IEC 62631-3-2:2023

IEC 62631-3-2 ®
Edition 2.0 2023-10
COMMENTED VERSION
INTERNATIONAL
STANDARD
colour
inside
Dielectric and resistive properties of solid insulating materials –
Part 3-2: Determination of resistive properties (DC methods) – Surface
resistance and surface resistivity
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IEC 62631-3-2 ®
Edition 2.0 2023-10
COMMENTED VERSION
INTERNATIONAL
STANDARD
colour
inside
Dielectric and resistive properties of solid insulating materials –
Part 3-2: Determination of resistive properties (DC methods) – Surface
resistance and surface resistivity
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 17.220.99, 29.035.01   ISBN 978-2-8322-7699-0

– 2 – IEC 62631-3-2:2023 CMV © IEC 2023
CONTENTS
FOREWORD .4
1 Scope .6
2 Normative references .6
3 Terms and definitions .6
4 Significance .8
5 Method of test .9
5.1 General .9
5.2 Voltage .9
5.3 Equipment .9
5.3.1 General .9
5.3.2 Accuracy . 10
5.3.3 Voltage source . 10
5.3.4 Electrode arrangements . 10
5.4 Test circuit . 15
5.5 Calibration . 16
5.6 Test specimen . 16
5.6.1 Recommended dimensions of test specimen and electrode
arrangements . 16
5.6.2 Manufacturing of test specimen . 16
5.6.3 Number of test specimens . 17
5.6.4 Application of electrodes conductive means . 17
5.6.5 Conditioning and pre-treatment of test specimen . 17
5.7 Test procedure . 18
6 Evaluation Calculation of surface resistivity . 18
6.1 For electrode arrangements A, B, D and E. 18
6.2 For electrode arrangement C . 18
7 Test report . 19
8 Repeatability and reproducibility . 19
Annex A (informative) Specimen dimensions and electrode arrangements . 20
Annex B (informative) Comparative verification study on surface resistivities using
different electrode arrangements (type C and type E) . 21
B.1 General . 21
B.2 Inter-laboratory trial conditions . 21
B.2.1 General . 21
B.2.2 Test specimens . 21
B.2.3 Electrode types, conductive materials and test voltage . 21
B.2.4 Test conditions . 22
B.3 Summary of the test results . 22
B.4 Inter-laboratory trial outcomes and suggestions for IEC 62631-3-2 . 23
B.5 Detailed inter-laboratory results . 23
B.5.1 General . 23
B.5.2 Laboratories results by different groups of electrode types and
conductive materials for the different test specimens . 24
B.5.3 Laboratory 2 results comparing different electrode types and conductive
materials . 30
B.5.4 Laboratory 3 results – Electrode type C with and without use of
conductive silver paint . 32

Bibliography . 34
List of comments . 35

Figure 1 – Electrode arrangement A (example) . 11
Figure 2 – Collector electrode for electrode arrangement B Electrode arrangement B
(example) . 12
Figure 3 – Electrode arrangement C (example) . 13
Figure 4 – Connection diagram of measurement with two- and three-terminal electrode
arrangements . 16
Figure B.1 – Surface resistivity equations for the used electrodes . 22

Table 1 – Typical electrode dimensions for electrode arrangement C . 14
Table A.1 – Recommended test specimen dimensions and electrode arrangements for
specific products . 20
Table B.1 – Test specimens characteristics . 21
Table B.2 – Test conditions per specific participant . 22
Table B.3 – Summary of the test results . 23
Table B.4 – Polybutylene terephthalate (PBT) test specimen results – Electrode type C
with conductive rubber . 24
Table B.5 – Polyamide 66 (PA66) test specimen results – Electrode type C with
conductive rubber . 25
Table B.6 – Polybutylene terephthalate (PBT) test specimen results – Electrode type C
with conductive silver paint . 26
Table B.7 – Polyamide 66 (PA66) test specimen results – Electrode type C with
conductive silver paint . 27
Table B.8 – Polybutylene terephthalate (PBT results) test specimen results – Electrode
type E with conductive silver paint . 28
Table B.9 – Polyamide 66 (PA66) test specimen results – Electrode type E with
conductive silver paint . 29
Table B.10 – Laboratory 2 results – Polybutylene terephthalate (PBT) – Different
electrodes and conductive materials . 30
Table B.11 – Laboratory 2 results – Polyamide 66 (PA66) – Different electrodes and
conductive materials . 31
Table B.12 – Laboratory 3 results – Polybutylene terephthalate (PBT) – Electrode type
C with and without conductive silver paint . 32
Table B.13 – Laboratory 3 results – Polyamide 66 (PA66) – Electrode type C with and
without conductive silver paint . 33

– 4 – IEC 62631-3-2:2023 CMV © IEC 2023
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
DIELECTRIC AND RESISTIVE PROPERTIES
OF SOLID INSULATING MATERIALS –

Part 3-2: Determination of resistive properties (DC methods) –
Surface resistance and surface resistivity

FOREWORD
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This commented version (CMV) of the official standard IEC 62631-3-2:2023 edition 2.0
allows the user to identify the changes made to the previous IEC 62631-3-2:2015
edition 1.0. Furthermore, comments from IEC TC 112 experts are provided to explain the
reasons of the most relevant changes, or to clarify any part of the content.
A vertical bar appears in the margin wherever a change has been made. Additions are in
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This publication contains the CMV and the official standard. The full list of comments is
available at the end of the CMV.

IEC 62631-3-2 has been prepared by IEC technical committee 112: Evaluation and qualification
of electrical insulating materials and systems. It is an International Standard.
This second edition cancels and replaces the first edition published in 2015. This edition
constitutes a technical revision.
This edition includes the following significant technical changes with respect to the previous
edition:
a) descriptions of the electrode arrangements have been clarified;
b) new descriptions of the conductive means have been added;
c) a new informative Annex B summarizing the results of the comparative verification study on
surface resistivities using different electrode arrangements has been added.
The text of this International Standard is based on the following documents:
Draft Report on voting
112/612/FDIS 112/619/RVD
Full information on the voting for its approval can be found in the report on voting indicated in
the above table.
The language used for the development of this International Standard is English.
This document was drafted in accordance with ISO/IEC Directives, Part 2, and developed in
accordance with ISO/IEC Directives, Part 1 and ISO/IEC Directives, IEC Supplement, available
at www.iec.ch/members_experts/refdocs. The main document types developed by IEC are
described in greater detail at www.iec.ch/publications.
A list of all parts in the IEC 62631 series, published under the general title Dielectric and
resistive properties of solid insulating materials, can be found on the IEC website.
The committee has decided that the contents of this document will remain unchanged until the
stability date indicated on the IEC website under webstore.iec.ch in the data related to the
specific document. At this date, the document will be
• reconfirmed,
• withdrawn, or
• revised.
IMPORTANT – The "colour inside" logo on the cover page of this document indicates
that it contains colours which are considered to be useful for the correct understanding
of its contents. Users should therefore print this document using a colour printer.

– 6 – IEC 62631-3-2:2023 CMV © IEC 2023
DIELECTRIC AND RESISTIVE PROPERTIES
OF SOLID INSULATING MATERIALS –

Part 3-2: Determination of resistive properties (DC methods) –
Surface resistance and surface resistivity

1 Scope
This part of IEC 62631 covers describes 1 methods of test for the determination of surface
resistance and surface resistivity of electrical insulation materials by applying DC voltage.
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 60212, Standard conditions for use prior to and during the testing of solid electrical
insulating materials
IEC 62631-3-1, Dielectric and resistive properties of solid insulating materials – Part 3-1:
Determination of resistive properties (DC methods) – Volume resistance and volume resistivity
– General method
IEC 62631-3-3, Dielectric and resistive properties of solid insulating materials – Part 3-3:
Determination of resistive properties (DC methods) – Insulation resistance
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminology databases for use in standardization at the following
addresses:
• IEC Electropedia: available at https://www.electropedia.org/
• ISO Online browsing platform: available at https://www.iso.org/obp
3.1
electrode arrangement
electrical conductive bodies on the surface of a test specimen
Note 1 to entry: The arrangement of electrodes should include procedures to ascertain sufficient contact to the
surface (e.g. by means of conducting paint) and/or the use of adequate mechanical system applying the necessary
contact force to the test specimen's surface or both.
___________
To be published.
3.1.1
annular electrode
central circular planar electrode with a surrounding ring electrode separated by a gap
SEE: Figure 3.
Note 1 to entry: Guarded electrode systems as described in IEC 62631-3-1 IEC 62321-3-1 are of similar shape. In
the case of surface resistance, the ring electrode does not have the function of a guard; guard functionality, however,
is provided by the opposite electrode.
3.1.2
line electrode
electrode arrangement provided by two parallel lines, separated by a gap, applied to the test
specimen's surface using a conductive material
SEE: Figure 2.
3.1.3
spring loaded electrode
line electrode system using two parallel lines of conducting spring tongues with sharp edges,
separated by a gap
SEE: Figure 1.
3.2
measured resistance
ratio of a DC voltage applied to an electrode arrangement in contact with a test specimen to the
current between them measured with sufficient precision
Note 1 to entry: A three-terminal electrode arrangement may can 2 be used to exclude undesired volume currents
from the determination of the measured resistance.
Note 2 to entry: A Wheatstone bridge may can 3 also be used to compare the measured resistance with a standard
resistor. However, Wheatstone bridges are not commonly used anymore.
Note 3 to entry: According to IEC 60050-121: Electromagnetism, "conductivity" (IEV 121-12-03) 4 is defined as
"the scalar or tensor quantity, the product of which by the electric field strength in a medium is equal to the electric
current density" and "resistivity" (IEV 121-12-04) as "the inverse of the conductivity when this inverse exists".
Measured in this way, the surface resistivity is an average of the resistivity over possible heterogeneities in the
volume incorporated in the measurement; it includes the effect of possible polarization phenomena at the electrodes.
Measured in this way, the surface resistivity integrates different electrical conduction pathways at the surface of the
material or in its nearby volume, with the possible presence of heterogeneities; it includes the effect of possible
polarization phenomena at the electrodes. Therefore, it is considered as an averaged value. 5
3.3
surface resistance
R
S
measured resistance between any electrode arrangement defined in IEC 62361-3-2
Note 1 to entry: Depending on the electrode arrangement used, it is designated as R , R , R , R or R with
SA SB SC SD SE
surface resistance, R expressed in Ω.
S
Note 2 to entry: An indeterminable part of the resistance inside the material is also included in surface resistance
during the measurement of this resistance.
3.4
R
SC
surface resistance between annular electrodes
measured resistance between the inner circular area of an annular electrode system and the
outer circular ring electrode
– 8 – IEC 62631-3-2:2023 CMV © IEC 2023
3.5
R
SD
surface resistance between line electrodes
measured resistance between line electrodes
3.6
R
SE
surface resistance between line electrodes for small plates
measured resistance between line electrodes for small plates
3.7
R
SB
surface resistance between small line electrodes
measured resistance between small line electrodes
3.8
R
SA
surface resistance between spring loaded electrodes
measured resistance between spring loaded electrodes
3.9
surface resistivity
σ/square
, R , R R or R referred to a square, expressed as σ , σ , σ , σ
surface resistance R
SA SB SC, SD SE A B C D
and σ respectively
E
Note 1 to entry: Surface resistivity σ , σ and σ is expressed by the unit Ω.
C D E
surface resistance reduced to a square
Note 1 to entry: The numerical value of surface resistivity is independent of the size of the square.
Note 2 to entry: Surface resistance R , R , R , R and R referred to a square, are expressed as σ , σ , σ ,
SA SB SC SD SE A B C
σ and σ respectively.
D E
Note 32 to entry: Surface resistivity is often expressed by the non-standardized unit Ω per square, to show that the
electrode dimension has been taken into account by calculating the specific value.
Note 43 to entry: The surface resistivity is often used to compare one kind of surface characteristic of a sample
material with those of other materials. It can be compared for materials only if identical standardized dimensions of
the electrodes are used. Recommended dimensions are given in 5.3. 6
4 Significance
Insulating materials are used in general to electrically isolate components of an electrical
system from each other and from the earth. Solid insulating materials can also provide
mechanical support. For this purpose, it is generally desirable to have the insulation resistance
as high as possible, consistent with acceptable mechanical, chemical and heat resistance
properties.
Surface resistance is, as volume resistance, a part of the insulating resistance.
Insulating resistance shall be determined according to IEC 62631-3-3 and volume resistance
according to IEC 62631-3-1.
Surface resistance supplies information on the electrical resistances on of 7 the surface of
materials and products. The surface resistance also permits monitoring of changes in the
resistance by external effects. 8 Surface resistance, however, for its major part is not a

materials' property. Surface resistance depends mainly on processing parameters,
environmental conditions, surface ageing phenomena and pollution, etc.
NOTE Depending on the specific application, different electrode arrangements can be preferable. 9
5 Method of test
5.1 General
This general method describes common values for general measurements. If a method for a
specific type of material is described in this document, the specific method shall be used.
Different types of electrodes can be used, depending on the specific measurement or product
demands. For instance, on surfaces with a curved shape, a small line electrode can be
advantageous. Spring loaded electrodes provide measurements with low effort on products and
are optimal for materials which have to be conditioned before the test. If not already stipulated
by a product standard, the choice of the electrode arrangement shall be made considering the
typical application.
If test specimens are made from materials (e.g. soft rubber) changing their whose dimensions
will change significantly when applying as a result of the force applied by the electrodes on
them 10, these electrodes are not applicable and an alternative arrangement shall be used.
If no information about the application is available, small line electrodes (R ) are
SB
recommended.
5.2 Voltage
The measuring voltage shall should 11 preferably be 10 V, 100 V, 500 V, 1 000 V, 10 000 V.
Other voltages may be applicable. If not otherwise stipulated specified by the relevant product
standard 12, a voltage of 100 V shall be used.
Technical committees shall specify the preferred test voltage when referring to this document. 13
NOTE 1 Partial discharge can lead to erroneous measurements when a specific inception voltage is exceeded. In
air, below 340 V, no partial discharges will occur.
−5
NOTE 2 The ripple of the voltage source is important. A typical value for 100 V is < 5 × 10 peak to peak.
5.3 Equipment
5.3.1 General
Care should be taken that the surface resistance is not negatively influenced by parasitic
resistances parallel to the electrode arrangement, such as the resistance of test supports or
cable isolation.
To prevent measuring errors for measured resistances higher than 10 Ω, shielded cables and
shielded measuring cabinets shall be used.
For the determination of surface resistance and surface resistivity, different electrode
arrangements can be used. The evaluation of surface resistivity is dependent on the selected
electrode arrangement.
NOTE Comparison between measurement results can be done only between measurements performed using the
same electrode arrangements and conductive means. 14

– 10 – IEC 62631-3-2:2023 CMV © IEC 2023
5.3.2 Accuracy
Any suitable equipment can be used. The measuring device shall be capable of determining the
unknown resistance with an overall accuracy of at least
• ±10 % for resistances less than 10 Ω;
10 14
• ±20 % for resistances between 10 Ω and 10 Ω; and
• ±50 % for values resistances higher than 10 Ω. 15
NOTE The provided accuracies have been confirmed through the round robin test results reported in Annex B. 16
5.3.3 Voltage source
A source of very steady direct voltage is required. This can be provided either by batteries or
by rectified and stabilized power supply. The degree of stability required is such that the change
in current due to any change in voltage is negligible compared with the current to be measured.
5.3.4 Electrode arrangements 17
5.3.4.1 General
Electrode arrangements consist of the combination of electrodes and conductive means. The
conductive means shall be applied to the test specimen before performing the measurements.
Electrodes are then placed in contact with the conductive means applied on the test specimen
in order to perform measurements. 18
NOTE Annex B contains the results of the comparative verification study on surface resistivities using different
electrode arrangements.
5.3.4.2 Electrode arrangement A – Spring loaded electrodes
The electrode arrangement A shall consist of two flexible metal knife-edges with a length of
100 mm and a gap distance of 10 mm as shown in Figure 1.
No guard electrode is used. The metal knife-edges shall consist of individual spring tongues
arranged next to each other about 0,3 mm apart and each with a length not exceeding 5,0 mm
and 0,3 mm thick. The contact force shall be high enough so that all tongues or segments rest
against the surface of the test specimen, but without damaging the surface.
A piece of metal exerting the contact force should shall 19 be applied with high-grade insulation
where in contact with the specimen.

Dimensions in millimetres
Key
1 guide bar (detachable)
2 metal knife-edges
3 specimen
Figure 1 – Electrode arrangement A (example)
5.3.4.3 Electrode arrangement B – Small line electrodes
Electrode arrangement B shall consist of two adhering line electrodes. No guard electrode is
used. For this purpose, two 1,5 mm wide lines with a length of 25 mm and a gap distance of
2 mm apart shall be applied, e.g. with conductive silver. They shall be applied before the
conditioning. The lines shall be contacted using a two terminal collector electrode arrangement
with conductive blades in attach to them (see Figure 2).

– 12 – IEC 62631-3-2:2023 CMV © IEC 2023
Electrode arrangement B shall consist of a two-terminal collector with conductive blades being
in contact with the conductive means on the test specimen, as shown in Figure 2. No guard
electrode is used.
For the purpose of electrode arrangement B, conductive means shall be applied as two 1,5 mm
wide lines with a length of 25,0 mm and a gap distance of 2,0 mm. Lines shall be applied before
conditioning. 20
Types of conductive means and the related applications are described in 5.6.4. 21

Figure 2 – Collector electrode for electrode arrangement B
Electrode arrangement B (example)
5.3.4.4 Electrode arrangement C – Annular electrodes
Electrode arrangement C is a three-terminal electrode system, as shown in Figure 3. On one
side of the test specimen, annular electrodes are applied. The opposite surface of the test
specimen is to shall 22 be covered by a guard electrode, not smaller than the area covered by
the corresponding electrodes. Adhesive electrodes can be applied before the conditioning (see
5.6.3).
Key
1 specimen
2 electrode 1
3 measuring area
4 electrode 2
5 electrode 3 (guard electrode)

d
d
d
m
d
IEC
Key 23
1 specimen
2 electrode 1
3 measuring area
4 electrode 2
5 electrode 3 (guard electrode)
a thickness of the test specimen
d electrode 1 diameter
d electrode 2 internal diameter
d electrode 2 external diameter
d median diameter of measuring area
m
Figure 3 – Electrode arrangement C (example) 24

a
– 14 – IEC 62631-3-2:2023 CMV © IEC 2023
Any electrode dimensions can be used, unless otherwise stipulated specified by the relevant
product standard 25. Typical electrode dimensions are given in Table 1. For comparison tests,
electrode arrangement C1 is recommended.
Table 1 – Typical electrode dimensions for electrode arrangement C
d d d
1 2 3
Electrode arrangement
mm mm mm
C1 50 60 80
C2 76 88 100
C3 25 38 50
With electrode arrangement C, the surface resistance between electrode 1 and electrode 2 shall
be measured. Electrode 3 shall be earthed.
Either of the conductive means described in 5.6.4 shall be placed or painted on the surface
areas where electrode 1, electrode 2 and electrode 3 are placed. The conductive means shall
not be applied on the surface between electrode 1 and electrode 2. 26
NOTE In the case of materials with limited conductivity and also occasionally films having a thickness of ≤ 10 µm,
it shall be noted that the input resistance of the ammeter is significantly smaller than the volume resistance of the
test specimen. 27
5.3.4.5 Electrode arrangement D – Line electrodes
Electrode arrangement D shall consist of two adhering line electrodes. No guard electrode is
used. The electrode dimensions are correspondent to electrode arrangement A with regard to
the electrode length and distance between electrodes. No guard electrode is used.
For this purpose, two parallel 1,5 mm wide lines with a length of (100 ± 1) mm and a gap
distance of (10 ± 0,5) mm apart shall be applied, e.g. with conductive silver. They can be
applied before the treatment. The lines shall be contacted using a two terminal collector
electrode arrangement with conductive blades attached to them (see Figure 2).
Electrode arrangement D shall consist of a two-terminal collector electrode arrangement with
conductive blades being in contact with the conductive means on the test specimen, as shown
in Figure 2. No guard electrode is used.
For the purpose of electrode arrangement D, the conductive means shall be applied as two
parallel 1,5 mm wide lines with a length of (100,0 ± 1,0) mm and a gap distance of
(10,0 ± 0,5) mm. They can be applied before the treatment.
The types of conductive means and the related applications are described in 5.6.4. 28
5.3.4.6 Electrode arrangement E – Line electrodes for small plates
Electrode arrangement E is a three terminal line electrode system. For this purpose, two parallel
1 mm to 2 mm wide lines with a length of (50 ± 1) mm and a gap distance of (5 ± 0,5) mm apart
shall be applied, e.g. with conductive silver.
The opposite surface of the test specimen is to be covered by a guard electrode not smaller
than the area covered by the corresponding electrodes. The electrodes can be applied before
conditioning of the test specimen. The lines shall be contacted using a three terminal collector
electrode arrangement (see Figure 4b).

NOTE Electrode arrangement E is preferable when small plates (≥ 60 mm × ≥ 60 mm) according to ISO 10350 are
in use.
Electrode arrangement E consists of a three-terminal collector electrode as shown in Figure 4,
item B).
For the purpose of electrode arrangement E the conductive means shall be applied as two
parallel 1,0 mm to 2,0 mm wide lines with a length of (50,0 ± 1,0) mm and a gap distance of
(5,0 ± 0,5) mm that can be applied before conditioning of the test specimen.
The opposite surface of the test specimen shall be covered by a guard electrode not smaller
than the area covered by the corresponding electrodes.
Types of conductive means and the related applications are described in 5.6.4.
NOTE Examples of combination of electrode types and dimensions of test specimens are provided in Annex A. 29
5.4 Test circuit
Depending on the electrode arrangement selected, two- or three-terminal measurements shall
be carried out (see Figure 4).
For annular electrodes (electrode arrangement C) and line electrode arrangement E,
a three-terminal test circuit is necessary as a grounded protective electrode is mandatory.
For any other line electrode arrangement (A, B and D), a two-terminal test circuit shall be used.

– 16 – IEC 62631-3-2:2023 CMV © IEC 2023

Key
a voltage source
b voltmeter
c ammeter
d electrode 1
e electrode 2 (shielded electrode)
f electrode 3 (protective electrode)
g specimen
Figure 4 – Connection diagram of measurement with two- and
three-terminal electrode arrangements
5.5 Calibration
The equipment shall be calibrated in the magnitude of the surface resistance measured.
NOTE Calibration resistors in a range up to 100 TΩ are commercially available.
5.6 Test specimen
5.6.1 Recommended dimensions of test specimen and electrode arrangements
The specimen’s dimensions need shall 30 be sufficient to apply the selected electrode
arrangement. Recommendations for products are given in Annex A.
5.6.2 Manufacturing of test specimen
The production and shape of the test specimen shall be determined by the relevant standards
for the material. During removal and production of the specimen, the condition of the material
shall not be changed and the specimen removed shall not be damaged.
If the surface of the test specimen is machined at the contact areas of the electrodes, the type
of machining shall be specified in the test report. The test specimen shall have a geometrically
simple shape (plate with parallel measuring areas, cylinder, etc.).

NOTE Machining of the test specimen can be performed on the specimen when it is representative of the application
target for the materials. 31
Specimen from products shall be prepared with the product thickness, if possible.
5.6.3 Number of test specimens
The number of test specimens to be tested shall be determined by the relevant product
standards. If no such data is available, at least three specimens shall be tested.
5.6.4 Application of electrodes conductive means 32
5.6.4.1 General
When using adhesive electrodes conductive means 33 (electrode arrangements B, C, D and E),
care shall be taken, ensure 34 that a proper contact is provided over the whole area covered
by the electrode 35. The electrode material conductive means 36 used shall, after an
appropriate time of conditioning, not influence the measured values for surface resistance.
NOTE 1 Conductive silver paint and suspensions of graphite have been found appropriate.
NOTE 2 Annex B contains the results of the comparative verification study on surface resistivities using different
electrode arrangements and conductive means. 37
5.6.4.2 Conductive silver paint
Certain types of commercially available, high-conductivity silver paints, either air-drying or low-
temperature-baking varieties, are sufficiently porous to permit diffusion of moisture through
them and thereby allow the test specimens to be conditioned after application of the conductive
means. This is a particularly useful feature in studying resistance-humidity effect as well as
changes with temperature. However, before conductive paint is used as a conductive means, it
should be established that the paint solvent does not affect the electrical properties of the
specimen. Reasonably smooth edges for use with guard electrodes can be obtained with a
fine-bristle brush. However, for use with circular electrodes, sharper edges can be obtained by
the use of a compass for drawing the outline circles of the electrodes and filling in the enclosed
areas by brush. Clamp-on masks can be used if the conductive paint is sprayed on. 38
5.6.4.3 Colloidal graphite
Colloidal graphite dispersed in water or other suitable medium, can be used under the same
conditions as given for conductive silver paint. 39
5.6.4.4 Conducting rubber
Conducting rubber can be used as conductive means. It has the advantage that it can be applied
and removed from the specimen quickly and easily. Since the conductive means are applied
only during the time of measurement, they do not interfere with the conditioning of the specimen.
The resistance of the rubber electrode shall be less than 1 000 Ω.
The conducting rubber material shall be soft enough to ensure that effective contact to the
specimen is obtained when a reasonable pressure, for example 2 kPa (0,2 N/cm ), is applied.
Shore A hardness according to ISO 48-4 in the range of 65 to 85 has been found suitable.
NOTE The results of resistivity measurements obtained with the application of electrodes made of conducting rubber
are always higher (few tens to few hundreds per cent) in comparison to that obtained for metallic electrodes. 40
5.6.5 Conditioning and pre-treatment of test specimen
Conditioning and any other pre-treatment of the test specimen shall be carried out according to
the relevant product standard.

– 18 – IEC 62631-3-2:2023 CMV © IEC 2023
If no product standard exists, conditioning shall be realized for at least four days at 23 °C and
50 % RH in accordance with IEC 60212 (standard climate B).
If not otherwise stipulated specified by the relevant product standard 41, no cleaning of the test
specimen shall be done. Any additional contamination shall be avoided.
5.7 Test procedure
Unless otherwise agreed specified 42, the measurement shall be conducted in normal air at
23 °C and 50 % RH in accordance with IEC 60212 (standard climate B).
The specimen shall be conditioned and pre-treated in accordance with 5.6.5. Immediately after
the treatment, the electrodes shall be connected with the measuring device.
Subsequently, but no more than 2 min after finishing the conditioning or pre-treatment, the
surface resistance R shall be determined between the electrodes. If not otherwise stipulated
S
specified 43, it shall be measured 1 min after voltage application.
NOTE Experience from the application of this test evidenced that, for material design and research purposes,
reaching the stabilization of the current before measuring the surface resistance provides better results. 44
6 Evaluation Calculation of surface resistivity 45
6.1 For electrode arrangements A, B, D and E
The measured value R for the respective
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