IEC 61558-2-4:2009

Safety of transformers, reactors, power supply units and similar products for supply voltages up to 1 100 V - Part 2-4: Particular requirements and tests for isolating transformers and power supply units incorporating isolating transformers

IEC 61558-2-4:2009 deals with the safety of isolating transformers for general applications and power supply units incorporating isolating transformers for general applications. Transformers incorporating electronic circuits are also covered by this standard. This second edition cancels and replaces the first edition published in 1997. It constitutes a technical revision. The main changes consist of updating this part in accordance with Part 1 (2005), and increasing the supply voltages up to 1 100 V to be in line with the standards of TC 14. This part has the status of a group safety publication in accordance with IEC Guide 104. 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. 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.

Sécurité des transformateurs, bobines d'inductance, blocs d'alimentation et produits analogues pour des tensions d'alimentation jusqu'à 1 100 V - Partie 2-4: Règles particulières et essais pour les transformateurs de séparation des circuits et les blocs d'alimentation incorporant des transformateurs de séparation des circuits

La CEI 61558-2-4:2009 traite de la sécurité des transformateurs de séparation des circuits pour applications d'ordre général et des blocs d'alimentation incorporant des transformateurs de séparation des circuits pour applications d'ordre général. Les transformateurs incorporant des circuits électroniques sont également couverts par cette norme. Cette deuxième édition annule et remplace la première édition publiée en 1997. Elle constitue une révision technique. Les principales modifications consistent en la mise à jour de la présente partie conformément à la Partie 1 (2005), et l'augmentation des tensions d'alimentation jusqu'à 1 100 V pour être en conformité avec les normes du TC 14. La présente partie a le statut de publication groupée de sécurité conformément au Guide CEI 104. La présente partie est destinée à être utilisée avec la dernière édition de la CEI 61558-1 et ses amendements. Elle est basée sur la seconde édition (2005) de cette norme. Le comité recommande que le contenu de cette publication soit entériné au niveau national au plus tôt 12 mois après la date de publication.

General Information

• Status: Published
• Publication Date: 10-Feb-2009
• ICS: 29.180 - Transformers. Reactors
• Technical Committee: TC 96 - Transformers and reactors
• Drafting Committee: MT 1 - TC 96/MT 1
• Current Stage: DELPUB - Deleted Publication
• Start Date: 18-May-2021
• Completion Date: 05-Jul-2019

Relations

• Revised: IEC 61558-2-4:2021 - 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
• Effective Date: 05-Sep-2023
• Revises: IEC 61558-2-4:1997 - Safety of power transformers, power supply units and similar - Part 2: Particular requirements for isolating transformers for general use
• Effective Date: 05-Sep-2023

Overview

IEC 61558-2-4:2009 is an essential international standard published by the International Electrotechnical Commission (IEC) that specifies the safety requirements and testing procedures for isolating transformers and power supply units incorporating isolating transformers. It applies to products designed for supply voltages up to 1,100 V AC or DC, covering both stationary and portable units. This standard specifically addresses transformers for general applications, including those with embedded electronic circuits.

The 2009 edition represents a technical revision that updates the first edition from 1997. Major updates align this part with IEC 61558-1 (2005) and TC 14 standards, enhancing safety coverage for transformers operating at higher supply voltages up to 1,100 V.

Key Topics

• Scope and Applicability

  • Covers isolating transformers and power supply units for general-purpose use.
  • Applies to single-phase or polyphase, dry-type, air-cooled transformers.
  • Rated output limits: up to 25 kVA for single-phase and 40 kVA for polyphase transformers.
  • Incorporates transformers with electronic circuits.
  • Limits supply frequency and internal operating frequency up to 500 Hz.

• Safety Requirements

  • Electrical safety: protection against electric shock, insulation requirements, and clearances.
  • Thermal safety: limits on heating under load and during no-load conditions.
  • Mechanical safety: robustness against mechanical stress and strength tests.
  • Protection against short circuits and overloads.
  • Resistance to environmental hazards such as dust, moisture, and corrosion.

• Testing Procedures

  • Verification of electrical insulation resistance and dielectric strength.
  • Measurement of output voltage and current characteristics under load and no-load conditions.
  • Mechanical strength tests to simulate operational stresses.
  • Heat resistance and fire tracking tests.
  • Verification of markings, protective earthing provisions, and compliance with classification rules.

• Markings and Information

  • Requirements for clear labeling of rated voltages, currents, and safety warnings.
  • Instructions related to input voltage settings and changes.
  • Ensuring transparency and traceability in transformer design.

Applications

IEC 61558-2-4:2009 is highly relevant to manufacturers, testing laboratories, and regulatory bodies involved with:

• Industrial and Commercial Power Supplies

  • Transformers providing electrical isolation and reliable power conversion in machinery and factory automation.

• Medical and Laboratory Equipment

  • Ensuring patient and user safety through isolation transformers that prevent electrical hazards.

• Consumer Electronics and Appliances

  • Providing safe isolation for small power supply units embedded in electrical devices.

• Electrical Engineering and Product Design

  • Guiding design specifications to comply with international safety standards.

• Testing and Certification

  • Facilitating conformity assessment to IEC’s safety benchmarks before market introduction.

This standard supports the development of transformers that deliver safety, reliability, and performance in various electrical systems with supply voltages up to 1,100 V.

Related Standards

IEC 61558-2-4 is part of the broader IEC 61558 series focused on the safety of transformers and power supply units:

• IEC 61558-1: General requirements for safety of transformers, reactors, and power supply units. IEC 61558-2-4 supplements and modifies clauses of IEC 61558-1 for isolating transformers.

• IEC 61558-2-16: Specific requirements for switch mode power supply units incorporating isolating transformers, complementary to IEC 61558-2-4.

• IEC 60664-1: Coordination of insulation for electrical equipment; relevant for understanding creepage distances and clearance requirements referred to in IEC 61558-2-4.

• IEC Guide 104: Guidance on preparation and use of group safety publications, providing context for classification of IEC 61558-2-4 as a group safety publication.

Adherence to these standards ensures compliance with international safety norms and facilitates harmonized regulatory acceptance.

---

Adopting IEC 61558-2-4:2009 supports the design, testing, and certification of isolating transformers and power supply units, enhancing electrical safety and product reliability across industries worldwide. For the latest updates and full details, visit the official IEC webstore or consult the IEC Central Office.

Standards Content (Sample)

IEC 61558-2-4 ®
Edition 2.0 2009-02
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
GROUP SAFETY PUBLICATION
PUBLICATION GROUPÉE DE SÉCURITÉ
Safety of transformers, reactors, power supply units and similar products for
supply voltages up to 1 100 V –
Part 2-4: Particular requirements and tests for isolating transformers and power
supply units incorporating isolating transformers

Sécurité des transformateurs, bobines d’inductance, blocs d'alimentation et
produits analogues pour des tensions d'alimentation jusqu'à 1 100 V –
Partie 2-4: Règles particulières et essais pour les transformateurs de séparation
des circuits et les blocs d'alimentation incorporant des transformateurs de
séparation des circuits
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IEC 61558-2-4 ®
Edition 2.0 2009-02
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
GROUP SAFETY PUBLICATION
PUBLICATION GROUPÉE DE SÉCURITÉ
Safety of transformers, reactors, power supply units and similar products for
supply voltages up to 1 100 V –
Part 2-4: Particular requirements and tests for isolating transformers and power
supply units incorporating isolating transformers

Sécurité des transformateurs, bobines d’inductance, blocs d'alimentation et
produits analogues pour des tensions d'alimentation jusqu'à 1 100 V –
Partie 2-4: Règles particulières et essais pour les transformateurs de séparation
des circuits et les blocs d'alimentation incorporant des transformateurs de
séparation des circuits
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
PRICE CODE
INTERNATIONALE
N
CODE PRIX
ICS 29.180 ISBN 978-2-88910-540-3
– 2 – 61558-2-4 © IEC:2009
CONTENTS
FOREWORD.3
1 Scope.5
2 Normative references .6
3 Terms and definitions .6
4 General requirements .6
5 General notes on tests .6
6 Ratings.6
7 Classification.7
8 Marking and other information .7
9 Protection against electric shock .7
10 Change of input voltage setting .7
11 Output voltage and output current under load .7
12 No-load output voltage .8
13 Short-circuit voltage .8
14 Heating .9
15 Short-circuit and overload protection .9
16 Mechanical strength .9
17 Protection against harmful ingress of dust, solid objects and moisture.9
18 Insulation resistance, dielectric strength and leakage current .9
19 Construction .9
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 .12
26 Creepage distances, clearances and distances through insulation.12
27 Resistance to heat, fire and tracking.12
28 Resistance to rusting.12
Annexes .13
Annex C Creepage distances (cr), clearances (cl) and distances through insulation
(dti) Material group II (400 ≤CTI <600) .13
Annex D Creepage distances (cr), clearances (cl) and distances through insulation
(dti) Material group I (CTI ≥600).13
Annex R Explanations of the application of 4.2 of IEC 60664-1:2007 (see IEC 61558-1
Subclause 26.2).13
Bibliography.14

Table 101 – Output voltage difference .

61558-2-4 © IEC:2009 – 3 –
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
SAFETY OF TRANSFORMERS, REACTORS, POWER SUPPLY UNITS
AND SIMILAR PRODUCTS FOR SUPPLY VOLTAGES UP TO 1 100 V –

Part 2-4: Particular requirements and tests
for isolating transformers and power supply units
incorporating isolating 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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2) The formal decisions or agreements of IEC on technical matters express, as nearly as possible, an international
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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 61558-2-4 has been prepared by IEC technical committee 96:
Transformers, reactors, power supply units and similar products for low voltages up to
1 100 V.
This second edition cancels and replaces the first edition published in 1997. It constitutes a
technical revision. The main changes consist of updating this part in accordance with Part 1
(2005), and increasing the supply voltages up to 1 100 V to be in line with the standards of TC
14.
This part has the status of a group safety publication in accordance with IEC Guide 104
(1997): The preparation of safety publications and the use of basic safety publications and
group safety publications.
– 4 – 61558-2-4 © IEC:2009
The text of this standard is based on the following documents:
FDIS Report on voting
96/316/FDIS 96/321/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 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.
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 isolating
transformers and power supply units incorporating isolating transformers.
A list of all parts of the IEC 61558 series can be found on the IEC website under the title:
Safety of transformers, reactors, power supply units and similar products for supply voltages
up to 1 100 V.
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 maintenance result 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.
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.

61558-2-4 © IEC:2009 – 5 –
SAFETY OF TRANSFORMERS, REACTORS, POWER SUPPLY UNITS
AND SIMILAR PRODUCTS FOR SUPPLY VOLTAGES UP TO 1 100 V –

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

1 Scope
Replacement:
This part of IEC 61558 deals with the safety of isolating transformers for general
applications and power supply units incorporating isolating transformers for general
applications. Transformers incorporating electronic circuits are also covered by this
standard.
NOTE 1 Safety includes electrical, thermal and mechanical aspects.
Unless otherwise specified, from here onward, the term transformer covers isolating
transformers for general applications and power supply units incorporating isolating
transformers for general applications.
NOTE 2 For power supply units (linear) this part is applicable. For switch mode power supply units, IEC 61558-2-16 is
applicable together with this part.
This part is applicable to stationary or portable, single-phase or polyphase, air-cooled
(natural or forced) independent or associated dry- type transformers. The windings may be
encapsulated or non-encapsulated.
The rated supply voltage does not exceed 1 100 V a.c., and the rated supply frequency
and the internal operating frequencies do not exceed 500 Hz.
The rated output does not exceed:
– 25 kVA for single-phase transformers;
– 40 kVA for polyphase transformers.
This part is applicable to transformers without limitation of the rated output subject to an
agreement between the purchaser and the manufacturer.
NOTE 3 Transformers intended to supply distribution networks are not included in the scope.
The no-load output voltage or the rated output voltage does exceed 50 V a.c. or 120 V
ripple-free d.c., and where applicable, 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.
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.
Transformers covered by this part are used in applications where double or reinforced
insulation between circuits is required by the installation rules or by the end product
standard.
– 6 – 61558-2-4 © IEC:2009
NOTE 4 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.) may 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 should also be considered;
- the different conditions for transportation, storage, and operation of the transformers should also be
considered;
- additional requirements in accordance with other appropriate standards and national rules may be applicable to
transformers intended for use in special environments.
NOTE 5 Future technological development of transformers may 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
3 Terms and definitions
This clause of Part 1 is applicable.
4 General requirements
This clause of Part 1 is applicable.
5 General notes on tests
This clause of Part 1 is applicable.
6 Ratings
This clause of Part 1 is applicable.
Addition:
6.101 The rated output voltage shall exceed 50 V a.c. or 120 V ripple-free d.c. but not
exceed;
– 250 V a.c. for single-phase portable transformers;
– 400 V a.c. for polyphase portable transformers, and
– 500 V a.c. or 708 V ripple-free d.c. for other transformers. In this case, the rated output
voltage may be up to 1 000 V a.c. or 1 415 V ripple-free d.c. to be in accordance with the
national wiring rules or for a special purpose. This output voltage limitation apply even
when output windings, not intended for interconnection, are connected in series.
6.102 The rated output shall not exceed:
– 25 kVA for single-phase transformers;
– 40 kVA for polyphase transformers;

61558-2-4 © IEC:2009 – 7 –
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 the internal operating frequencies shall not
exceed 500 Hz.
6.104 The rated supply voltage shall not exceed 1 100 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:
8.1 h) Replacement:
Replace the first sentence by the following: relevant graphical symbols shown in 8.11
indicating the kind of transformer;
8.11 Addition:
Symbol or
Explanation or title Identification
Graphical symbol
Fail-safe isolating transformer 60417-5221

or
F
F
Non-short-circuit-proof isolating transformer 60417-5944
or
Short-circuit-proof isolating transformer 60417-5945
or (inherently or non-inherently)

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.

– 8 – 61558-2-4 © IEC:2009
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 defined by Part 1.
12.101 The no-load output voltage shall exceed 50 V a.c. or 120 V ripple-free d.c. but not
exceed:
– 300 V a.c. for single-phase portable transformers;
– 500 V a.c. for polyphase portable transformers, and
– 500 V a.c. or 708 V ripple-free d.c. for other transformers. In this case, the no-load
output voltage may be up to 1 000 V a.c. or 1 415 V ripple-free d.c. to be in accordance
with the national wiring rules or for special purpose.
For independent transformers, this output voltage limitation applies even when output
windings, not intended for interconnection, are connected in series.
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 U is the output voltage under load.
no-load load
Compliance with the requirements of 12.101 and 12.102 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.
The difference shall not exceed the values shown in Table 101.
Table 101 – Output voltage difference
Type of transformer Difference between no-load output voltage and
Rated output 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
13 Short-circuit voltage
This clause of Part 1 is applicable.

61558-2-4 © IEC:2009 – 9 –
14 Heating
This clause of Part 1 is applicable.
15 Short-circuit and overload protection
This clause of Part 1 is applicable.
16 Mechanical strength
This clause of Part 1 is applicable.
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.
19 Construction
This clause of Part 1 is applicable except as follows:
Replace 19.1 by the following:
19.1 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.
19.1.1 The insulation between input and output winding(s) shall consist of double or
reinforced insulation (rated for the working voltage) unless the requirements in 19.1.3 are
complied with:
In addition, the following applies:
– for class I transformers not intended for connection to the mains supply by means of
a plug, the insulation between the input windings and the body connected to earth
shall consist of at least basic insulation rated for the input voltage. The insulation
between the output windings and the body connected to earth, shall consist of at
least basic insulation (rated for the output voltage);
– for class I transformers intended for connection to the mains supply by means of a
plug, the insulation between the input windings and the body shall consist of at least
basic insulation, and the insulation between the output windings and the body shall
consist of at least supplementary insulation (both basic and supplementary
insulations rated for the working voltage);
– for class II transformers, the insulation between the input windings and the body
shall consist of double or reinforced insulation (rated for the input voltage). The
insulation between the output windings and the body, shall consist of double or
reinforced insulation (rated for the output voltage).

– 10 – 61558-2-4 © IEC:2009
19.1.2 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 following
requirements are applicable:
19.1.2.1 for class I and class II transformers, the insulation between the input and
output windings via the intermediate conductive parts shall consist of double or
reinforced insulation (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 via the intermediate
conductive parts shall consist of double or reinforced insulation (rated for the
input and output voltage), for SELV circuits basic insulation only is required.
– for transformer different from independent (IP00), the insulation between the input
and output windings via the intermediate conductive parts shall consist of
double or reinforced insulation (rated for the working voltage).
19.1.2.2 as alternative to 19.1.2.1 for class I transformer not intended to be
connected by means of a plug and for transformer different from independent (IP00),
if the construction assure that all laminated plates of the iron core are connected to
earth (e.g by soldering / welding) and if in the data sheet or instruction sheet clearly
state that the safety of the transformer depends on the earth connection and that is
not possible to use in class II equipment, than the following apply: the insulation
between the input windings and the intermediate conductive part connected to
earth, and between the output windings and the intermediate conductive part
connected to earth, shall consist of at least basic insulation (rated for the input and
output voltage);
19.1.2.3 in addition to 19.1.2.1 and 19.1.2.2 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
input and output voltage). An intermediate conductive part not separated from the
input or output windings or the body by at least basic insulation is considered to
be connected to the relevant part(s).
19.1.3 For class I transformers not intended for connection to the mains supply by means
of a plug, the insulation between the input and output windings may consist of basic
insulation plus protective screening instead of double or reinforced insulation, provided
the following conditions are complied with:
– the insulation between the input winding and the protective screen shall comply with
the requirements for basic insulation (rated for the input voltage );
– the insulation between the protective screen and the output winding shall comply with
the requirements for basic insulation (rated for the output voltage);
– the protective screen shall, unless otherwise specified, consist of a metal foil or of a
wire wound screen extending at least the full width of the input winding and shall
have no gaps or holes;
– where the protective screen does not cover the entire width of the input winding,
additional adhesive tapes or equivalent insulation shall be used to ensure double
insulation in that area;
– if the protective screen is made of a foil, the turns shall be insulated from each other.
In case of only one turn, it shall have an isolated overlap of at least 3 mm;
– the wire of a wire wound screen and the lead out wire of the protective screen shall
have a cross-sectional area at least corresponding to the rated current of the overload
device to ensure that if a breakdown of insulation should occur, the overload
protective device will open the circuit before the lead-out wire is destroyed;
– the lead-out wire shall be soldered to the protective screen or secured in an equally
reliable manner.
61558-2-4 © IEC:2009 – 11 –
NOTE For the purpose of this subclause, the term "winding" does not include internal circuits
Examples of construction of windings are given in Annex M of Part 1.
19.1.4 There shall be no connection between output circuits and the protective earth,
unless this is allowed for associated transformers by the relevant equipment standard.
19.1.5 There shall be no connection between output circuits and the body, unless this is
allowed for associated transformers by the relevant equipment standard.
Compliance is checked by inspection.
19.1.6 The input and output terminals for the connection of external wiring shall be so
located that the distance measured between the points of introduction of the conductors into
these terminals is not less than 25 mm. If a barrier is used to obtain this distance, the
measurement shall be made over and around the barrier which shall be of insulating material
and permanently fixed to the transformer.
Compliance is checked by inspection and by measurement disregarding intermediate
conductive parts.
Addition:
19.101 Portable transformers having a rated output not exceeding 630 VA shall be
class II.
19.102 There shall be no connection between the output circuits and the body, unless - for
associated transformers - allowed by the relevant equipment standard.
19.103 For transformers for connection to the mains by the means of a plug of any type
(incorporating or not), the alternative with basic insulation plus protective screening is not
allowed.
20 Components
This clause of Part 1 is applicable.
21 Internal wiring
This clause of Part 1 is applicable.
22 Supply connection and other external flexible cable or cords
This clause of Part 1 is applicable.
23 Terminals for external conductors
This clause of Part 1 is applicable.
24 Provisions for protective earthing
This clause of Part 1 is applicable.

– 12 – 61558-2-4 © IEC:2009
25 Screws and connections
This clause of Part 1 is applicable.
26 Creepage distances, clearances and distances through insulation
This clause of Part 1 is applicable except as follows:
Addition:
The values for creepage distances, clearances and distances through insulation for
26.101
working voltages above 1 000 V may be found by extrapolation.
27 Resistance to heat, fire and tracking
This clause of Part 1 is applicable.
28 Resistance to rusting
This clause of Part 1 is applicable.

61558-2-4 © IEC:2009 – 13 –
Annexes
The annexes of Part 1 are applicable except as follows:

Annex C
Creepage distances (cr), clearances (cl) and distances through
insulation (dti) Material group II (400 ≤CTI <600)

This annex of Part 1 is applicable, except as follows:
Addition:
The values for creepage distances, clearances and distances through insulation for working
voltages above 1 000 V may be found by extrapolation.

Annex D
Creepage distances (cr), clearances (cl) and distances through
insulation (dti) Material group I (CTI ≥600)

This annex of Part 1 is applicable, except as follows:
Addition:
The values for creepage distances, clearances and distances through insulation for working
voltages above 1 000 V may be found by extrapolation.

Annex R
Explanations of the application of 4.2 of IEC 60664-1:2007
(see IEC 61558-1 Subclause 26.2)

This annex of Part 1 is applicable, except as follows:
Addition:
The values for working voltage above 1 000 V may be found by extrapolation.

– 14 – 61558-2-4 © IEC:2009
Bibliography
IEC 61558-2-16, Safety of transformers, reactors, power supply units and similar products for
supply voltages up to 1 100 V – Part 2-16: Particular requirements and tests for switch mode
power supply units and transformers for switch mode power supply units

___________
___________
To be published.
– 16 – 61558-2-4 © CEI:2009
SOMMAIRE
AVANT-PROPOS .17
1 Domaine d’application.20
2 Références normatives .21
3 Termes et définitions .21
4 Exigences générales.21
5 Généralités sur les essais.21
6 Caractéristiques assignées .21
7 Classification .22
8 Marquage et indications .22
9 Protection contre les chocs électriques .23
10 Changement de la tension primaire d’alimentation.23
11 Tension secondaire et courant secondaire en charge .23
12 Tension secondaire à vide .23
13 Tension de court-circuit .24
14 Echauffements.24
15 Protection contre les courts-circuits et les surcharges .24
16 Résistance mécanique.24
17 Protection contre les effets nuisibles dus à la pénétration de poussière, d’objets
solides et de l’humidité .
18 Résistance d'isolement, rigidité diélectrique et courant de fuite .24
19 Construction .24
20 Composants .27
21 Conducteurs internes.27
22 Raccordement à l’alimentation et câbles souples externes .27
23 Bornes pour conducteurs externes .27
24 Dispositions en vue de la mise à la terre .27
25 Vis et connexions .27
26 Lignes de fuite, distances d’isolement et distances à travers l’isolation.27
27 Résistance à la chaleur, au feu et aux courants de cheminement .27
28 Protection contre la rouille .27
Annexes.28
Annexe C Lignes de fuite (Idf), distances d'isolement (d) et distances à travers
l'isolation (dti) – Matériau groupe II (400 ≤ CTI <600).28
Annexe D Lignes de fuite (Idf), distances d'isolement (d) et distances à travers
l'isolation (dti) Matériau groupe I (CTI (600).28
Annexe R Explications de l’application de 4.2 de la CEI 60664-1:2007 (voir la
CEI 61558-1 Paragraphe 26.2) .28
Bibliographie .29

Tableau 101 – Différence de la tension secondaire.24

61558-2-4 © CEI:2009 – 17 –
COMMISSION ÉLECTROTECHNIQUE INTERNATIONALE
_________
SÉCURITÉ DES TRANSFORMATEURS, BOBINES D’INDUCTANCE,
BLOCS D'ALIMENTATION ET PRODUITS ANALOGUES
POUR DES TENSIONS D'ALIMENTATION JUSQU'À 1 100 V –

Partie 2-4: Règles particulières et essais pour les transformateurs
de séparation des circuits et les blocs d'alimentation incorporant
des transformateurs de séparation des circuits

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