IEC 61558-2-4:2021

IEC 61558-2-4 ®
Edition 3.0 2021-05
INTERNATIONAL
STANDARD
GROUP SAFETY PUBLICATION
Safety of transformers, reactors, power supply units and combinations thereof –
Part 2-4: Particular requirements and tests for isolating transformers and power
supply units incorporating isolating transformers for general applications

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IEC 61558-2-4 ®
Edition 3.0 2021-05
INTERNATIONAL
STANDARD
GROUP SAFETY PUBLICATION
Safety of transformers, reactors, power supply units and combinations thereof –

Part 2-4: Particular requirements and tests for isolating transformers and power

supply units incorporating isolating transformers for general applications

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 29.180 ISBN 978-2-8322-9790-2

– 2 – IEC 61558-2-4:2021 © IEC 2021
CONTENTS
FOREWORD . 3
INTRODUCTION . 6
1 Scope . 7
2 Normative references . 8
3 Terms and definitions . 8
4 General requirements . 8
5 General notes on tests . 8
6 Ratings . 9
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 . 10
12 No-load output voltage . 10
13 Short-circuit voltage . 11
14 Heating . 11
15 Short-circuit and overload protection . 11
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 . 12
20 Components . 12
21 Internal wiring . 12
22 Supply connection and other external flexible cable or cords . 12
23 Terminals for external conductors . 12
24 Provisions for protective earthing. 12
25 Screws and connections . 12
26 Creepage distances, clearances and distances through insulation . 12
27 Resistance to heat, fire and tracking . 12
28 Resistance to rusting . 13
Annexes . 14
Bibliography . 15

Table 101 – Symbols indicating the kind of transformer . 10
Table 102 – Output voltage ratio . 11

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

Part 2-4: Particular requirements and tests
for isolating transformers and power supply units
incorporating isolating 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
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International standard IEC 61558-2-4 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 2009. 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) a new symbol for power supply unit with linearly regulated output voltage.

– 4 – IEC 61558-2-4:2021 © IEC 2021
The text of this International Standard is based on the following documents:
FDIS Report on voting
96/505/FDIS 96/511/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 isolating
transformers and power supply units incorporating isolating 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.
– 6 – IEC 61558-2-4:2021 © IEC 2021
INTRODUCTION
IEC/TC 96 has group safety
...