EN 60664-1:2007

SLOVENSKI STANDARD
01-november-2007
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Insulation coordination for equipment within low-voltage systems - Part 1: Principles,
requirements and tests
Isolationskoordination für elektrische Betriebsmittel in Niederspannungsanlagen - Teil 1:
Grundsätze, Anforderungen und Prüfungen
Coordination de l'isolement des matériels dans les systemes (réseaux) a basse tension -
Partie 1: Principes, exigences et essais
Ta slovenski standard je istoveten z: EN 60664-1:2007
ICS:
29.080.30 Izolacijski sistemi Insulation systems
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EUROPEAN STANDARD
EN 60664-1
NORME EUROPÉENNE
July 2007
EUROPÄISCHE NORM
ICS 29.080.30; 29.080 Supersedes EN 60664-1:2003

English version
Insulation coordination for equipment
within low-voltage systems -
Part 1: Principles, requirements and tests
(IEC 60664-1:2007)
Coordination de l'isolement  Isolationskoordination
des matériels dans les systèmes für elektrische Betriebsmittel
(réseaux) à basse tension - in Niederspannungsanlagen -
Partie 1: Principes, exigences Teil 1: Grundsätze, Anforderungen
et essais und Prüfungen
(CEI 60664-1:2007) (IEC 60664-1:2007)

This European Standard was approved by CENELEC on 2007-07-01. 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 Central Secretariat 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 Central Secretariat has the same status as the official versions.

CENELEC members are the national electrotechnical committees of Austria, Belgium, Bulgaria, Cyprus, the
Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia,
Lithuania, Luxembourg, Malta, the Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain,
Sweden, Switzerland and the United Kingdom.

CENELEC
European Committee for Electrotechnical Standardization
Comité Européen de Normalisation Electrotechnique
Europäisches Komitee für Elektrotechnische Normung

Central Secretariat: rue de Stassart 35, B - 1050 Brussels

© 2007 CENELEC - All rights of exploitation in any form and by any means reserved worldwide for CENELEC members.
Ref. No. EN 60664-1:2007 E
Foreword
The text of document 109/58/CDV, future edition 2 of IEC 60664-1, prepared by IEC TC 109, Insulation
co-ordination for low-voltage equipment, was submitted to the IEC-CENELEC parallel Unique Acceptance
Procedure and was approved by CENELEC as EN 60664-1 on 2007-07-01.
This European Standard supersedes EN 60664-1:2003.
In addition to a number of editorial improvements, the following main changes have been made with
respect to EN 60664-1:2003:
− amendment of Japanese mains conditions with regard to the rated impulse voltages, the rationalized
voltages and the nominal voltages of supply systems for different modes of overvoltage control;
− amendment of dimensioning of clearances smaller than 0,01 mm;
− alignment of the table and the corresponding formula regarding test voltages for verifying clearances
at different altitudes;
− amendment of interpolation of the creepage distance values for functional insulation;
− amendment of creepage distance dimensioning taking into account ribs;
− revision of the former Clause 4 "Tests and measurements" (now Clause 6) to achieve a more detailed
description of the tests and their purpose, the test equipment and possible alternatives;
− change of Annex C "Partial discharge test methods" from a former technical report, Type 2 (now called
TS), to a normative Annex C.
The following dates were fixed:
– latest date by which the EN has to be implemented
at national level by publication of an identical
national standard or by endorsement (dop) 2008-04-01
– latest date by which the national standards conflicting
with the EN have to be withdrawn (dow) 2010-07-01
Annex ZA has been added by CENELEC.
__________
Endorsement notice
The text of the International Standard IEC 60664-1:2007 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 standards indicated:
ISO/IEC Guide 2 NOTE  Harmonized as EN 45020:1998 (not modified).
IEC 60529 NOTE  Harmonized as EN 60529:1991 + A1:2000 (not modified).
+ A1
__________
- 3 - EN 60664-1:2007
Annex ZA
(normative)
Normative references to international publications
with their corresponding European publications

The following referenced documents are indispensable for the application 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  When an international publication has been modified by common modifications, indicated by (mod), the relevant EN/HD
applies.
Publication Year Title EN/HD Year

1)
IEC 60038 1983 IEC standard voltages HD 472 S1 1989
+ corr. February 2002
+ A1 1995
IEC 60050-151 2001 International Electrotechnical Vocabulary - -
(IEV) -
Part 151: Electrical and magnetic devices

IEC 60050-212 1990 International Electrotechnical Vocabulary - -
(IEV) -
Chapter 212: Insulating solids, liquids and
gases
IEC 60050-604 1987 International Electrotechnical Vocabulary - -
+ A1 1998 (IEV) -
Chapter 604: Generation, transmission and
distribution of electricity - Operation

IEC 60050-826 2004 International Electrotechnical Vocabulary - -
(IEV) -
Part 826: Electrical installations

2)
IEC 60068-1 1988 Environmental testing - EN 60068-1 1994
Part 1: General and guidance
3)
IEC 60068-2-2 1974 Environmental testing - EN 60068-2-2 1993
Part 2: Tests - Tests B: Dry heat

4)
IEC 60068-2-14 1984 Environmental testing - EN 60068-2-14 1999
Part 2: Tests - Test N: Change of temperature

IEC 60068-2-78 2001 Environmental testing - EN 60068-2-78 2001
Part 2-78: Tests - Test Cab: Damp heat,
steady state
IEC 60085 2004 Electrical insulation - Thermal classification EN 60085 2004

IEC 60099-1 1991 Surge arresters - EN 60099-1 1994
Part 1: Non-linear resistor type gapped surge
arresters for a.c. systems
1)
The title of HD 472 S1 is: Nominal voltages for low voltage public electricity supply systems.
2)
EN 60068-1 includes A1:1992 to IEC 60068-1 + corr. October.
3)
EN 60068-2-2 includes supplement A to IEC 60068-2-2.
4)
EN 60068-2-14 includes A1:1986 to IEC 60068-2-14.

Publication Year Title EN/HD Year
IEC 60112 2003 Method for the determination of the proof and EN 60112 2003
the comparative tracking indices of solid
insulating materials
IEC 60216 Series Electrical insulating materials - Properties of EN 60216 Series
thermal endurance
IEC 60243-1 1998 Electrical strength of insulating materials - EN 60243-1 1998
Test methods -
Part 1: Tests at power frequencies

IEC 60270 2000 High-voltage test techniques - Partial EN 60270 2001
discharge measurements
IEC 60364-4-44 2001 Electrical installations of buildings - - -
+ A1 (mod) 2003 Part 4-44: Protection for safety - Protection
against voltage disturbances and
electromagnetic disturbances
IEC 60664-4 2005 Insulation coordination for equipment within EN 60664-4 2006
low-voltage systems - + corr. October 2006
Part 4: Consideration of high-frequency
voltage stress
5) 6)
IEC 60664-5 - Insulation coordination for equipment within EN 60664-5 2003
low-voltage systems -
Part 5: A comprehensive method for
determining clearances and creepage
distances equal to or less than 2 mm

IEC 61140 2001 Protection against electric shock - Common EN 61140 2002
A1 (mod) 2004 aspects for installation and equipment A1 2006

IEC 61180-1 1992 High-voltage test techniques for low-voltage EN 61180-1 1994
equipment -
Part 1: Definitions, test and procedure
requirements
IEC 61180-2 1994 High-voltage test techniques for low-voltage EN 61180-2 1994
equipment -
Part 2: Test equipment
IEC Guide 104 1997 The preparation of safety publications and the - -
use of basic safety publications and group
safety publications
5)
Undated reference.
6)
Valid edition at date of issue.

IEC 60664-1
Edition 2.0 2007-04
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
BASIC SAFETY PUBLICATION
PUBLICATION FONDAMENTALE DE SÉCURITÉ
Insulation coordination for equipment within low-voltage systems –
Part 1: Principles, requirements and tests

Coordination de l’isolement des matériels dans les systèmes (réseaux)
à basse tension –
Partie 1: Principes, exigences et essais

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
PRICE CODE
INTERNATIONALE
XB
CODE PRIX
ICS 29.080; 29.080.30 ISBN 2-8318-9137-X

– 2 – 60664-1 © IEC:2007
CONTENTS
1 Scope and object.7
2 Normative references .7
3 Terms and definitions .9
4 Basis for insulation coordination .14
4.1 General .14
4.2 Insulation coordination with regard to voltage.14
4.2.1 General .14
4.2.2 Insulation coordination with regard to long-term a.c. or d.c. voltages .15
4.2.3 Insulation coordination with regard to transient overvoltage.15
4.2.4 Insulation coordination with regard to recurring peak voltage.15
4.2.5 Insulation coordination with regard to temporary overvoltage.15
4.2.6 Insulation coordination with regard to environmental conditions.16
4.3 Voltages and voltage ratings .16
4.3.1 General .16
4.3.2 Determination of voltage for long-term stresses .16
4.3.3 Determination of rated impulse voltage.17
4.3.4 Determination of recurring peak voltage .19
4.3.5 Determination of temporary overvoltage .19
4.4 Frequency .20
4.5 Time under voltage stress .20
4.6 Pollution.20
4.6.1 General .20
4.6.2 Degrees of pollution in the micro-environment .21
4.6.3 Conditions of conductive pollution .21
4.7 Information supplied with the equipment.21
4.8 Insulating material.21
4.8.1 Comparative tracking index (CTI) .21
4.8.2 Electric strength characteristics .22
4.8.3 Thermal characteristics .22
4.8.4 Mechanical and chemical characteristics .22
5 Requirements and dimensioning rules .23
5.1 Dimensioning of clearances.23
5.1.1 General .23
5.1.2 Dimensioning criteria .23
5.1.3 Electric field conditions.24
5.1.4 Altitude.24
5.1.5 Dimensioning of clearances of functional insulation .24
5.1.6 Dimensioning of clearances of basic, supplementary and reinforced
insulation.24
5.1.7 Isolating distances.25
5.2 Dimensioning of creepage distances .25
5.2.1 General .25
5.2.2 Influencing factors .25
5.2.3 Dimensioning of creepage distances of functional insulation.27
5.2.4 Dimensioning of creepage distances of basic, supplementary and
reinforced insulation .27
5.2.5 Reduction of creepage distances with the use of a rib (ribs) .27

60664-1 © IEC:2007 – 3 –
5.3 Requirements for design of solid insulation .28
5.3.1 General .28
5.3.2 Stresses .28
5.3.3 Requirements .30
6 Tests and measurements .32
6.1 Tests.32
6.1.1 General .32
6.1.2 Test for verification of clearances .33
6.1.3 Tests for the verification of solid insulation .36
6.1.4 Performing dielectric tests on complete equipment .41
6.1.5 Other tests .42
6.1.6 Measurement accuracy of test parameters .42
6.2 Measurement of creepage distances and clearances.43

Annex A (informative) Basic data on withstand characteristics of clearances .48
Annex B (informative) Nominal voltages of supply systems for different modes of
overvoltage control .53
Annex C (normative) Partial discharge test methods .55
Annex D (informative) Additional information on partial discharge test methods .60
Annex E (informative) Comparison of creepage distances specified in Table F.4 and
clearances in Table A.1 .63
Annex F (normative) Tables .64

Bibliography.73

Figure 1 – Recurring peak voltage .19
Figure 2 – Determination of the width (W) and height (H) of a rib .28
Figure 3 – Test voltages .40
Figure A.1 – Withstand voltage at 2 000 m above sea level .50
Figure A.2 – Experimental data measured at approximately sea level and their low
limits for inhomogeneous field.51
Figure A.3 – Experimental data measured at approximately sea level and their low
limits for homogeneous field .52
Figure C.1 – Earthed test specimen .55
Figure C.2 – Unearthed test specimen .55
Figure C.3 – Calibration for earthed test specimen .58
Figure C.4 – Calibration for unearthed test specimen.58
Figure D.1 – Partial discharge test circuits.60

– 4 – 60664-1 © IEC:2007
Figure E.1 – Comparison of creepage distances specified in Table F.4 and clearances
in Table A.1 .63

Table A.1 – Withstand voltages in kilovolts for an altitude of 2 000 m above sea level .48
Table A.2 – Altitude correction factors .49
Table B.1 – Inherent control or equivalent protective control.53
Table B.2 – Cases where protective control is necessary and control is provided by
surge arresters having a ratio of clamping voltage to rated voltage not smaller than
that specified by IEC 60099-1 .54
Table F.1 – Rated impulse voltage for equipment energized directly from the low-
voltage mains .64
Table F.2 – Clearances to withstand transient overvoltages.65
Table F.3a – Single-phase three or two-wire a.c. or d.c. systems.66
Table F.3b – Three-phase four or three-wire a.c. systems.67
Table F.4 – Creepage distances to avoid failure due to tracking .68
Table F.5 – Test voltages for verifying clearances at different altitudes.70
Table F.6 – Severities for conditioning of solid insulation .70
Table F.7 – Clearances to withstand steady-state voltages, temporary overvoltages or
recurring peak voltages.71
Table F.7a – Dimensioning of clearances to withstand steady-state voltages,
temporary overvoltages or recurring peak voltages .71
Table F.7b – Additional information concerning the dimensioning of clearances to
avoid partial discharge.71
Table F.8 – Altitude correction factors.72

60664-1 © IEC:2007 – 5 –
INTERNATIONAL ELECTROTECHNICAL COMMISSION
___________
INSULATION COORDINATION FOR EQUIPMENT
WITHIN LOW-VOLTAGE SYSTEMS –
Part 1: Principles, requirements and tests

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 provides no marking procedure to indicate its approval and cannot be rendered responsible for any
equipment declared to be in conformity with an IEC Publication.
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 60664 has been prepared by technical committee 109: Insulation
coordination for low-voltage equipment.
This second edition cancels and replaces the first edition, published in 1992, amendments 1
(2000) and 2 (2002) and a corrigendum (2002).
It has the status of a basic safety publication in accordance with IEC Guide 104.
In addition to a number of editorial improvements, the following main changes have been
made with respect to the previous edition:
• Amendment of Japanese mains conditions with regard to the rated impulse voltages, the
rationalized voltages and the nominal voltages of supply systems for different modes of
overvoltage control
• Amendment of dimensioning of clearances smaller than 0,01 mm

– 6 – 60664-1 © IEC:2007
• Alignment of the table and the corresponding formula regarding test voltages for verifying
clearances at different altitudes
• Amendment of interpolation of the creepage distance values for functional insulation
• Amendment of creepage distance dimensioning taking into account ribs
• Revision of the former Clause 4 "Tests and measurements" (now Clause 6) to achieve a
more detailed description of the tests and their purpose, the test equipment and possible
alternatives
• Change of Annex C "Partial discharge test methods" from a former technical report,
Type 2 (now called TS), to a normative Annex C.
The text of this standard is based on the following documents:
CDV Report on voting
109/58/CDV 109/62/RVC
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.
A list of all parts in the IEC 60664 series, under the general title Insulation coordination for
equipment within low-voltage systems, can be found on the IEC website.
The committee has decided that the contents of this publication will remain unchanged until
the maintenance result date indicated on the IEC web site under "http://webstore.iec.ch" in
the data related to the specific publication. At this date, the publication will be
• reconfirmed;
• withdrawn;
• replaced by a revised edition, or
• amended.
60664-1 © IEC:2007 – 7 –
INSULATION COORDINATION FOR EQUIPMENT
WITHIN LOW-VOLTAGE SYSTEMS –
Part 1: Principles, requirements and tests

1 Scope and object
This part of IEC 60664 deals with insulation coordination for equipment within low-voltage
systems. It applies to equipment for use up to 2 000 m above sea level having a rated voltage
up to a.c. 1 000 V with rated frequencies up to 30 kHz, or a rated voltage up to d.c. 1 500 V.
It specifies the requirements for clearances, creepage distances and solid insulation for
equipment based upon their performance criteria. It includes methods of electric testing with
respect to insulation coordination.
The minimum clearances specified in this standard do not apply where ionized gases occur.
Special requirements for such situations may be specified at the discretion of the relevant
technical committee.
This standard does not deal with distances
– through liquid insulation,
– through gases other than air,
– through compressed air.
NOTE 1 Insulation coordination for equipment within low-voltage systems with rated frequencies above 30 kHz is
given in IEC 60664-4.
NOTE 2 Higher voltages may exist in internal circuits of the equipment.
NOTE 3 Guidance for dimensioning for altitudes exceeding 2 000 m is given in Table A.2.
The object of this basic safety standard is to guide technical committees responsible for
different equipment in order to rationalize their requirements so that insulation coordination is
achieved.
It provides the information necessary to give guidance to technical committees when
specifying clearances in air, creepage distances and solid insulation for equipment.
Care should be taken to see that manufacturers and technical committees are responsible for
application of the requirements, as specified in this basic safety publication, or make
reference to it, where necessary, in standards for equipment within their scope.
In the case of missing specified values for clearances, creepage distances and requirements
for solid insulation in the relevant product standards, or even missing standards, this standard
is applicable.
2 Normative references
The following referenced documents are indispensable for the application 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 60038:1983, IEC standard voltages

– 8 – 60664-1 © IEC:2007
IEC 60050(151):2001, International Electrotechnical Vocabulary (IEV) – Chapter 151:
Electrical and magnetic devices
IEC 60050(212):1990, International Electrotechnical Vocabulary – Chapter 212: Insulating
solids, liquids and gases
IEC 60050(604):1987, International Electrotechnical Vocabulary (IEV) – Chapter 604:
Generation, transmission and distribution of electricity – Operation
Amendment 1 (1998)
IEC 60050(826):2004, International Electrotechnical Vocabulary (IEV) – Part 826: Electrical
installations
IEC 60068-1:1988, Environmental testing – Part 1: General and guidance
IEC 60068-2-2:1974, Environmental testing – Part 2: Tests – Tests B: Dry heat
IEC 60068-2-14:1984, Environmental testing – Part 2: Tests – Test N: Change of temperature
IEC 60068-2-78:2001, Environmental testing – Part 2-78: Tests – Test Cab: Damp heat,
steady state
IEC 60085:2004, Electrical insulation – Thermal classification
IEC 60099-1:1991, Surge arresters – Part 1: Non-linear resistor type gapped surge arresters
for a.c. systems
IEC 60112:2003, Method for the determination of the proof and the comparative tracking
indices of solid insulating materials
IEC 60216, (all parts) Electrical insulating materials – Properties for thermal endurance
IEC 60243-1:1998, Electrical strength of insulating materials – Test methods – Part 1: Tests
at power frequencies
IEC 60270:2000, High-voltage test techniques – Partial discharge measurements
IEC 60364-4-44:2001, Electrical installations of buildings – Part 4-44: Protection for safety –
Protection against voltage disturbances and electromagnetic disturbances
Amendment 1 (2003)
IEC 60664-4:2005, Insulation coordination for equipment within low-voltage systems – Part 4:
Consideration of high-frequency voltage stress
IEC 60664-5, Insulation coordination for equipment within low-voltage systems – Part 5:
A comprehensive method for determining clearances and creepage distances equal to or less
than 2 mm
IEC 61140:2001, Protection against electric shock – Common aspects for installation and
equipment
Amendment 1 (2004)
IEC 61180-1:1992, High-voltage test techniques for low-voltage equipment – Part 1:
Definitions, test and procedure requirements
—————————
A second edition of IEC 60664-5 will be published shortly.

60664-1 © IEC:2007 – 9 –
IEC 61180-2:1994, High-voltage test techniques for low-voltage equipment – Part 2: Test
equipment
IEC Guide 104:1997, The preparation of safety publications and the use of basic safety
publications and group safety publications
3 Terms and definitions
For the purposes of this document, the following definitions apply.
3.1
insulation coordination
mutual correlation of insulation characteristics of electrical equipment taking into account the
expected micro-environment and other influencing stresses
NOTE Expected voltage stresses are characterized in terms of the characteristics defined in 3.5 to 3.7.
3.2
clearance
shortest distance in air between two conductive parts
3.3
creepage distance
shortest distance along the surface of a solid insulating material between two conductive
parts
(IEV 151-15-50)
3.4
solid insulation
solid insulating material interposed between two conductive parts
3.5
working voltage
highest r.m.s. value of the a.c. or d.c. voltage across any particular insulation which can occur
when the equipment is supplied at rated voltage
NOTE 1 Transients are disregarded.
NOTE 2 Both open-circuit conditions and normal operating conditions are taken into account.
3.6
recurring peak voltage
U
rp
maximum peak value of periodic excursions of the voltage waveform resulting from distortions
of an a.c. voltage or from a.c. components superimposed on a d.c. voltage
NOTE Random overvoltages, for example due to occasional switching, are not considered to be recurring peak
voltages.
3.7
overvoltage
any voltage having a peak value exceeding the corresponding peak value of maximum
steady-state voltage at normal operating conditions
3.7.1
temporary overvoltage
overvoltage at power frequency of relatively long duration

– 10 – 60664-1 © IEC:2007
3.7.2
transient overvoltage
short duration overvoltage of a few milliseconds or less, oscillatory or non-oscillatory, usually
highly damped
(IEV 604-03-13)
3.7.3
switching overvoltage
transient overvoltage at any point of the system due to specific switching operation or fault
3.7.4
lightning overvoltage
transient overvoltage at any point of the system due to a specific lightning discharge
3.7.5
functional overvoltage
deliberately imposed overvoltage necessary for the function of a device
3.8
withstand voltage
voltage to be applied to a specimen under prescribed test conditions which does not cause
breakdown and/or flashover of a satisfactory specimen
(IEV 212-01-31)
3.8.1
impulse withstand voltage
highest peak value of impulse voltage of prescribed form and polarity which does not cause
breakdown of insulation under specified conditions
3.8.2
r.m.s. withstand voltage
highest r.m.s. value of a voltage which does not cause breakdown of insulation under
specified conditions
3.8.3
recurring peak withstand voltage
highest peak value of a recurring voltage which does not cause breakdown of insulation under
specified conditions
3.8.4
temporary withstand overvoltage
highest r.m.s. value of a temporary overvoltage which does not cause breakdown of insulation
under specified conditions
3.9
rated voltage
value of voltage assigned by the manufacturer, to a component, device or equipment and to
which operation and performance characteristics are referred
NOTE Equipment may have more than one rated voltage value or may have a rated voltage range.
3.9.1
rated insulation voltage
r.m.s. withstand voltage value assigned by the manufacturer to the equipment or to a part of
it, characterizing the specified (long-term) withstand capability of its insulation
NOTE The rated insulation voltage is not necessarily equal to the rated voltage of equipment which is primarily

60664-1 © IEC:2007 – 11 –
related to functional performance.
3.9.2
rated impulse voltage
impulse withstand voltage value assigned by the manufacturer to the equipment or to a part of
it, characterizing the specified withstand capability of its insulation against transient overvoltages
3.9.3
rated recurring peak voltage
recurring peak withstand voltage value assigned by the manufacturer to the equipment or to a
part of it, characterizing the specified withstand capability of its insulation against recurring
peak voltages
3.9.4
rated temporary overvoltage
temporary withstand overvoltage value assigned by the manufacturer to the equipment, or to
a part of it, characterizing the specified short-term withstand capability of its insulation against
a.c. voltages
3.10
overvoltage category
numeral defining a transient overvoltage condition
NOTE 1 Overvoltage categories I, II, III and IV are used, see 4.3.3.2.
NOTE 2 The term ‘overvoltage category’ in this standard is synonymous with ‘impulse withstand category’ used in
IEC 60364-4-44, Clause 443.
3.11
pollution
any addition of foreign matter, solid, liquid, or gaseous that can result in a reduction of
electric strength or surface resistivity of the insulation
3.12
environment
surrounding which may affect performance of a device or system
NOTE Examples are pressure, temperature, humidity, pollution, radiation and vibration.
(IEV 151-16-03, modified)
3.12.1
macro-environment
environment of the room or other location in which the equipment is installed or used
3.12.2
micro-environment
immediate environment of the insulation which particularly influences the dimensioning of the
creepage distances
3.13
pollution degree
numeral characterizing the expected pollution of the micro-environment
NOTE Pollution degrees 1, 2, 3 and 4 are established in 4.6.2.
3.14
homogeneous field
electric field which has an essentially constant voltage gradient between electrodes (uniform
field), such as that between two spheres where the radius of each sphere is greater than the
distance between them
– 12 – 60664-1 © IEC:2007
NOTE The homogeneous field condition is referred to as case B.
3.15
inhomogeneous field
electric field which does not have an essentially constant voltage gradient between electrodes
(non-uniform field)
NOTE The inhomogeneous field condition of a point-plane electrode configuration is the worst case with regard to
voltage withstand capability and is referred to as case A. It is represented by a point electrode having a 30 μm
radius and a plane of 1 m × 1 m.
3.16
controlled overvoltage condition
condition within an electrical system wherein the expected transient overvoltages are limited
to a defined level
3.17
insulation
that part of an electrotechnical product which separates the conducting parts at different
electrical potentials
(IEV 212-01-05)
3.17.1
functional insulation
insulation between conductive parts which is necessary only for the proper functioning of the
equipment
3.17.2
basic insulation
insulation of hazardous-live-parts which provides basic protection
NOTE The concept does not apply to insulation used exclusively for functional purposes.
(IEV 826-12-14)
3.17.3
supplementary insulation
independent insulation applied in addition to basic insulation for fault protection
(IEV 826-12-15)
3.17.4
double insulation
insulation comprising both basic insulation and supplementary insulation
(IEV 826-12-16)
3.17.5
reinforced insulation
insulation of hazardous-live-parts which provides a degree of protection against electric shock
equivalent to double insulation
NOTE Reinforced insulation may comprise several layers which cannot be tested singly as basic insulation or
supplementary insulation.
(IEV 826-12-17)
3.18
partial discharge
PD
electric discharge that partially bridges the insulation

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3.18.1
apparent charge
q
electric charge which can be measured at the terminals of the specimen under test
NOTE 1 The apparent charge is smaller than the partial discharge.
NOTE 2 The measurement of the apparent charge requires a short-circuit condition at the terminals of the
specimen (see Clause D.2) under test.
3.18.2
specified discharge magnitude
magnitude of the apparent charge which is regarded as the limiting value according to the
objective of this standard
NOTE The pulse with the maximum amplitude should be evaluated.
3.18.3
pulse repetition rate
average number of pulses per second with an apparent charge higher than the detection level
NOTE Within the scope of this standard it is not permitted to weigh discharge magnitudes according to the pulse
repetition rate.
3.18.4
partial discharge inception voltage

U
i
lowest peak value of the test voltage at which the apparent charge becomes greater than the
specified discharge magnitude when the test voltage is increased above a low value for which
no discharge occurs
NOTE For a.c. tests the r.m.s. value may be used.
3.18.5
partial discharge extinction voltage
U
e
lowest peak value of the test voltage at which the apparent charge becomes less than the
specified discharge magnitude when the test voltage is reduced below a high level where
such discharges have occurred
NOTE For a.c. tests the r.m.s. value may be used.
3.18.6
partial discharge test voltage
U
t
peak value of the test voltage for the procedure of 6.1.3.5.3 where the apparent charge is less
than the specified discharge magnitude
NOTE For a.c. tests the r.m.s. value may be used.
3.19
test
technical operation that consists of the determination of one or more characteristics of a given
product, process or service according to a specified procedure
[1]
(13.1 of ISO/IEC Guide 2:1996)
NOTE A test is carried out to measure or classify a characteristic or a property of an item by applying to the item
a set of environmental and operating conditions and/or requirements.
—————————
References in square brackets refer to the bibliography.

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(IEV 151-16-13)
3.19.1
type test
test of one or more devices made to a certain design to show that the design meets certain
specifications
3.19.2
routine test
test to which each individual device is subjected during or after manufacture to ascertain
whether it complies with certain criteria
3.19.3
sampling test
test on a number of devices taken at random from a batch
3.20
electrical breakdown
failure of insulation under electric stress when the discharge completely bridges the
insulation, thus reducing the voltage between the electrodes almost to zero
3.20.1
sparkover
electrical breakdown in a gaseous or liquid medium
3.20.2
flashover
electrical breakdown along a surface of solid insulation located in a gaseous or liquid medium
3.20.3
puncture
electrical breakdown through solid insulation
4 Basis for insulation coordination
4.1 General
Insulation coordination implies the selection of the electric insulation characteristics of the
equipment with regard to its application and in relation to its surroundings.
Insulation coordination can only be achieved if the design of the equipment is based on the
stresses to which it is likely to be subjected during its anticipated lifetime.
4.2 Insulation coordination with regard to voltage
4.2.1 General
Consideration shall be given to
– the voltages which can appear within the system,
– the voltages generated by the equipment (which could adversely affect other equipment in
the system),
– the degree of continuity of service desired,
– the safety of persons and property, so that the probability of undesired incidents due to
voltage stresses does not lead to an unacceptable risk of harm.

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4.2.2 Insulation coordination with regard to long-term a.c. or d.c. voltages
Insulation coordination with regard to long-term voltages is based on
– rated voltage,
– rated insulation voltage,
– working voltage.
4.2.3 Insulation coordination with regard to transient overvoltage
Insulation coordination with regard to transient overvoltage is based on controlled overvoltage
conditions. There are two kinds of control:
– inherent control: the condition within an electrical system wh
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