating separating 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 stat
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