IEC 61558-2-8:2010

Safety of transformers, reactors, power supply units and combinations thereof - Part 2-8: Particular requirements and tests for transformers and power supply units for bells and chimes

IEC 61558-2-8:2010 deals with the safety of bell and chime transformers and power supply units incorporating bell and chime transformers. Transformers incorporating electronic circuits are also covered by this standard. This second edition cancels and replaces the first edition published in 1998. It constitutes a technical revision. The main changes consist of updating this part in accordance with IEC 61558-1:2005. This part has the status of a group safety publication in accordance with IEC Guide 104. 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. In the meantime, the previous edition can still be ordered by contacting your local IEC member National Committee or the IEC Central Office.
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 2-8: Règles particulières et essais pour les transformateurs et blocs d'alimentation pour sonneries et carillons

La CEI 61558-2-8:2010 traite de la sécurité des transformateurs pour sonneries et carillons et des blocs d'alimentation incorporant des transformateurs pour sonneries et carillons. Les transformateurs incorporant des circuits électroniques sont également couverts par la présente norme. Cette deuxième édition annule et remplace la première édition publiée en 1998. Elle constitue une révision technique. Les principales modifications comprennent la mise à jour de la présente partie conformément à la CEI 61558-1:2005. La présente partie a le statut de publication groupée de sécurité conformément au Guide CEI 104. 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. Pendant ce temps, l'édition précédente peut toujours être commandée auprès du Comité National CEI de votre pays ou auprès du bureau Central de la CEI.
Cette publication doit être lue conjointement avec la CEI 61558-1:2005.

General Information

• Status: Published
• Publication Date: 28-Jun-2010
• 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: 07-Jun-2024
• Completion Date: 17-Oct-2022

Relations

• Revises: IEC 61558-2-8:1998 - Safety of small power transformers, power supply units and similar - Part 2-8: Particular requirements for bell and chime transformers
• Effective Date: 05-Sep-2023
• Revised: IEC 61558-2-8:2024 - Safety of transformers, reactors, power supply units and combinations thereof - Part 2-8: Particular requirements and tests for transformers and power supply units for bells and chimes
• Effective Date: 05-Sep-2023

Overview

IEC 61558-2-8:2010 is an international safety standard published by the International Electrotechnical Commission (IEC) that establishes particular requirements and tests for transformers and power supply units specifically designed for bells and chimes. This updated edition supersedes the original 1998 version, aligning with the technical revisions introduced in IEC 61558-1:2005. The scope of this standard primarily includes stationary, single-phase, air-cooled, dry-type bell and chime transformers, including those that incorporate electronic circuits and linear power supply units. The standard covers transformers with rated supply voltages not exceeding 250 V AC, rated output not exceeding 100 VA, and specific limitations on output voltages aimed at domestic sound signaling equipment and associated devices.

The primary focus of IEC 61558-2-8:2010 is to ensure the electrical, thermal, and mechanical safety of bell and chime transformers, guaranteeing reliable operation and protection for both users and connected equipment.

Key Topics

• Scope and Applicability
  The standard applies to dry-type bell and chime transformers, including linear power supplies used in sound signaling devices such as doorbells and chimes. It covers transformers with voltages up to 250 V AC supply, output voltages capped at 24 V AC or 33 V ripple-free DC, and rated output power up to 100 VA. Transformers used with double or reinforced insulation requirements are also included.

• Safety Requirements
  IEC 61558-2-8 addresses electrical shock protection, thermal resistance, insulation integrity, as well as mechanical robustness. It prescribes tests for insulation resistance, dielectric strength, leakage current, and protection against ingress by dust or moisture.

• Testing Procedures
  The standard details mandatory tests, including short-circuit and overload protection, heating measurements, voltage output verification under load and no-load conditions, mechanical strength, and resistance to rusting and fire. These procedures validate compliance with safety limits and ensure reliable transformer performance in typical operating environments.

• Marking and Documentation
  Transformers and power units must be marked clearly with ratings, warnings, and manufacturer information to facilitate correct installation and safe use. Electrical ratings, including voltage, current, and frequency, should be prominently displayed.

• Integration with Other Standards
  IEC 61558-2-8 is designed to be read together with IEC 61558-1:2005, which outlines general safety requirements. When conflicts arise, the more stringent safety protocols take precedence, ensuring comprehensive risk mitigation.

Applications

IEC 61558-2-8:2010 plays a critical role in the design, manufacturing, and certification of bell and chime transformers used in:

• Residential and Commercial Doorbell Systems
  The transformers power sound signaling devices reliably and safely, suited for intermittent operation typical of doorbells.

• Chime and Alert Systems
  Applications requiring specific voltage characteristics for short-duration sound alerts benefit from transformers tested and certified under this standard.

• Linear Power Supply Units with Embedded Transformers
  Systems combining power supply units with bell/chime transformers fall under this scope, ensuring safety across integrated devices.

• Domestic Sound Signaling Equipment
  The standard ensures that the transformers meet strict safety requirements to prevent electrical hazards in household environments.

Manufacturers, testing organizations, and installation professionals benefit from the clear safety and performance criteria outlined, aiding in compliance with international safety regulations and enhancing end-user protection.

Related Standards

• IEC 61558-1:2005 – General requirements for transformers, reactors, and power supply units. This standard provides the foundation for specific parts like IEC 61558-2-8 and covers broad safety aspects applicable to all related equipment.

• IEC 61558-2-16 – Particular requirements for switch mode power supply units (SMPS) associated with transformers. When higher internal operating frequencies are involved, this standard complements IEC 61558-2-8.

• IEC Guide 104 – Provides guidance on group safety publications, under which IEC 61558-2-8 is classified, supporting consistent safety standard development.

• National and Regional Safety Standards – Compliance with IEC 61558-2-8 facilitates the adoption and harmonization of transformer safety requirements across different jurisdictions.

Summary

IEC 61558-2-8:2010 is an essential standard that ensures the safety and reliability of bell and chime transformers and power supply units. By stipulating stringent requirements for design, testing, and marking, it minimizes electrical and mechanical hazards associated with these devices. This standard is a key resource for manufacturers, certification bodies, and end users dedicated to maintaining high safety standards in sound signaling and related electrical equipment. Ensuring adherence to IEC 61558-2-8 supports global harmonization of safety practices and enhances consumer confidence in bell and chime transformer products.

Standards Content (Sample)

IEC 61558-2-8 ®
Edition 2.0 2010-06
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
GROUP SAFETY PUBLICATION
PUBLICATION GROUPÉE DE SÉCURITÉ

Safety of transformers, reactors, power supply units and combinations thereof –
Part 2-8: Particular requirements and tests for transformers and power supply
units for bells and chimes
Sécurité des transformateurs, bobines d’inductance, blocs d’alimentation et des
combinaisons de ces éléments –
Partie 2-8: Règles particulières et essais pour les transformateurs et blocs
d’alimentation pour sonneries et carillons

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IEC 61558-2-8 ®
Edition 2.0 2010-06
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
GROUP SAFETY PUBLICATION
PUBLICATION GROUPÉE DE SÉCURITÉ

Safety of transformers, reactors, power supply units and combinations thereof –
Part 2-8: Particular requirements and tests for transformers and power supply
units for bells and chimes
Sécurité des transformateurs, bobines d’inductance, blocs d’alimentation et des
combinaisons de ces éléments –
Partie 2-8: Règles particulières et essais pour les transformateurs et blocs
d’alimentation pour sonneries et carillons
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
PRICE CODE
INTERNATIONALE
N
CODE PRIX
ICS 29.180 ISBN 978-2-88912-036-9
– 2 – 61558-2-8 © IEC:2010
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.8
10 Change of input voltage setting .8
11 Output voltage and output current under load .8
12 No-load output voltage.9
13 Short-circuit voltage.9
14 Heatingss .9
15 Short-circuit and overload protection .10
16 Mechanical strength.10
17 Protection against harmful ingress of dust, solid objects and moisture.10
18 Insulation resistance, dielectric strength and leakage current .10
19 Construction .10
20 Components .12
21 Internal wiring .12
22 Supply connection and other external flexible cables or cords.12
23 Terminals for external conductors .12
24 Provisions for protective earthing .12
25 Screws and connections .13
26 Creepage distances, clearances and distances through insulation .13
27 Resistance to heat, fire and tracking .13
28 Resistance to rusting .13
Annexes.14
Annex F Requirements for manually operated switches which are parts of transformer
assemblies.14
Bibliography .14

61558-2-8 © IEC:2010 – 3 –
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
SAFETY OF TRANSFORMERS, REACTORS,
POWER SUPPLY UNITS AND COMBINATIONS THEREOF –

Part 2-8: Particular requirements and tests
for transformers and power supply units for bells and chimes

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
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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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3) IEC Publications have the form of recommendations for international use and are accepted by IEC National
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6) All users should ensure that they have the latest edition of this publication.
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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 61558-2-8 has been prepared by IEC technical committee 96:
Transformers, reactors, power supply units and combinations thereof.
This second edition cancels and replaces the first edition published in 1998. It constitutes a
technical revision. The main changes consist of updating this part in accordance with
IEC 61558-1:2005.
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 – 61558-2-8 © IEC:2010
The text of this standard is based on the following documents:
FDIS Report on voting
96/354/FDIS 96/361/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 transformers and
power supply units for bell and chime.
A list of all parts of the IEC 61558 series, 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 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 adopted accordingly.
In this part, the following print types are used:
– requirements proper: in roman type;
– test specifications: in italic type;
– explanatory matters: in smaller roman type.
In the text of this part, the words in bold are defined in Clause 3.
Subclauses 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.
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.

61558-2-8 © IEC:2010 – 5 –
SAFETY OF TRANSFORMERS, REACTORS,
POWER SUPPLY UNITS AND COMBINATIONS THEREOF –

Part 2-8: Particular requirements and tests
for transformers and power supply units for bells and chimes

1 Scope
Replacement:
This part of IEC 61558 deals with the safety of bell and chime transformers and power
supply units incorporating bell and chime transformers. 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 bell and chime
transformers and power supply units incorporating bell and chime transformers.
This part is applicable to stationary, single-phase, air-cooled (natural or forced) independent
or associated dry-type transformers. The windings may be encapsulated or non-
encapsulated.
This standard is applicable to transformers and power supply (linear).
This standard used in combination with part 2-16 for switch mode power supply (SMPS) units
is also applicable to power supplies with internal operating frequencies higher than 500 Hz.
Where the two requirements are in conflict, the most severe takes precedence.
The rated supply voltage does not exceed 250 V a.c., and the rated supply frequency and
does not exceed 500 Hz. This standard is applicable to transformers and linear power supply
units with internal operating frequency not exceeding 500 Hz.
The rated output shall not exceed 100 VA.
The no-load output voltage does not exceed 33 V a.c. or 46 V ripple-free d.c., and the rated
output voltage does not exceed 24 V a.c., or 33 V ripple-free d.c.
Bell and chime transformers are generally intended to supply domestic sound signalling
equipment and other similar devices where the load is applied for short periods of time.
NOTE 2 A partial load may be applied for illumination purposes.
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 only in applications where double or reinforced
insulation between circuits is required by the installation rules or by the end product standard.
NOTE 3 Normally, the 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 earth.

– 6 – 61558-2-8 © IEC:2010
This part is applicable to transformers associated with specific equipment, to the extent
decided upon by the relevant IEC technical committees.
NOTE 4 Attention is drawn to the following:
- 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 transformer 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, such as tropical environment.
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 except as follows:
Addition:
3.1.101
bell and chime transformer
single-phase safety isolating transformer specifically intended to supply household sound
signalling equipment and other similar devices
4 General requirements
This clause of Part 1 is applicable.
5 General notes on tests
This clause of Part 1 is applicable.
6 Ratings
Replacement:
6.101 The rated output voltage shall not exceed 24 V a.c. or 33 V ripple-free d.c.
For independent transformers, this output voltage limitation applies even when output
windings, not intended for interconnection, are connected in series.
6.102 The rated output shall not exceed 100 VA.

61558-2-8 © IEC:2010 – 7 –
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 250 V a.c.
Compliance with the requirements 6.101 to 6.104 is checked by inspection of the marking.
7 Classification
This clause of Part 1 is applicable except as follows:
7.2 Replacement:
According to short-circuit protection or protection against abnormal use:
– inherently short-circuit proof transformers;
– non-inherently short-circuit proof transformers;
– fail-safe transformers.
7.4 Replacement:
According to their mobility:
– fixed transformers.
7.5 Replacement:
According to their duty-type:
– short-time duty cycle;
– intermittent duty cycle.
NOTE A partial load for illumination may be applied continuously.
Addition:
7.101 According to the method of mounting:
– mounting in a distribution assembly;
– mounting in sound signalling devices (bells, chimes, buzzers, etc.);
– mounting on an outlet box or cabinet;
– flush mounted;
– surface mounted.
8 Marking and other information
This clause of Part 1 is applicable except as follows:
8.1 h) Replacement:
The transformers shall be marked with one of the graphical symbols shown in 8.11;

– 8 – 61558-2-8 © IEC:2010
8.11 Addition:
Symbol or graphical symbol Explanation or title Identification
Fail-safe bell and chime transformer Based on
Symbol
IEC 60417-
F
5013 (2009-
05)
Short-circuit proof bell and chime
IEC 60417-
transformer (inherently or non-inherently)
5013 (2009-
05)
9 Protection against electric shock
This clause of Part 1 is applicable except as follows:
Addition:
9.101 Protection against accidental contact with windings and hazardous live parts of the
input circuit shall be ensured while connecting conductors to the output terminals.
Compliance is checked by inspection and by the application of the standard test finger shown
in Figure 2. It shall not be possible to touch windings or hazardous live parts of the input
circuit with the test finger.
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:
11.1 Replacement
When the transformer is connected to the rated supply voltage, at the rated supply
frequency, and loaded with an impedance resulting in the rated output at the rated output
voltage and, for a.c. current, at the rated power factor, the output voltage shall not differ from
the rated value by more than:
a) 15 % for the output voltage of inherently short-circuit proof transformers with one
rated output voltage;
b) 15 % for the highest output voltage of inherently short-circuit proof transformers
with more than one rated output voltage;
c) 20 % for the other output voltages of inherently short-circuit proof transformers with
more than one rated output voltage;
d) 15 % for the output voltages of other transformers.
Compliance is checked by measuring the output voltage 2 min after the transformer is
connected to the rated supply voltage, at the rated supply frequency, and loaded with an
impedance resulting in the rated output, at the rated output voltage and the rated power
factor.
For transformers with more than one rated supply voltage, the requirement is applicable for
each of the rated supply voltages.

61558-2-8 © IEC:2010 – 9 –
For transformers with multiple output windings, the loads are applied to every multiple
section simultaneously, unless otherwise declared.
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.
12.101 The no-load output voltage shall not exceed 33 V a.c. or 46 V ripple free d.c. The
output voltage limitation applies even when independent 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 between the no-load output voltage measured in this clause and the output
voltage under load measured during the test of Clause 11, expressed as a percentage of the
latter voltage, shall not exceed 100 %.
U – U
no-load
load
NOTE The ratio is defined as follows: × 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 frequency.
13 Short-circuit voltage
This clause of Part 1 is applicable.
14 Heatingss
This clause of Part 1 is applicable except as follows:
14.1 Replacement of the second paragraph by the following:
Temperatures are determined under the following conditions.
Replacement of the tenth paragraph by the following:
Transformers are supplied at rated supply voltage and loaded with an impedance Z
producing rated output at the rated output voltage and, for a.c. current, at the rated power
factor. The value of output current is measured after 1 min. Then the supply voltage is
increased by 10 % and the output impedance is adjusted so that the new impedance Z’ gives
the same output current than the value measured before. Transformers are submitted to 20
cycles of 1 min operation with the impedance Z’ and 5 min operation with 5 times the
impedance Z’. Temperature rises are measured during the last cycle.

– 10 – 61558-2-8 © IEC:2010
Addition:
Addition of the following footnote to table “f“ to "external enclosures" in Table 1:
f The external enclosure of a transformer only includes the parts accessible to the standard test finger when
mounted in accordance with 14.1.
Addition of the following footnote to table “g“ to "supports" in Table 1:
g Support includes any area of the black painted plywood support, but excludes any metal parts of the mounting
system (rails, outlet boxes, etc.).
15 Short-circuit and overload protection
This clause of Part 1 is applicable except as follows:
Addition:
15.101 The maximum short-circuit output current shall not exceed 10 A, measured 5 s after
applying the short-circuit, the transformer being supplied with 1,1 times the rated supply
voltage.
16 Mechanical strength
This clause of Part 1 is applicable except as follows:
Replacement:
16.2 The impact hammer shall have an energy of (0,2 ± 0,05) J.
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:
Replacement:
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, through 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).

61558-2-8 © IEC:2010 – 11 –
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
s rated for the working voltage);
insulation
– 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).
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 insulation
between the input windings and any intermediate conductive part shall consist of at least
basic insulation, and the insulation between the output windings and any intermediate
conductive part shall consist of at least supplementary insulation (both basic and
supplementary insulations rated for the working voltage);
NOTE 1 An intermediate conductive part not separated from the input or output windings or the body by at
least insulation is considered to be connected to the relevant part(s).
NOTE 2 Basic insulation and supplementary insulation are interchangeable.
In addition, the following applies:
– for class I transformers, the insulation between the input and output windings via the
intermediate conductive parts (even if they are connected to earth) 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 via
the intermediate conductive parts (if any) shall consist of double or reinforced
insulation (rated for the input voltage), and the insulation between the body and the
output windings via the intermediate conductive parts (if any) and the body via the
intermediate conductive parts shall consist of double or reinforced insulation (rated
for the input and output voltage);
– for transformers 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).
NOTE 3 In this clause the possibility to consider the intermediate metal part connected to earth and consequently
to require basic insulation in both circuit (primary and secondary) is not allowed for the following reason:
– the intermediate metal part is normally the iron core made by laminated plates insulated each other by
oxide. It is not assured that all foils are correctly connected to the earth.
– for transformer different from independent, it is not assured that in the final applications the iron core will
be connected to earth.
Addition:
19.101 There shall be no connections between the output circuit and the protective earth,
unless – for associated transformers - allowed by the relevant equipment standard.
19.102 There shall be no connections between the output circuit and the body, unless this
is allowed by the relevant equipment standard for associated transformers.

– 12 – 61558-2-8 © IEC:2010
Compliance is checked by inspection.
19.103 These 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.
20 Components
This clause of Part 1 is applicable except as follows:
Modification:
20.4 If the transformer incorporates a switch intended to disconnect the input winding from
the supply, this switch may be of single-pole micro-gap construction and may disconnect either
pole.
21 Internal wiring
This clause of Part 1 is applicable.
22 Supply connection and other external flexible cables or cords
This clause of Part 1 is applicable except as follows:
Modification:
22.3 Replace the first paragraph as follows:
Flush-type transformers may be so designed that connection of the "external" conductors to
the terminals has to be made before the transformer is fitted into a flush mounting box.
Replacement:
22.5 Power supply cords of transformers shall not be lighter than light polyvinyl chloride
sheathed flexible cords (code designation 60227 IEC 53) or ordinary tough rubber sheathed
flexible cords (code designation 60245 IEC 53).
23 Terminals for external conductors
This clause of Part 1 is applicable.
24 Provisions for protective earthing
This clause of Part 1 is applicable.

61558-2-8 © IEC:2010 – 13 –
25 Screws and connections
This clause of Part 1 is applicable except as follows:
25.3 Addition:
This requirement is not applicable to electrical connections other than protective earthing
connections on the output circuits of the transformers with a rated output not exceeding
12 VA.
26 Creepage distances, clearances and distances through insulation
This clause of Part 1 is applicable.
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.

– 14 – 61558-2-8 © IEC:2010
Annexes
The annexes of Part 1 are applicable except as follows:

Annex F
Requirements for manually operated switches which are parts
of transformer assemblies
This annex of Part 1 is applicable with the following addition:
F.2 Addition:
Add a third dash after the first paragraph of F.2:
– subclause 7.1.4.4: the number of operating cycles shall be 1 000.

Bibliography
The Bibliography of Part 1 is applicable except as follows:
Addition:
IEC 61558-2-16:2009, 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

___________
– 16 – 61558-2-8 © CEI:2010
SOMMAIRE
AVANT-PROPOS .17
1 Domaine d’application.19
2 Références normatives .20
3 Termes et définitions .20
4 Exigences générales.20
5 Généralités sur les essais.20
6 Caractéristiques assignées .21
7 Classification .21
8 Marquage et autres indications .22
9 Protection contre les chocs électriques .22
10 Changement de la tension primaire d’alimentation.22
11 Tension secondaire et courant secondaire en charge .22
12 Tension secondaire à vide .23
13 Tension de court-circuit .23
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 .25
19 Construction .25
20 Composants .26
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 .28
Annexes.29
Annexe F Exigences pour les interrupteurs manuels faisant partie d’un transformateur .29
Bibliographie .29

61558-2-8 © CEI:2010 – 17 –
COMMISSION ÉLECTROTECHNIQUE INTERNATIONALE
_____________
SÉCURITÉ DES TRANSFORMATEURS, BOBINES D’INDUCTANCE,
BLOCS D’ALIMENTATION ET DES COMBINAISONS DE CES ÉLÉMENTS –

Partie 2-8: Règles particulières et essais pour les transformateurs
et blocs d’alimentation pour sonneries et carillons

AVANT-PROPOS
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La Norme internationale CEI 61558-2-8 a été établie par le comité d'études 96 de la CEI:
Transformateurs, bobines d’inductance, blocs d'alimentation et
...