IEC 60216-1:2013

Electrical insulating materials - Thermal endurance properties - Part 1: Ageing procedures and evaluation of test results

IEC 60216-1:2013 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 the standard. 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 standard, 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 the standard, no transition, in particular no first-order transition should occur in the temperature range under study. This sixth edition cancels and replaces the fifth edition, published in 2001. It constitutes an editorial revision where the simplified method has been removed and now forms Part 8 of the IEC 60216 series: Instructions for calculating thermal endurance characteristics using simplified procedures.

Matériaux isolants électriques - Propriétés d'endurance thermique - Partie 1: Méthodes de vieillissement et évaluation des résultats d'essai

La CEI 60216-1:2013 spécifie les conditions générales de vieillissement et les méthodes à utiliser pour en extraire les caractéristiques d'endurance thermique, et fixe des orientations pour l'utilisation des instructions détaillées et des directives précisées dans les autres parties de la norme. Même si à l'origine elles ont été développées pour être utilisées sur les matériaux isolants électriques et des combinaisons simples de tels matériaux, ces méthodes sont considérées comme étant applicables plus généralement et sont largement utilisées pour vérifier des matériaux non destinés à être utilisés comme isolants électriques. Dans l'application de cette norme, on suppose qu'une relation pratiquement linéaire existe entre le logarithme du temps nécessaire pour provoquer la modification prédéterminée de la propriété, et l'inverse de la température absolue correspondante (relation d'Arrhenius). Pour que la norme soit valable, il convient qu'il n'y ait pas de transition, en particulier de transition du premier ordre, dans la gamme de températures à l'étude. Cette sixième édition annule et remplace la cinquième édition, parue en 2001. Cette édition constitue une révision éditoriale de laquelle à été retirée la méthode simplifiée qui constitue maintenant la Partie 8 de la CEI 60216: Instructions pour le calcul des caractéristiques d'endurance thermique en utilisant les méthodes simplifiées.

General Information

• Status: Published
• Publication Date: 14-Mar-2013
• 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 1 - TC 112/WG 1
• Current Stage: PPUB - Publication issued
• Start Date: 15-Mar-2013
• Completion Date: 31-Mar-2013

Relations

• Revises: IEC 60216-1:2001 - Electrical insulating materials - Properties of thermal endurance - Part 1: Ageing procedures and evaluation of test results
• Effective Date: 05-Sep-2023
• Revised: IEC 60216-1:2025 - Electrical insulating materials - Thermal endurance properties - Part 1: Ageing procedures and evaluation of test results
• Effective Date: 05-Sep-2023

IEC 60216-1:2013 Overview

IEC 60216-1:2013 is an international standard published by the International Electrotechnical Commission (IEC) that specifies ageing procedures and evaluation methods for assessing the thermal endurance properties of electrical insulating materials. This sixth edition focuses on generalized ageing conditions to derive thermal endurance characteristics and guides the proper interpretation of test results.

Originally created for electrical insulations and simple material combinations, the procedures outlined in IEC 60216-1 are broadly applicable to other materials where thermal aging assessment is necessary. The standard uses the widely accepted Arrhenius relationship between the logarithm of time to failure and the reciprocal absolute temperature to model material degradation, requiring stable temperature ranges without phase transitions.

Key Topics

• Ageing Procedures for Thermal Endurance: Detailed methods for accelerated ageing tests under controlled temperatures and durations to simulate long-term material performance.
• Test Specimen Preparation: Guidelines on specimen numbers and preparation ensuring statistically valid results.
• End-Point Determination: Selection criteria for property changes that signify material failure or unacceptable degradation.
• Evaluation of Test Data: Comprehensive numerical and statistical procedures, including regression analysis and confidence limit calculations, to derive meaningful thermal endurance characteristics.
• Thermal Endurance Graphs: Visualization tools for representing the relationship between temperature and time to end-point, facilitating material comparison.
• Statistical Validation: Incorporates statistical tests to confirm the applicability of the Arrhenius model and to handle data variability.
• Environmental Conditions: Specifications on maintaining atmospheres during ageing to ensure repeatability and accuracy.
• Exclusion of Simplified Methods: The simplified calculation procedures have been removed from this part and defined in IEC 60216-8, focusing this document on full, detailed procedures.

Applications

IEC 60216-1:2013 is essential for industries and laboratories involved in:

• Electrical Equipment Manufacturing: Ensuring insulating materials meet stringent thermal durability requirements under operational conditions.
• Material Qualification: Providing a standardized, reproducible method to evaluate new insulation materials and validate their suitability for high-temperature electrical applications.
• Product Development: Supporting product lifecycle prediction and quality assurance through accelerated ageing tests.
• Non-electrical Material Assessment: Applying the ageing methods to non-insulating materials requiring thermal endurance data for performance and safety evaluations.
• Certification and Compliance: Assisting manufacturers and testing agencies in demonstrating conformity with international safety and reliability standards for electrical insulation.

Related Standards

• IEC 60216 Series: Other parts address specific instructions for calculating thermal endurance (e.g., Part 8 for simplified procedures).
• IEC 60493-1: Provides statistical methods for reliability testing relevant to the analysis of ageing data.
• ISO/IEC Directives: Framework guidelines on the preparation and maintenance of international standards.
• IEC 60216-2 to IEC 60216-7: Various parts specifying procedures for particular materials or additional test methodologies related to thermal endurance.

---

IEC 60216-1:2013 is a critical reference for engineers, quality assurance professionals, and researchers focusing on the durability and reliability of electrical insulating materials. Its rigorous ageing procedures and statistical evaluation methods ensure accurate assessments of material performance under thermal stress, contributing to safer and more reliable electrical products globally.

Standards Content (Sample)

IEC 60216-1 ®
Edition 6.0 2013-03
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Electrical insulating materials – Thermal endurance properties –
Part 1: Ageing procedures and evaluation of test results

Matériaux isolants électriques – Propriétés d'endurance thermique –
Partie 1: Méthodes de vieillissement et évaluation des résultats d'essai

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IEC 60216-1 ®
Edition 6.0 2013-03
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Electrical insulating materials – Thermal endurance properties –

Part 1: Ageing procedures and evaluation of test results

Matériaux isolants électriques – Propriétés d'endurance thermique –

Partie 1: Méthodes de vieillissement et évaluation des résultats d'essai

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
PRICE CODE
INTERNATIONALE
CODE PRIX V
ICS 17.220.99; 29.035.01 ISBN 978-2-83220-680-5

– 2 – 60216-1 © IEC:2013
CONTENTS
FOREWORD . 4
INTRODUCTION . 6
1 Scope . 7
2 Normative references . 7
3 Terms, definitions, symbols and abbreviations . 8
3.1 Terms and definitions . 8
3.2 Symbols and abbreviations . 10
4 Synopsis of procedures – Full procedures . 11
5 Detailed experimental procedures . 11
5.1 Selection of test procedures . 11
5.1.1 General considerations . 11
5.1.2 Selection of test properties for TI . 11
5.1.3 Determination of TI for times other than 20 000 h . 12
5.2 Selection of end-points . 12
5.3 Preparation and number of test specimens . 12
5.3.1 Preparation . 12
5.3.2 Number of specimens . 13
5.4 Establishment of initial property value . 14
5.5 Exposure temperatures and times . 14
5.6 Ageing ovens . 14
5.7 Environmental conditions . 15
5.7.1 General . 15
5.7.2 Atmospheric conditions during ageing . 15
5.7.3 Conditions for property measurement . 15
5.8 Procedure for ageing . 15
5.8.1 General . 15
5.8.2 Procedure using a non-destructive test . 15
5.8.3 Procedure using a proof test . 16
5.8.4 Procedure using a destructive test . 16
6 Evaluation . 16
6.1 Numerical analysis of test data . 16
6.2 Thermal endurance characteristics and formats . 17
6.3 Times to end-point, x- and y-values . 18
6.3.1 General . 18
6.3.2 Non-destructive tests . 18
6.3.3 Proof tests . 19
6.3.4 Destructive tests . 19
6.4 Means and variances . 21
6.4.1 Complete data . 21
6.4.2 Incomplete (censored) data . 22
6.5 General means and variances and regression analysis. 22
6.6 Statistical tests and data requirements . 22
6.6.1 General . 22
6.6.2 Data of all types . 22
6.6.3 Proof tests . 23
6.6.4 Destructive tests . 23

60216-1 © IEC:2013 – 3 –
6.7 Thermal endurance graph and thermal endurance characteristics . 24
6.8 Test report . 24
Annex A (informative) Dispersion and non-linearity . 26
Annex B (informative) Exposure temperatures and times . 28
Annex C (informative) Concepts in earlier editions . 31
Bibliography . 33

Figure 1 – Thermal endurance graph . 17
Figure 2 – Property variation – Determination of time to end-point at each temperature
(destructive and non-destructive tests) . 19
Figure 3 – Estimation of times to end-point – Property value (ordinate, arbitrary units)
versus time (abscissa, log scale, arbitrary units) . 20
Figure 4 – Destructive tests – Estimation of time to end-point . 21
Figure C.1 – Relative temperature index (Adapted from Figure 3, IEC 60216-1:1990,
4th edition) . 32

Table 1 – Suggested exposure temperatures and times . 25
Table B.1 – Groups . 29

– 4 – 60216-1 © IEC:2013
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
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8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is
indispensable for the correct application of this publication.
9) Attention is drawn to the possibility that some of the elements of this IEC Publication may be the subject of
patent rights. IEC shall not be held responsible for identifying any or all such patent rights.
International Standard IEC 60216-1 has been prepared by IEC technical committee 112:
Evaluation and qualification of electrical insulating materials and systems.
This sixth edition cancels and replaces the fifth edition, published in 2001. It constitutes an
editorial revision where the simplified method has been removed and now forms Part 8 of the
IEC 60216 series: Instructions for calculating thermal endurance characteristics using
simplified procedures.
The text of this standard is based on the following documents:
FDIS Report on voting
112/235/FDIS 112/243/RVD
Full information on the voting for the approval of this standard can be found in the report on
voting indicated in the above table.

60216-1 © IEC:2013 – 5 –
This publication has been drafted in accordance with the ISO/IEC Directives, Part 2.
A list of all parts in the IEC 60216 series, published under the general title Electrical insulating
materials – Thermal endurance properties, can be found on the IEC website.
The committee has decided that the contents of this publication will remain unchanged until
the stability date indicated on the IEC web site under "http://webstore.iec.ch" in the data
related to the specific publication. At this date, the publication will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
– 6 – 60216-1 © IEC:2013
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 required to obtain the
necessary information. The IEC 60216 series 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 °C 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 standard.
The large statistical scatter of test data which was found, together with the frequent
occurrence of substantial deviations from the ideal behavior, 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, 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 may not
all deteriorate at the same rate, and different end-points may be relevant for different
applications. Consequently, a material may 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, other standards were being developed in ISO, intended to satisfy a similar
requirement for plastics and rubber materials. These are ISO 2578 and ISO 11346
respectively, which use less rigorous statistical procedures and more restricted experimental
techniques. A simplified calculation procedure is described in IEC 60216-8.

60216-1 © IEC:2013 – 7 –
ELECTRICAL INSULATING MATERIALS –
THERMAL ENDURANCE PROPERTIES –

Part 1: Ageing procedures and evaluation of test results

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 the standard.
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 standard, 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 the standard, no transition, in particular no first-order transition
should occur in the temperature range under study.
Throughout the rest of this standard the term "insulating materials" is always taken to mean
"insulating materials and simple combinations of such materials".
2 Normative references
The following documents, in whole or in part, are normatively referenced in this document and
are indispensable for its application. 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 60216-2, Electrical insulating materials – Thermal endurance properties – Part 2:
Determination of thermal endurance properties of electrical insulating materials – Choice of
test criteria
IEC 60216-3:2006, Electrical insulating materials – Thermal endurance properties – Part 3:
Instructions for calculating thermal endurance characteristics
IEC 60216-4 (all Parts 4), Electrical insulating materials – Thermal endurance properties –
Part 4: Ageing ovens
IEC 60216-4-1, Electrical insulating materials – Thermal endurance properties – Part 4-1:
Ageing ovens – Single-chamber ovens
IEC 60216-8, Electrical insulating materials – Thermal endurance properties – Part 8:
Instructions for calculating thermal endurance characteristics using simplified procedures
––––––––
To be published.
– 8 – 60216-1 © IEC:2013
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
3 Terms, definitions, symbols and abbreviations
3.1 Terms and definitions
For the purposes of this document, the following terms and definitions apply:
3.1.1
temperature index
TI
numerical value of the temperature in degrees Celsius derived from the thermal endurance
relationship at a time of 20 000 h (or other specified time)
3.1.2
halving interval
HIC
numerical value of the temperature interval in Kelvin which expresses the halving of the time
to end-point taken at the temperature equal to TI
[SOURCE: IEC 60050-212:2010, definition 212-12-13, modified – "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 in a thermal endurance
test is plotted against the reciprocal thermodynamic (absolute) test temperature
[SOURCE: IEC 60050-212:2010, definition 212-12-10, modified – "insertion of word
"(absolute)"]
3.1.4
thermal endurance graph paper
graph paper having a logarithmic time scale as the ordinate, graduated in powers of ten
(from 10 h to 100 000 h is often a convenient range)
Note 1 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
ordered data
set of data arranged in sequence so that, in the appropriate direction through the sequence,
each member is greater than, or equal to, its predecessor
Note 1 to entry: Ascending order in this standard implies that the data is ordered in this way, the first order-
statistic being the smallest.
3.1.6
order-statistics
each individual value in a set of ordered data is referred to as an order-statistics identified by
its numerical position in the sequence
3.1.7
incomplete data
ordered data, where the values above and/or below defined points are not known

60216-1 © IEC:2013 – 9 –
3.1.8
censored data
incomplete data, where the number of unknown values is known
Note 1 to entry: If the censoring is begun above/below a specified numerical value, the censoring is of type 1.
If above/below a specified order-statistic, it is of type 2. This standard is concerned only with type 2.
3.1.9
degrees of freedom
number of data values minus the number of parameter values
3.1.10
variance of a data set
sum of the squares of the deviations of the data from a reference level defined by one or more
parameters, divided by the number of degrees of freedom
Note 1 to entry: The reference level may for example, be a mean value (one parameter) or a line (two parameters,
slope and intercept).
3.1.11
covariance of data sets
for two sets of data with equal numbers of elements where each element in one set
corresponds to one in the other, the sum of the products of the deviations of the corres-
ponding members from their set means, divided by the number of degrees of freedom
3.1.12
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.
3.1.13
correlation coefficient
number expressing the completeness of the relation between members of two data sets, equal
to the covariance divided by the square root of the product of the variances of the sets
Note 1 to entry: The value of its square is between 0 (no correlation) and 1 (complete correlation).
3.1.14
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
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 % may sometimes be used; for example, in
the linearity test for destructive test data.
3.1.15
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

– 10 – 60216-1 © IEC:2013
3.1.16
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 may be
made after appropriate treatment
3.1.17
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
3.1.18
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 may be referred to
simply as groups.
3.1.19
test group
test group of specimens
number of specimens removed together from a temperature group (as above) for destructive
testing
3.1.20
end point
property level that is effected by practical application to the equipment in the thermal
endurance test
3.2 Symbols and abbreviations
Symbol Meaning
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
r Correlation coefficient
F Fisher distributed stochastic variable
x
Reciprocal thermodynamic temperature (1/Θ)
y Logarithm of time to end-point
Temperature, °C
ϑ
Temperature, thermodynamic (Kelvin)
Θ
Θ Value in Kelvin (0 °C = 273,15 K)
Time (to end-point)
τ
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
RTI Relative temperature index

60216-1 © IEC:2013 – 11 –
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.
It is strongly 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 under item c) above); 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 6.8.
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 as far as 6.8.
A simplified procedure is given in IEC 60216-8.
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.
To provide uniform conditions, the conditioning of specimens after removal from the oven and
before measurement may need to be specified.
5.1.2 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. (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.)

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5.1.3 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 standard (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 may lead into temperature regions which include transition points, for example,
glass transition temperature or partial melting, with consequent non-linearity. Very long
specification times may also lead to non-linearity (see also Annex A).
5.2 Selection of end-points
The thermal endurance of materials may need to be characterized by different endurance data
(derived using different properties and/or end-points), in order to facilitate the adequate
selection of the material in respect of its particular application in an insulation system. See
IEC 60216-2.
There are two alternative ways in which the end-point may 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 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 might 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 are to 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. If not, the thickness shall be
reported. Some physical properties are sensitive even to minor variations of specimen
thickness. In such cases, the thickness after each ageing period may need to be determined
and reported if required in the relevant specification.
The thickness is also important because the rate of ageing may vary with thickness. Ageing
data of materials with different thicknesses are not always comparable. Consequently, a
material may be assigned more than one thermal endurance characteristic derived from the
measurement of properties at different thicknesses.

60216-1 © IEC:2013 – 13 –
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 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 may 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, molding, curing, 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. 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 may 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 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.
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 may be
simpler if the number of specimens in each group is odd. Further guidance will be found in
IEC 60216-3.
5.3.2.4 Number of specimens for destructive tests
This number (N) is derived as follows: N = n × n × n + n
a b c d
where
n is the number of specimens in a test group undergoing identical treatment at one
a
temperature and 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
n is the number of ageing temperature levels;
c
n is the number of specimens in the group used to establish the initial value of the property.
d
Normal practice is to select n = 2n when the diagnostic criterion is a percentage change
d a
is
of the property from its initial level. When the criterion is an absolute property level, n
d
usually given the value of zero, unless reporting of the initial value is required.

– 14 – 60216-1 © IEC:2013
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).
In some cases (for example, very thick specimens), times greater than two days may be
necessary 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), 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,
the overall temperature range of thermal exposure needs to be carefully selected, observing
the following requirements (if the required thermal endurance characteristics are for a
projected duration of 20 000: see also 5.1.3):
a) the lowest exposure temperature shall be one which will result in a mean or median time
to end-point of more than 5 000 h when determining TI (see also 5.1.3);
b) the extrapolation necessary to establish TI shall not be more than 25 K;
c) the highest exposure temperature shall be one which will result in a mean or median time
to end-point of more than 100 h (if possible, less than 500 h).
For some materials, it is not possible to achieve a time to end-point of less than 500 h while
retaining satisfactory linearity. However, it is important that a smaller range of mean times to
end-point will lead to a larger confidence interval of the result for the same data dispersion.
Relevant and detailed instructions on how to proceed using non-destructive, proof or
destructive test criteria are provided in 5.8.
Table 1 gives guidance in making initial selections.
A number of recommendations and suggestions, useful in establishing times and tempe-
ratures, will be found in Annex B.
5.6 Ageing ovens
Throughout the heat ageing period, ageing ovens shall maintain, in that part of the working
space where specimens are placed, a temperature with tolerances as given in the
IEC 60216-4 series. Unless otherwise specified, IEC 60216-4-1 shall apply.
The circulation of the air within the oven and the exchange of the air content should be
adequate to ensure that the rate of thermal degradation is not influenced by accumulation of
decomposition products or oxygen depletion (see 5.7).

60216-1 © IEC:2013 – 15 –
5.7 Environmental conditions
5.7.1 General
The effects of special environmental conditions such as extreme humidity, chemical
contamination or vibration in many cases may be more appropriately evaluated by insulation
systems tests. However, environmental conditioning, the influence of atmospheres other than
air and immersion in liquids such as oil may be important, but these are not the concern of
this standard.
5.7.2 Atmospheric conditions during ageing
Unless otherwise specified, ageing shall be carried out in ovens operating in the normal
laboratory atmosphere. However, for some materials very sensitive to the humidity in the
ovens, more reliable results are obtained when the absolute humidity in the ageing oven room
is controlled and equal to the absolute humidity corresponding to standard atmosphere B
according to IEC 60212. This, or other specified conditions, shall then be reported.
5.7.3 Conditions for property measurement
Unless otherwise specified, the specimens shall be conditioned before measurement and
measured under conditions as specified in the material standard specification.
5.8 Procedure for ageing
5.8.1 General
This subclause relat
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