EN IEC 60940:2026

SLOVENSKI STANDARD
01-oktober-2026
Nadomešča:
SIST EN 60940:2015
Uporaba kondenzatorjev, uporov, tuljav in celotnih filtrskih enot za dušenje
elektromagnetnih motenj - Splošna pravila in varnostne zahteve (IEC 60940:2026)
Application of capacitors, resistors, inductors and complete filter units for
electromagnetic interference suppression - General rules and safety requirements (IEC
60940:2026)
Grundlagen für die Anwendung von Kondensatoren, Widerständen, Drosseln und
vollständigen Filtereinheiten zur Unterdrückung elektromagnetischer Störungen (IEC
60940:2026)
Emploi des condensateurs, résistances, inductances et filtres complets d’antiparasitage -
Règles générales et exigences de sécurité (IEC 60940:2026)
Ta slovenski standard je istoveten z: EN IEC 60940:2026
ICS:
31.020 Elektronske komponente na Electronic components in
splošno general
33.100.01 Elektromagnetna združljivost Electromagnetic compatibility
na splošno in general
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EUROPEAN STANDARD EN IEC 60940

NORME EUROPÉENNE
EUROPÄISCHE NORM August 2026
ICS 33.100.01 Supersedes EN 60940:2015
English Version
Application of capacitors, resistors, inductors and complete filter
units for electromagnetic interference suppression - General
rules and safety requirements
(IEC 60940:2026)
Guide d'emploi des condensateurs, résistances, Grundlagen für die Anwendung von Kondensatoren,
inductances et filtres complets d'antiparasitage - Règles Widerständen, Drosseln und vollständigen Filtereinheiten
générales et exigences de sécurité zur Unterdrückung elektromagnetischer Störungen
(IEC 60940:2026) (IEC 60940:2026)
This European Standard was approved by CENELEC on 2026-08-04. CENELEC members are bound to comply with the CEN/CENELEC
Internal Regulations which stipulate the conditions for giving this European Standard the status of a national standard without any alteration.
Up-to-date lists and bibliographical references concerning such national standards may be obtained on application to the CEN-CENELEC
Management Centre or to any CENELEC member.
This European Standard exists in three official versions (English, French, German). A version in any other language made by translation
under the responsibility of a CENELEC member into its own language and notified to the CEN-CENELEC Management Centre has the
same status as the official versions.
CENELEC members are the national electrotechnical committees of Austria, Belgium, Bulgaria, Croatia, Cyprus, the Czech Republic,
Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, the
Netherlands, Norway, Poland, Portugal, Republic of North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland,
Türkiye and the United Kingdom.

European Committee for Electrotechnical Standardization
Comité Européen de Normalisation Electrotechnique
Europäisches Komitee für Elektrotechnische Normung
CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels
© 2026 CENELEC All rights of exploitation in any form and by any means reserved worldwide for CENELEC Members.
Ref. No. EN IEC 60940:2026 E
European foreword
The text of document 40/3300/FDIS, future edition 3 of IEC 60940, prepared by TC 40 "Capacitors
and resistors for electronic equipment" was submitted to the IEC-CENELEC parallel vote and
approved by CENELEC as EN IEC 60940:2026.
The following dates are fixed:
• latest date by which the document has to be implemented at national (dop) 2027-08-31
level by publication of an identical national standard or by endorsement
• latest date by which the national standards conflicting with the (dow) 2029-08-31
document have to be withdrawn
This document supersedes EN 60940:2015 and all of its amendments and corrigenda (if any).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. CENELEC shall not be held responsible for identifying any or all such patent rights.
Any feedback and questions on this document should be directed to the users’ national committee. A
complete listing of these bodies can be found on the CENELEC website.
Endorsement notice
The text of the International Standard IEC 60940:2026 was approved by CENELEC as a European
Standard without any modification.
In the official version, for Bibliography, the following notes have to be added for the standard indicated:
IEC 60068-1:2013 NOTE Approved as EN 60068-1:2014 (not modified)
IEC 60664-3 NOTE Approved as EN 60664-3
IEC 60664-4 NOTE Approved as EN 60664-4
IEC 60721-3-9 NOTE Approved as EN IEC 60721-3-9
IEC 60938 (series) NOTE Approved as EN IEC 60938 (series)
IEC 60938-1 NOTE Approved as EN IEC 60938-1
IEC 60938-2 NOTE Approved as EN IEC 60938-2
IEC 61558-2-16:2021 NOTE Approved as EN IEC 61558-2-16:2025 (not modified)
Annex ZA
(normative)
Normative references to international publications
with their corresponding European publications
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any amendments)
applies.
NOTE 1  Where an International Publication has been modified by common modifications, indicated by (mod),
the relevant EN/HD applies.
NOTE 2  Up-to-date information on the latest versions of the European Standards listed in this annex is available
here: www.cencenelec.eu.
Publication Year Title EN/HD Year
IEC 60384-14 - Fixed capacitors for use in electronic EN IEC 60384-14 -
equipment - Part 14: Sectional
specification - Fixed capacitors for
electromagnetic interference suppression
and connection to the supply mains
IEC 60664-1 2020 Insulation coordination for equipment EN IEC 60664-1 2020
within low-voltage supply systems - Part 1:
Principles, requirements and tests
+ AMD1 2025 + A1 2025
IEC 60939-3 2024 Passive filter units for electromagnetic EN IEC 60939-3 2024
interference suppression - Part 3: Passive
filter units for which safety tests are
appropriate
IEC 61140 2016 Protection against electric shock - EN 61140 2016
Common aspects for installation and
equipment
IEC Guide 104 - The preparation of safety publications and - -
the use of basic safety publications and
group safety publications
IEC Guide 116 - Guidelines for safety related risk - -
assessment and risk reduction for low
voltage equipment
CISPR 17 - Methods of measurement of the EN 55017 -
suppression characteristics of passive
EMC filtering devices
ISO/IEC Guide 51 - Safety aspects - Guidelines for their - -
inclusion in standards
IEC 60940 ®
Edition 3.0 2026-06
INTERNATIONAL
STANDARD
Application of capacitors, resistors, inductors and complete filter units for
electromagnetic interference suppression - General rules and safety
requirements
ICS 33.100.01  ISBN 978-2-8327-1348-8

IEC 60940:2026-06(en)
IEC 60940:2026 © IEC 2026
CONTENTS
FOREWORD . 3
1 Scope . 5
2 Normative references . 5
3 Terms and definitions . 5
3.1 Voltage terms . 6
3.2 Safety terms . 6
4 Electromagnetic and radio frequency interference suppression (EMI/RFI) . 7
4.1 General . 7
4.2 Limits of interference . 7
4.3 Classification of suppression components . 8
4.3.1 Suppression components . 8
4.3.2 Capacitors . 9
4.3.3 Resistors . 9
4.3.4 Inductors . 9
4.3.5 Filters . 10
5 General safety aspects . 10
5.1 EMI suppression components as a protective provision . 10
5.1.1 General considerations . 10
5.1.2 Single fault conditions. 11
5.1.3 Series connection of components . 11
5.2 Earth leakage current . 11
5.3 Hazards related to EMI suppression components caused by failures . 11
5.4 Information requirements . 12
6 Selection of EMI suppression components . 12
6.1 Choice of ratings for specific applications . 12
6.1.1 General aspects . 12
6.1.2 Voltages . 12
6.1.3 Current . 14
6.1.4 Environmental classification. 14
6.1.5 Insertion loss . 15
6.1.6 Capacitors . 15
6.1.7 Inductors . 16
6.1.8 Complete filter units . 16
6.2 Rules for capacitors in three phase EMI suppression filters. 16
7 Rules for determination of clearance and creepage distances . 17
7.1 General rules . 17
7.1.1 Dimensioning of clearances . 17
7.1.2 Dimensioning of creepage distances . 18
7.1.3 Precautions in handling and operation . 19
7.2 Rules for cased or conformal coated components with leads . 19
7.2.1 Measurement principle. 19
7.2.2 Creepage distance between terminals . 20
7.2.3 Clearance between terminals . 21
7.2.4 Clearance in mounted stage . 21
7.2.5 Conductors between terminals . 23
7.3 Rules for surface mounted components . 23
IEC 60940:2026 © IEC 2026
7.3.1 Clearances and creepage distances – Component body . 23
7.3.2 Clearances and creepage distances – Components in mounted stage . 24
7.3.3 Requirements . 24
8 Passive and active flammability . 25
9 Use of X and Y capacitors in AC mains up to 400 Hz . 25
9.1 Overview. 25
9.2 Background. 25
9.3 Guidelines . 25
9.3.1 General . 25
9.3.2 Capacitors >10 µF . 25
9.3.3 Voltage derating with frequency . 26
Bibliography . 27

Figure 1 – Example use of suppression components in an EMI-filter . 8
Figure 2 – EMI capacitors star-connected . 17
Figure 3 – Cased and conformal coated types . 19
Figure 4 – Description . 20
Figure 5 – Creepage distance – cased style . 20
Figure 6 – Creepage distance – conformal coated style . 21
Figure 7 – Clearance between terminals . 21
Figure 8 – Clearance in mounted stage – Cased style . 22
Figure 9 – Clearance – Component body larger than lead pitch . 22
Figure 10 – Clearance – Component body smaller than lead pitch . 23
Figure 11 – Clearance and creepage distances – Different component styles . 24
Figure 12 – Clearance and creepage distances in mounted stage . 24
Figure 13 – Voltage derating versus frequency . 26

IEC 60940:2026 © IEC 2026
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
Application of capacitors, resistors, inductors and complete filter
units for electromagnetic interference suppression -
General rules and safety requirements

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) IEC draws attention to the possibility that the implementation of this document may involve the use of (a)
patent(s). IEC takes no position concerning the evidence, validity or applicability of any claimed patent rights in
respect thereof. As of the date of publication of this document, IEC had not received notice of (a) patent(s), which
may be required to implement this document. However, implementers are cautioned that this may not represent
the latest information, which may be obtained from the patent database available at https://patents.iec.ch. IEC
shall not be held responsible for identifying any or all such patent rights.
IEC 60940 has been prepared by IEC technical committee 40: Capacitors and resistors for
electronic equipment. It is an International Standard.
This third edition cancels and replaces the second edition published in 2015. This edition
constitutes a technical revision.
This edition includes the following significant technical changes with respect to the previous
edition:
a) new title to change the document from “guidance” into “general rules and safety
requirements;
b) new content added (Clause 5 to Clause 9);
c) the previous edition is partly contained in Clause 4.
IEC 60940:2026 © IEC 2026
The text of this International Standard is based on the following documents:
Draft Report on voting
40/ 3300/FDIS 40/ 3314/RVD
Full information on the voting for its approval can be found in the report on voting indicated in
the above table.
The language used for the development of this International Standard is English.
This document was drafted in accordance with ISO/IEC Directives, Part 2, and developed in
accordance with ISO/IEC Directives, Part 1 and ISO/IEC Directives, IEC Supplement, available
at www.iec.ch/members_experts/refdocs. The main document types developed by IEC are
described in greater detail at www.iec.ch/publications.
The committee has decided that the contents of this document will remain unchanged until the
stability date indicated on the IEC website under webstore.iec.ch in the data related to the
specific document. At this date, the document will be
– reconfirmed,
– withdrawn, or
– revised.
IEC 60940:2026 © IEC 2026
1 Scope
This document establishes general rules and safety requirements on the application of
capacitors, resistors, inductors, and complete filter units for electromagnetic interference
suppression which will be connected to an AC mains or other supply (DC or AC) with a nominal
voltage not exceeding 1 000 V AC having a nominal frequency not exceeding 400 Hz, or
1 500 V DC.
It facilitates drafters of product safety standards and other stakeholders such as designers,
manufacturers, service providers, policy makers and regulators to consider safety aspects for
the intended use and the reasonably foreseeable misuse of these components in its products
and systems and apply risk reduction measures to achieve a tolerable risk level.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies.
For undated references, the latest edition of the referenced document (including any
amendments) applies.
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
IEC 60664-1:2020, Insulation coordination for equipment within low-voltage supply systems –
Part 1: Principles, requirements and tests
IEC 60664-1:2020/AMD1:2025
IEC 60939-3:2024, Passive filter units for electromagnetic interference suppression - Part 3:
Passive filter units for which safety tests are appropriate
IEC 61140:2016, Protection against electric shock - Common aspects for installation and
equipment
IEC Guide 104, The preparation of safety publications and the use of basic safety publications
and group safety publications
IEC Guide 116, Guidelines for safety related risk assessment and risk reduction for low voltage
equipment
CISPR 17, Methods of measurement of the suppression characteristics of passive EMC filtering
devices
ISO/IEC Guide 51, Safety aspects - Guidelines for their inclusion in standards
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO/IEC Guide 51,
IEC Guide 104, IEC Guide 116, IEC 60664-1:2020 and the following apply.
ISO and IEC maintain terminology databases for use in standardization at the following
addresses:
– IEC Electropedia: available at https://www.electropedia.org/
– ISO Online browsing platform: available at https://www.iso.org/obp
IEC 60940:2026 © IEC 2026
3.1 Voltage terms
3.1.1
overvoltage category
numeral defining a transient overvoltage condition
Note 1 to entry: Overvoltage categories I, II, III and IV are used, see IEC 60664-1:2020, 4.3.2.
[SOURCE: IEC 60050-426:2020, 426-04-48]
3.1.2
transient overvoltage
short duration overvoltage of a few milliseconds or less, oscillatory or non-oscillatory, usually
highly damped
[SOURCE: IEC 60664-1:2020, 3.1.13]
3.1.3
recurring peak voltage
maximum peak value of periodic excursions of the voltage waveform resulting from distortions
of an AC voltage or from AC components superimposed on a DC voltage
Note 1 to entry: Random overvoltages, for example due to occasional switching, are not considered to be recurring
peak voltages.
[SOURCE: IEC 60664-1:2020, 3.1.10]
3.1.4
slash rating
voltage in 3-phase systems indicated where the lower value represents the line-to-ground and
the higher value the line-to-line voltage
Example: 230/400 V (50 Hz).
3.2 Safety terms
3.2.1
fault protection
protection against electric shock under single fault conditions
[SOURCE: IEC 61140:2016, 3.1.2]
3.2.2
single fault condition
condition in which one means for protection against electric shock is defective or one fault is
present which could cause a hazard
Note 1 to entry: If a single fault condition results in one or more other fault conditions, all are considered as one
single fault condition.
[SOURCE: IEC 61140:2016, 3.1.4]
3.2.3
clearance
shortest distance in air between two conductive parts
[SOURCE: IEC 60050-581:2008, 581-27-76]
IEC 60940:2026 © IEC 2026
3.2.4
creepage distance
shortest distance along the surface of a solid insulating material between two conductive parts
[SOURCE: IEC 60050-151:2001, 151-15-50]
3.2.5
earth leakage current
current flowing from the live parts of an installation to earth, in the absence of an insulation
fault
[SOURCE: IEC 60050-442:1998, 442-01-24]
4 Electromagnetic and radio frequency interference suppression (EMI/RFI)
4.1 General
Electromagnetic interference (EMI) is any electromagnetic disturbance which causes an
undesirable response, malfunctioning or degradation in the performance of electrical
equipment. Radio frequency interference (RFI) is any electrical energy within the frequency
range dedicated to radio frequency transmission.
The lower frequency range up to 30 MHz is often analysed by means of voltage or current
measurements. The measured spectra are called “conducted interference” at certain points in
a circuit. The higher frequency range up to many GHz is often analysed by means of field
measurements like electric field E, magnetic field H or radiated power. The measured spectra
are called “radiated interference” as they are measured with special antennas for each field
type and frequency range instead of a voltage or current probe. Radiated interference is always
analysed in a defined distance to the device under test.
Electrical machines and apparatus can generate EMI which is fed back into its power supply
mains. This electromagnetic interference can be picked up by apparatus connected to the same
power system up to a certain distance from the machine or apparatus. EMI-filters limit this
interference to certain levels which do not make any harm.
Differential-mode interference occurs symmetrically between lines of different polarity.
Common-mode interference occurs asymmetrically between line(s) and ground. These two
types of interference have different sources and different propagation paths and need different
counter measures.
EMI can be suppressed by providing a low impedance path for interference currents providing
a short path back to its source by means of EMI-capacitors in accordance with IEC 60384-14.
This can be combined with a high impedance element in series to prevent interference from
taking this way. Such a high impedance can be a choke according to IEC 60938 series. Using
the principle of current compensation makes so-called common-mode chokes very effective
against common-mode interference.
Besides filtering with capacitors and chokes, shielding with metal enclosures can be very
effective against interference.
4.2 Limits of interference
In Europe and many other countries, mandatory limits are set for both emission of interference
and immunity against interference by EMC standards. The compatibility levels are defined for
different applications and apparatus in the CISPR standards or other product standards for
different environments like household or industrial surroundings.
IEC 60940:2026 © IEC 2026
Some sensitive electrical equipment requires an interference-free power-supply to a greater
extent than that guaranteed by the common compatibility levels. In these cases, additional
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.
4.3 Classification of suppression components
4.3.1 Suppression components
An example of use of suppression components in an EMI-filter is shown in Figure 1.

a) Single phase EMI-filter
b) Three phase EMI-filter
Key
1 Star point
P1, P2 Input, output terminals for a line conductor (single phase system)
N1, N2 Input, output terminals for a neutral conductor
U1, U2 Input, output terminals for line conductor U (phase 1)
V1, V2 Input, output terminals for line conductor V (phase 2)
W1, W2 Input, output terminals for line conductor W (phase 3)
Figure 1 – Example use of suppression components in an EMI-filter
IEC 60940:2026 © IEC 2026
4.3.2 Capacitors
Capacitors for electromagnetic interference suppression can 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 can 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 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) Capacitor-resistor parallel combinations: Consisting of a capacitor in parallel with a resistor
which is used for discharging the capacitor for safety reasons.
e) Capacitor-resistor series combinations: Consisting of a capacitor with a resistor in series.
The resistor can be integrated into the capacitor by using the resistance of the capacitor
connector. This combination is often used for the suppression of switching coils to handle
the inductive surge pulse.
4.3.3 Resistors
An electrical resistor is a component that reduces the voltage or limits the current flowing
through a circuit. For a safe use, power loss generated in the resistor shall be considered.
Resistors can be divided into two groups:
a) Fixed resistors, which offer one resistance value.
b) Variable resistors, which offer broad resistance values - predominantly used to control either
current or voltage by changing the resistance value.
4.3.4 Inductors
For inductors using ferromagnetic cores, it is important to be aware of the possible loss of
suppression caused by saturation of the core. This saturation can be caused by peaks of load
current or interference current, or continuous excessive load current.
Inductors for electromagnetic interference suppression can be divided into the following groups:
a) Simple air coils or coils with magnetic core
They are used for attenuating both symmetrical or asymmetrical voltages. They attenuate
common mode and differential mode currents equally well. They are often characterized by
an extensive independence of the inductance from the pre-magnetization of the operating
current. The constructive structure can ensure low winding capacity, which leads to a broad
interference suppression effect. UHF chokes are one example of this type of inductor.
b) Coils wound on a closed magnetic core
These inductors can have two or more coils wound on the same core. Using the principle of
current compensation, the windings are often arranged, so that there is no resultant
magnetization in the core due to the power current. This makes it possible to use high
permeable cores, so that large inductances per winding can be achieved. Only the leakage
inductance affects the operating current. Accordingly, the symmetrical interference
suppression of the current compensated choke is relatively low.
c) Ferrite bead
This type of inductor suppresses high frequency noise simply by applying them to lead wires,
conductors or cables. Large ferrite beads are commonly seen on external cabling. Various
smaller ferrite beads are used internally in circuits or around the pins of small circuit-board
components, such as transistors or connectors.
IEC 60940:2026 © IEC 2026
4.3.5 Filters
Filters for electromagnetic interference suppression are mostly passive low-pass filters without
active elements. They essentially consist of various combinations of chokes and capacitors for
electromagnetic interference suppression.
In addition, resistors or overvoltage elements such as varistors can be used.
Two different types can be distinguished:
a) Filters assembled with approved components either as an unprotected assembly or with a
simple protective housing. The approval testing of these can be simplified based on already
existing approval tests of the components themselves.
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 General safety aspects
5.1 EMI suppression components as a protective provision
5.1.1 General considerations
An EMI suppression component or assembly of EMI suppression components is considered a
protective provision if its impedance and construction limit electrical parameters such as
current, voltage and electric charge or a combination of these parameters to safe values safe
values, following the principles for protective provisions described in IEC 61140:2016, Clause 5
and Clause 6.
The protective provision for basic protection limits the electrical parameters to safe values under
normal conditions (operation in intended use and absence of fault). An example of this is a
capacitor that bridges a basic insulation.
The protective provision for fault protection limits the electrical parameters to safe values under
single-fault conditions. This is achieved usually by a further protective provision, independent
of that for basic protection. An example of this is a capacitor that bridges a supplementary
insulation.
Enhanced protective provision limits the electrical parameters to safe values under both normal
and single fault conditions. An example of this is a capacitor that bridges a reinforced insulation.
Such EMI suppression component or assembly of EMI suppression components is also referred
to as protective impedance or protective impedance device.
NOTE In equipment standards, the enhanced protective provision is also referred to as reinforced provision or
reinforced safeguard.
An EMI suppression component or assembly of EMI suppression components connected
between electrically separated circuits shall withstand the electrical stresses specified for the
bridged insulation and its impedance shall limit the expected current through the component to
non-hazardous values specified in a corresponding equipment standard.
Dangerous situation shall not arise due to a failure of the component.
For the enhanced protective provision, these requirements also apply to any probable failure of
a single component of the protective impedance device.
IEC 60940:2026 © IEC 2026
5.1.2 Single fault conditions
Based on the concept of IEC 61140, simultaneous failure of independent protective provisions
is unlikely and need not normally be taken into consideration. Reliance is placed on the
unaffected protective provisions remaining. This concept is also adopted in this document. The
single fault conditions are considered for fault evaluation.
A single fault condition is a condition in which one means for protection against electric shock
is defective or one fault is present which could cause a hazard.
A component failure is simulated usually by following two situations:
– short-circuiting any two leads;
– disconnecting any one lead of the component one at a time.
This also applies to a single component in the assembly of EMI suppression components.
The degradation of EMI suppression components parameters (e.g. impedance) is usually not
referred to as a single fault condition in the equipment standard. It is assumed that the reliability
over the lifetime of an EMI suppression component is handled by the use of an appropriate
component standard and a component approval.
5.1.3 Series connection of components
Where components are connected in series, the failure of a single component can cause a
breakdown of other components within the chain. Thus,
– the components shall provide a safety margin sufficient to comply with the requirements for
its function as protective provision in the equipment in case that double or reinforced
insulation is bridged,
– the voltage sharing ratio shall be considered, which, in case of AC voltage is applied, is
determined by the impedance, in case of DC voltage is applied, is determined by the internal
resistance of the components (in case of capacitors by the insulation resistance).
For rules specific for components refer to 6.1.
5.2 Earth leakage current
Earth leakage current appears when EMI suppression components (for example capacitors) are
connected from line to earth.
Under operating conditions, the earth leakage current of the appliance shall not exceed the
limits given in the relevant product safety standard. If the calculated leakage current exceeds
3,5 mA RMS, a warning "Connect to earth before connecting to supply" or equivalent text shall
be applied. Details for calculation of the earth leakage current can be found in
IEC 60939-3:2024, Annex A.
5.3 Hazards related to EMI suppression components caused by failures
EMI suppression components can fail, for example by short or open circuit, breakdown of
insulation or drift of electrical parameters.
The hazards associated with these failures can roughly be categorized into electrical shock,
temperature rise, fire and evaporation of gases. If the components are located in a tight
container, the evaporation of gases in addition can cause bursting of the container or explosion,
if gases can ignite.
In depth information on safety related risk assessment and risk reduction can be found in
IEC Guide 116 and in group and product safety standards relevant for the application.
IEC 60940:2026 © IEC 2026
5.4 Information requirements
It is the responsibility of manufacturers of EMI suppression components to provide information
related to failure modes and probability in order to enable users to perform the necessary risk
assessment.
In case the safety related risk assessment performed as described in 5.3 results in an
unacceptable risk, additional protective provisions can become necessary, as for example surge
protectors, fuses, additional insulation or housing.
6 Selection of EMI suppression components
6.1 Choice of ratings for specific applications
6.1.1 General aspects
The selection of EMI suppression components requires consideration of technical
characteristics with regard to application and in relation to surroundings and environmental
conditions present at the component’s body (operating conditions and micro-climate inside
equipment).
6.1.2 Voltages
6.1.2.1 Overview
Requirements to components connected to public mains (AC or DC) and those connected to
other voltage sources shall be based on related overvoltage categories and internally created
transients (impulse voltages). See IEC 60664-1:2020, 4.3.2 for information.
The following voltages are generated externally by AC or DC power distribution systems,
electrical installation, external circuits or internally within the equipment:
– transient overvoltages (external and internally generated);
– temporary overvoltages;
– recurring peak voltage;
– steady-state voltage (peak).
NOTE See IEC 60664-1 for definitions and further information.
It is important to note, that the definitions of rated voltage, nominal voltage and working voltage
can be different for the system, equipment or a component.
When considering the performances of EMI suppression components, the voltages described
in 6.1.2.2 to 6.1.2.5, which occur at the component’s terminations, are relevant for the selection
of EMI suppression components.
6.1.2.2 Steady-state voltage
A steady-state voltage (e.g. rated voltage, rated insulation voltage, nominal voltage, working
voltage) is an operating voltage that is applied continuously (steady-state) to the terminations
of EMI suppression components. Short-term voltage variations, transient and random
overvoltages are not taken into account.
This voltage:
– can appear externally as a rated voltage, nominal voltage
• of any AC or DC power distribution system,
• from external circuits;
IEC 60940:2026 © IEC 2026
– can be defined by rules of insulation coordination as a rated insulation voltage;
– can be generated internally as a working voltage.
The operating voltage can be lower, equal, or higher than the rated voltage or nominal voltage
of the equipment. Especially for internal circuits, the steady-state voltage at the EMI
suppression component’s termination can be significantly higher than the rated voltage of
equipment. This voltage can also differ in the form and frequency from power distribution system
voltages and from external circuits’ voltages and can contain recurring peaks.
The following rules shall be taken into consideration for the selection of EMI suppression
components with regard to steady-state voltages, further or different rules can be required by
product safety standards:
– Steady-state voltage: The highest operating or by equipment design defined steady-state
voltage (RMS value of the AC or DC value) at EMI suppression component’s termination.
– Steady-state peak voltage: The peak value of the steady-state working voltage.
• The rated voltage of the EMI suppression component multiplied by 1,41 shall be at least
equal to the steady-state peak voltage at EMI suppression component’s termination.
• The rated DC voltage, if defined for the EMI suppression component, shall be at least
equal to the steady-state peak voltage at EMI suppression component’s termination.
6.1.2.3 Overvoltage
– Temporary overvoltages
The concept and values of temporary overvoltages is based on the IEC 60364-4-44:2024,
Clause 442. The temporary overvoltage is an overvoltage at mains power frequency for
relatively long duration. The temporary overvoltage appears in the AC mains distribution
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