IEC 60068-2-78:2025

IEC 60068-2-78 ®
Edition 3.0 2025-08
INTERNATIONAL
STANDARD
REDLINE VERSION
Environmental testing -
Part 2-78: Tests - Test Cab: Damp heat, steady state
ICS 19.040; 29.020 ISBN 978-2-8327-0641-1
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CONTENTS
FOREWORD . 2
INTRODUCTION . 4
1 Scope and object . 5
2 Normative references . 5
3 Terms and definitions . 5
4 General test procedure . 5
4.1 General . 5
4.2 Description of test chamber and measuring system . 6
4.3 Severity . 7
4.4 Pre-conditioning . 8
4.5 Testing procedure . 9
4.6 Recovery procedure . 12
5 Measurements . 12
5.1 Initial measurements . 12
5.2 Intermediate measurements . 12
5.3 Final measurements. 12
6 Information to be given in the relevant specification . 12
7 Information to be given in the test report . 13
Bibliography . 14

Figure 1 – Examples of pre-conditioning phases with transition to the conditioning
periods for a) Method II and b) Method IV . 8
Figure 2 – Test Cab – Method I . 10
Figure 3 – Test Cab – Method II . 10
Figure 4 – Test Cab – Method III . 11
Figure 5 – Test Cab – Method IV . 11

Table 1 – Preferred values for the temperature and relative humidity . 7

INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
Environmental testing -
Part 2-78: Tests - Test Cab: Damp heat, steady state

FOREWORD
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8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is
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This redline version of the official IEC Standard allows the user to identify the changes made
to the previous edition IEC 60068-2-78:2012. A vertical bar appears in the margin wherever a
change has been made. Additions are in green text, deletions are in strikethrough red text.

IEC 60068-2-78 has been prepared by 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 2012. This edition
constitutes a technical revision.
This edition includes the following significant technical changes with respect to the previous
edition:
a) revision of the requirements for the test chamber;
b) revision of the severities and including the dew point temperatures;
c) change of the temperature tolerances of the test to limits;
d) inclusion of a specified preconditioning procedure;
e) inclusion of a new figure for clarification purposes;
f) revision of standardized requirements for the test report.
The text of this International Standard is based on the following documents:
Draft Report on voting
104/1109/FDIS 104/1126/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 the parts in the IEC 60068 series, 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, or
• revised.
INTRODUCTION
This part of IEC 60068 provides a test method of high humidity at constant temperature without
condensation on the specimen over a prescribed specified period. This test is performed to
evaluate the specimen as it is influenced by the absorption and diffusion of moisture and
moisture vapour.
1 Scope and object
This part of IEC 60068 establishes a test method for determining the ability of components or
equipment to withstand transportation, storage and use under conditions of high humidity.
The object of this document is to investigate the effect of high humidity at constant temperature
without condensation on a specimen over a prescribed specified period.
It is applicable to small equipment or components as well as large equipment, and can be
applied to both heat-dissipating and non-heat-dissipating specimens.
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 60068-1:2013, Environmental testing - Part 1: General and guidance
IEC 60068-2-67, Environmental testing - Part 2-67: Tests - Test Cy: Damp heat, steady state,
accelerated test primarily intended for components
IEC 60068-3-6, Environmental testing – Part 3-6: Supporting documentation and guidance –
Confirmation of the performance of temperature and humidity chambers
IEC Guide 104, The preparation of safety publications and the use of basic safety publications
and group safety publications
3 Terms and definitions
None.
For the purposes of this document, the terms and definitions given in IEC 60068-1 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
4 General test procedure
4.1 General
Test Cab can be applied to both heat-dissipating and non-heat-dissipating specimens.
The temperature and relative humidity limits given in this document are intended to take into
account errors in the measurement, slow changes of temperature, and temperature variations
of the working space.
NOTE 1 For further information on the working space, see IEC 60068-3-6.
The temperature and relative humidity refer to the control sensor of the test chamber, if not
specified otherwise.
The limits stated in this document do not take measurement uncertainty into consideration.
NOTE 2 These limits are valid for an empty test space during stabilized temperature/humidity conditions of the test.
In some conditions, where the specimen has a negligible impact on the chamber control, the limits can still be valid
for the chamber with specimen(s). For further information on the operation of a test chamber with specimens, see
IEC 60068-3-7.
NOTE 3 To maintain the relative humidity within the required limits, it can be necessary to keep the temperature
difference between any two points in the working space at any moment within narrower limits.
The dimensions of the test sample shall be such that it is entirely within the working space of
the test chamber. The specimen shall not be placed directly on the floor of the test chamber.
The position of the specimen shall be specified in the relevant specification.
4.2 Description of test chamber and measuring system
The temperature and humidity chamber shall be constructed and verified in accordance with
specifications IEC 60068-3-6.
The chamber and measuring system shall be such that
– sensing devices can be located in the working space to monitor the temperature and
humidity,
NOTE For heat-dissipating specimens, the temperature and humidity near the specimen may be influenced by
the effect of heat dissipation from the specimen.
– condensed water is drained from the chamber and not re-used unless purified,
– no condensed water from the walls and roof of the test chamber can fall on the specimen(s),
– water utilized to maintain humidity levels has electrical conductivity of not more than
20 µS/cm,
– the specimen under test shall not be subjected to radiant heat from the chamber conditioning
devices,
– injected moisture, when applicable, is injected remotely from the specimen and without
being directly on it,
– the volume of the test chamber is at least five times the total volume of the specimen under
test,
– a mounting device, when used, has minimum influence on the heat and humidity exchanges
between specimen and surrounding conditions, unless otherwise specified in the relevant
specification.
The chamber shall be so constructed that:
a) it can produce the temperature and relative humidity given in Table 1 for the requested time
duration;
a) the temperature and relative humidity in the working space can be maintained within the
limits given in Table 1 and 4.5;
b) the conditions prevailing at any point in the working space are uniform and are as similar as
possible to those prevailing in the immediate vicinity of suitably located temperature- and
humidity-sensing devices; the air in the chamber will therefore be continuously stirred at a
rate necessary to maintain the specified conditions of temperature and humidity;
c) the specimen under test is not subjected to radiant heat from the chamber conditioning
processes;
d) the water used for the chamber humidity system complies with the limits given in
IEC 60068-2-67;
e) any water is continuously drained from the chamber and not re-used unless purified;
f) the materials used in the construction do not cause any significant corrosion of the
specimen, or degradation of the quality of the humidifying water;
g) injected moisture, when applicable, is not directly applied to the specimen but injected
remotely from the specimen. Precautions shall be taken that no water droplets can deposit
on the specimen as a result of water injection.
Precautions should be taken to ensure that no condensed water from the walls and roof of the
test chamber can fall on the specimens. The specimen should not significantly impede the air
flow.
Where no specific mounting is specified, the thermal conduction of the mounting shall be low,
so that for all practical purposes the specimen is thermally isolated.
4.3 Severity
The test severity is defined by a combination of temperature, relative humidity and total test
duration. Temperature and relative humidity severities may be selected from the methods given
in Table 1, if not specified otherwise.
Table 1 – Preferred values for the temperature and relative humidity
Temperature Relative humidity
°C % RH
30 ± 2 93 ± 3
30 ± 2 85 ± 3
40 ± 2 93 ± 3
40 ± 2 85 ± 3
Method Temperature Relative humidity Dew point temperature
°C % RH °C
I 28 to 32 82 to 88 24,6 to 29,8
II 28 to 32 90 to 96 26,2 to 31,3
III 38 to 42 82 to 88 34,4 to 39,6
IV 38 to 42 90 to 96 36,1 to 41,2

Preferred test durations are 12 h, 16 h, 24 h, 2 days, 4 days, 10 days, 21 days or 56 days.
The total temperature tolerance of ± 2 K is intended to take account of absolute errors in the
measurement, slow changes of temperature and temperature variations of the working space.
However, in order to maintain the RH within the required tolerances, it is necessary to keep the
temperature difference between any two points in the working space at any moment within
narrower limits. The required humidity conditions will not be achieved if such temperature
differences exceed 1 K. It may also be necessary to keep short-term fluctuations within ± 0,5 K
to maintain the required humidity.
NOTE 1 As detailed in IEC 60068-1:2013, Annex A, this test is used to express component climatic category in the
third set of digits, which denotes the number of days of the damp heat, steady state test Ca.
NOTE 2 The dew point temperatures given in Table 1 are intended as an aid in order to be able to determine
whether condensation can have occurred during the test. If the specimen temperature exceeds the maximum dew
point temperature given in Table 1, the risk of condensation on the specimen can be considered minimal.
Condensation shall not occur on the specimen at any time during the test.
4.4 Pre-conditioning
The relevant specification may call for pre-conditioning.
The specimen shall be introduced into the test chamber either in the unpacked, switched-off,
ready-for-use state, or as otherwise specified in the relevant specification. The temperature of
the specimen shall be high enough to prevent condensation when the specimen is introduced
into the test chamber.
Condensation on the specimen shall always be avoided. Therefore, the specimen shall be
subjected to the temperature of the specified severity, i.e. 28 °C to 32 °C or 38 °C to 42 °C and
a relative humidity of 30 % RH or less for a period of 24 h prior to the test, if not specified
otherwise. Example of pre-conditioning phases for Method II and Method IV are given in
Figure 1.
a) example of pre-conditioning phase for b) example or pre-conditioning phase for
Method II Method IV
Figure 1 – Examples of pre-conditioning phases with transition to the conditioning
periods for a) Method II and b) Method IV
The pre-conditioning phase should be longer than 24 h, if the specimen temperature is still
lower than the dew point temperature applicable for the selected test condition (see Table 1).
If the specimen temperature reaches the pre-conditioning temperature within 24 h, the
pre-conditioning step may be terminated.
4.5 Testing procedure
The specimen shall be introduced into the chamber as required by the relevant specification.
The specimen shall be introduced in the unpacked, switched-off, ready-for-use state, or as
otherwise specified in the relevant specification.
In certain cases the relevant specification may allow the introduction of the specimen in the
chamber when this is already in the condition prescribed for the test; however, condensation
on the specimen shall always be avoided. This can be obtained for small specimens by pre-
heating them to the chamber temperature.
Adjust the temperature in the chamber to the prescribed severity. In order to avoid condensation
on the specimen, control the specimen temperature or allow the specimen to reach the
temperature first and then adjust the humidity in the chamber to the prescribed severity.
Adjust the humidity to the prescribed severity within a period of time of not more than 2 h.
Expose the specimen to the test conditions and duration as specified in the relevant
specification. The duration is measured from the time the specified conditions are achieved.
The relevant specification shall define the operating conditions and the period (or periods) in
which they shall be carried out.
After conditioning at the prescribed severity and before the final measurement, the recovery
procedure shall be followed.
Following the preconditioning procedure, the relative humidity in the test chamber shall be
raised to the relative humidity appropriate to the specified severity in a period of not more than
2 h.
The temperature and relative humidity shall then be maintained within the specified limits for a
duration as specified in the relevant specification. The duration shall commence as soon as the
conditions have stabilized. Figure 2 to Figure 5 show the test procedures with the preceding
stabilization periods according to Method I to Method IV.
The relevant specification shall define the operating conditions and the period (or periods) in
which they shall be carried out.
After conditioning at the specified severity and before the final measurement, the specimen
shall be subjected to the recovery procedure.
Figure 2 – Test Cab – Method I

Figure 3 – Test Cab – Method II
Figure 4 – Test Cab – Method III

Figure 5 – Test Cab – Method IV
4.6 Recovery procedure
The relevant specification shall prescribe the recovery method and duration. Recovery
conditions are described in IEC 60068-1.
At the end of the test, the specimen shall be subjected to the standard atmospheric conditions
for measurements and tests (see IEC 60068-1) for not less than 2 h and not more than 24 h, if
not specified otherwise.
5 Measurements
5.1 Initial measurements
Initial measurements should be performed under standard atmospheric conditions for
measurements and tests (see IEC 60068-1).
The specimen shall be visually inspected and electrically and mechanically checked, as
required by the relevant specification.
5.2 Intermediate measurements
The relevant specification may call for measurements during the test procedure while the
specimen is still in the chamber. If such measurements are required, the relevant specification
shall define the measurements and the period (periods) at which they shall be carried out. For
these measurements, the specimen shall not be removed from the chamber.
The relevant specification can require functional checks during conditioning.
Measurements preceded by a recovery, which would require removal of the specimens from the
test chamber, are not permissible during the conditioning. If it is desired to make intermediate
measurements, the relevant specification should define the measurements and the period(s)
during the conditioning after which they will be carried out.
5.3 Final measurements
The specimen shall be visually inspected and electrically and mechanically checked, as
required by the relevant
...