EN IEC 60216-1:2026

SLOVENSKI STANDARD
01-marec-2026
Električni izolacijski materiali - Lastnosti toplotne vzdržljivosti - 1. del: Postopki
staranja in vrednotenje rezultatov preskušanja (IEC 60216-1:2025)
Electrical insulating materials - Thermal endurance properties - Part 1: Ageing
procedures and evaluation of test results (IEC 60216-1:2025)
Elektroisolierstoffe - Eigenschaften hinsichtlich des thermischen Langzeitverhaltens - Teil
1: Warmlagerungsverfahren und Auswertung von Prüfergebnissen (IEC 60216-1:2025)
Matériaux isolants électriques - Propriétés d'endurance thermique - Partie 1: Méthodes
de vieillissement et évaluation des résultats d'essai (IEC 60216-1:2025)
Ta slovenski standard je istoveten z: EN IEC 60216-1:2026
ICS:
17.220.99 Drugi standardi v zvezi z Other standards related to
elektriko in magnetizmom electricity and magnetism
29.035.01 Izolacijski materiali na Insulating materials in
splošno general
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EUROPEAN STANDARD EN IEC 60216-1

NORME EUROPÉENNE
EUROPÄISCHE NORM January 2026
ICS 17.220.99; 29.035.01 Supersedes EN 60216-1:2013
English Version
Electrical insulating materials - Thermal endurance properties -
Part 1: Ageing procedures and evaluation of test results
(IEC 60216-1:2025)
Matériaux isolants électriques - Propriétés d'endurance Elektroisolierstoffe - Eigenschaften hinsichtlich des
thermique - Partie 1: Méthodes de vieillissement et thermischen Langzeitverhaltens - Teil 1:
évaluation des résultats d'essai Warmlagerungsverfahren und Auswertung von
(IEC 60216-1:2025) Prüfergebnissen
(IEC 60216-1:2025)
This European Standard was approved by CENELEC on 2026-01-16. CENELEC members are bound to comply with the CEN/CENELEC
Internal Regulations which stipulate the conditions for giving this European Standard the status of a national standard without any alteration.
Up-to-date lists and bibliographical references concerning such national standards may be obtained on application to the CEN-CENELEC
Management Centre or to any CENELEC member.
This European Standard exists in three official versions (English, French, German). A version in any other language made by translation
under the responsibility of a CENELEC member into its own language and notified to the CEN-CENELEC Management Centre has the
same status as the official versions.
CENELEC members are the national electrotechnical committees of Austria, Belgium, Bulgaria, Croatia, Cyprus, the Czech Republic,
Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, the
Netherlands, Norway, Poland, Portugal, Republic of North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland,
Türkiye and the United Kingdom.

European Committee for Electrotechnical Standardization
Comité Européen de Normalisation Electrotechnique
Europäisches Komitee für Elektrotechnische Normung
CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels
© 2026 CENELEC All rights of exploitation in any form and by any means reserved worldwide for CENELEC Members.
Ref. No. EN IEC 60216-1:2026 E

European foreword
The text of document 112/698/FDIS, future edition 7 of IEC 60216-1, prepared by TC 112 "Evaluation
and qualification of electrical insulating materials and systems" was submitted to the IEC-CENELEC
parallel vote and approved by CENELEC as EN IEC 60216-1:2026.
The following dates are fixed:
• latest date by which the document has to be implemented at national (dop) 2027-01-31
level by publication of an identical national standard or by endorsement
• latest date by which the national standards conflicting with the (dow) 2029-01-31
document have to be withdrawn
This document supersedes EN 60216-1:2013 and all of its amendments and corrigenda (if any).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. CENELEC shall not be held responsible for identifying any or all such patent rights.
Any feedback and questions on this document should be directed to the users’ national committee. A
complete listing of these bodies can be found on the CENELEC website.
Endorsement notice
The text of the International Standard IEC 60216-1:2025 was approved by CENELEC as a European
Standard without any modification.
In the official version, for Bibliography, the following notes have to be added for the standard indicated:
IEC 60216 series NOTE Approved as EN 60216 series
ISO 2578:1993 NOTE Approved as EN ISO 2578:1998 (not modified)
IEC 60216-8 NOTE Approved as EN 60216-8
IEC 60216-2 NOTE Approved as EN 60216-2
IEC 60216-3 NOTE Approved as EN IEC 60216-3
IEC 60212 NOTE Approved as EN 60212
IEC 60216-3:2021 NOTE Approved as EN IEC 60216-3:2021 (not modified)
IEC 60216-8:2013 NOTE Approved as EN 60216-8:2013 (not modified)
Annex ZA
(normative)
Normative references to international publications
with their corresponding European publications
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.
NOTE 1  Where an International Publication has been modified by common modifications, indicated by (mod),
the relevant EN/HD applies.
NOTE 2  Up-to-date information on the latest versions of the European Standards listed in this annex is available
here: www.cencenelec.eu.
Publication Year Title EN/HD Year
IEC 60212 - Standard conditions for use prior to and EN 60212 -
during the testing of solid electrical
insulating materials
IEC 60216-3 2021 Electrical insulating materials - Thermal EN IEC 60216-3 2021
endurance properties - Part 3: Instructions
for calculating thermal endurance
characteristics
IEC 60216-3 - Electrical insulating materials - Thermal EN IEC 60216-3 -
endurance properties - Part 3: Instructions
for calculating thermal endurance
characteristics
IEC 60216-4-1 - Electrical insulating materials - Thermal EN 60216-4-1 -
endurance properties - Part 4-1: Ageing
ovens - Single-chamber ovens
IEC 60493-1 2011 Guide for the statistical analysis of ageing - -
test data - Part 1: Methods based on mean
values of normally distributed test results
IEC 60216-4 series Guide for the determination of thermal EN IEC 60216-4 series
endurance properties of electrical
insulating materials. Part 4: Ageing Ovens

Under preparation. Stage at the time of publication: prEN IEC 60216-4.
IEC 60216-1 ®
Edition 7.0 2025-12
INTERNATIONAL
STANDARD
Electrical insulating materials - Thermal endurance properties -
Part 1: Ageing procedures and evaluation of test results
ICS 17.220.99; 29.035.01 ISBN 978-2-8327-0931-3

IEC 60216-1:2025-12(en)
IEC 60216-1:2025 © IEC 2025
CONTENTS
FOREWORD . 3
INTRODUCTION . 5
1 Scope . 6
2 Normative references . 6
3 Terms, definitions, symbols and abbreviated terms . 6
3.1 Terms and definitions. 6
3.2 Symbols and abbreviated terms . 8
4 Synopsis of procedures - Full procedures . 8
5 Detailed experimental procedures . 9
5.1 Selection of test procedures. 9
5.1.1 General considerations . 9
5.1.2 Selection of material . 9
5.1.3 Selection of test properties for TI . 9
5.1.4 Determination of TI for times other than 20 000 h . 10
5.2 Selection of end-points . 10
5.3 Preparation and number of test specimens . 10
5.3.1 Preparation . 10
5.3.2 Number of specimens . 11
5.4 Establishment of initial property value . 11
5.5 Exposure temperatures and times . 12
5.6 Ageing ovens . 12
5.7 Environmental conditions . 12
5.7.1 General . 12
5.7.2 Atmospheric conditions during ageing. 13
5.7.3 Conditions for property measurement . 13
5.8 Procedure for ageing . 13
5.8.1 General . 13
5.8.2 Procedure using a non-destructive test . 13
5.8.3 Procedure using a proof test . 14
5.8.4 Procedure using a destructive test . 14
6 Evaluation . 14
6.1 Numerical analysis of test data . 14
6.2 Thermal endurance characteristics and formats . 15
6.3 Times to end-point, x- and y-values . 16
6.3.1 General . 16
6.3.2 Non-destructive tests . 16
6.3.3 Proof tests . 17
6.3.4 Destructive tests . 17
6.4 Means and variances . 19
6.4.1 Complete data . 19
6.4.2 Incomplete (censored) data . 20
6.5 General means and variances and regression analysis . 20
6.6 Thickness dependence . 20
6.7 Statistical tests and data requirements . 20
6.7.1 General . 20
6.7.2 Data of all types . 20
IEC 60216-1:2025 © IEC 2025
6.7.3 Proof tests . 21
6.7.4 Destructive tests . 22
6.8 Thermal endurance graph and thermal endurance characteristics . 22
6.9 Test report . 22
Annex A (informative) Dispersion and non-linearity . 25
A.1 Data dispersion . 25
A.2 Non-linearity . 25
A.2.1 Mechanisms of thermal degradation . 25
A.2.2 Non-linearity of data groups . 25
Annex B (informative) Exposure temperatures and times . 27
B.1 General . 27
B.2 Temperatures . 27
B.3 Times . 27
B.3.1 Cyclic ageing . 27
B.3.2 Continuous ageing . 27
B.4 Delayed groups of specimens . 28
Bibliography . 30

Figure 1 – Thermal endurance graph . 15
Figure 2 – Property variation - Determination of time to end-point at each temperature
(destructive tests and non-destructive tests) . 17
Figure 3 – Estimation of times to end-point - Property value (ordinate, arbitrary units)
versus time (abscissa, log scale, arbitrary units) . 18
Figure 4 – Destructive tests - Estimation of time to end-point . 19

Table 1 – Suggested exposure temperatures and times . 23
Table B.1 – Groups . 28

IEC 60216-1:2025 © IEC 2025
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
Electrical insulating materials - Thermal endurance properties -
Part 1: Ageing procedures and evaluation of test results

FOREWORD
1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising
all national electrotechnical committees (IEC National Committees). The object of IEC is to promote international
co-operation on all questions concerning standardization in the electrical and electronic fields. To this end and
in addition to other activities, IEC publishes International Standards, Technical Specifications, Technical Reports,
Publicly Available Specifications (PAS) and Guides (hereafter referred to as "IEC Publication(s)"). Their
preparation is entrusted to technical committees; any IEC National Committee interested in the subject dealt with
may participate in this preparatory work. International, governmental and non-governmental organizations liaising
with the IEC also participate in this preparation. IEC collaborates closely with the International Organization for
Standardization (ISO) in accordance with conditions determined by agreement between the two organizations.
2) The formal decisions or agreements of IEC on technical matters express, as nearly as possible, an international
consensus of opinion on the relevant subjects since each technical committee has representation from all
interested IEC National Committees.
3) IEC Publications have the form of recommendations for international use and are accepted by IEC National
Committees in that sense. While all reasonable efforts are made to ensure that the technical content of IEC
Publications is accurate, IEC cannot be held responsible for the way in which they are used or for any
misinterpretation by any end user.
4) In order to promote international uniformity, IEC National Committees undertake to apply IEC Publications
transparently to the maximum extent possible in their national and regional publications. Any divergence between
any IEC Publication and the corresponding national or regional publication shall be clearly indicated in the latter.
5) IEC itself does not provide any attestation of conformity. Independent certification bodies provide conformity
assessment services and, in some areas, access to IEC marks of conformity. IEC is not responsible for any
services carried out by independent certification bodies.
6) All users should ensure that they have the latest edition of this publication.
7) No liability shall attach to IEC or its directors, employees, servants or agents including individual experts and
members of its technical committees and IEC National Committees for any personal injury, property damage or
other damage of any nature whatsoever, whether direct or indirect, or for costs (including legal fees) and
expenses arising out of the publication, use of, or reliance upon, this IEC Publication or any other IEC
Publications.
8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is
indispensable for the correct application of this publication.
9) IEC draws attention to the possibility that the implementation of this document may involve the use of (a)
patent(s). IEC takes no position concerning the evidence, validity or applicability of any claimed patent rights in
respect thereof. As of the date of publication of this document, IEC had not received notice of (a) patent(s), which
may be required to implement this document. However, implementers are cautioned that this may not represent
the latest information, which may be obtained from the patent database available at https://patents.iec.ch. IEC
shall not be held responsible for identifying any or all such patent rights.
IEC 60216-1 has been prepared by IEC technical committee 112: Evaluation and qualification
of electrical insulating materials and systems. It is an International Standard.
This seventh edition cancels and replaces the sixth edition published in 2013. This edition
constitutes a technical revision.
This edition includes the following significant technical changes with respect to the previous
edition:
a) the definition for temperature index (TI) has been updated;
b) requirements for selection of related materials used, e.g. in different colours (5.1.2), have
been added;
c) test procedure for thickness sensitivity (5.5 and 6.6) has been added;
d) Annex C "Concepts in earlier editions" has been deleted.
IEC 60216-1:2025 © IEC 2025
The text of this International Standard is based on the following documents:
Draft Report on voting
112/698/FDIS 112/706/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.
A list of all parts in the IEC 60216 series [1], published under the general title Electrical
insulating materials – Thermal endurance properties, can be found on the IEC website.
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.
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.
IEC 60216-1:2025 © IEC 2025
INTRODUCTION
The listing of the thermal capabilities of electrical insulating materials, based on service
experience, was found to be impractical, owing to the rapid development of polymer and
insulation technologies and the long time necessary to acquire appropriate service experience.
Accelerated ageing and test procedures were therefore needed to obtain the necessary
information. The IEC 60216 series [1] has been developed to formalize these procedures and
the interpretation of their results.
Physico-chemical models postulated for the ageing processes led to the almost universal
assumption of the Arrhenius equations to describe the rate of ageing. Out of this arose the
concept of the temperature index (TI) as a single-point characteristic based upon accelerated
ageing data. This is the numerical value of the temperature in degrees Celsius at which the
time taken for deterioration of a selected property to reach an accepted end-point is that
specified (usually 20 000 h).
NOTE The term Arrhenius is widely used (and understood) to indicate a linear relationship between the logarithm
of a time and the reciprocal of the thermodynamic (absolute or kelvin) temperature. The correct usage is restricted
to such a relationship between a reaction rate constant and the thermodynamic temperature. The common usage is
employed throughout this document.
The large statistical scatter of test data which was found, together with the frequent occurrence
of substantial deviations from the ideal behaviour, demonstrated the need for tests to assess
the validity of the basic physico-chemical model. The application of conventional statistical
tests, as set out in IEC 60493-1:2011 [2], fulfilled this requirement, resulting in the confidence
limit (TC) of TI, but the simple, single-point TI was found inadequate to describe the capabilities
of materials. This led to the concept of the thermal endurance profile (TEP), incorporating the
temperature index, its variation with specified ageing time, and a confidence limit.
A complicating factor is that the properties of a material subjected to thermal ageing possibly
do not all deteriorate at the same rate, and different end-points can be relevant for different
applications. Consequently, a material can be assigned more than one temperature index,
derived, for example, from the measurement of different properties and the use of different end-
point times.
It was subsequently found that the statistical confidence index included in the TEP was not
widely understood or used. However, the statistical tests were considered essential, particularly
after minor modifications to make them relate better to practical circumstances: the concept of
the halving interval (HIC) was introduced to indicate the rate of change of ageing time with
temperature. TEP was then abandoned, with the TI and HIC being reported in a way which
indicated whether or not the statistical tests had been fully satisfied. At the same time, the
calculation procedures were made more comprehensive, enabling full statistical testing of data
obtained using a diagnostic property of any type, including the particular case of partially
incomplete data. Simultaneously with the development of the IEC 60216 series [1], other
standards were being developed in ISO, intended to satisfy a similar requirement for plastics
and rubber materials. These are ISO 2578:1993 [3] and ISO 11346 [4], respectively, which use
less rigorous statistical procedures and more restricted experimental techniques. A simplified
calculation procedure is defined in IEC 60216-8 [5].
IEC 60216-1:2025 © IEC 2025
1 Scope
This part of IEC 60216 specifies the general ageing conditions and procedures to be used for
deriving thermal endurance characteristics and gives guidance in using the detailed instructions
and guidelines in the other parts of IEC 60216.
Although originally developed for use with electrical insulating materials and simple
combinations of such materials, the procedures are considered to be of more general
applicability and are widely used in the assessment of materials not intended for use as
electrical insulation.
In the application of this document, it is assumed that a practically linear relationship exists
between the logarithm of the time required to cause the predetermined property change and
the reciprocal of the corresponding absolute temperature (Arrhenius relationship).
For the valid application of this document, no transition, in particular no first-order transition, is
expected to occur in the temperature range under study.
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 60216-3:2021, Electrical insulating materials - Thermal endurance properties - Part 3:
Instructions for calculating thermal endurance characteristics
IEC 60216-3, Electrical insulating materials - Thermal endurance properties - Part 3:
Instructions for calculating thermal endurance characteristics
IEC 60216-4-1, Electrical insulating materials - Thermal endurance properties - Part 4-1: Ageing
ovens - Single-chamber ovens
IEC 60493-1:2011, Guide for the statistical analysis of ageing test data - Part 1: Methods based
on mean values of normally distributed test results
IEC 60216-4 series, Electrical insulating materials – Thermal endurance properties – Part 4:
Ageing ovens
3 Terms, definitions, symbols and abbreviated terms
3.1 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
IEC 60216-1:2025 © IEC 2025
3.1.1
temperature index
TI
numerical value of the temperature in degrees Celsius determined by test by itself
Note 1 to entry: This rating is based on 20 000 h life, unless otherwise specified, based on one of the end-of-life
criteria listed in IEC 60216-2 [6].
3.1.2
halving interval
HIC
numerical value of the temperature interval in kelvin which expresses the halving of the time to
end-point (3.1.12) taken at the temperature equal to TI (3.1.1)
[SOURCE: IEC 60050-212:2010 [7], 212-12-13, modified – In the definition, "equal to TI"
replaces "corresponding to the temperature index or the relative temperature index".]
3.1.3
thermal endurance graph
graph in which the logarithm of the time to reach a specified end-point (3.1.12) in a thermal
endurance test is plotted against the reciprocal thermodynamic (absolute) test temperature
[SOURCE: IEC 60050-212:2010 [7], 212-12-10, modified – In the definition, the word
"(absolute)" has been added.]
3.1.4
thermal endurance graph paper
graph paper having a logarithmic time scale as the ordinate, graduated in powers of ten
Note 1 to entry: 10 h to 100 000 h is often a convenient range for the ordinate.
Note 2 to entry: Values of the abscissa are proportional to the reciprocal of the thermodynamic (absolute)
temperature. The abscissa is usually graduated in a non-linear (Celsius) temperature scale oriented with temperature
increasing from left to right.
3.1.5
regression analysis
process of deducing the best-fit line expressing the relation of corresponding members of two
data groups by minimizing the sum of squares of deviations of members of one of the groups
from the line
Note 1 to entry: The parameters are referred to as the regression coefficients.
3.1.6
confidence limit
TC
statistical parameter, calculated from the test data, which with 95 % confidence constitutes a
lower limit for the true value of the temperature index estimated by TI (3.1.1)
Note 1 to entry: 95 % confidence implies that there is only 5 % probability that the true value of the temperature
index is actually smaller than TC.
Note 2 to entry: In other connections, confidence values other than 95 % can sometimes be used; for example, in
the linearity test for destructive test (3.1.7) data.
3.1.7
destructive test
diagnostic property test where the test specimen is irreversibly changed by the property
measurement in a way which precludes a repeated measurement on the same specimen
IEC 60216-1:2025 © IEC 2025
3.1.8
non-destructive test
diagnostic property test where the properties of the test specimen are not permanently changed
by the measurement, so that a further measurement on the same specimen can be made after
appropriate treatment
3.1.9
proof test
diagnostic property test where each test specimen is, at the end of each ageing cycle, subjected
to a specified stress, further ageing cycles being conducted until the specimen fails on testing
3.1.10
temperature group
test group of specimens
number of specimens being exposed together to the same temperature ageing in the same oven
Note 1 to entry: Where there is no risk of ambiguity, either temperature groups or test groups (3.1.11) may be
referred to simply as groups.
3.1.11
test group
test group of specimens
number of specimens removed together from a temperature group (3.1.10) for destructive
testing
3.1.12
end-point
property level that is effected by practical application to the equipment in the thermal endurance
test
3.2 Symbols and abbreviated terms
a, b regression coefficients
n numbers of specimens for destructive tests
a,b,c,d
n number of y-values
N total number of test specimens
m number of specimens in temperature group i (censored data)
i
F Fisher distributed stochastic variable
x reciprocal thermodynamic temperature (1/Θ)
y logarithm of time to end-point
ϑ temperature, °C
Θ temperature, thermodynamic (kelvin)
Θ value in kelvin (0 °C = 273,15 K)
τ time (to end-point)
2 2
χ χ -distributed stochastic variable
TI temperature index
TC lower 95 % confidence limit of TI
HIC halving interval at temperature equal to TI
4 Synopsis of procedures - Full procedures
The standardized procedure for the evaluation of thermal properties of a material consists of a
sequence of steps, as follows.
IEC 60216-1:2025 © IEC 2025
It is recommended that the full evaluation procedure, as described below and in 5.1 to 5.8, be
used.
a) Prepare suitable specimens appropriate for the intended property measurements (see 5.3).
b) Subject groups of specimens to ageing at several fixed levels of elevated temperature,
either continuously, or cyclically for a number of periods between which the specimens are
normally returned to room temperature or another standard temperature (see 5.5).
c) Subject specimens to a diagnostic procedure in order to reveal the degree of ageing.
Diagnostic procedures may be non-destructive or destructive determinations of a property
or potentially destructive proof tests (see 5.1 and 5.2).
d) Extend the continuous heat exposure or the thermal cycling until the specified end-point,
i.e. failure of specimens or a specified degree of change in the measured property, is
reached (see 5.1, 5.2 and 5.5).
e) Report the test results, showing the kind of ageing procedure (continuous or cyclic) and
diagnostic procedure (see Clause 4, list item c); the ageing curves, or time or number of
cycles to reach the end-point, for each specimen.
f) Evaluate these data numerically and present them graphically, as explained in 6.1 and 6.9.
g) Express the complete information in abbreviated numerical form, as described in 6.2 by
means of the temperature index and halving interval.
The full experimental and evaluation procedures are given in Clause 5 and Clause 6.
A simplified procedure is given in IEC 60216-8 [5].
5 Detailed experimental procedures
5.1 Selection of test procedures
5.1.1 General considerations
Each test procedure should specify the shape, dimensions and number of the test specimens,
the temperatures and times of exposure, the property to which TI is related, the methods of its
determination, the end-point, and the derivation of the thermal endurance characteristics from
the experimental data.
The chosen property should reflect, in a significant fashion if possible, a function of the material
in practical use. A choice of properties is given in IEC 60216-2 [6].
To provide uniform conditions, specification of the conditioning of specimens after removal from
the oven and before measurement will possibly be required.
5.1.2 Selection of material
Commercially available brands of insulating materials are usually obtainable in different
molecular weights and colours, and with differing types and quantities of fillers and additives.
A separate analysis of each of these variations is not necessary to an evaluation in a thermal-
endurance programme. The least favourable performance of the unfilled and maximum-level
filled or reinforced material shall be considered representative of intermediate levels of filler or
reinforcement without additional testing.
5.1.3 Selection of test properties for TI
If IEC material specifications are available, property requirements in terms of acceptable lower
limits of TI values are usually given. If such material specifications are not available, a selection
of properties and methods for the evaluation of thermal endurance is given in IEC 60216-2 [6].
(If such a method cannot be found, an international, national, or institution standard, or a
specially devised method should be used, and in that order of preference.)
IEC 60216-1:2025 © IEC 2025
5.1.4 Determination of TI for times other than 20 000 h
In the majority of cases, the required thermal endurance characteristics are for a projected
duration of 20 000 h. However, there is often a need for such information related to other longer
or shorter times. In cases of longer times, for example, the times given as requirements or
recommendations in the text of this document (for example, 5 000 h for the minimum value of
the longest time to end-point) shall be increased in the ratio of the actual specification time to
20 000 h. In the same way, the ageing cycle durations should be changed in approximately the
same ratio. The temperature extrapolation again shall not exceed 25 K. In cases of shorter
specification times, the related times may be decreased in the same ratio if necessary.
Particular care will be needed for very short specification times, since the higher ageing
temperatures can lead into temperature regions which include transition points, for example,
glass transition temperature or partial melting, with consequent non-linearity. Very long
specification times can also lead to non-linearity (see also Annex A).
5.2 Selection of end-points
The thermal endurance of materials can be characterized by different endurance data (derived
using different properties or different end-points or both), in order to facilitate the adequate
selection of the material in respect of its particular application in an insulation system. See IEC
60216-2 [6].
There are two alternative ways in which the end-point can be defined.
a) As a percentage increase or decrease in the measured value of the property from the
original level. This approach will provide comparisons among materials but bears a poorer
relationship than 5.2, list item b) to the property values required in normal service. For the
determination of the initial value, see 5.4.
b) As a fixed value of the property. This value can be selected with respect to usual service
requirements. End-points of proof tests are predominantly given in the form of fixed values
of the property.
The end-point should be selected to indicate a degree of deterioration of the insulating material
which has reduced its ability to withstand a stress encountered in actual service in an insulation
system. The degree of degradation indicated as the end-point of the test should be related to
the allowable safe value for the material property which is desired in practice.
5.3 Preparation and number of test specimens
5.3.1 Preparation
The specimens used for the ageing test should constitute a random sample from the population
investigated and shall be treated uniformly.
The material specifications or the test standards will contain all necessary instructions for the
preparation of specimens.
The thickness of specimens is in some cases specified in the list of property measurements for
the determination of thermal endurance. See IEC 60216-2 [6]. If not, the thickness shall be
reported. Some physical properties are sensitive even to minor variations of specimen
thickness. In such cases, it is important that the thickness after each ageing period is
determined and reported if required in the relevant specification.
Consequently, a material may be assigned more than one thermal endurance characteristic
derived from the measurement of properties at different thicknesses.
The tolerances of specimen dimensions should be the same as those normally used for general
testing; where specimen dimensions need smaller tolerances than those normally used, these
IEC 60216-1:2025 © IEC 2025
special tolerances should be given. Screening measurements ensure that specimens are of
uniform quality and typical of the material to be tested.
Since processing conditions can significantly affect the ageing characteristics of some
materials, it shall be ensured that, for example, sampling, cutting sheet from the supply roll,
cutting of anisotropic material in a given direction, moulding, curing and pre-conditioning are
performed in the same manner for all specimens.
5.3.2 Number of specimens
5.3.2.1 General
The accuracy of endurance test results depends largely on the number of specimens aged at
each temperature. Instructions for an adequate number of specimens are given in IEC 60216-
3 [8].Generally, the following instructions (5.3.2.1 to 5.3.2.3), which influence the testing
procedure given in 5.8, shall apply.
It is good practice to prepare additional specimens, or at least to provide a reserve of the original
material batch from which such specimens may subsequently be prepared. In this way, any
required ageing of additional specimens in case of unforeseen complications will introduce a
minimum risk of producing systematic differences between groups of specimens. Such
complications can arise, for example, if the thermal endurance relationship turns out to be non-
linear, or if specimens are lost due to thermal runaway of an oven.
Where the test criterion for non-destructive tests or proof tests is based upon the initial value
of the property, this should be determined from a group of specimens of at least twice the
number of specimens in each temperature group. For destructive tests, see 5.3.2.4.
5.3.2.2 Number of specimens for non-destructive tests
For each exposure temperature, in most cases a group of five specimens will be adequate.
However, further guidance will be found in IEC 60216-3 [8].
5.3.2.3 Number of specimens for proof tests
In most cases, a group of at least 11 specimens for each exposure temperature will be required.
For graphical derivation and in some other cases, the treatment of data can be simpler if the
number of specimens in each group is odd. Further guidance will be found in IEC 60216-3 [8].
5.3.2.4 Number of specimens for destructive tests
×𝑛𝑛 ×𝑛𝑛 +𝑛𝑛
This number (N) is derived as follows: 𝑁𝑁 =𝑛𝑛
a b c d
is the number of specimens in a test group undergoing identical treatment at one temperature and
n
a
discarded after determination of the property (usually five);
n is the number of treatments, i.e. total number of exposure times, at one temperature;
b
is the number of ageing temperature levels;
n
c
is the number of specimens in the group used to establish the initial value of the property. Normal practice
n
d
is to select n = 2n when the diagnostic criterion is a percentage change of the property from its initial
d a
level. When the criterion is an absolute property level, n is usually given the value of zero, unless
d
reporting of the initial value is required.
5.4 Establishment of initial property value
Select the specimens for the determination of the initial value of the property to constitute a
random subset of those prepared for ageing. Before determining the property value, these
specimens shall be conditioned by exposure to the lowest level of ageing temperature of the
test (see 5.5) for two days (48 h ± 6 h).
IEC 60216-1:2025 © IEC 2025
In some cases (for example, very thick specimens), times greater than two days can be required
in order to establish a stable value.
Unless otherwise stated in the method for determining the diagnostic property (for example,
parts of material specifications dealing with methods of test, or a method listed in IEC 60216-2
[6]), the initial value is the arithmetic mean of the test results.
5.5 Exposure temperatures and times
For TI determinations, test specimens should be exposed to not less than three, preferably at
least four, temperatures covering a sufficient range to demonstrate a linear relationship
between time to end-point and reciprocal thermodynamic (absolute) temperature.
To reduce the uncertainties in calculating the appropriate thermal endurance characteristic, it
is important that the overall temperature range of thermal exposure is carefully selected,
observing the following requirements (if the required thermal endurance characteristics are for
a projected duration of 20 000 h, see also 5.1.3):
a) the lowest exposure temperature shall be one which wi
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