IEC 60068-3-1:2023

IEC 60068-3-1 ®
Edition 3.0 2023-06
REDLINE VERSION
INTERNATIONAL
STANDARD
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Environmental testing –
Part 3-1: Supporting documentation and guidance – Cold and dry heat tests

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IEC 60068-3-1 ®
Edition 3.0 2023-06
REDLINE VERSION
INTERNATIONAL
STANDARD
colour
inside
Environmental testing –
Part 3-1: Supporting documentation and guidance – Cold and dry heat tests
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 19.040 ISBN 978-2-8322-7181-0

– 2 – IEC 60068-3-1:2023 RLV © IEC 2023
CONTENTS
FOREWORD . 3
1 Scope . 5
2 Normative references . 5
3 Terms and definitions . 5
4 Selection of test procedures . 6
4.1 General background . 6
4.1.1 General . 6
4.1.2 Ambient temperature . 6
4.1.3 Specimen temperatures . 6
4.1.4 Specimens without heat dissipation Non heat-dissipating specimens . 6
4.1.5 Specimens with heat dissipation Heat-dissipating specimens. 7
4.2 Mechanisms of heat transfer . 7
4.2.1 Convection . 7
4.2.2 Radiation . 10
4.2.3 Thermal conduction . 11
4.2.4 Forced air circulation . 11
4.3 Test chambers . 11
4.3.1 General . 11
4.3.2 Methods of achieving the required conditions in the test chamber . 12
4.4 Measurements . 12
4.4.1 Temperature . 12
4.4.2 Air velocity . 12
Annex A (informative) Effect of airflow on chamber conditions and on surface
temperatures of test specimens . 13
A.1 Calculation . 13
A.2 Specimen temperature . 13
A.3 Gradient between incoming and outgoing air . 13
Bibliography . 15

Figure 1 – Experimental data on the effect of airflow on the surface temperature of a
wire-wound resistor – Radial airflow . 8
Figure 2 – Experimental data on the effect of airflow on the surface temperature of a
wire-wound resistor – Axial airflow . 9
Figure 3 – Temperature distribution on a cylinder with homogeneous heat generation in
−1
airflow of velocities (0,5, 1 and 2) m · s . 10

Table 1 – Influence parameters when testing heat-dissipating specimens . 12

INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
ENVIRONMENTAL TESTING –
Part 3-1: Supporting documentation and guidance –
Cold and dry heat tests
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
can 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) Attention is drawn to the possibility that some of the elements of this IEC Publication can be the subject of patent
rights. IEC shall not be held responsible for identifying any or all such patent rights.
This redline version of the official IEC Standard allows the user to identify the changes
made to the previous edition IEC 60068-3-1:2011. A vertical bar appears in the margin
wherever a change has been made. Additions are in green text, deletions are in
strikethrough red text.
– 4 – IEC 60068-3-1:2023 RLV © IEC 2023
IEC 60068-3-1 has been prepared by IEC technical committee 104: Environmental conditions,
classification and methods of test. It is an International Standard.
This third edition cancels and replaces the second edition published in 2011. This edition
constitutes a technical revision.
This edition includes the following significant technical changes with respect to the previous
edition:
a) information relating to specimen temperatures has been revised;
b) information relating to tests of multiple specimens has been revised;
c) the effect of air density has been added;
d) a recommendation for corrective actions regarding IR radiation has been added;
e) the requirements for the mounting and supports of the specimen have been revised.
The text of this International Standard is based on the following documents:
Draft Report on voting
104/986/FDIS 104/1002/RVD
Full information on the voting for its approval can be found in the report on voting indicated in
the above table.
The language used for the development of this International Standard is English.
This document was drafted in accordance with ISO/IEC Directives, Part 2, and developed in
accordance with ISO/IEC Directives, Part 1 and ISO/IEC Directives, IEC Supplement, available
at www.iec.ch/members_experts/refdocs. The main document types developed by IEC are
described in greater detail at www.iec.ch/publications.
A list of all parts in the IEC 60068 series, published under the general title Environmental
testing, 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,
• replaced by a revised edition, or
• amended.
IMPORTANT – The "colour inside" logo on the cover page of this document indicates that it
contains colours which are considered to be useful for the correct understanding of its
contents. Users should therefore print this document using a colour printer.

ENVIRONMENTAL TESTING –
Part 3-1: Supporting documentation and guidance –
Cold and dry heat tests
1 Scope
This part of IEC 60068 provides guidance regarding the performance of cold and dry heat tests.
2 Normative references
The following referenced documents are indispensable for the application 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 60068-1, Environmental testing – Part 1: General and guidance
IEC 60068-2-1, Environmental testing – Part 2-1: Tests – Test A: Cold
IEC 60068-2-2, Environmental testing – Part 2-2: Tests – Test B: Dry heat
There are no normative references in this document.
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
heat-dissipating specimen
specimen on which the hottest point on its surface, measured in free-air conditions and under
the air pressure as specified in IEC 60068-1, is more than 5 K above the ambient temperature
of the surrounding atmosphere after thermal stability has been reached
[SOURCE: IEC 60068-1:2013, 3.6, modified – The definition has been slightly adapted and
Note 1 to entry has been deleted.]
3.2
non heat-dissipating specimen
specimen that does not produce heat to a level that can affect the air temperature surrounding
the specimen or those specimens located nearby
specimen on which the hottest point on its surface, measured in free-air conditions and under
the air pressure as specified in IEC 60068-1, is equal or less than 5 K above the ambient
temperature of the surrounding atmosphere after thermal stability has been reached

– 6 – IEC 60068-3-1:2023 RLV © IEC 2023
3.3
free-air conditions
conditions within an infinite space where the movement of the air is affected only by the heat-
dissipating specimen
Note 1 to entry: Free-air conditions can apply to the laboratory environment. The conditions during the
measurement should be stated in the test report (if not specified otherwise).
[SOURCE: IEC 60068-1:2013, 3.7, modified – In the preferred term "free" has been added, in
the definition "itself" has been deleted and the Note 1 to entry has been added.]
4 Selection of test procedures
4.1 General background
4.1.1 General
Specimen performance may can be influenced or limited by the temperatures in which the
specimen is operated. The level of influence may can be affected by test gradients that exist
within the test system (climatic or environmental chamber) and internal temperatures within the
specimen itself. In order to determine the level of influence that exists and to ensure that the
specimen is designed appropriately, cold and/or dry heat tests or both are performed.
4.1.2 Ambient temperature
The maximum and minimum ambient temperature values, where in which the specimen will be
subjected is intended to operate, should be known. Preferred values for testing purposes are
provided in IEC 60068‑2‑1 or IEC 60068-2-2 or both.
Difficulties can arise due to the fact that heat transfer causes temperature variations in the area
surrounding the specimen. Consequently, the effect from the transfer of heat to the ambient
temperature of the surrounding atmosphere should be considered. Airflow related to spacing
between specimens should also be considered when performing a test.
4.1.3 Specimen temperatures
The performance of the specimen can be affected by its own temperature in the case of heat-
dissipating specimens. Because of this, when controlling the test environment, it may can be
necessary to measure the temperature of the specimen under test at different locations, both
internally and externally.
The change of temperature at a point on the surface of a specimen follows approximately an
exponential law. Inside large specimens, temperature equalization can be reached with
significant delay.
In case of doubt, how the temperature change is reflected by the specimen, the monitoring of
the temperature of the specimens at a representative point (or points) is recommended.
NOTE For further information on the influence of test temperatures on specimens, IEC 60068-2-14 or
IEC 60068-3-11 can be helpful.
4.1.4 Specimens without heat dissipation Non heat-dissipating specimens
lf the ambient temperature is uniform and constant and there is no generation of heat within the
specimen, heat will flow from the ambient atmosphere into the specimen if the ambient
atmosphere is at a higher temperature. Conversely, heat will flow from the specimen into the
ambient atmosphere if the specimen is at a higher temperature. This heat transfer will continue
until the specimen has completely reached thermal equilibrium with the surrounding
atmosphere. From that moment on, the heat transfer ceases and will not start again unless the
ambient temperature changes.
4.1.5 Specimens with heat dissipation Heat-dissipating specimens
If heat is generated within the specimen, the temperature of the specimen will rise to a
stabilization point above the ambient temperature. It follows that if a steady temperature is
reached, heat will flow continuously from the specimen by convection, radiation, and/or
conduction into the atmosphere whereby the specimen is cooled.
If more than one specimen is subjected to a dry heat test in the same chamber, it is necessary
to ensure that all specimens are in the same ambient temperature and have identical mounting
conditions. It has not, however, been found It can become necessary to differentiate between
testing of single specimens and multiple specimens when the cold test is being performed.
NOTE If more than one specimen is tested in the same test chamber, a uniform incoming airflow can be disturbed.
4.2 Mechanisms of heat transfer
4.2.1 Convection
Heat transfer through convection is an important factor when testing heat-dissipating
specimens. The coefficient of heat transfer from the surface of the test specimen to the ambient
air is affected by the velocity and density of the surrounding air. The greater the air velocity,
the more efficient the heat transfer is. Therefore, the higher the air velocity, the lower the
surface temperature of the test specimen will be with the same temperature of the ambient air.
This effect is illustrated in Figure 1 and Figure 2.
Air density also has a significant influence on heat transfer. Cold air is denser than warm air.
Therefore, hot air causes a lower heat transfer than cold air.

– 8 – IEC 60068-3-1:2023 RLV © IEC 2023

Figure 1 – Experimental data on the effect of airflow on the surface temperature
of a wire-wound resistor – Radial airflow

Figure 2 – Experimental data on the effect of airflow on the surface temperature
of a wire-wound resistor – Axial airflow
In addition to the influence on the surface temperature of the test specimen, the airflow within
the chamber will also affect the temperature distribution over the surface of the specimen under
test. This effect is illustrated in Figure 3.
Therefore, when testing heat-dissipating specimens, the effects of airflow around or over the
specimen should be known to ensure that the conditions approximate as close as possible
typical free-air conditions or those conditions expected when the specimen is in use.

– 10 – IEC 60068-3-1:2023 RLV © IEC 2023

Figure 3 – Temperature distribution on a cylinder with homogeneous heat generation
−1
in airflow of velocities (0,5, 1 and 2) m · s
4.2.2 Radiation
Heat transfer by thermal radiation cannot be neglected when test chamber conditions for testing
of heat-dissipating specimens are considered. In a "free air" condition, the heat transferred from
the test specimen is absorbed by its surroundings.
Corrective actions should be considered to minimize the effect of IR radiation.
NOTE IR radiation through the chamber window (observing window) can impact the specimen’s temperature. This
effect can be increased by radiation heating systems in the laboratory or windows in the laboratory allowing IR
radiation of the sun to enter the test space.

4.2.3 Thermal conduction
Heat transfer by thermal conduction depends on the thermal characteristics of mounting and
other connections. These should be known in advance of the test.
Many heat-dissipating specimens are intended to be mounted on heat sinks or other well-
conducting elements, with the result that a certain amount of heat is effectively transferred
through thermal conduction.
The relevant specification shall should define the thermal characteristics of the mounting and
these characteristics should be reproduced when the test is made.
If a specimen can be mounted in more than one manner with different values of thermal
conduction, the mounting device with the lowest thermal conductivity for dry heat tests on a
specimen with heat dissipation and the mounting device with the highest thermal conductivity
for all the other tests (dry heat tests on specimens without heat dissipation, cold tests on
specimens with or without heat dissipation) should be used.
The thermal conduction of the mounting or supports should be low, such that for practical
purposes the specimen is thermally isolated, if not specified otherwise. When testing several
specimens simultaneously they should be so placed that free circulation is provided between
specimens, and between specimens and chamber surfaces.
4.2.4 Forced air circulation
To verify that the temperature at representative points on the surface of the test specimen is
not unduly influenced by the air velocity used in the chamber, measurements should be made
with the specimen inside the chamber, with the chamber operating at standard atmospheric
conditions for measurement and tests (see IEC 60068-1). If the surface temperature at any
point of the test specimen is not reduced by more than 5 K by the influence of the air circulation
used in the chamber, the cooling effect of the forced air circulation may can be ignored.
Where the reduction of surface temperature exceeds 5 K, the temperatures from a
representative number of points on the surface of the test specimen should be measured in
order to give a basis for calculation of the surface temperatures at the specified test conditions.
These measurements should be carried out under those load conditions which are specified for
the test temperature by the relevant specification.
For small temperature differences below 5 K between the ambient temperature and surface
temperature of the specimen, the surface temperature can be assumed to be the same when
tested at different ambient temperatures.
The choice of representative points to be checked should be based on a detailed knowledge of
the test specimen (thermal distribution, thermally critical points, etc.). A single chamber
characterization may can cover the chamber performance for a long series of the same type of
tests with similar specimens, whereas in other cases it can be necessary for a characterization
may need to be made prior to each test for different types of specimens.
4.3 Test chambers
4.3.1 General
Even in very large chambers, the air circulation and temperature distribution around the test
specimen will not be identical with actual free-air conditions. It is not practical for testing
purposes to try to reproduce free-air conditions, but it is possible to simulate the effects of these
conditions. Nevertheless, it is established by experimental results and test experience that a
reasonably large chamber with low air flow through the workspace will affect the temperature
of the test specimen in approximately the same way as would free-air conditions.

– 12 – IEC 60068-3-1:2023 RLV © IEC 2023
Table 1 lists the parameters of a test chamber that should be considered when testing heat-
dissipating specimens.
Table 1 – Influence parameters when testing heat-dissipating specimens
Convection
Transfer
Radiation Conduction
Free air Forced air
mechanism
circulation
Chamber Chamber Chamber dimensions, Emissivity of the Thermal characteristic
parameter dimensions air velocity chamber walls of mounting

4.3.2 Methods of achieving the required conditions in the test chamber
4.3.2.1 Design of chambers for simulating the effect of free-air conditions
Heating and cooling components used to control the temperature of the working space should
not be placed in the working space.
4.3.2.2 Design of chambers with forced air circulation
The airflow should be as uniform as possible and should be directed in such a way to minimize
the variation that would occur due to convection. The effects of airflow are given in more detail
in Annex A.
4.4 Measurements
4.4.1 Temperature
Measurement of the temperature at various points on or in a specimen are recommended for
tests involving heat-dissipating specimens in conditions other than "free air". The choice of
representative points should be based on a detailed knowledge of the test specimen (thermal
distribution, thermally critical points, etc.).
4.4.2 Air velocity
The velocity of the air in the test chamber should be known to ensure uniformity of conditions
within the chamber in the case of testing multiple specimens in the same chamber.
Measurements should be made based on the working space within the chamber and the size
and shape of the test specimen.
If more than one specimen is tested in the same test chamber, a uniform incoming airflow can
be disturbed. It should be taken into consideration that one specimen can shield the other.

Annex A
(informative)
Effect of airflow on chamber conditions and
on surface temperatures of test specimens
A.1 Calculation
For the calculation of the effect of airflow on a specimen temperature and on the temperature
gradient in the chamber the following symbols are used, where:
−1
V is the air velocity (m ⋅ s );
−2 −1
λ(V) is the heat transfer coefficient (W ⋅ m ⋅ K );
P is the quantity of heat transferred in unit time (W);
F is the effective area of the heat-dissipating surface (m );
t is the time (s);
−1
G is the mass of incoming or outgoing air per unit time (kg ⋅ s );
−1 −1
C is the specific heat of air at constant pressure (1 000 J ⋅ kg ⋅ K );
p
−3
γ is the density of air (1,29 kg ⋅ m );
S is the cross-sectional area of the chamber (m );
T is the temperature (K).
A.2 Specimen temperature
The following equation expresses a specimen temperature:
1 P
T ×
λ(V) F
where
λ(V) = a + bV
a ≅ 10
a
–1
V < < 3 m ⋅ s
b
Experimental results indicate that, at the low air velocities relevant to the tests, b ≅ 3; b
–1
increases with increasing air velocity until at 3 m ⋅ s , b ≅ 8.
−1
If V = 0,3 m ⋅ s , the error in T ≤ 10 %.
A.3 Gradient between incoming and outgoing air
The gradient between incoming and outgoing air is expressed as:
P
∆T =
air
CG
p
=
– 14 – IEC 60068-3-1:2023 RLV © IEC 2023
Substituting numerical values for a cubic chamber of 0,5 m side length with an airflow of
–1
0,3 m ⋅ s and a power dissipation within the chamber of 100 W gives:
S = 0,25 m
∆T = K ≅ 1 K
air
1000 × 0,25 × 0,3 ×1,29
100 W
ΔT ≅ 1 K
air
J m kg
1000 × 0,25 m × 0,,3 ×1 29
kg ⋅ K s
m
Up to 100 W dissipation, there is little concern. At 1 kW, a chamber with a larger volume or
higher air exchange should be considered.

=
Bibliography
IEC 60068-1:2013, Environmental testing – Part 1: General and guidance
IEC 60068-2-1, Environmental testing – Part 2-1: Tests – Test A: Cold
IEC 60068-2-2, Environmental testing – Part 2-2: Tests – Test B: Dry heat
IEC 60068-2-14, Environmental testing – Part 2-14: Tests – Test N: Change of temperature
IEC 60068-3-11, Environmental testing – Part 3-11: Supporting documentation and guidance –
Calculation of uncertainty of conditions in climatic test chambers

___________
IEC 60068-3-1 ®
Edition 3.0 2023-06
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Environmental testing –
Part 3-1: Supporting documentation and guidance – Cold and dry heat tests

Essais d'environnement –
Partie 3-1: Documentation d'accompagnement et recommandations – Essais de
froid et de chaleur sèche
– 2 – IEC 60068-3-1:2023 © IEC 2023
CONTENTS
FOREWORD . 3
1 Scope . 5
2 Normative references . 5
3 Terms and definitions . 5
4 Selection of test procedures . 6
4.1 General background . 6
4.1.1 General . 6
4.1.2 Ambient temperature . 6
4.1.3 Specimen temperatures . 6
4.1.4 Non heat-dissipating specimens . 6
4.1.5 Heat-dissipating specimens . 6
4.2 Mechanisms of heat transfer . 7
4.2.1 Convection . 7
4.2.2 Radiation . 10
4.2.3 Thermal conduction . 11
4.2.4 Forced air circulation . 11
4.3 Test chambers . 11
4.3.1 General . 11
4.3.2 Methods of achieving the required conditions in the test chamber . 12
4.4 Measurements . 12
4.4.1 Temperature . 12
4.4.2 Air velocity . 12
Annex A (informative) Effect of airflow on chamber conditions and on surface
temperatures of test specimens . 13
A.1 Calculation . 13
A.2 Specimen temperature . 13
A.3 Gradient between incoming and outgoing air . 13
Bibliography . 15

Figure 1 – Experimental data on the effect of airflow on the surface temperature of a
wire-wound resistor – Radial airflow . 8
Figure 2 – Experimental data on the effect of airflow on the surface temperature of a
wire-wound resistor – Axial airflow . 9
Figure 3 – Temperature distribution on a cylinder with homogeneous heat generation in
−1
airflow of velocities (0,5, 1 and 2) m · s . 10

Table 1 – Influence parameters when testing heat-dissipating specimens . 12

INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
ENVIRONMENTAL TESTING –
Part 3-1: Supporting documentation and guidance –
Cold and dry heat tests
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
can 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) Attention is drawn to the possibility that some of the elements of this IEC Publication can be the subject of patent
rights. IEC shall not be held responsible for identifying any or all such patent rights.
IEC 60068-3-1 has been prepared by IEC technical committee 104: Environmental conditions,
classification and methods of test. It is an International Standard.
This third edition cancels and replaces the second edition published in 2011. This edition
constitutes a technical revision.
This edition includes the following significant technical changes with respect to the previous
edition:
a) information relating to specimen temperatures has been revised;
b) information relating to tests of multiple specimens has been revised;
c) the effect of air density has been added;
d) a recommendation for corrective actions regarding IR radiation has been added;
e) the requirements for the mounting and supports of the specimen have been revised.

– 4 – IEC 60068-3-1:2023 © IEC 2023
The text of this International Standard is based on the following documents:
Draft Report on voting
104/986/FDIS 104/1002/RVD
Full information on the voting for its approval can be found in the report on voting indicated in
the above table.
The language used for the development of this International Standard is English.
This document was drafted in accordance with ISO/IEC Directives, Part 2, and developed in
accordance with ISO/IEC Directives, Part 1 and ISO/IEC Directives, IEC Supplement, available
at www.iec.ch/members_experts/refdocs. The main document types developed by IEC are
described in greater detail at www.iec.ch/publications.
A list of all parts in the IEC 60068 series, published under the general title Environmental
testing, 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,
• replaced by a revised edition, or
• amended.
ENVIRONMENTAL TESTING –
Part 3-1: Supporting documentation and guidance –
Cold and dry heat tests
1 Scope
This part of IEC 60068 provides guidance regarding the performance of cold and dry heat tests.
2 Normative references
There are no normative references in this document.
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
heat-dissipating specimen
specimen on which the hottest point on its surface, measured in free-air conditions and under
the air pressure as specified in IEC 60068-1, is more than 5 K above the ambient temperature
of the surrounding atmosphere after thermal stability has been reached
[SOURCE: IEC 60068-1:2013, 3.6, modified – The definition has been slightly adapted and
Note 1 to entry has been deleted.]
3.2
non heat-dissipating specimen
specimen on which the hottest point on its surface, measured in free-air conditions and under
the air pressure as specified in IEC 60068-1, is equal or less than 5 K above the ambient
temperature of the surrounding atmosphere after thermal stability has been reached
3.3
free-air conditions
conditions within an infinite space where the movement of the air is affected only by the heat-
dissipating specimen
Note 1 to entry: Free-air conditions can apply to the laboratory environment. The conditions during the
measurement should be stated in the test report (if not specified otherwise).
[SOURCE: IEC 60068-1:2013, 3.7, modified – In the preferred term "free" has been added, in
the definition "itself" has been deleted and the Note 1 to entry has been added.]

– 6 – IEC 60068-3-1:2023 © IEC 2023
4 Selection of test procedures
4.1 General background
4.1.1 General
Specimen performance can be influenced or limited by the temperatures in which the specimen
is operated. The level of influence can be affected by test gradients that exist within the test
system (climatic or environmental chamber) and internal temperatures within the specimen
itself. In order to determine the level of influence that exists and to ensure that the specimen is
designed appropriately, cold or dry heat tests or both are performed.
4.1.2 Ambient temperature
The maximum and minimum ambient temperature values, in which the specimen is intended to
operate, should be known. Preferred values for testing purposes are provided in IEC 60068‑2‑1
or IEC 60068-2-2 or both.
Difficulties can arise due to the fact that heat transfer causes temperature variations in the area
surrounding the specimen. Consequently, the effect from the transfer of heat to the ambient
temperature of the surrounding atmosphere should be considered. Airflow related to spacing
between specimens should also be considered when performing a test.
4.1.3 Specimen temperatures
The performance of the specimen can be affected by its own temperature in the case of heat-
dissipating specimens. Because of this, when controlling the test environment, it can be
necessary to measure the temperature of the specimen under test at different locations, both
internally and externally.
The change of temperature at a point on the surface of a specimen follows approximately an
exponential law. Inside large specimens, temperature equalization can be reached with
significant delay.
In case of doubt, how the temperature change is reflected by the specimen, the monitoring of
the temperature of the specimens at a representative point (or points) is recommended.
NOTE For further information on the influence of test temperatures on specimens, IEC 60068-2-14 or
IEC 60068-3-11 can be helpful.
4.1.4 Non heat-dissipating specimens
lf the ambient temperature is uniform and constant and there is no generation of heat within the
specimen, heat will flow from the ambient atmosphere into the specimen if the ambient
atmosphere is at a higher temperature. Conversely, heat will flow from the specimen into the
ambient atmosphere if the specimen is at a higher temperature. This heat transfer will continue
until the specimen ha
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