IEC 60664-5:2007

INTERNATIONAL IEC
STANDARD
CEI
60664-5
NORME
Second edition
INTERNATIONALE
Deuxième édition
2007-07
PUBLICATION FONDAMENTALE DE SÉCURITÉ
BASIC SAFETY PUBLICATION
Insulation coordination for equipment within
low-voltage systems –
Part 5:
Comprehensive method for determining
clearances and creepage distances equal to
or less than 2 mm
Coordination de l'isolement des matériels
dans les systèmes (réseaux) à basse tension –
Partie 5:
Méthode détaillée de détermination des distances
d’isolement dans l’air et des lignes de fuite
inférieures ou égales à 2 mm
Reference number
Numéro de référence
IEC/CEI 60664-5:2007
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INTERNATIONAL IEC
STANDARD
CEI
60664-5
NORME
Second edition
INTERNATIONALE
Deuxième édition
2007-07
PUBLICATION FONDAMENTALE DE SÉCURITÉ
BASIC SAFETY PUBLICATION
Insulation coordination for equipment within
low-voltage systems –
Part 5:
Comprehensive method for determining
clearances and creepage distances equal to
or less than 2 mm
Coordination de l'isolement des matériels
dans les systèmes (réseaux) à basse tension –
Partie 5:
Méthode détaillée de détermination des distances
d’isolement dans l’air et des lignes de fuite
inférieures ou égales à 2 mm
PRICE CODE
X
CODE PRIX
Commission Electrotechnique Internationale
International Electrotechnical Commission
МеждународнаяЭлектротехническаяКомиссия
For price, see current catalogue
Pour prix, voir catalogue en vigueur

– 2 – 60664-5 © IEC:2007
CONTENTS
FOREWORD.4
INTRODUCTION.6

1 Scope and object .7
2 Normative references.7
3 Terms and definitions .8
4 Fundamentals of clearance and creepage distance dimensioning .8
4.1 Introductory remark .8
4.2 Basic principles .8
4.3 Voltages and voltage ratings .9
4.4 Frequency .11
4.5 Time under voltage stress.11
4.6 Pollution .11
4.7 Information supplied with the equipment .12
4.8 Insulating material .12
5 Requirements and dimensioning procedures .14
5.1 General .14
5.2 Dimensioning of clearances .14
5.3 Dimensioning of creepage distances .18
5.4 Requirements for design of solid insulation .23
6 Tests and measurements.26
6.1 Tests.26
6.2 Measurement of creepage distances and clearances.33

Annex A (informative) Dimensioning to maintain minimum insulation resistance.34
Annex B (normative) Water adsorption test.36
Annex C (informative) Dimensioning diagrams.40
Annex D (informative) Withstand voltage test for creepage distance under humid
conditions .43

Bibliography .44

Figure 1 – Test voltages.32
Figure B.1 – Layout of the test sample.37
Figure B.2 – Test circuit .38
Figure B.3 – Critical relative humidity of insulating materials .39
Figure C.1 – Diagram for dimensioning clearances for circuits directly connected to the
supply mains.40
Figure C.2 – Diagram for dimensioning clearances for circuits not directly connected to
the supply mains .41
Figure C.3 – Diagram for dimensioning of creepage distances .42
Figure D.1 – The arrangement for the withstand voltage test.43

60664-5 © IEC:2007 – 3 –
Table 1 – Relation between the humidity levels and macro-environmental classes .12
Table 2 – Clearances to withstand transient overvoltages .15
Table 3 – Clearances to withstand steady-state voltages, temporary overvoltages or
recurring peak voltages .16
Table 4 – Creepage distances to avoid failure due to tracking.20
Table 5 – Creepage distances to avoid flashover .21
Table A.1 – Minimum insulation resistance .34
Table A.2 – Creepage distances to maintain minimum insulation resistance.35

– 4 – 60664-5 © IEC:2007
INTERNATIONAL ELECTROTECHNICAL COMMISSION
_____________
INSULATION COORDINATION FOR EQUIPMENT
WITHIN LOW-VOLTAGE SYSTEMS –
Part 5: Comprehensive method for determining clearances
and creepage distances equal to or less than 2 mm

FOREWORD
1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising
all national electrotechnical committees (IEC National Committees). The object of IEC is to promote
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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 60664-5 has been prepared by IEC technical committee 109:
Insulation coordination for low-voltage equipment.
This second edition cancels and replaces the first edition, published in 2003 and constitutes a
technical revision.
The revision of Part 1 of IEC 60664 also required a revision of Part 5 of IEC 60664, as Part 5 is
closely linked to Part 1. In addition to a number of editorial improvements, the following major
technical changes made in Part 1 also apply for Part 5:
• 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.

60664-5 © IEC:2007 – 5 –
• 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.
• 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.
It has the status of a basic safety publication in accordance with IEC Guide 104.
It is to be used in conjunction with IEC 60664-1.
NOTE For the purposes of this standard, all references to IEC 60664-1 are written as “to Part 1”. Where a
subclause is cited without reference to a Part, it is assumed that the reference is to the current Part 5.
The text of this standard is based on the following documents:
CDV Report on voting
109/61/CDV 109/63/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.
– 6 – 60664-5 © IEC:2007
INTRODUCTION
This part of IEC 60664 specifies humidity levels regarding the effects of humidity on creepage
distances.
This part introduces the following dimensioning criteria which need to be taken into account:
– new minimum clearances having more precise values for dimensions up to 2 mm under
pollution degrees 2 and 3 than those specified in Table F.2 of Part 1;
– smaller minimum creepage distances for printed wiring boards and equivalent constructions
under pollution degree 3 than those specified in Table F.4 of Part 1;
– a specification of minimum creepage distances to avoid flashover of the insulating
surfaces, the values being based on the water adsorption characteristics of the material;
– a specification of minimum creepage distances to ensure adequate insulation resistance
under humid conditions.
NOTE Table A.2 provides information on the dimensioning of creepage distances in order to maintain adequate
insulation resistance for r.m.s. voltages up to 10 000 V, corresponding to creepage distances up to 250 mm.
[1, 2]
The information in this standard is based on research data published in 1989 .
The following details from this research provide background information:
– the research was carried out on test samples that were manufactured using the same
process as for printed wiring boards with spacing of circuit patterns from 0,16 mm to
6,3 mm;
– ten different materials were used for the test samples. The influence of the manufacturing
process on the surface of the material, e.g. moulding or machining, was not part of the
research project;
– the test samples were placed in different locations, such as city, rural, industrial, desert,
and coastal;
– the samples were periodically exposed to a voltage stress and the data accumulated over a
long period of time.
Annex B specifies a water adsorption test method for allocating unclassified insulating material
to the relevant water adsorption group. This annex will be reviewed when further experience is
gained using the test method for different materials.
———————
Figures in square brackets refer to the bibliography.

60664-5 © IEC:2007 – 7 –
INSULATION COORDINATION FOR EQUIPMENT
WITHIN LOW-VOLTAGE SYSTEMS –
Part 5: Comprehensive method for determining clearances
and creepage distances equal to or less than 2 mm

1 Scope and object
This part of IEC 60664 specifies the dimensioning of clearances and creepage distances for
spacings equal to or less than 2 mm for printed wiring board and equivalent constructions,
where the clearance and the creepage distance are identical and are along the surface of solid
insulation, such as the paths described in 6.2 of Part 1 (Examples 1, 5 and 11).
The dimensioning in this standard is more precise than that provided by Part 1. However, if the
precision provided by this standard is not required, Part 1 may be applied instead.
This standard can only be used in its entirety. It is not permitted to select one or more clauses
from this standard and to use them in place of the corresponding clauses of Part 1. In addition,
this part of IEC 60664 can only be used together with Part 1.
When this Part 5 is applied to the dimensioning of clearances and creepage distances equal to
or less than 2 mm, all clauses are used in place of the corresponding clauses given in Part 1.
For clearances and creepage distances larger than 2 mm, and for solid insulation in general,
Part 1 applies.
NOTE 1 The limitation to distances equal to or less than 2 mm applies to basic or supplementary insulation. The
total distance of a reinforced or double insulation may be larger than 2 mm.
This standard is based on the following criteria for dimensioning:
– minimum clearances independent of the micro-environment (see Table 2);
– minimum creepage distances for pollution degrees 1, 2 and 3 to avoid failure due to
tracking (see Table 4);
– minimum creepage distances to avoid flashover across the insulating surface (see
Table 5).
NOTE 2 For minimum creepage distances to maintain adequate insulation resistance, see Table A.2.
NOTE 3 This standard is not applicable to micro-environmental conditions worse than pollution degree 3 or
humidity level 3.
A test method is specified for allocating unclassified insulating material to the relevant water
adsorption group.
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.
Clause 2 of Part 1 is applicable, as well as the following:
———————
“Part 1” refers to IEC 60664-1.

– 8 – 60664-5 © IEC:2007
IEC 60364-5-51:2005, Electrical installations of buildings – Part 5-51: Selection and erection of
electrical equipment – Common rules
IEC 60664-1:2007, Insulation coordination for equipment within low-voltage systems − Part 1:
Principles, requirements and tests
IEC 60721-3-3:1994, Classification of environmental conditions − Part 3-3: Classification of
groups of environmental parameters and their severities –Stationary use at weatherprotected
locations
IEC 60721-3-7:1995, Classification of environmental conditions − Part 3-7: Classification of
groups of environmental parameters and their severities – Portable and non-stationary use
IEC 60721-3-9:1993, Classification of environmental conditions − Part 3-9: Classification of
groups of environmental parameters and their severities – Microclimates inside products
3 Terms and definitions
For the purposes of this document, the following terms and definitions, in addition to those
given in Part 1, apply.
3.1
water adsorption
capability of insulating material to adsorb water on its surface
3.2
critical relative humidity
value of the relative humidity when the impulse withstand voltage of a creepage distance has
dropped to 95 % of the value that was measured at 70 % relative humidity
4 Fundamentals of clearance and creepage distance dimensioning
4.1 Introductory remark
The first publication on this subject was IEC 60664, 1980. It only covered clearances, the data
being based on fundamental data of breakdown voltages. Subsequently, in 1981 IEC 60664A
was published concerning creepage distances based on data obtained over many years of
experience, as well as data obtained from testing printed wiring boards. In 1992, the
publications were combined and published as IEC 60664-1 (Part 1). However, the revision did
not change the basic data.
4.2 Basic principles
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.
Subclause 4.2 of Part 1 is applicable if not specified otherwise below.

60664-5 © IEC:2007 – 9 –
4.2.5 Insulation coordination with regard to temporary overvoltage
Insulation coordination with regard to temporary overvoltages is based on the temporary
overvoltage specified in Clause 442 of IEC 60364-4-44 (see 5.4.3.2.3 of this Part 5).
NOTE Currently available surge protective devices (SPDs) are not able to adequately deal with the energy
associated with temporary overvoltages.
4.2.6 Insulation coordination with regard to environmental conditions
The micro-environmental conditions for the insulation shall be taken into account. They depend
primarily on the macro-environmental conditions in which the equipment is located and, in
many cases, the environments are identical. However, the micro-environment can be better or
worse than the macro-environment where, for example, enclosures, heating, ventilation or dust
influence the micro-environment.
[3]
NOTE Protection by enclosures provided according to the degrees of protection specified in IEC 60529 may
increase the humidity of the micro-environment.
The main environmental parameters are as follows:
– for clearances
• air pressure,
• temperature, if it has a wide variation;
– for creepage distances
• air pressure,
• pollution,
• relative humidity,
• condensation;
– for solid insulation
• temperature,
• relative humidity.
4.3 Voltages and voltage ratings
4.3.1 General
Subclause 4.3.1 of Part 1 is applicable.
4.3.2 Determination of voltage for long-term stresses
4.3.2.1 General
Subclause 4.3.2.1 of Part 1 is applicable.
4.3.2.2 Voltage for dimensioning basic insulation
4.3.2.2.1 Equipment energized directly from the low-voltage mains
The nominal voltages of the low-voltage mains have been rationalized according to Tables F.3a
and F.3b of Part 1 and these voltages are the minimum to be used for the selection of
creepage distances. They may also be used for the selection of rated insulation voltages.

– 10 – 60664-5 © IEC:2007
For equipment having several rated voltages so that it may be used at different nominal
voltages of the low-voltage mains, the voltage selected shall be appropriate for the highest
rated voltage of the equipment.
Technical committees shall consider whether the voltage is to be selected
– based on line-to-line voltage, or
– based on line-to-neutral voltage.
In the latter case the technical committee shall specify how the user is to be informed that the
equipment is for use on neutral-earthed systems only.
4.3.2.2.2 Systems, equipment and internal circuits not energized directly
from the low-voltage mains
Subclause 4.3.2.2.2 of Part 1 is applicable.
4.3.2.3 Voltage for dimensioning functional insulation
Subclause 4.3.2.3 of Part 1 is applicable.
4.3.3 Determination of rated impulse voltage
4.3.3.1 General
Subclause 4.3.3.1 of Part 1 is applicable.
4.3.3.2 Overvoltage categories
4.3.3.2.1 General
Subclause 4.3.3.2.1 of Part 1 is applicable.
4.3.3.2.2 Equipment energized directly from the supply mains
Subclause 4.3.3.2.2 of Part 1 is applicable.
4.3.3.2.3 Systems and equipment not energized directly from the low-voltage mains
Subclause 4.3.3.2.3 of Part 1 is applicable.
4.3.3.3 Selection of rated impulse voltage for equipment
Subclause 4.3.3.3 of Part 1 is applicable.
4.3.3.4 Impulse voltage insulation coordination within equipment
4.3.3.4.1 Parts or circuits within equipment significantly influenced by external
transient overvoltages
Subclause 4.3.3.4.1 of Part 1 is applicable.
4.3.3.4.2 Parts or circuits within equipment specifically protected against transient
overvoltages
For such parts are not significantly influenced by external transient overvoltages, the impulse
withstand voltage required for basic insulation is not related to the rated impulse voltage of the
equipment but to the actual conditions for that part or circuit. Application of the preferred series

60664-5 © IEC:2007 – 11 –
of impulse voltage values as introduced in 4.2.3 of Part 1 is, however, recommended to permit
standardization. In other cases, interpolation of Table 2 values of this Part 5 is allowed.
4.3.3.5 Switching overvoltage generated by the equipment
Subclause 4.3.3.5 of Part 1 is applicable.
4.3.3.6 Interface requirements
Subclause 4.3.3.6 of Part 1 is applicable.
4.3.4 Determination of recurring peak voltage
Subclause 4.3.4 of Part 1 is applicable.
4.3.5 Determination of temporary overvoltage
4.3.5.1 General
Subclause 4.3.5.1 of Part 1 is applicable.
4.3.5.2 Fault voltage
Subclause 4.3.5.2 of Part 1 is applicable.
4.3.5.3 Stress due to temporary overvoltages
The magnitude and duration of a temporary overvoltage in low-voltage equipment due to an
earth fault in the high-voltage system are given in 5.4.3.2.3.
4.4 Frequency
Subclause 4.4 of Part 1 applies.
4.5 Time under voltage stress
Not applicable.
4.6 Pollution
4.6.1 General
Pollution does not only impair insulation with regard to long-term r.m.s. voltage stress causing
tracking, but also impairs it with regard to peak voltages and water adsorption. Pollution causes
reduced impulse withstand capability of short distances and thus flashover may occur across
the insulation surface.
The influence of humidity on the surface of insulation is identified by the humidity levels
specified in 4.6.4. The influence of the water adsorption characteristics on the surface of
insulation is identified by the water adsorption groups specified in 4.8.6.
4.6.2 Degrees of pollution in the micro-environment
Subclause 4.6.2 of Part 1 applies.
4.6.3 Conditions of conductive pollution
Not applicable.
– 12 – 60664-5 © IEC:2007
4.6.4 Humidity levels
For the purpose of evaluating creepage distances with regard to flashover across the surface
or minimum insulation resistance, the following three levels in the micro-environment are
defined:
– humidity level 1 (HL 1): the relative humidity at the insulation surface never reaches a level
where condensation occurs. Therefore flashover is not influenced by humidity;
– humidity level 2 (HL 2): the relative humidity at the insulation surface is such that
condensation occurs occasionally during transient changes in the micro-environment.
Therefore flashover is influenced by humidity;
– humidity level 3 (HL 3): the relative humidity at the insulation surface is such that
condensation may occur frequently. Therefore flashover is strongly influenced by humidity.
4.6.5 Relation of humidity levels to the macro-environment
Macro-environmental conditions are specified in IEC 60364-5-51, IEC 60721-3-3,
IEC 60721-3-7 and IEC 60721-3-9.
NOTE In IEC 60721-3-9 different expressions of climatic classes are used.
The relationship between humidity levels of the micro-environment and the defined macro-
environmental classes is shown in Table 1.
Table 1 – Relation between the humidity levels and macro-environmental classes
Standard Humidity
specifying Climatic (macro-environmental) classes levels
climatic classes
IEC 60721-3-9 Y2 Y3 Y4
---------------------- ----------- ----------- -----------
IEC 60721-3-3 3K1 3K3 3K6
---------------------- ----------- ----------- -----------
IEC 60721-3-7 7K1 7K3
---------------------- ----------- ----------- -----------
IEC 60364-5-51 AB5 AB7
↓ ↓ ↓
= (–) (–)
→ HL 1
(+) = (–) → HL 2
(+) (+) =
→ HL 3
Key
= micro-environment has the same humidity as the macro-environment
(–) micro-environment is less humid than the macro-environment
(+) micro-environment is more humid than the macro-environment

4.7 Information supplied with the equipment
Subclause 4.7 of Part 1 is applicable.
4.8 Insulating material
4.8.1 General
Insulating material shall be classified into groups according their CTI values.
The electric strength characteristics as well as the thermal, mechanical, chemical and water
adsorption characteristics of insulating material shall be considered by the technical
committees. Regarding the requirements for solid insulation, 5.4 of this Part 5 applies.

60664-5 © IEC:2007 – 13 –
4.8.2 Comparative tracking index (CTI)
4.8.2.1 Behaviour of insulating material in the presence of scintillations
Subclause 4.8.1.1 of Part 1 is applicable.
4.8.2.2 CTI values to categorize insulating materials
Subclause 4.8.1.2 of Part 1 is applicable.
4.8.2.3 Material groups
Subclause 4.8.1.3 of Part 1 is applicable.
4.8.2.4 Test for comparative tracking index (CTI)
Subclause 4.8.1.4 of Part 1 is applicable.
4.8.2.5 Non tracking materials
For glass, ceramics or other inorganic insulating materials which do not track, creepage
distances need not be greater than their associated clearance for the purpose of insulation
coordination. The dimensions of Table 2 for inhomogeneous field conditions are appropriate.
4.8.3 Electric strength characteristics
Subclause 4.8.2 of Part 1 is applicable.
4.8.4 Thermal characteristics
Subclause 4.8.3 of Part 1 is applicable.
4.8.5 Mechanical and chemical characteristics
Subclause 4.8.4 of Part 1 is applicable.
4.8.6 Water adsorption characteristics
Water adsorption is a surface-related phenomenon that depends on the characteristics of the
insulating material. With regard to the effect of water adsorption on voltage withstand
capability, insulating materials are allocated to a water adsorption group according to the test
procedure in Annex B as follows:
– water adsorption group WAG 1 (negligible influence);
– water adsorption group WAG 2 (weak influence);
– water adsorption group WAG 3 (medium influence);
– water adsorption group WAG 4 (strong influence).
NOTE 1 The classification of materials with respect to water adsorption groups may be influenced by fillers,
additives and manufacturing procedures.
NOTE 2 The classification of various insulating materials with respect to water adsorption groups is given in
5.3.2.3.5.
– 14 – 60664-5 © IEC:2007
5 Requirements and dimensioning procedures
5.1 General
Clearances shall be dimensioned to withstand voltages in accordance with 5.2.2 of this Part 5.
The associated creepage distance shall fulfil the requirements of 5.3.2.3.3 and 5.3.2.3.4 of
this Part 5. Solid insulation shall be designed to meet the requirements of 5.4 of this Part 5.
5.2 Dimensioning of clearances
5.2.1 General
Clearances shall be dimensioned to withstand the required impulse withstand voltage. For
equipment directly connected to the low-voltage mains, the required impulse withstand voltage
is the rated impulse voltage established on the basis of 4.3.3.3 of Part 1. If a steady-state
r.m.s. voltage, a temporary overvoltage or a recurring peak voltage requires larger clearances
than required for the impulse withstand voltage, the corresponding values of Table 3 shall be
used. The largest clearance shall be selected, resulting from consideration of impulse
withstand voltage, steady-state r.m.s. voltage, temporary overvoltages and recurring peak
voltages.
NOTE Dimensioning for steady-state r.m.s. or recurring peak voltage leads to a situation in which there is no
margin to breakdown with the continuous application of these voltages. Technical committees should take this into
account.
5.2.2 Dimensioning criteria
5.2.2.1 General
Clearances shall be selected taking into account the following influencing factors:
– impulse withstand voltage according to 5.2.5 of this Part 5 for functional insulation and
5.2.6 of this Part 5 for basic, supplementary and reinforced insulation;
– steady-state withstand voltages and temporary overvoltages (see 5.2.2.3 of this Part 5);
– recurring peak voltages (see 5.2.2.3 of this Part 5);
– electric field conditions (see 5.2.3 of this Part 5);
– altitude. The clearance dimensions specified in Table 2 and Table 3 give withstand
capability for equipment for use in altitudes up to 2 000 m. For equipment for use in higher
altitudes, 5.2.4 of this Part 5 applies.
Larger clearances may be required in the case of mechanical influences such as vibration or
applied forces.
5.2.2.2 Dimensioning to withstand transient overvoltages
Clearances shall be dimensioned to withstand the required impulse withstand voltage,
according to Table 2. For equipment directly connected to the supply mains, the required
impulse withstand voltage is the rated impulse voltage established on the basis of Table F.1 of
Part 1.
60664-5 © IEC:2007 – 15 –
Table 2 – Clearances to withstand transient overvoltages
Minimum clearances in air up to 2 000 m above sea level
Required impulse
Case A Case B
a) c)
withstand voltage
Inhomogeneous field conditions homogeneous field conditions
kV
(see 3.15 of Part 1) (see 3.14 of Part 1)
mm mm
b)
0,33 0,01 0,01
0,40 0,02 0,02
b)
0,50 0,04 0,04
0,60 0,06 0,06
b)
0,80 0,10 0,10
1,0 0,15 0,15
1,2 0,25 0,20
b)
1,5 0,50 0,30
2,0 1,0 0,45
b)
2,5 1,5 0,60
3,0 2,0 0,80
b)
4,0 1,2
5,0 1,5
b)
6,0 2,0
a)
This voltage is
– for functional insulation, the maximum impulse voltage expected to occur across the clearance (see 5.2.5 of
this Part 5);
– for basic insulation directly exposed to or significantly influenced by transient overvoltages from the low voltage
mains (see 4.3.3.3 of Part 1, 4.3.3.4.1 of Part 1 and 5.2.6 of this Part 5), the rated impulse voltage of the
equipment;
– for other basic insulation (see 4.3.3.4.2 of this Part 5), the highest impulse voltage that can occur in the circuit.
For reinforced insulation, see 5.2.6 of this Part 5.
b)
Preferred values specified as in 4.2.3 of Part 1.
c) For parts or circuits within equipment subject to impulse voltages according to 4.3.3.4.2 of this Part 5,
interpolation of values is allowed. However, standardization is achieved by using the preferred series of
impulse voltage values in 4.2.3 of Part 1.

5.2.2.3 Dimensioning to withstand steady-state voltages and temporary overvoltages
or recurring peak voltages
Clearances shall be dimensioned according to Table 3 to withstand the peak value of the
steady-state (d.c. or 50/60 Hz voltage), the temporary overvoltage or recurring peak voltage.
Dimensioning according to Table 2 shall be compared with Table 3. The larger clearance shall
be selected.
NOTE 1 Dimensioning requirements for frequencies higher than 30 kHz are specified in IEC 60664-4.

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Table 3 – Clearances to withstand steady-state voltages, temporary overvoltages
or recurring peak voltages
Minimum clearances in air up to 2 000 m above sea level
a)
Voltage
Case A Case B
b)
(peak value)
Inhomogeneous field conditions Homogeneous field conditions
kV
(see 3.15 of Part 1) (see 3.14 of Part 1)
mm mm
c) c)
0,04 0,001 0,001
c) c
0,06 0,002 0,002
c) c
0,10 0,003 0,003
c) c
0,12 0,004 0,004
c) c
0,15 0,005 0,005
c) c
0,20 0,006 0,006
c) c
0,25 0,008 0,008
0,33 0,01 0,01
0,4 0,02 0,02
0,5 0,04 0,04
0,6 0,06 0,06
0,8 0,13 0,10
1,0 0,26 0,15
1,2 0,42 0,20
1,5 0,76 0,30
2,0 1,27 0,45
2,5 1,8 0,6
d)
3,0 2,4 0,8
4,0 1,2
5,0 1,5
6,0 2,0
a)
The clearances for other voltages are obtained by interpolation.
b)
See Figure 1 of Part 1 for recurring peak voltage.
c)
These values are based on experimental data obtained at atmospheric pressure.
d)
This value is only given to allow interpolation of the peak voltage from one step lower to a value corresponding to
2 mm (maximum value according to this standard).

NOTE 2 If clearances are stressed with steady-state voltages of 2,5 kV (peak) and above, dimensioning according
to the breakdown values in Table 3 may not provide operation without corona (partial discharges), especially for
inhomogeneous fields. In order to provide corona-free operation, it is either necessary to use larger clearances as
given in Table F.7b of Part 1 or to improve the field distribution.
5.2.3 Electric field conditions
5.2.3.1 General
The shape and arrangement of the conductive parts (electrodes) influence the homogeneity of
the field and consequently the clearance needed to withstand a given voltage (see Tables 2
and 3 of this Part 5 and Table A.1 of Part 1).

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5.2.3.2 Inhomogeneous field conditions (case A of Table 2)
Clearances not less than those specified in Table 2 for inhomogeneous field conditions can be
used irrespective of the shape and arrangement of the conductive parts and without verification
by a voltage withstand test.
Clearances through openings in enclosures of insulating material shall not be less than those
specified for inhomogeneous field conditions since the configuration is not controlled, which
may have an adverse effect on the homogeneity of the electric field.
5.2.3.3 Homogeneous field conditions (case B of Table 2)
Values for clearances in Table 2 for case B are only applicable for homogeneous fields. They
can only be used where the shape and arrangement of the conductive parts is designed to
achieve an electric field having an essentially constant voltage gradient.
Clearances smaller than those for inhomogeneous field conditions require verification by a
voltage withstand test (see 6.1.2).
NOTE For small values of clearances, the uniformity of the electric field can deteriorate in the presence of
pollution, making it necessary to increase the clearances above the values of case B.
5.2.4 Altitude
As the dimensions in Table 2 and Table 3 are valid for altitudes up to 2 000 m above sea level,
the altitude correction factors specified in Table A.2 of Part 1 are applicable for clearances for
altitudes above 2 000 m.
NOTE The breakdown voltage of a clearance in air for a homogeneous field (withstand voltage in Table A.1 case B
of Part 1) is, according to Paschen's Law, proportional to the product of the distance between electrodes and the
atmospheric pressure. Therefore, experimental data recorded at approximately sea level is corrected according to
the difference in atmospheric pressure between 2 000 m and sea level. The same correction is made for
inhomogeneous fields and for creepage distances with respect to flashover; see 5.3.2.3.4.
5.2.5 Dimensioning of clearances of functional insulation
For a clearance of functional insulation, the required withstand voltage is the maximum impulse voltage
or steady-state voltage (with reference to Table 3) or recurring peak voltage (with reference to Table 3)
expected to occur across it under rated conditions of the equipment, and in particular the rated voltage
and rated impulse voltage (refer to Table 2),.
5.2.6 Dimensioning of clearances of basic, supplementary and reinforced insulation
Clearances of basic and supplementary insulation shall each be dimensioned as specified in
Table 2 corresponding to
– the rated impulse voltage, according to 4.3.3.3 of Part 1 or 4.3.3.4.1 of Part 1, or
– the impulse withstand voltage requirements according to 4.3.3.4.2 of this Part 5;
and as specified in Table 3 corresponding to
– the steady-state voltage according to 4.3.2.2 of this Part 5;
– and the recurring peak voltage according to 4.3.4 of Part 1;
– and the temporary overvoltage according to 4.3.5 of this Part 5.
With respect to impulse voltages, clearances of reinforced insulation shall be dimensioned as
specified in Table 2 corresponding to the rated impulse voltage but one step higher in the
preferred series of values in 4.2.3 of Part 1 than that specified for basic insulation. If the
impulse withstand voltage required for basic insulation according to 4.3.3.4.2 of this Part 5 is
other than a value taken from the preferred series, reinforced insulation shall be dimensioned
to withstand 160 % of the impulse withstand voltage required for basic insulation.

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NOTE 1 The limitation to distances equal to or less than 2 mm applies to basic or supplementary insulation. The
total distance of a reinforced or double insulation may be larger than 2 mm.
NOTE 2 In a coordinated system, clearances above the minimum required are unnecessary for a required impulse
withstand voltage. However, it may be necessary, for reasons other than insulation coordination, to increase
clearances (for example due to mechanical influences). In such in
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