IEC TR 63040:2016

IEC TR 63040 ®
Edition 1.0 2016-09
TECHNICAL
REPORT
colour
inside
Guidance on clearances and creepage distances in particular for distances
equal to or less than 2 mm – Test results of research on influencing parameters

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IEC TR 63040 ®
Edition 1.0 2016-09
TECHNICAL
REPORT
colour
inside
Guidance on clearances and creepage distances in particular for distances

equal to or less than 2 mm – Test results of research on influencing parameters

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 29.080.30 ISBN 978-2-8322-3656-7

– 2 – IEC TR 63040:2016 © IEC 2016
CONTENTS
FOREWORD .4
INTRODUCTION .6
1 Scope .7
2 Normative references .7
3 Terms and definitions .7
4 Fundamental aspects and phenomena of clearance and creepage distances .9
4.1 Mutual correlation of insulation characteristics with regard to environmental
conditions .9
4.2 Pollution .9
4.2.1 General .9
4.2.2 Humidity level (HL) . 10
4.2.3 Relation of humidity levels to macro-environment . 10
4.2.4 Comparative tracking index (CTI) . 11
4.2.5 Flashover characteristics . 11
5 Clearances and creepage distances . 12
5.1 General . 12
5.2 Clearances . 12
5.2.1 Influencing criteria . 12
5.2.2 Altitude . 14
5.3 Creepage distances . 16
5.3.1 General . 16
5.3.2 Influencing factors . 16
5.3.3 Dimensioning of creepage distances of functional insulation . 22
6 Additional information regarding creepage distance characteristics – surface
current over a creepage distance (minimum insulation resistance) . 22
7 Water adsorption test . 24
7.1 Object . 24
7.2 Withstand characteristics of creepage distances under high humidity . 24
7.3 Recommended test method . 25
7.3.1 Test specimen . 25
7.3.2 Measurement of the impulse withstand voltage . 25
7.3.3 Procedure for characterization of the insulating materials . 25
7.4 Definitions of the water adsorption groups . 26
8 Dimensioning diagrams . 28
9 Withstand voltage test for creepage distance under humidity conditions . 32
Bibliography . 33

Figure 1 – Clearances in air for mutual correlation of insulation characteristics to
withstand transient overvoltages up to 2 000 m above sea level . 14
Figure 2 – Creepage distances for mutual correlation of insulation characteristics to
avoid failure due to tracking . 19
Figure 3 – Creepage distances for mutual correlation of insulation characteristics to
avoid flashover. 21
Figure 4 – Creepage distances required to maintain minimum insulation resistance . 24
Figure 5 – Layout of the test specimen. 27

Figure 6 – Test circuit . 27
Figure 7 – Critical relative humidity of insulating materials . 28
Figure 8 – Diagram for dimensioning of clearances ≤ 2 mm for circuits directly
connected to the supply mains (for low-voltage equipment up to 2 000 m) . 29
Figure 9 – Diagram for dimensioning of clearances ≤ 2 mm for circuits not directly
connected to the supply mains (for low-voltage equipment up to 2 000 m) . 30
Figure 10 – Diagram for dimensioning of creepage distances ≤ 2 mm (for low-voltage
equipment up to 2 000 m) . 31
Figure 11 – Withstand voltage test for creepage distance under humidity conditions. 32

Table 1 – Relation of the humidity levels to macro-environments . 10
Table 2 – Clearances for mutual correlation of insulation characteristics to withstand
transient overvoltages . 13
Table 3 – Clearances to withstand steady-state voltages, temporary overvoltages or
recurring peak voltages . 15
Table 4 – Creepage distances for mutual correlation of insulation characteristics in
equipment to avoid failure due to tracking . 18
Table 5 – Creepage distances for mutual correlation of insulation characteristics to
avoid flashover. 20
Table 6 – Minimum insulation resistance . 22
Table 7 – Creepage distances to maintain minimum insulation resistance (without
condensation) . 23

– 4 – IEC TR 63040:2016 © IEC 2016
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
GUIDANCE ON CLEARANCES AND CREEPAGE
DISTANCES IN PARTICULAR FOR DISTANCES EQUAL
TO OR LESS THAN 2 mm – TEST RESULTS OF RESEARCH
ON INFLUENCING PARAMETERS
FOREWORD
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The main task of IEC technical committees is to prepare International Standards. However, a
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data of a different kind from that which is normally published as an International Standard, for
example "state of the art".
IEC TR 63040, which is a Technical Report, has been prepared by IEC technical committee
109: Insulation co-ordination for low-voltage equipment.
The text of this Technical Report is based on the following documents:
Enquiry draft Report on voting
109/140/DTR 109/144/RVC
Full information on the voting for the approval of this Technical Report 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.
The committee has decided that the contents of this publication will remain unchanged until
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related to the specific publication. At this date, the publication will be
• reconfirmed,
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A bilingual version of this publication may be issued at a later date.
The contents of the corrigendum of January 2019 have been included in this copy.

IMPORTANT – The 'colour inside' logo on the cover page of this publication indicates
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– 6 – IEC TR 63040:2016 © IEC 2016
INTRODUCTION
This document provides information on printed board assemblies and other equivalent plane
arrangements of insulation, where the clearance and the creepage distance follows the same
path along the surface of solid insulation.
This document is based on German research data published in May 1989 [9], [10] . SC 28A,
the predecessor of TC 109, began analysing this research data in November 1990.
The following points provide background information to the research.
• The research was carried out on test samples that were manufactured with the same
technology being used for printed circuit boards (PCBs) with selected spacing of circuit
patterns from 0,16 mm to 6,3 mm.
• Ten types of materials were used for the test samples. The influence of manufacturing
operations on the surface of a material, for example moulding or machining, was not part
of this research project.
• The test samples were placed in different locations, such as large city, rural, industrial,
desert, sea side, and periodically exposed to a voltage stress and the data was
accumulated over a long period of time.

____________
1 Numbers in square brackets refer to the bibliography.

GUIDANCE ON CLEARANCES AND CREEPAGE
DISTANCES IN PARTICULAR FOR DISTANCES EQUAL
TO OR LESS THAN 2 mm – TEST RESULTS OF RESEARCH
ON INFLUENCING PARAMETERS
1 Scope
This document describes test results of research on dimensioning of clearances and creepage
distances, for spacing equal to or less than 2 mm for printed wiring material and other
equivalent arrangements of insulation, where the clearance and the creepage distance follows
the same path along the surface of solid insulation.
The information contained in this document is the result of research only and cannot be used
for dimensioning the clearances and creepage distances for equipment within low-voltage
systems, where IEC 60664-1 applies. However distances can be taken into account for
functional reasons.
This document provides results of research related to the following criteria:
1) clearances independent from the micro-environment;
2) creepage distances for pollution degree 1, 2 and 3 which extends the use of smaller
distances to products having design features similar to printed circuit boards;
3) creepage distances to avoid flashover of the insulating surface;
4) information on minimum creepage distances to maintain minimum insulation resistance.
A test method for the evaluation of the relevant water adsorption group for the surface of any
insulating material which has not yet been classified is described.
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 60664-1:2007, Insulation coordination for equipment within low-voltage systems – Part 1:
Principles, requirements and tests
3 Terms and definitions
For the purposes of this document, the terms and definitions given in IEC 60664-1 and the
following apply.
ISO and IEC maintain terminological databases for use in standardization at the following
addresses:
• IEC Electropedia: available at http://www.electropedia.org/
• ISO Online browsing platform: available at http://www.iso.org/obp

– 8 – IEC TR 63040:2016 © IEC 2016
3.1
inhomogeneous field
non-uniform field
electric field which does not have an essentially constant voltage gradient between electrodes
Note 1 to entry: 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.
3.2
homogeneous field
uniform field
electric field which has an essentially constant voltage gradient between electrodes
Note 1 to entry: The electric field between two spheres where the radius of each sphere is greater than the
distance between them is an example of a homogeneous field (case B).
3.3
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
Note 1 to entry: For the purposes of this document the above definition is used, as the definition in
IEC 60050-212:2010, 212-11-33 [1] is broader than the scope of this document.
3.4
flashover
electrical breakdown along a surface of solid insulation located in a gaseous or liquid medium
Note 1 to entry: For the purposes of this document the above definition is used, as the definition in
IEC 60050-212, 212-11-47 is broader than the scope of this document.
3.5
humidity level
HL
level defining the expected humidity influences in the micro-environment and expressed
numerically
3.6
water adsorption
capability of an insulating material to adsorb water on its surface
3.7
critical relative humidity
value of the relative humidity when the impulse withstand voltage of a creepage distance has
dropped to 95 % of the value which was measured at 70 % humidity
3.8
water adsorption group
group characterizing the extent of the dependence of the critical relative humidity upon the
creepage distance
3.9
working voltage
highest r.m.s. value of the AC or DC voltage across any particular insulation which can occur
when the equipment is supplied at rated voltage
Note 1 to entry: Transients are disregarded.
Note 2 to entry: Both open-circuit conditions and normal operating conditions are taken into account.

3.10
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 1 to entry: The rated insulation voltage is not necessarily equal to the rated voltage of equipment which is
primarily related to functional performance.
3.11
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 1 to entry: Equipment may have more than one rated voltage value or may have a rated voltage range.
4 Fundamental aspects and phenomena of clearance and creepage distances
4.1 Mutual correlation of insulation characteristics with regard to environmental
conditions
The micro-environmental conditions for the insulation 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.
NOTE Protection by enclosures provided according to the degrees of protection specified in IEC 60529 [4] can
increase or decrease the humidity of the micro-environment.
The most important environmental parameters are the following.
– For clearances:
• air pressure;
• temperature, if it has a wide variation.
– For creepage distances:
• pollution;
• relative humidity;
• condensation.
– For solid insulation:
• temperature;
• relative humidity.
4.2 Pollution
4.2.1 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, causing
reduced impulse withstand capability in case of short distances and thus flashover may occur
along the insulation surface.
The influence of humidity on the surface of insulation is identified by the humidity levels.
These levels also apply to a macro-environment having the same humidity as the micro-
environment.
The influence of the water adsorption characteristics on the surface of insulation is identified
by the water adsorption categories.

– 10 – IEC TR 63040:2016 © IEC 2016
4.2.2 Humidity level (HL)
For the purpose of evaluating creepage distances with regard to flashover along the surface,
respectively minimum insulation resistance, the following three levels in the micro-
environment are established.
• Humidity level 1 (HL 1):
The relative humidity at the insulation never reaches a level where condensation occurs
on the insulation.
Therefore, the flashover is not influenced by humidity. Humidity Level HL 1 is considered
to be pollution degree 1.
• Humidity level 2 (HL 2):
The relative humidity at the insulation is such that condensation on the insulation occurs
only occasionally during transient changes in the micro-environment.
Therefore, the flashover is influenced by humidity.
• Humidity level 3 (HL 3):
The relative humidity at the insulation is such that condensation on the insulation may
occur frequently.
Therefore, the flashover is strongly influenced by humidity.
4.2.3 Relation of humidity levels to macro-environment
Macro-environmental conditions are specified in IEC 60364-5-51, in IEC 60721-3-3,
IEC 60721-3-7, and IEC 60721-3-9. The relation of humidity levels to defined macro-
environmental classes is shown in Table 1.
Table 1 – Relation of the humidity levels to macro-environments
Standard Climatic (macro-environmental) classes Humidity
specifying levels
climatic classes
IEC 60721-3-9 Y3 Y4
Y2
---------------------- ----------- ----------- -----------
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
NOTE In IEC 60721-3-9 different expressions of climatic classes are used.

4.2.4 Comparative tracking index (CTI)
With regard to tracking, an insulating material can be roughly characterized according to the
damage it suffers from the concentrated release of energy during scintillations when a surface
leakage current is interrupted due to the drying-out of the contaminated surface. The following
behaviour of an insulating material in the presence of scintillations can occur:
• no decomposition of the insulating material;
• the wearing of insulating material by action of electrical discharges (electrical erosion);
• the progressive formation of conductive paths which are produced on the surface of
insulating material due to the combined effects of electric stress and electrolytically
conductive contamination on the surface (tracking).
NOTE Tracking or erosion will occur when
• a liquid film carrying the surface leakage current breaks,
• the applied voltage is sufficient to break down the small gap formed when the film breaks, and
• the current is above a limiting value which is necessary to provide sufficient energy locally to thermally
decompose the insulating material beneath the film. Deterioration increases with the time for which the current
flows.
The behaviour of the insulating material under various contaminants and voltages is extremely
complex. Under these conditions many materials may exhibit two or even all three of the
characteristics stated. However, it has been found by experience and tests that insulating
materials having a higher relative performance also have approximately the same relative
ranking according to the comparative tracking index (CTI). Therefore, this document uses the
CTI values to categorize insulating materials.
Materials are classified into four groups (MG) according to their CTI values. These values are
determined in accordance with IEC 60112 using solution A. The groups are:
Material Group I 600 ≤ CTI
Material Group II 400 ≤ CTI < 600
Material Group IIIa 175 ≤ CTI < 400
Material Group IIIb 100 ≤ CTI < 175
The proof tracking index (PTI) is used to verify the tracking characteristics of materials. A
material may be included in one of these four groups on the basis that the PTI, verified by the
method of IEC 60112 using solution A, is not less than the lower value specified for the group.
The test for comparative tracking index (CTI) in accordance with IEC 60112 is designed to
compare the performance of various insulating materials under test conditions. It gives a
qualitative comparison and in the case of insulating materials having a tendency to form
tracks it also gives a quantitative comparison.
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 mutual
correlation of insulation characteristics. The dimensions for inhomogeneous field conditions
are appropriate. However, the behaviour with regard to flashover is important.
4.2.5 Flashover characteristics
Electric strength, thermal, mechanical and chemical characteristics of insulating material can
be considered, taking into account the stresses likely to occur during the lifetime of the
equipment.
Water adsorption is a surface-related phenomenon which depends on the characteristics of
the insulating material. With regard to the effect of water adsorption on flashover behaviour,

– 12 – IEC TR 63040:2016 © IEC 2016
insulating materials are allocated to a water adsorption group according to the test procedure
in Clause 7:
• Water adsorption group W1 (negligible influence)
• Water adsorption group W2 (weak influence)
• Water adsorption group W3 (medium influence)
• Water adsorption group W4 (strong influence)
NOTE Classification of materials with respect to water adsorption groups can be different if caused by fillers,
additives, moulding method, surface tooling etc.
5 Clearances and creepage distances
5.1 General
Clearances need to withstand transient overvoltages and steady state voltages. The
dimensioning of the associated creepage distance avoids failure due to tracking and flashover
under humid conditions.
5.2 Clearances
5.2.1 Influencing criteria
5.2.1.1 Influencing factors on clearance dimensions
Selected clearance dimensions take into account the following influencing factors:
• impulse overvoltages;
• steady-state voltages and temporary overvoltages;
• recurring peak voltages;
• electric field conditions;
• altitude.
NOTE 1 The clearance dimensions given in Table 2 have sufficient impulse withstand capability for equipment for
use at altitudes up to 2 000 m. For equipment for use at higher altitudes, see 5.2.2.
NOTE 2 Mechanical influences such as vibration and the effects of applied forces can require larger clearances.
5.2.1.2 Clearances to withstand transient overvoltages
Clearance dimensions according Table 2 can withstand impulse overvoltages with distances
equal to or less than 2 mm.
For equipment directly connected to the supply mains, the required impulse withstand voltage
is the rated impulse voltage (see IEC 60664-1:2007, Table F.1).

Table 2 – Clearances for mutual correlation of insulation
characteristics to withstand transient overvoltages
Minimum clearances up to 2 000 m above sea level
a c c
Impulse withstand voltage Case A Case B

inhomogeneous field conditions homogeneous field conditions
(see IEC 60664-1) (see IEC 60664-1)
kV 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 0,2
b
1,5 0,5 0,3
2,0 1,0 0,45
b
2,5 1,5 0,6
3,0 2,0 0,8
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 IEC 60664-1;
the rated impulse voltage of the equipment; see Table F.1 of IEC 60664-1:2007.
b
Preferred values specified in IEC 60664-1.
c
The values given in case A and case B are informative and cannot replace the values given in IEC 60664-1.

5.2.1.3 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.
It is advisable that clearances through openings in enclosures of insulating material are not
less than those specified for inhomogeneous field conditions since the configuration is not
controlled. This can have an adverse effect on the homogeneity of the electric field.
5.2.1.4 Homogeneous field conditions (case B of Table 2)
Values for clearances in Table 2 for case B are only for homogeneous fields. They may 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 specified in Table 2 for inhomogeneous field condition (case A)
need verification by a voltage withstand test. Figure 1 illustrates Table 2.

– 14 – IEC TR 63040:2016 © IEC 2016
0,1
0,01
100 1 000 10 000
U (V)
peak
Inhomogeneous field Homogeneous field
IEC
NOTE See also Table 2 from which the figure is derived.
Figure 1 – Clearances in air for mutual correlation of insulation characteristics to
withstand transient overvoltages up to 2 000 m above sea level
5.2.2 Altitude
5.2.2.1 General
As the values in Table 2 and Table 3 are valid for altitudes up to and including 2 000 m above
sea level, clearances for altitudes above 2 000 m need to be multiplied by the altitude
correction factor specified in IEC 60664-1:2007, Table A.2.
The dimensions in Table 5 are valid for altitudes up to and including 2 000 m above sea level,
creepage dimensions to avoid flashover for altitudes above 2 000 m need to be multiplied by
the altitude correction factor specified in IEC 60664-1:2007, Table A.2.
NOTE The breakdown voltage of a clearance in air for a homogeneous field 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
d (mm)
pressure between 2 000 m and sea level. The same correction is made for inhomogeneous fields and for creepage
distances with respect to flashover.
5.2.2.2 Steady-state voltages, temporary overvoltages or recurring peak voltages
Clearances dimensioned according to Table 3 withstand the peak value of the steady-state
(direct current or 50/60 Hz voltage) temporary overvoltage or recurring peak voltage.
The larger clearance of the dimensioning in Table 2 and Table 3 is applicable.
NOTE Dimensioning requirements for frequencies higher than 30 kHz are specified in IEC 60664-4.
Table 3 – Clearances to withstand steady-state voltages,
temporary overvoltages or recurring peak voltages
e
Minimum clearances in air up to 2 000 m above sea level
a
Voltage
Case A Case B
b
(peak value)
Inhomogeneous field conditions (see 3.1) Homogeneous field conditions (see 3.2)
kV
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 )
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 IEC 60664-1:2007 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 document).
e
The values given in this table are informative and cannot replace the values given in IEC 60664-1.

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-

– 16 – IEC TR 63040:2016 © IEC 2016
free operation, it is either necessary to use larger clearances as given in IEC 60664-1:2007,
Table F.7b or to improve the field distribution.
5.2.2.3 Clearances
Clearances are dimensioned as specified in Table 2 corresponding to
• the rated impulse voltage, according Table F.1 of IEC 60664-1:2007, or
• the required impulse withstand voltage
and as specified in Table 3 corresponding to peak value of the
• the steady-state voltage,
• the recurring peak voltage, and
• the temporary overvoltage.
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
mutual correlation of insulation characteristics, to increase clearances (for example due to
mechanical influences). In such instances, the test voltage is to remain based on the rated
impulse voltage of the equipment, otherwise undue stress of associated solid insulation can
occur.
5.3 Creepage distances
5.3.1 General
Creepage distances equal to or less than 2 mm are dimensioned taking into account 5.3.2.
The distance values obtained from the tables applying to the relevant stresses and conditions
are compared and the largest is chosen. (see dimensioning diagrams in Clause 8).
5.3.2 Influencing factors
5.3.2.1 General
Creepage distances selected from Table 4 together with Table 5, take into account the
tracking phenomema and the influence of humidity on flashover. The larger value from
Table 4 and Table 5 is applicable.
The following influencing factors are taken into account in Table 4:
• voltage (r.m.s. or DC) with regard to tracking;
• pollution degrees (PD) within the micro-environment;
• insulating materials.
The following influencing factors are taken into account in Table 5:
• voltage (peak value) with regard to flashover along the surface of the insulating material;
• humidity levels (HL) within the micro-environment;
• insulating materials;
• altitude.
The dimensions in Table 5 are valid for altitudes up to and including 2 000 m above sea level,
creepage distances to avoid flashover for altitudes above 2 000 m are to be multiplied by the
altitude correction factor specified in Table A.2 of IEC 60664-1:2007.

5.3.2.2 Voltage
The basis for the determination of a creepage distance with regard to tracking is the long-term
r.m.s. value of the voltage existing across this creepage distance. This voltage is the working
voltage, the rated insulation voltage or the rated voltage.
With regard to flashover, however, the basis for the determination of a creepage distance is
the peak value of the relevant voltage according to Table 5. The relevant peak voltage is the
maximum value of any voltage expected to occur across the creepage distance under rated
conditions.
5.3.2.3 Climatic conditions
5.3.2.3.1 General
For dimensioning of creepage distances, the influence of the climatic conditions in the micro-
environment, in terms of the humidity levels (HL), is taken into account in Table 5. The
following criteria can be considered for dimensioning:
• minimum insulation resistance;
• failure due to tracking;
• flashover;
• continuous paths of conductive pollution.
NOTE In equipment, different micro-environmental conditions can exist.
5.3.2.3.2 Minimum insulation resistance
A minimum insulation resistance applies when a maximum leakage current between live parts
or between live parts and an accessible surface of equipment is specified by technical
committees. The same applies for functional insulation when insufficient insulation resistance
could lead to excessive leakage current impairing proper functioning of the equipment.
5.3.2.3.3 Failure due to tracking
In order to avoid failure due to tracking, creepage distances are dimensioned as specified in
Table 4.
5.3.2.3.4 Flashover
In order to comply with the requirement to avoid flashover along the surface insulating
material, the values according to Table 5 are considered. Table 5 covers humidity levels HL 2
and HL 3. For HL 1, flashover is not influenced by humidity. Dimensioning according to the
clearances of Table 2 and Table 3 is applicable.
NOTE 1 The influence of the water adsorption characteristics on the surface flashover withstand capability is
strongly dependent on the distance. For distances larger than 2 mm this influence is rather small. For distances
equal to or less than 2 mm this influence is of very high significance.
NOTE 2 There is no physical relationship between the minimum clearance in air and the minimum acceptable
creepage distance, except for dimensioning to avoid flashover.
If creepage distances according to Table 5 are stressed with steady-state voltages in excess
of approximately 500 V (peak), partial discharges (corona) can be expected. Also with respect
to this effect, the ranking of the insulating materials is according to the relevant adsorption
characteristics (see Clause 7).
NOTE 3 As partial discharges at the polluted insulator surface are caused by local micro-disturbances of the field
distribution in the surface layer, the shape of the electrodes is of secondary influence on this phenomenon.

– 18 – IEC TR 63040:2016 © IEC 2016
Table 4 – Creepage distances for mutual correlation of insulation
characteristics in equipment to avoid failure due to tracking
b c
Minimum creepage distances in millimetres

a
Voltage Pollution Pollution Pollution
r.m.s degree 1 degree 2 degree 3
MG I, II, IIIa MG I, II and IIIa MG I MG II MG IIIa

and IIIb
V mm mm mm mm mm
0,025 0,04 1,0 1,0 1,0
≤ 40
50 0,025 0,04 1,0 1,0 1,0
63 0,04 0,06 1,0 1,0 1,0
80 0,063 0,10 1,0 1,1 1,25
100 0,1 0,16 1,25 1,4 1,6
125 0,16 0,25 1,6 1,8 2,0
160 0,25 0,40 2,0 see IEC 60664-1 see IEC 60664-1
200 0,4 0,63 see IEC 60664-1
250 0,56 1,0
320 0,75 1,6
400 1 2
500 1,3 see the column
for printed wiring
material in
IEC 60664-1
630 1,8
800 see the column
for printed wiring
material in
IEC 60664-1
a
For functional insulation, this voltage is the working voltage.
b
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 mutual correlation of insulation characteristics. The
dimensions of Table 2 or Table 3 for inhomogeneous field conditions are appropriate. However, the behaviour
with regard to flashover according to Table 5 is taken into account.
c
The values given in this table are informative and cannot replace the values given in IEC 60664-1.

Figure 2 illustrates Table 4.
PD 1: MG I - III
PD 2: MG I - IIIa
PD 3: MG I
PD 3: MG II
0,1
PD 3: MG IIIa
0,01
10 100 1 000
U (r.m.s.)
IEC1
NOTE See also Table 4 from which the figure is derived.
Figure 2 – Creepage distances for mutual correlation of insulation
characteristics to avoid failure due to tracking
d (mm)
– 20 – IEC TR 63040:2016 © IEC 2016
Table 5 – Creepage distanc
...