IEC TS 60721-4-3:2023

IEC TS 60721-4-3
®

Edition 1.0 2023-07
TECHNICAL
SPECIFICATION



Classification of environmental conditions –
Part 4-3: Guidance for the correlation and transformation of environmental
condition classes of IEC 60721-3 to the environmental tests of IEC 60068 –
Stationary use at weatherprotected locations

IEC TS 60721-4-3:2023-07(en)

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IEC TS 60721-4-3

®


Edition 1.0 2023-07




TECHNICAL



SPECIFICATION



















Classification of environmental conditions –

Part 4-3: Guidance for the correlation and transformation of environmental

condition classes of IEC 60721-3 to the environmental tests of IEC 60068 –

Stationary use at weatherprotected locations























INTERNATIONAL

ELECTROTECHNICAL


COMMISSION





ICS  19.040 ISBN 978-2-8322-7300-5




  Warning! Make sure that you obtained this publication from an authorized distributor.


® Registered trademark of the International Electrotechnical Commission

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− 2 − IEC TS 60721-4-3:2023  IEC 2023
CONTENTS
FOREWORD . 3
INTRODUCTION . 5
1 Scope . 6
2 Normative references . 6
3 Terms and definitions . 6
4 General . 7
4.1 General remarks concerning IEC 60721-3-3 . 7
4.2 General remarks concerning the IEC 60068-2 series . 7
4.3 Recommended test procedures and severities . 7
4.4 Environmental tests for in-use classes . 7
4.5 Test durations . 8
4.6 Ambient . 8
5 Climate conditions, classes 3K20 to 3K24 from IEC 60721-3-3 . 8
5.1 Class 3K20 (fully air-conditioned enclosed locations) . 8
5.2 Class 3K21 (continuously temperature-controlled enclosed locations) . 8
5.3 Class 3K22 (temperature-controlled enclosed locations) . 10
5.4 Class 3K23 (enclosed locations having no temperature or humidity control) . 12
5.5 Class 3K24 (enclosed locations having neither temperature nor humidity
control) . 14
6 Special climate conditions, classes 3Z12 to 3Z14 from IEC 60721-3-3 . 16
7 Biological conditions, classes 3B1 to 3B3 from IEC 60721-3-3 . 16
8 Mechanical conditions, classes 3M10 to 3M12 from IEC 60721-3-3 . 17
Annex A (informative) Interdependence of air temperature, relative air humidity, and
absolute air humidity . 18
Bibliography . 19

Figure A.1 – Climatogram of interdependence of air temperature, relative air humidity,
and absolute air humidity . 18

Table 1 – Class 3K21 (continuously temperature-controlled enclosed locations) . 8
Table 2 – Class 3K22 (temperature-controlled enclosed locations) . 10
Table 3 – Class 3K23 (enclosed locations having no temperature or humidity control) . 12
Table 4 – Class 3K24 (enclosed locations having neither temperature nor humidity
control) . 14
Table 5 – Class 3Z12 to 3Z14 . 16
Table 6 – Class 3B1 to 3B3 . 16
Table 7 – Class 3M10 to 3M12 . 17

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IEC TS 60721-4-3:2023  IEC 2023 − 3 −
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________

CLASSIFICATION OF ENVIRONMENTAL CONDITIONS –

Part 4-3: Guidance for the correlation and transformation of
environmental condition classes of IEC 60721-3 to the environmental tests
of IEC 60068 – Stationary use at weatherprotected locations

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
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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
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4) In order to promote international uniformity, IEC National Committees undertake to apply IEC Publications
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between any IEC Publication and the corresponding national or regional publication shall be clearly indicated in
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5) IEC itself does not provide any attestation of conformity. Independent certification bodies provide conformity
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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
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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) 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 TS 60721-4-3 has been prepared by IEC technical committee 104: Environmental
conditions, classification, and methods of test. It is a Technical Specification.
This first edition cancels and replaces IEC TR 60721-4-3:2001 and IEC TR 60721-4-
3:2001/AMD1:2003. This edition constitutes a technical revision.
This edition includes the following significant technical changes with respect to
IEC TR 60721-4-3:2001 and IEC TR 60721-4-3:2001/AMD1:2003:
a) the document has been totally reworked;
b) all figures have been removed, except in Annex A;

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− 4 − IEC TS 60721-4-3:2023  IEC 2023
c) severities have been aligned with those of IEC 60721-3-3:2019.
The text of this Technical Specification is based on the following documents:
Draft Report on voting
104/977/DTS 104/1014/RVDTS

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 Technical Specification 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, availa-
ble 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 60721 series, published under the general title Classification of
environmental conditions, 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.

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IEC TS 60721-4-3:2023  IEC 2023 − 5 −
INTRODUCTION
It is essential to emphasize the guidance nature of this document since it is virtually
impossible to specify mandatory requirements for worldwide use. However, for those cases
which require different tests from those recommended in this document, the guidance given
should establish principles and methodology to determine alternative tests.
The reasons for correlation are provided to enable specification writers to modify a test if their
application warrants it.

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− 6 − IEC TS 60721-4-3:2023  IEC 2023
CLASSIFICATION OF ENVIRONMENTAL CONDITIONS –

Part 4-3: Guidance for the correlation and transformation of
environmental condition classes of IEC 60721-3 to the environmental tests
of IEC 60068 – Stationary use at weatherprotected locations



1 Scope
This part of IEC 60721 deals with the correlation and transformation of the conditions given in
IEC 60721-3-3 to the environmental test procedures defined in IEC 60068-2.
This document provides test procedures and test severities for electrotechnical equipment
operated at stationary weatherprotected locations for the product classes set out in
IEC 60721-3-3.
An environment can consist of several environmental conditions such as dynamic, climatic,
and biological, and other effects due to chemically and mechanically active substances. In
this document, dynamic, air pressure, biological and climatic conditions have been
considered.
The purpose of this document is to provide the specification writer with guidance together with
a set of easy-to-use tables which correlate and transform these environmental conditions.
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 60721-1, Classification of environmental conditions – Part 1: Environmental parameters
and their severities
IEC 60721-3-3:2019, Classification of environmental conditions – Part 3-3: Classification of
groups of environmental parameters and their severities – Stationary use at weatherprotected
locations
3 Terms and definitions
For the purposes of this document, the terms and definitions given IEC 60721-1 and the
following apply.
ISO and IEC maintain terminology databases for use in standardization at the following
addresses:
• IEC Electropedia: available at http://www.electropedia.org
• ISO Online browsing platform: available at http://www.iso.org/obp
3.1
enclosed location
location at which a product is protected from direct exposure to meteorological conditions

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IEC TS 60721-4-3:2023  IEC 2023 − 7 −
4 General
4.1 General remarks concerning IEC 60721-3-3
IEC 60721-3-3 provides classes of groups of environmental parameters with their associated
environmental conditions to which the products can be exposed during use. For more
information of the classes used in this document, IEC 60721-3-3 shall be used.
Parameters in these classes are given individually, but the product can be exposed to
conditions simultaneously. Some of the parameters are independent whilst others can be
strongly correlated, for example, solar radiation and temperature.
4.2 General remarks concerning the IEC 60068-2 series
The IEC 60068-2 series provides a series of environmental test procedures. Each test
procedure can contain a list of several recommended test severities.
Selection of test severities depends upon the failure consequences of the product. Two
different types of products can be placed at a location covered by the same environmental
class. However, one of the products can be tested under significantly more severe conditions
than the other, because of the different failure consequences of the products. This document
only addresses normal failure consequences; for more critical failure consequences, it can be
necessary for the test severity to be increased on the basis of specialist knowledge of the
product.
4.3 Recommended test procedures and severities
Table 1, Table 2, Table 3, Table 4, Table 5, Table 6 and Table 7 provided within this
document set out recommended test procedures and severities, related to classes of groups
of environmental parameters provided within IEC 60721-3-3. These test procedures and
severities are those considered to be suitable for testing most electrotechnical products.
IEC 60721-3-3 specifies severities which have a low probability of being exceeded within that
environmental class. The suggested test severities given in Table 1 to Table 7 of this
document take this into account. For further information, refer to IEC TR 60721-4-0, which
serves as an introduction to the IEC TR 60721-4 series.
The value for the recommended test duration or number of applications provided in Table 1 to
Table 7 are selected on the basis that experience has shown them to be sufficient to
demonstrate the effect of the condition on most products. It is possible that the durations
recommended will not be suitable if the purpose of the test is to establish the durability, safety
or life of an equipment or to quantify reliability. The combination of severity and applied test
duration can also be unsuitable if the purpose of the test is to improve reliability.
4.4 Environmental tests for in-use classes
The in-use classes specify environmental conditions to which the product is exposed whilst
being used, including assembly, non-operational state, maintenance, and repair.
Environmental conditions created by co-located equipment within an enclosure are not
included in this class. The relevant specification should detail when, during the environmental
test programme, the product is in its operational state and which performance requirements
should be measured before, during and after the test, together with the failure criteria.
It is important for the product specification, when referring to a certain class in the
IEC 60721-3 series, to define whether the product is required to be capable of operating or
only to survive without permanent damage when being exposed to the conditions described by
the class.

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− 8 − IEC TS 60721-4-3:2023  IEC 2023
4.5 Test durations
The durations recommended in Table 1 to Table 7 are selected on the basis that experience
has shown them to be sufficient to demonstrate the effect of the condition on most products. It
is possible that the durations recommended will not be suitable if the purpose of the test is to
establish the durability or life of an equipment or to quantify reliability. The combination of
severity and applied test duration can also be unsuitable if the purpose of the test is to
improve reliability.
4.6 Ambient
The term "ambient" which is used for some recommended tests refers to the standard
atmospheric conditions for measurements and tests specified in IEC 60068-1, which shall be
used. The temperature shall be between 15 °C and 35 °C and relative humidity shall be
3
between 25 % and 75 % RH with a maximum absolute humidity of 22 g/m and at air pressure
between 86 kPa and 106 kPa.
5 Climate conditions, classes 3K20 to 3K24 from IEC 60721-3-3
5.1 Class 3K20 (fully air-conditioned enclosed locations)
No tests are recommended for class 3K20 as the severities are within standard atmosphere
conditions as defined in IEC 60068-1 and are therefore considered benign for most products.
5.2 Class 3K21 (continuously temperature-controlled enclosed locations)
Table 1 – Class 3K21
(continuously temperature-controlled enclosed locations)
Recommended
test duration
Environmental Environmental Recommended Recommended
Class and Note
parameter severity test procedure test severity
number of
applications
IEC 60068-2-1,
a
Low air temperature +15 °C Test Ab/Ae: No No
Cold
IEC 60068-2-2:
b
High air temperature +32 °C Dry heat, test +32 °C 16 h
Bb/Be
Low relative humidity 10 %
High relative humidity 75 %
IEC 60068-2-
78, Test Cab:
c
Low absolute
3 No No
2 g/m
Damp heat
humidity
steady state
High absolute
3
22 g/m
humidity
IEC 60068-2-
2 cycles
0,5 K/min
Rate of change of 14, Test Nb:
d
0,5 K/min
3K21
temperature Change of t = 3 h
+15 °C to +32 °C
1
temperature
IEC 60068-2-
e
Low air pressure 70 kPa 13, Test M: Low 70 kPa 30 min
air pressure
IEC 60068-2-
f
High air pressure 106 kPa 13, Test M: Low No No
air pressure
No suitable IEC
2 g
Solar radiation 500 W/m test procedure None None
exists
h i
Heat radiation See - - -
No suitable IEC
Movement of
j
1,0 m/s test procedure None None
surrounding air
exists

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IEC TS 60721-4-3:2023  IEC 2023 − 9 −
Condensation No No No No
Water from sources
No No No No
other than rain
Formation of ice and
frost (including No No No No
freeze-thaw)
a
The low temperature conditions are within the standard atmospheric conditions described in IEC 60068-1, and
so no test is recommended.
b
The choice of the duration of 16 h is sufficient for most products to demonstrate that its design is adequately
toleranced to function at this temperature.
c
The high humidity conditions are within the standard atmospheric conditions described in IEC 60068-1, and so
no test is recommended. For the interdependence of air temperature, relative air humidity and absolute air
humidity see Annex A.
d
Only recommended for products that are sensitive to temperature change. In other cases, no test is recom-
mended as the severities are within the standard atmospheric conditions described in IEC 60068-1.
e
Test normally not required as this air pressure is covered by standard atmospheric conditions according to
IEC 60068-1. For sealed products or for products containing liquids, test M is recommended or if a special
value is required, see Clause 6.
f
Test normally not required as this air pressure is covered by standard atmospheric conditions according to
IEC 60068-1. If a special value is required, see Clause 6.
g
As this condition is secondary effects of the solar radiation through e.g. a window, no test is recommended.
The heating effect is normally included in the high air temperature severity. For products mounted near e.g. a
window, special precautions such as heat shields or insulation can be necessary, or an additional elevated
temperature test can be required.
h
User selection from classes 3Z1, 3Z2, 3Z3.
i
No test is recommended. No value is available in IEC 60721-3-3 for heat radition and the effect is normally
included in the dry heat test. For products mounted near sources of high heat radiation, special precautions
such as heat shields or insulation can be necessary or an additional elevated temperature test can be re-
quired, the degree of elevation being dependent on the severity of the heat source.
j
No test is recommended. No suitable test exists in the IEC 60068-2 series, and the condition is considered as
benign for most products. Precautions should be taken, especially for large products, and it is possible that
the users will have to develop their own methodology if the condition is to be evaluated.

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− 10 − IEC TS 60721-4-3:2023  IEC 2023
5.3 Class 3K22 (temperature-controlled enclosed locations)
Table 2 – Class 3K22
(temperature-controlled enclosed locations)
Recommended
test duration
Environmental Environmental Recommended Recommended
and
Class Note
parameter severity test procedure test severity
number of
applications
IEC 60068-2-1,
a
Low air temperature +5 °C Test Ab/Ae: +5 °C 16 h
Cold
IEC 60068-2-2:
a
High air temperature +40 °C Dry heat, test +40 °C 16 h
Bb/Be
Low relative humidity 5 %
High relative humidity 85 %
IEC 60068-2-78,
Test Cab: Damp
b
Low absolute
3 +30 °C, 85 % RH 4 days
1 g/m
heat steady
humidity
state
High absolute
3
25 g/m
humidity
IEC 60068-2-14,
2 cycles
0,5 K/min
Rate of change of
c
0,5 K/min Test Nb: Change
temperature t = 3 h
+5 °C to +40 °C
1
of temperature
3K22 IEC 60068-2-13,
d
Low air pressure 70 kPa Test M: Low air 70 kPa 2 h
pressure
IEC 60068-2-13,
e
High air pressure 106 kPa Test M: Low air No No
pressure
2 f
Solar radiation 700 W/m No No No
g h
Heat radiation See - - -
Movement of
i
1 m/s No No No
surrounding air
Condensation No No No No
Water from sources
No No No No
other than rain
Formation of ice and
frost (including No No No No
freeze-thaw)

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IEC TS 60721-4-3:2023  IEC 2023 − 11 −
a
The choice of the duration of 16 h is sufficient for most products to demonstrate that its design is adequately
toleranced to function at this temperature.
b
These severities are the nearest preferred values in the IEC 60068-2 series, and the minor differences in both
temperature and humidity from the environmental parameter of IEC 60721-3-3 are considered to be insignifi-
cant and are within normal measurement tolerances. The duration of 4 days is considered to be sufficient for
most products to demonstrate that its design is adequately toleranced to function at this humidity. For the in-
terdependence of air temperature, relative air humidity and absolute air humidity see Annex A.
c
In this class, the temperature range is small and condensation is unlikely to occur, so it is recommended that,
with the possible exception of hermetically sealed products, products containing oscillators, this test should be
omitted.
d
Test normally not required as this air pressure is covered by standard atmospheric conditions according to
IEC 60068-1. For sealed products or for products containing liquids, test M is recommended or if a special val-
ue is required, see Clause 6.
e
Test normally not required as this air pressure is covered by standard atmospheric conditions according to
IEC 60068-1. If a special value is required, see Clause 6.
f
As this condition is secondary effects of the solar radiation through e.g. a window. No test is recommended.
The heating effect is normally included in the high air temperature severity. For products mounted near e.g. a
window, special precautions such as heat shields or insulation can be necessary, or an additional elevated
temperature test can be required.
g
User selection from classes 3Z1, 3Z2, 3Z3.
h
No test is recommended. No value is available in IEC 60721-3-3 for heat radiation and the effect is normally
included in the dry heat test. For products mounted near sources of high heat radiation, special precautions
such as heat shields or insulation can be necessary or an additional elevated temperature test can be re-
quired, the degree of elevation being dependent on the severity of the heat source.
i
No test is recommended. No suitable test exists in the IEC 60068-2 series, and the condition is considered as
benign for most products. Precautions should be taken, especially for large products, and it is possible that the
users will have to develop their own methodology if the condition is to be evaluated.

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− 12 − IEC TS 60721-4-3:2023  IEC 2023
5.4 Class 3K23 (enclosed locations having no temperature or humidity control)
Table 3 – Class 3K23
(enclosed locations having no temperature or humidity control)
Recommended
test duration
Environmental Environmental Recommended Recommended
and
Class Note
parameter severity test procedure test severity
number of
applications
IEC 60068-2-1,
a
Low air temperature −5 °C Test Ab/Ae: −5 °C 16 h
Cold
IEC 60068-2-2:
a
High air temperature +55 °C Dry heat, test +55 °C 16 h
Bb/Be
Low relative humidity 10 %
High relative humidity 100 %
IEC 60068-2-78,
Test Cab: Damp
b
Low absolute
3 +30 °C, 93 % RH 4 days
0,5 g/m
heat steady
humidity
state
High absolute
3
29 g/m
humidity
2 cycles
0,5 K/min
...