IEC 62631-3-12:2024

Dielectric and resistive properties of solid insulating materials - Part 3-12: Determination of resistive properties (DC methods) - Volume resistance and volume resistivity - Method for casting resins

IEC 62631-3-12:2024 specifies a method of test for the determination of volume resistance and volume resistivity of electrical insulation materials by applying a DC voltage. It covers casting resins described in IEC 60455-3-1, IEC 60455-3-2, IEC 60455-3-3, IEC 60455-3-4, IEC 60455-3-8 and similar products.
For other specific types of materials, other standards or the general method described in IEC 62631-3-1 can be more suitable.

Propriétés diélectriques et résistives des matériaux isolant solides - Partie 3-12: Détermination des propriétés résistives (méthodes en courant continu) - Résistance volumique et résistivité volumique - Méthode pour résines de coulée

L’IEC 62631-3-12:2024 spécifie la méthode d'essai pour la détermination de la résistance volumique et de la résistivité volumique des matériaux isolants électriques par l'application d'une tension continue. Elle couvre les résines de coulée décrites dans l’IEC 60455-3-1, l’IEC 60455-3-2, l’IEC 60455-3-3, l’IEC 60455-3-4, l’IEC 60455-3-8 et les produits analogues.
Pour d'autres types de matériaux spécifiques, d'autres normes ou la méthode générale décrite dans l’IEC 62631-3-1 peuvent être plus appropriées.

General Information

• Status: Published
• Publication Date: 04-Jul-2024
• ICS: 17.220.99 - Other standards related to electricity and magnetism
• ICS: 29.035.01 - Insulating materials in general
• Technical Committee: TC 112 - Evaluation and qualification of electrical insulating materials and systems
• Drafting Committee: WG 4 - TC 112/WG 4
• Current Stage: PPUB - Publication issued
• Start Date: 05-Jul-2024
• Completion Date: 02-Aug-2024

Standards Content (Sample)

IEC 62631-3-12 ®
Edition 1.0 2024-07
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Dielectric and resistive properties of solid insulating materials –
Part 3-12: Determination of resistive properties (DC methods) – Volume
resistance and volume resistivity – Method for casting resins

Propriétés diélectriques et résistives des matériaux isolant solides –
Partie 3-12: Détermination des propriétés résistives (méthodes en courant
continu) – Résistance volumique et résistivité volumique – Méthode pour
résines de coulée
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IEC 62631-3-12 ®
Edition 1.0 2024-07
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Dielectric and resistive properties of solid insulating materials –

Part 3-12: Determination of resistive properties (DC methods) – Volume

resistance and volume resistivity – Method for casting resins

Propriétés diélectriques et résistives des matériaux isolant solides –

Partie 3-12: Détermination des propriétés résistives (méthodes en courant

continu) – Résistance volumique et résistivité volumique – Méthode pour

résines de coulée
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
INTERNATIONALE
ICS 17.220.99, 29.035.01 ISBN 978-2-8322-9299-0

– 2 – IEC 62631-3-12:2024 © IEC 2024
CONTENTS
FOREWORD . 3
INTRODUCTION . 5
1 Scope . 6
2 Normative references . 6
3 Terms and definitions . 6
4 Significance . 7
5 Method of test . 7
5.1 General . 7
5.2 Power supply and voltage . 7
5.3 Equipment . 8
5.3.1 Accuracy . 8
5.3.2 Guarding . 8
5.3.3 Electrodes . 8
5.3.4 Calibration . 8
5.4 Test specimen . 8
5.5 Procedure for volume resistivity as function of temperature . 8
5.5.1 General . 8
5.5.2 Equipment . 9
5.5.3 Test set-up . 9
5.5.4 Procedure . 9
5.5.5 Calculation . 9
5.6 Procedure for volume resistivity after seven days of immersion into water . 9
5.6.1 General . 9
5.6.2 Equipment . 10
5.6.3 Test set-up . 10
5.6.4 Procedure . 10
5.6.5 Calculation . 10
6 Report . 10
7 Repeatability and reproducibility . 11
Bibliography . 12

INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
DIELECTRIC AND RESISTIVE PROPERTIES
OF SOLID INSULATING MATERIALS –

Part 3-12: Determination of resistive properties (DC methods) –
Volume resistance and volume resistivity – Method for casting resins

FOREWORD
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IEC 62631-3-12 has been prepared by IEC technical committee 112: Evaluation and
qualification of electrical insulating materials and systems. It is an International Standard.
The text of this International Standard is based on the following documents:
Draft Report on voting
112/645/FDIS 112/652/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.

– 4 – IEC 62631-3-12:2024 © IEC 2024
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.
INTRODUCTION
Many segments of the electrotechnical industry use volume resistance and volume resistivity
data of solid insulating materials. This part of the IEC 62631-3 series is focused on the method
for casting resins. Clear guidelines will provide the user of this document a uniform approach
to sample preparation and test procedures.

– 6 – IEC 62631-3-12:2024 © IEC 2024
DIELECTRIC AND RESISTIVE PROPERTIES
OF SOLID INSULATING MATERIALS –

Part 3-12: Determination of resistive properties (DC methods) –
Volume resistance and volume resistivity – Method for casting resins

1 Scope
This part of IEC 62631 specifies a method of test for the determination of volume resistance
and volume resistivity of electrical insulation materials by applying a DC voltage. It covers
casting resins described in IEC 60455-3-1, IEC 60455-3-2, IEC 60455-3-3, IEC 60455-3-4,
IEC 60455-3-8 and similar products.
For other specific types of materials, other standards or the general method described in
IEC 62631-3-1 can be more suitable.
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 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
ISO 2808, Paints and varnishes – Determination of film thickness
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
volume resistance
part of the insulation resistance which is due to conduction through the volume
Note 1 to entry: Volume resistance is expressed in Ω.

3.2
volume resistivity
ratio of the potential gradient (parallel to the current in a material) to the current density
Note 1 to entry: Volume resistivity is expressed in ohm metre (Ω m).
Note 2 to entry: For insulating materials the volume resistivity is usually determined by means of measuring
electrodes arranged on a sheet of the material.
Note 3 to entry: According to IEC 60050-121, "conductivity" (IEV 121-12-03) is defined as "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"
as "the inverse of the conductivity when this inverse exists". Measured in this way, the volume 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.
4 Significance
The materials applicable to the test method described in this document are used to cast
electrical or electronic equipment to fix the construction, protect it from humidity, dirt and other
environmental influence. Main field applications are electric motors, transformers, electronic
devices and similar appliances.
Additional electrical insulation is desirable but not essential. In many cases mechanical support,
thermal and chemical resistance are more important. In particular, the changes in resistivity
with temperature or humidity, or both, are of great importance and need to be known when
designing the equipment for operation conditions.
When a direct voltage is applied between electrodes in contact with a specimen, the current
through it decreases asymptotically towards a steady-state value. The decrease of current with
time can be due to dielectric polarization and the sweep of mobile ions to the electrodes. For
materials having a volume resistivity less than about 10 Ω m the steady state is generally
reached within 1 min and the resistance is determined after this time of electrification. For
materials with higher volume resistivity the current can continue decreasing for several minutes,
hours, days or even weeks. However, the result is taken after one minute.
NOTE For very high electric field strengths different behaviours can occur.
5 Method of test
5.1 General
The method described in this document is used for casting resins. For other specific types of
materials other standards or the general method described in IEC 62631-3-1 can be more
suitable.
For a casting resin the absolute value of volume resistance or resistivity is of minor interest.
More important is the change of this value as a function of temperature or after immersion into
water.
5.2 Power supply and voltage
A source of very steady direct voltage is required. This may 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
NOTE The ripple of the voltage source is important. A typical value for 100 V is < 5 × 10 peak to peak.
A voltage of 500 V shall be used, if not otherwise stipulated. Other test voltages may be 10 V,
100 V or 1 000 V.
– 8 – IEC 62631-3-12:2024 © IEC 2024
To avoid migration effects during measurement, the field strength shall be less than
3 000 V/mm.
5.3 Equipment
5.3.1 Accuracy
The measuring device shall be capable of determining the unknown resistance with an overall
accuracy of at least:
• ±10 % for resistances below 10 Ω;
10 14
• ±20 % for resistances between 10 Ω and 10 Ω;
• ±50 % for values higher than 10 Ω.
5.3.2 Guarding
For routine measurements, especially in production control to determine the specified minimum
values, guarding is not necessary. This allows smaller and simplified specimens.
If the exact absolute value is of interest, or the value is above 10 Ω, or in case of doubt,
guarding is recommended. Further information related to guarding can be found in
IEC 62631-3-1.
5.3.3 Electrodes
For simple measurements a permanent electrode (e.g. conductive silver paint) may be used.
In case of measurements before and after a treatment (e.g. immersion into water) a removable
electrode shall be used. Further information related to electrodes can be found in
IEC 62631-3-1.
5.3.4 Calibration
The equipment shall be calibrated in the magnitude of the volume resistance measured.
NOTE Calibration resistors in the range up to 100 TΩ are commercially available.
5.4 Test specimen
A casted plate of resin with a length and a width of at least 60 mm shall be used, unless
otherwise specified.
The casting resin shall be mixed in accordance with the manufacturer's instructions, degassed
and poured into a mould. A closed mould is preferred, however if an open mould is necessary,
precautions shall be taken to obtain flat, smooth and plan parallel surfaces.
The thickness of the resin after curing shall be determined by one of the procedures specified
in ISO 2808. Do not intentionally use specimens with widely different thickness. The thickness
shall be not less than 0,5 mm.
5.5 Procedure for volume resistivity as function of temperature
5.5.1 General
The following procedure describes an established method used for quality control and is meant
as an example. Any other method in line with the general requirements may be used. However,
measuring parameters (time, temperatures, environmental influences, etc.) can vary widely and
are dependent on the purpose of the measurement and the intended use of the material.

5.5.2 Equipment
The following equipment shall be used:
• tera-ohmmeter according to 5.3;
• metal cylinder to be used as voltage electrode (top electrode) of at least 40 mm diameter
having a mass to provide a pressure of about 0,015 MPa;
• conductive silver paint.
5.5.3 Test set-up
Three specimens shall be tested. The thickness of each specimen shall be measured at least
at five points within the test area before application of the electrodes. Conductive silver paint is
applied on the test area on both sides and dried according to the paint manufacturer's
recommendations.
The specimen shall be placed on a flat solid electrically conductive surface in an oven. The
conductive surface shall have contact with the electrode on the bottom side, be grounded and
used as one electrode.
The metal cylinder is placed on the test area on top of the silver paint and used as the other
electrode.
5.5.4 Procedure
The volume resistivity at room temperature is measured in accordance with IEC 62631-3-1
using an electrification of 1 min and a voltage not higher than 500 V. To avoid migration effects,
the field strength shall be less than 3 000 V/mm.
The oven is turned on and adjusted to the first temperature. After the temperature has
stabilized, the measurement of the volume resistivity is repeated and recorded along with the
temperature.
The necessary time for temperature stabilization is for example influenced by the construction
and tolerances of the oven, the electrode arrangement specimen and other technical details.
However, ensure the specimen has stabilized. The time characteristics of the individual oven
shall be determined or extrapolated from experience.
The oven is set to the second temperature and the process is repeated until the maximum
temperature is reached. The maximum temperature shall be at least the thermal class
temperature.
5.5.5 Calculation
The calculation of the volume resistivity shall be in accordance with IEC 62631-3-1. A graph
using a logarithmic scale of the volume resistivity versus temperature has been found useful.
5.6 Procedure for volume resistivity after seven days of immersion into water
5.6.1 General
The following procedure describes an established method used for quality control and is meant
as an example. Any other method in line with the general requirements may be used. However,
measuring parameters (time, temperatures, environmental influences, etc.) can vary widely and
are dependent on the purpose of the measurement and the intended use of the material.

– 10 – IEC 62631-3-12:2024 © IEC 2024
5.6.2 Equipment
The following equipment shall be used:
• tera-ohmmeter according to 5.3;
• metal cylinder to be used as voltage electrode (top electrode) of at least 40 mm diameter
having a mass to provide a pressure of about 0,015 MPa;
• a disc of conductive rubber with the same diameter as the top electrode;
• a disc of conductive rubber with a diameter of at least 60 mm.
5.6.3 Test set-up
Three specimens shall be tested. The thickness of each specimen shall be measured at least
at five points within the test area. The greater conductive rubber disk is placed on an electrically
conductive surface. The specimen is placed on it and the smaller conductive rubber disk is
placed on the test area, preferably centrically over the greater rubber disk. Finally, the metal
cylinder is placed on the smaller rubber disc.
The electrically conductive surface is grounded and used as one electrode; the metal cylinder
is used as the other electrode.
5.6.4 Procedure
The initial value of volume resistivity at room temperature is measured in accordance with
IEC 62631-3-1 using an electrification of 1 min and a voltage not higher than 500 V. To avoid
migration effects, the field strength shall be less than 3 000 V/mm.
After this initial measurement the specimens are immersed into demineralized water of
(23 ± 2) °C for (168 ± 1) h (seven days). Sufficient water shall be used, so that the specimen
does not dry out.
After immersion in water the test set-up shall be made immediately after removing the specimen
from the water and blotting it between filter papers to remove excessive water. The resistance
measurement shall be taken (15 ± 1) min after the test set-up is made.
The volume resistivity is measured again in accordance with IEC 62631-3-1 using an
electrification of 1 min and a voltage not higher than 500 V. To avoid migration effects, the field
strength shall be less than 3 000 V/mm.
5.6.5 Calculation
The calculation of the volume resistivity shall be in accordance with IEC 62631-3-1.
6 Report
The report shall include the following:
– complete identification and description of the material tested, including source and
manufacturer's code;
– shape and thickness of test specimens (average);
– test voltage;
– accuracy of the instrument and calibration method, depending on the measured values of
resistance if necessary;
– curing conditions of the material and any pretreatment;
– conditioning of samples and climatic conditions under test;

– description of test
...