IEC 60940:2015

Guidance information on the application of capacitors, resistors, inductors and complete filter units for electromagnetic interference suppression

IEC 60940:2015 provides guidance applicable to information on application of capacitors, resistors, inductors, and complete filter units for electromagnetic interference suppression. This second edition cancels and replaces the first edition published in 1988. This second edition is a result of maintenance activities related to the previous edition. All changes that have been agreed upon can be categorized as minor revisions.

Guide d'emploi des condensateurs, résistances, inductances et filtres complets d'antiparasitage

L'IEC 60940:2015 constitue un guide d'emploi des condensateurs, résistances, inductances et filtres complets d'antiparasitage. Cette deuxième édition annule et remplace la première édition parue en 1988. Cette deuxième édition est le résultat des activités de maintenance relatives à l'édition précédente. Toutes les modifications ayant fait l'objet d'un accord peuvent être considérées comme des révisions mineures.

General Information

• Status: Published
• Publication Date: 09-Mar-2015
• ICS: 33.100.01 - Electromagnetic compatibility in general
• Technical Committee: TC 40 - Capacitors and resistors for electronic equipment
• Drafting Committee: MT 60940 - TC 40/MT 60940
• Current Stage: PPUB - Publication issued
• Start Date: 10-Mar-2015
• Completion Date: 31-Mar-2015

Relations

• Revises: IEC 60940:1988/COR1:1998 - Corrigendum 1 - Guidance information on the application of capacitors, resistors, inductors and complete filter units for radio interference suppression
• Effective Date: 05-Sep-2023

Overview

IEC 60940:2015 is an international standard published by the International Electrotechnical Commission (IEC). It provides comprehensive guidance on the application of capacitors, resistors, inductors, and complete filter units specifically designed for electromagnetic interference (EMI) suppression. The second edition of this standard updates and replaces the original 1988 version, incorporating minor but important revisions to reflect current technologies and practices.

The standard is a crucial resource for engineers, designers, and manufacturers working in fields where electromagnetic and radio-frequency interference (EMI/RFI) management is vital. It helps ensure that electrical and electronic equipment operate reliably by minimizing disturbances caused by unwanted electromagnetic emissions.

Key Topics

• Electromagnetic Interference (EMI) and Radio Frequency Interference (RFI):

  • Definition of EMI as any electromagnetic emission causing undesirable responses or functional degradation.
  • Classification of RFI, focusing on conducted interference (150 kHz to 30 MHz) and radiated interference (30 MHz to 10 GHz).
  • Explanation of how EMI propagates via conduction through power lines and radiation through space.

• Suppression Components:

  • Types of suppression components used, including capacitors, resistors, inductors, and complete filter units.
  • Classification of capacitors into two-terminal capacitors, combination capacitors, lead-through capacitors, and resistor-capacitor combinations.
  • Use of inductors and filters for creating low impedance paths to divert unwanted interference currents.

• Ratings and Selection Criteria:

  • Guidelines for selecting voltage and current ratings appropriate for specific EMI suppression applications.
  • Environmental and climatic considerations affecting component performance.
  • Importance of insertion loss measurements in evaluating filter efficacy.

• Connection and Safety:

  • Best practices for mounting and connecting interference suppression components to optimize performance.
  • Safety requirements, including the use of Class X and Y capacitors for mains connection.
  • Addressing leakage currents and electrical shock hazard protections to align with safety standards such as IEC 60335-1.

• Compliance and Regulatory Limits:

  • Insight into national and international limits on allowable radio-frequency emissions from electrical equipment.
  • Reference to relevant EMC standards like CISPR 11 that define interference limits.
  • Necessity of interference suppression near the power supply input, especially for shielded equipment.

Applications

IEC 60940:2015 is essential for a wide range of industries where electromagnetic compatibility (EMC) is critical. Practical applications include:

• Consumer Electronics: Ensuring household appliances meet regulatory EMC requirements to prevent malfunction or interference with other devices.
• Industrial Machinery: Suppression of EMI generated by large motors, drives, and machinery to protect sensitive control systems and communication infrastructure.
• Telecommunications: Minimizing RFI that can degrade radio communications, data transmission, and broadcasting.
• Medical Equipment: Protecting medical devices from electromagnetic disturbances to maintain operational safety and accuracy.
• Automotive and Transportation: Reducing EMI effects from onboard electronics and power systems to enhance safety and system reliability.

By following IEC 60940 guidance, designers can improve product performance, meet legal compliance, and facilitate international market access through harmonized EMI suppression practices.

Related Standards

• IEC 60335-1: Safety requirements for household and similar electrical appliances covering general requirements, including electrical shock hazards.
• IEC 60384-14: Specifications for fixed capacitors used in electronic equipment for EMI suppression, complementing IEC 60940’s guidance on capacitor application.
• CISPR 11: Defines limits for radio-frequency electromagnetic disturbances from industrial, scientific, and medical equipment.
• EMC Directives and National Regulations: Various regional and international guidelines that enforce EMI/RFI emission limits for electrical apparatus.

Conclusion

IEC 60940:2015 offers detailed, practical guidance on applying key electronic components for the suppression of electromagnetic interference. This standard supports the design and implementation of effective EMI filters and suppression techniques crucial for compliance, safety, and optimal device performance. Engineers and manufacturers benefit from its classification, selection criteria, and safety practices, enabling the development of reliable and interference-resilient electrical and electronic systems worldwide.

Standards Content (Sample)

IEC 60940 ®
Edition 2.0 2015-03
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Guidance information on the application of capacitors, resistors, inductors and
complete filter units for electromagnetic interference suppression

Guide d'emploi des condensateurs, résistances, inductances et filtres complets
d'antiparasitage
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized in any form
or by any means, electronic or mechanical, including photocopying and microfilm, without permission in writing from
either IEC or IEC's member National Committee in the country of the requester. If you have any questions about IEC
copyright or have an enquiry about obtaining additional rights to this publication, please contact the address below or
your local IEC member National Committee for further information.

Droits de reproduction réservés. Sauf indication contraire, aucune partie de cette publication ne peut être reproduite
ni utilisée sous quelque forme que ce soit et par aucun procédé, électronique ou mécanique, y compris la photocopie
et les microfilms, sans l'accord écrit de l'IEC ou du Comité national de l'IEC du pays du demandeur. Si vous avez des
questions sur le copyright de l'IEC ou si vous désirez obtenir des droits supplémentaires sur cette publication, utilisez
les coordonnées ci-après ou contactez le Comité national de l'IEC de votre pays de résidence.

IEC Central Office Tel.: [phone]
3, rue de Varembé Fax: [phone]
CH-1211 Geneva 20 [e-mail]
Switzerland www.iec.ch
About the IEC
The International Electrotechnical Commission (IEC) is the leading global organization that prepares and publishes
International Standards for all electrical, electronic and related technologies.

About IEC publications
The technical content of IEC publications is kept under constant review by the IEC. Please make sure that you have the
latest edition, a corrigenda or an amendment might have been published.

IEC Catalogue - webstore.iec.ch/catalogue Electropedia - www.electropedia.org
The stand-alone application for consulting the entire The world's leading online dictionary of electronic and
bibliographical information on IEC International Standards, electrical terms containing more than 30 000 terms and
Technical Specifications, Technical Reports and other definitions in English and French, with equivalent terms in 15
documents. Available for PC, Mac OS, Android Tablets and additional languages. Also known as the International
iPad. Electrotechnical Vocabulary (IEV) online.

IEC publications search - www.iec.ch/searchpub IEC Glossary - std.iec.ch/glossary
The advanced search enables to find IEC publications by a More than 60 000 electrotechnical terminology entries in
variety of criteria (reference number, text, technical English and French extracted from the Terms and Definitions
committee,…). It also gives information on projects, replaced clause of IEC publications issued since 2002. Some entries
and withdrawn publications. have been collected from earlier publications of IEC TC 37,

77, 86 and CISPR.
IEC Just Published - webstore.iec.ch/justpublished
Stay up to date on all new IEC publications. Just Published IEC Customer Service Centre - webstore.iec.ch/csc
details all new publications released. Available online and If you wish to give us your feedback on this publication or
also once a month by email. need further assistance, please contact the Customer Service
Centre: [e-mail].
A propos de l'IEC
La Commission Electrotechnique Internationale (IEC) est la première organisation mondiale qui élabore et publie des
Normes internationales pour tout ce qui a trait à l'électricité, à l'électronique et aux technologies apparentées.

A propos des publications IEC
Le contenu technique des publications IEC est constamment revu. Veuillez vous assurer que vous possédez l’édition la
plus récente, un corrigendum ou amendement peut avoir été publié.

Catalogue IEC - webstore.iec.ch/catalogue Electropedia - www.electropedia.org
Application autonome pour consulter tous les renseignements
Le premier dictionnaire en ligne de termes électroniques et
bibliographiques sur les Normes internationales,
électriques. Il contient plus de 30 000 termes et définitions en
Spécifications techniques, Rapports techniques et autres
anglais et en français, ainsi que les termes équivalents dans
documents de l'IEC. Disponible pour PC, Mac OS, tablettes
15 langues additionnelles. Egalement appelé Vocabulaire
Android et iPad.
Electrotechnique International (IEV) en ligne.

Recherche de publications IEC - www.iec.ch/searchpub
Glossaire IEC - std.iec.ch/glossary
Plus de 60 000 entrées terminologiques électrotechniques, en
La recherche avancée permet de trouver des publications IEC
en utilisant différents critères (numéro de référence, texte, anglais et en français, extraites des articles Termes et
comité d’études,…). Elle donne aussi des informations sur les Définitions des publications IEC parues depuis 2002. Plus
projets et les publications remplacées ou retirées. certaines entrées antérieures extraites des publications des

CE 37, 77, 86 et CISPR de l'IEC.
IEC Just Published - webstore.iec.ch/justpublished

Service Clients - webstore.iec.ch/csc
Restez informé sur les nouvelles publications IEC. Just
Published détaille les nouvelles publications parues. Si vous désirez nous donner des commentaires sur cette
Disponible en ligne et aussi une fois par mois par email. publication ou si vous avez des questions contactez-nous:
[e-mail].
IEC 60940 ®
Edition 2.0 2015-03
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Guidance information on the application of capacitors, resistors, inductors and

complete filter units for electromagnetic interference suppression

Guide d'emploi des condensateurs, résistances, inductances et filtres complets

d'antiparasitage
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
INTERNATIONALE
ICS 33.100 ISBN 978-2-8322-2290-4

– 2 – IEC 60940:2015  IEC 2015
CONTENTS
FOREWORD . 3
1 Scope . 5
2 Normative references . 5
3 Electromagnetic and Radio frequency interference suppression (EMI/RFI) . 5
3.1 General . 5
3.2 Limits of interference . 6
4 Classification of suppression components . 6
4.1 Suppression components . 6
4.2 Capacitors . 8
4.3 Inductors . 8
4.4 Filters . 8
5 Choice of ratings for specific applications . 8
5.1 Voltage . 8
5.2 Current . 9
5.3 Environmental classification (climatic category) . 9
5.4 Insertion loss . 9
6 Connection of suppression components . 9
7 Safety aspects . 10
7.1 Class X and Y capacitors . 10
7.2 Leakage current . 11
7.3 Mounting of radio interference suppression components in equipment and
appliances . 11
7.4 Electrical shock hazard protection testing . 11
Bibliography . 12

Figure 1 – Example use of suppression components in EMI filter . 7

INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
GUIDANCE INFORMATION ON THE APPLICATION OF CAPACITORS,
RESISTORS, INDUCTORS AND COMPLETE FILTER UNITS FOR
ELECTROMAGNETIC INTERFERENCE SUPPRESSION

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 in addition to other activities, IEC publishes International Standards, Technical Specifications,
Technical Reports, Publicly Available Specifications (PAS) and Guides (hereafter referred to as “IEC
Publication(s)”). Their preparation is entrusted to technical committees; any IEC National Committee interested
in the subject dealt with may participate in this preparatory work. International, governmental and non-
governmental organizations liaising with the IEC also participate in this preparation. IEC collaborates closely
with the International Organization for Standardization (ISO) in accordance with conditions determined by
agreement between the two organizations.
2) The formal decisions or agreements of IEC on technical matters express, as nearly as possible, an international
consensus of opinion on the relevant subjects since each technical committee has representation from all
interested IEC National Committees.
3) IEC Publications have the form of recommendations for international use and are accepted by IEC National
Committees in that sense. While all reasonable efforts are made to ensure that the technical content of IEC
Publications is accurate, IEC cannot be held responsible for the way in which they are used or for any
misinterpretation by any end user.
4) In order to promote international uniformity, IEC National Committees undertake to apply IEC Publications
transparently to the maximum extent possible in their national and regional publications. Any divergence
between any IEC Publication and the corresponding national or regional publication shall be clearly indicated in
the latter.
5) IEC itself does not provide any attestation of conformity. Independent certification bodies provide conformity
assessment services and, in some areas, access to IEC marks of conformity. IEC is not responsible for any
services carried out by independent certification bodies.
6) All users should ensure that they have the latest edition of this publication.
7) No liability shall attach to IEC or its directors, employees, servants or agents including individual experts and
members of its technical committees and IEC National Committees for any personal injury, property damage or
other damage of any nature whatsoever, whether direct or indirect, or for costs (including legal fees) and
expenses arising out of the publication, use of, or reliance upon, this IEC Publication or any other IEC
Publications.
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 60940 has been prepared by IEC technical committee 40:
Capacitors and resistors for electronic equipment.
This second edition cancels and replaces the first edition published in 1988. This second
edition is a result of maintenance activities related to the previous edition. All changes that
have been agreed upon can be categorized as minor revisions.
The text of this standard is based on the following documents:
FDIS Report on voting
40/2337/FDIS 40/2362/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.

– 4 – IEC 60940:2015  IEC 2015
The committee has decided that the contents of this publication will remain unchanged until
the stability date indicated on the IEC website 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.
GUIDANCE INFORMATION ON THE APPLICATION OF CAPACITORS,
RESISTORS, INDUCTORS AND COMPLETE FILTER UNITS FOR
ELECTROMAGNETIC INTERFERENCE SUPPRESSION

1 Scope
This international standard provides guidance applicable to information on application of
capacitors, resistors, inductors, and complete filter units for electromagnetic interference
suppression.
2 Normative references
The following documents, in whole or in part, are normatively referenced in this document and
are indispensable for its application. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any
amendments) applies.
IEC 60335-1, Household and similar electrical appliances – Safety – Part 1: General
requirements
IEC 60384-14, Fixed capacitors for use in electronic equipment – Part 14: Sectional
specification – Fixed capacitors for electromagnetic interference suppression and connection
to the supply mains
3 Electromagnetic and Radio frequency interference suppression (EMI/RFI)
3.1 General
Electromagnetic interference, EMI, is any electromagnetic emission or any electric or
electronic disturbance which causes an undesirable response, malfunctioning or degradation
in the performance of electrical equipment.
Radio frequency interference, RFI, is any electrical energy with content within the frequency
range dedicated to radio frequency transmission.
Conducted RFI is most often found in the low frequency range from 150 kHz to 30 MHz.
Radiated RFI is most often found in the frequency range from 30 MHz to 10 GHz.
EMI or RFI propagate through conduction over signal and power lines and through radiation in
free space.
Electrical machines and apparatus may generate electromagnetic interferences (EMI) which
are fed back into power supply mains. These electromagnetic interferences may be picked up
by apparatus connected to or placed close to the same power system up to a certain distance
from the machine or apparatus.
The radio-frequency voltages may be generated both between conductors (phases) of the
power system (symmetrical interference) and also between conductors (phases) and earth
(asymmetrical interference). These voltages can cause electromagnetic radiation from the
power lines.
– 6 – IEC 60940:2015  IEC 2015
Radio interference can be suppressed by providing a low impedance path for radio frequency
currents close to the place where the radio frequency voltages are generated. This may be
combined with a high impedance element which prevents the radio frequency currents from
penetrating into the power supply system, but has no appreciable effect on the flow of power
current.
3.2 Limits of interference
In various countries, mandatory limits are set to the radio-frequency in a given frequency
range emanating from electrical machines and apparatus.
A survey of these limits is given in relevant EMC-standards such as CISPR 11.
Some electrical apparatus require for their operation a power-supply voltage free from radio-
interference to a greater extent than that guaranteed by the requirements mentioned above. In
these cases, similar measures should be taken at a place in the power supply system close to
the place where the apparatus is connected. When the apparatus is shielded (or placed in a
shielded room), interference suppression will generally be applied at each point where the
power supply system enters the shielded enclosure.
4 Classification of suppression components
4.1 Suppression components
An example of use of suppression components in EMI filter is shown in Figure 1.

IEC
a) Single phase EMI filter
3 3
4 4
IEC
b) Three phase three wires EMI filter
N
3 3
IEC
c) Three phase four wires EMI filter
Key
1 Mains
2 Inductor
3 X-capacitor
4 Y-capacitor
N Neutral
Figure 1 – Example use of suppression components in EMI filter

– 8 – IEC 60940:2015  IEC 2015
4.2 Capacitors
Radio interference suppression capacitors may be divided into the following groups:
a) Two-terminal capacitors, which can be connected to the machine, apparatus or supply
system to provide for either symmetrical or asymmetrical interference suppression.
b) Combinations of capacitors (either combinations of separate capacitors or multi-section
capacitor the sections of which may be connected in a certain manner), which can be
connected to the machine, apparatus or supply system to provide for both symmetrical and
asymmetrical interference suppression.
c) Lead-through capacitors (asymmetrical or symmetrical) or combinations thereof, in which
one or more sets of terminations are interconnected by means of a conductor intended to
carry the power supply current. These capacitors are especially suited to provide
interference suppression at the place where the supply system phases through a shielded
housing.
d) Resistor-capacitor combinations consisting of a capacitor with the capacitor utilizing the
resistance of the capacitor electrodes. RC combinations are often used for the
suppression of switching surges.
4.3 Inductors
Radio interference suppression inductors may be divided into the following groups:
a) Simple coils either with an air core or wound on a magnetic core. The UHF choke is an
example of this type of inductor.
b) Coils wound on a closed magnetic core. These inductors may have two or more coils
wound on the same core, which is often of ferrite material. The windings are often
arranged so that there is no resultant magnetization induced in the core due to the power
current, when the inductor is known as current-compensated.
c) Inductance, at high frequencies, may be obtained for suppression purposes by threading
ferrite beads on to lead wires.
d) Some core materials, especially ferrite materials, can be designed to introduce fairly high
resistive losses at VHF and UHF, adding to the suppression obtained by the inductance of
the coil.
4.4 Filters
Radio interference filters are construed from inductors and capacitors, sometimes with the
addition of resistors, varistors, etc. Two different types may be distinguished:
a) Filters constructed from approved components either as an unprotected assembly or with
a simple protective casing. The approval testing of these filters can be simplified since it is
not necessary to repeat the tests already carried out on the components.
b) Filters constructed from components which are not approved, or which are constructed
from capacitive, inductive or resistive elements all contained in housing. For such filters it
is necessary to carry out a full range of qualification approval tests.
5 Choice of ratings for specific applications
5.1 Voltage
When selecting components for connection to a.c. mains, consideration shall be given to
possible mains voltage fluctuations. When operation under high pulse conditions is required
for capacitors connected across the mains, then class X1 capacitors should be used (see
IEC 60384-14).
For d.c. components the rated voltage shall be the maximum which the component will
encounter, unless there is a special test for behaviour under transient conditions.

5.2 Current
The rated current is the maximum which the component can carry at a temperature up to the
rated temperature. Lower currents can be carried at higher temperature up to the upper
category temperature. Higher currents may be carried if the component is fitted to a heat sink
as specified by the manufacturer. The manufacturer may specify both a still air rated current
and higher rated current when the component is used with a specified heat sink.
5.3 Environmental classification (climatic category)
This is comprised of three figures, e.g. (25/085/21). This indicates that the lower category
temperature is –25 °C, the upper category temperature +85 °C and the duration of the damp
heat, steady state test is 21 days.
When the suppression component is mounted and working in the equipment the case
temperature should not be outside the category temperature range under any conditions of
operation.
The selection of the humidity classification depends on the environment in which the
equipment is expected to work. 21 days is frequently chosen for domestic appliances, for
example.
5.4 Insertion loss
The performance of a component or a filter is normally described by its insertion loss
measured over a range of frequencies when terminated by fixed real impedances. In practice
the filter is connected between the mains supply and the source of the interference, both of
which have complex impedances which vary with frequency. As a consequence insertion loss
curves can only be used as an indication of suppression performance, which can be
determined decisively only by connecting the filter to the apparatus and then measuring the
remaining interference.
The measurement of insertion loss is useful to check stability after environmental and
endurance tests, and to compare filters of different construction, but since the effectiveness of
a given suppressor may be determined without insertion loss measurements the manufacturer
may not declare insertion loss figures.
Where insertion loss figures are declared, it is important that it should be carefully stated
whether the test circuit is asymmetric or symmetric, what test method is used, what the values
of the terminating impedances are and whether the component is carrying any power current
during measurements.
NOTE Methods of Measurement of Suppression Characteristics are described in CISPR 17.
6 Connection of suppression components
Symmetrical interference suppression is effected by connecting a capacitor between phases
of power supply (between phase and neutral for single-phase power supply).
Asymmetrical interference suppression on machines or apparatus is usually effected by
connecting a capacitor from each phase (or phase and neutral) to earthed metallic parts or
the frame, metallic housing etc., where this is not earthed.
The suppression will often be more effective if the electrical parts of the apparatus are
completely in the metal shielding, asymmetrical interference suppression is usually effected
by connecting a capacitor from each phase (or phase and neutral) to the shielding.

– 10 – IEC 60940:2015  IEC 2015
During operation, the capacitors are subjected to the supply mains voltage with a
superimposed radio interference voltage. In many cases, the extra load caused by the radio-
frequency voltage is not important, but in other cases an appreciable radio-frequency current
through the capacitor may occur or high voltage peaks may be present. This must be taken
into account when choosing the capacitor and a check should be made with the capacitor
under its working conditions to make sure that its ratings are not exceeded.
The presence of inductance in the supply circuits in series with the capacitor may cause the
voltage at power frequency applied to the capacitor to exceed the supply voltage.
For inductors using ferromagnetic cores, it is important to be aware of the possible loss of
suppression caused by saturation of the core causing decrease of inductance. This saturation
may be caused by peaks of load current or interference current, or continuous excessive load
current. Unbalance of winding in current-compensated inductors will also contribute to the
effect.
The effectiveness of interference suppression is a function of suppression component
construction, mounting of the component in the machine or apparatus, the radio-frequency
voltage spectrum generated by the machine or apparatus and of characteristics of the
external circuit.
Due to the complexity of the problem it is not possible to estimate with sufficient accuracy
from the radio-frequency characteristics of a component how effective it will be under various
conditions.
On the other hand, components for use under similar conditions can be compared on the
basis of their radio-frequency characteristics. For this purpose the resonance frequency
measured under given conditions and the radio-frequency resistive at resonance may be of
use. For these reasons it is not required that the radio-frequency characteristics be marked on
the components nor has it been attempted to standardize certain values for these
characteristics.
7 Safety aspects
7.1 Class X and Y capacitors
Radio interference suppression capacitors are divided into X- and Y- capacitors.

X-capacitors are intended to be connected across the line.
Y-capacitors are allowed to be connected between line and earth for mains voltages up to
500 V.
In a.c. applications, Y-capacitors can be substituted with two X-capacitors connected in series
provided that the U of the X-capacitors are not less than the U of the Y-capacitor and that
R
R
the filter withstands the voltage proof as required in IEC 60939 series. In case of Y1-capacitor
substitution, the X-capacitors shall be X1-capacitors.
In DC-Filters with a rated voltage of 150 V d.c. or less, a Y2- and Y4-capacitor may be
substituted by X-capacitor with a rated voltage 250 V d.c. or higher.
In the case of failure by short circuit of a class X-capacitor connected between phases (or
between phase and neutral) no problem arises since the apparatus will be disconnected by
means of the normal short-circuit protection of the mains supply. For such capacitors a
voltage proof test level appropriate for general purpose capacitors is sufficient. Such
capacitors are subdivided into class X1 and class X2 according to their ability to handle
levels of peak pulse voltage (see IEC 60384-14). However in the case of failure by short

circuit of a class Y-capacitor connected between phase and an accessible metal part of the
apparatus, the latter can become alive with a dangerous voltage. From an electrical shock
hazard protection point of view the dielectric strength of these capacitors shall be at least
equal to the required dielectric strength of the apparatus or system in which the capacitor will
be used.
7.2 Leakage current
Earth leakage current is defined as “current flowing from the live parts of an installation to
earth, in the absence of an insulation fault” (IEC 60050-442:1998, 442-01-24).
At operating temperature, the leakage current of the appliance shall not be excessive and its
electric strength shall be adequate.
Limits are given in the relevant equipment standards such as IEC 60335-1, IEC 60204-1 or
IEC 60950-1.
If the Leakage Current exceeds 3,5 mA (r.m.s.), a warning with similar wording shall be
marked:
Warning
High Leakage Current
Earth Connection Essential
Before Connecting Supply
When choosing the capacitance of capacitors to be connected between live parts and
accessible metal parts, these limits have to be taken into account, so that the appropriate limit
for the whole equipment is not exceeded.
7.3 Mounting of radio interference suppression components in equipment and
appliances
The creepage and clearance distances on the outside of the suppression component should
be at least of the standard required for the appliance itself. The clearances quoted in
IEC 60939-series are taken from IEC 60335-1 and apply to domestic applications. Other
clearances may be appropriate in other types of equipment.
7.4 Electrical shock hazard protection testing
In the IEC 60938- and IEC 60939-series and in IEC 60384-14 separate test schedules are
provided for tests where certification for electrical shock hazard protection only is to be
carried out. No detail specification is permitted to reduce any of these requirements. The
schedule of electrical shock hazard protection tests only is the appropriate one to be followed
by a certifying test laboratory.

– 12 – IEC 60940:2015  IEC 2015
Bibliography
IEC 60050-442:1998, International Electrotechnical Vocabulary – Part 442: Electrical
accessories
IEC 60068-2-78, Environmental testing – Part 2-78: Tests – Test Cab: Damp heat, steady
state
IEC 60204-1, Safety of machinery – Electrical equipment of machines – Part 1: General
requirements
IEC 60384-14-1, Fixed capacitors for use in electronic equipment – Part 14-1: Blank detail
specification: Fixed capacitors for electromagnetic interference suppression and connection to
the supply mains – Assessment level D
IEC 60384-14-2, Fixed capacitors for use in electronic equipment – Part 14-2: Blank detail
specification – Fixed capacitors for electromagnetic interference suppression and connection
to the supply mains – Safety tests only
IEC 60384-14-3, Fixed capacitors for use in electronic equipment – Part 14-3: Blank detail
specification – Fixed capacitors for electromagnetic interference suppression and connection
to the supply mains – Assessment level DZ
IEC 60664-1, Insulation coordination for equipment within low-voltage systems – Part 1:
Principles, requirements and tests
IEC 60938-1, Fixed inductors for electromagnetic interference suppression – Part 1: Generic
specification
IEC 60938-2, Fixed inductors for electromagnetic interference suppression – Part 2: Sectional
specification
IEC 60938-2-1, Fixed inductors for electromagnetic interference suppression – Part 2-1: Blank
detail specification – Inductors for which safety tests are required – Assessment level D
IEC 60938-2-2, Fixed inductors for electromagnetic interference suppression – Part 2-2: Blank
detail specification – Inducto
...