IEC 62305-3:2024

SLOVENSKI STANDARD
01-april-2000
Guidance concerning the permissible temperature rise for parts of electrical
equipment, in particular for terminals
Guidance concerning the permissible temperature rise for parts of electrical equipment,
in particular for terminals
Guide concernant l'échauffement admissible des parties des matériels électriques, en
particulier les bornes de raccordement
Ta slovenski standard je istoveten z: IEC/TR 60943
ICS:
29.020 Elektrotehnika na splošno Electrical engineering in
general
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

RAPPORT
CEI
TECHNIQUE – TYPE 3
IEC
TECHNICAL
Deuxième édition
REPORT – TYPE 3
Second edition
1998-01
Guide concernant l’échauffement admissible
des parties des matériels électriques,
en particulier les bornes de raccordement
Guidance concerning the permissible
temperature rise for parts of electrical equipment,
in particular for terminals
 IEC 1998 Droits de reproduction réservés  Copyright - all rights reserved
Aucune partie de cette publication ne peut être reproduite ni No part of this publication may be reproduced or utilized in
utilisée sous quelque forme que ce soit et par aucun any form or by any means, electronic or mechanical,
procédé, électronique ou mécanique, y compris la photo- including photocopying and microfilm, without permission in
copie et les microfilms, sans l'accord écrit de l'éditeur. writing from the publisher.
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CODE PRIX
Commission Electrotechnique Internationale
PRICE CODE XA
International Electrotechnical Commission
Pour prix, voir catalogue en vigueur
For price, see current catalogue

60943 © IEC:1998 – 3 –
CONTENTS
Page
FOREWORD . 7
INTRODUCTION . 11
Clause
Section 1: General
1 General. 15
1.1 Scope and object . 15
1.2 Reference documents. 15
1.3 Definitions. 17
1.4 Symbols. 17
Section 2: Theory
2 General considerations concerning the nature of electric contact and the calculation
and measurement of the ohmic resistance of contacts . 19
2.1 Electric contacts and connection terminals . 19
2.2 Nature of electrical contact. 19
2.3 Calculation of contact resistance . 23
3 Ageing mechanisms of contacts and connection terminals . 31
3.1 General. 31
3.2 Contacts of dissimilar metals. 33
3.3 Oxidation ageing mechanisms. 37
3.4 Results concerning ageing of copper contacts . 41
3.5 Usage and precautions to be taken in the use of copper contact materials . 47
4 Calculation of temperature rise of conductors, contacts and connection terminals . 49
4.1 Symbolic representation. 49
4.2 Temperature rise ΔT of a conductor with respect to the temperature T of the
s e
surrounding medium. 53
4.3 Temperature rise ΔT in the vicinity of the contact: temperature rise
o
of connection terminals . 55
4.4 Temperature rise of the elementary contact points. 55
Section 3: Application
5 Permissible temperature and temperature rise values. 57
5.1 Ambient air temperature Θ . 57
a
5.2 Temperature and temperature rise of various equipment components . 59
5.3 Temperature and temperature rise of conductors connecting electrical
equipment. 75
5.4 Temperature and temperature rise of connection terminals for electrical
equipment – Influence on connected conductors. 77

60943 © IEC:1998 – 5 –
Clause Page
6 General procedure to be followed for determining permissible temperature and
temperature rise. 79
6.1 Basic parameters. 79
6.2 Method to be followed for determining maximum permissible temperature
and temperature rise . 79
Annexes
A Numerical examples of the application of the theory and other data . 83
B Physical characteristics of selected metals and alloys. 89
C Physical characteristics of fluid dielectrics . 91
D Information on the reaction of contact metals with substances in the atmosphere. 93
E Temperature rise of a conductor cooled by radiation and convection
in the vicinity of a terminal . 95
F List of symbols used in this report. 113
G Bibliography . 117

60943 © IEC:1998 – 7 –
INTERNATIONAL ELECTROTECHNICAL COMMISSION
__________
GUIDANCE CONCERNING THE PERMISSIBLE TEMPERATURE RISE
FOR PARTS OF ELECTRICAL EQUIPMENT,
IN PARTICULAR FOR TERMINALS
FOREWORD
1) The IEC (International Electrotechnical Commission) is a worldwide organization for standardization comprising
all national electrotechnical committees (IEC National Committees). The object of the 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, the IEC publishes International Standards. Their preparation is
entrusted to technical committees; any IEC National Committee interested in the subject dealt with may
participate in this preparatory work. International, governmental and non-governmental organizations liaising
with the IEC also participate in this preparation. The 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 the 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 National Committees.
3) The documents produced have the form of recommendations for international use and are published in the form
of standards, technical reports or guides and they are accepted by the National Committees in that sense.
4) In order to promote international unification, IEC National Committees undertake to apply IEC International
Standards transparently to the maximum extent possible in their national and regional standards. Any
divergence between the IEC Standard and the corresponding national or regional standard shall be clearly
indicated in the latter.
5) The IEC provides no marking procedure to indicate its approval and cannot be rendered responsible for any
equipment declared to be in conformity with one of its standards.
6) Attention is drawn to the possibility that some of the elements of this International Standard may be the subject
of patent rights. The IEC shall not be held responsible for identifying any or all such patent rights.
The main task of IEC technical committees is to prepare International Standards. In
exceptional circumstances, a technical committee may propose the publication of a technical
report of one of the following types:
• type 1, when the required support cannot be obtained for the publication of an
International Standard, despite repeated efforts;
• type 2, when the subject is still under technical development or where for any other
reason there is the future but no immediate possibility of an agreement on an International
Standard;
• type 3, when a technical committee has collected data of a different kind from that
which is normally published as an International Standard, for example "state of the art".
Technical reports of types 1 and 2 are subject to review within three years of publication to
decide whether they can be transformed into International Standards. Technical reports of
type 3 do not necessarily have to be reviewed until the data they provide are considered to be
no longer valid or useful.
IEC 60943, which is a technical report of type 3, has been prepared by IEC technical
committee 32: Fuses.
This second edition cancels and replace the first edition which was issued in 1989.

60943 © IEC:1998 – 9 –
The text of this technical report is based on the following documents:
Committee draft Report on voting
32/142/CDV 32/148/RVC
Full information on the voting for the approval of this technical report can be found in the report
on voting indicated in the above table.
Annexes are for information only.

60943 © IEC:1998 – 11 –
INTRODUCTION
a) The temperature rise encountered in electrical assemblies as a result of the various losses
in the conductors, contacts, magnetic circuits, etc. is of growing importance as a result of
the development of new techniques of construction and operation of equipment.
This development has been particularly significant in the field of assemblies, where
numerous components dissipating energy (contactors, fuses, resistors, etc.), in particular
modular devices are found within enclosures of synthetic materials which are somewhat
impermeable to heat.
This temperature rise results in a relatively high temperature of the basic elements
constituting the electric contacts: a high temperature favours oxidation at the contact
interface, increases its resistance and thereby leads to further heating, and thus to an even
higher temperature. If the component material of the contact is unsuitable or insufficiently
protected, the contact may be irreparably damaged before the calculated useful life of the
equipment has expired.
Such temperature rises also affect connection terminals and the connected conductors, and
their effects should be limited in order to ensure that the insulation of the conductors
remains satisfactory throughout the life of the installation.
b) In view of these problems, this report has been prepared with the following objectives:
– to analyze the various heating and oxidation phenomena to which the contacts, the
connection terminals and the conductors leading to them are subjected, depending on
their environment and their arrangement;
– to provide elementary rules to product committees to enable them to specify permissible
temperatures and temperature rises.
c) Attention is drawn to the precautions to be taken for sets of components when parts are
grouped together in the same enclosure.
The attention of users should be drawn particularly to the fact that the temperature rise of
terminals permitted by particular switchgear standards results from conventional situations
during type tests; these can differ appreciably from the situations met with in practice, which
have to be taken into account, particularly because of the temperatures permitted by the
insulation of the conductors which may be connected to the terminals under normal
conditions.
d) Attention is drawn to the fact that in the relevant product standards, the permissible
temperature and temperature rise for the external terminals are measured during
conventional type tests and therefore they may not reflect the actual situation likely to occur
in normal use.
Suitable precautions should then be adopted to avoid exposure to temperatures that may
affect the life of materials adjacent to the terminals of components.
In this case, it is essential to distinguish the concept of "external ambient temperature"
which prevails outside the enclosure from that of "the temperature of the fluid surrounding a
part" which comprises the external ambient temperature plus the internal temperature rise
due to the parts. These concepts, as well as other complementary concepts such as the
thermal resistance of an enclosure, are dealt with in clause 5 and explained by means of
numerical examples.
In order to facilitate complete calculation, this report links up the temperature of the fluid
surrounding a component to the external ambient temperature by the introduction of the
concept of "coefficient of filling" and gives a numerical example (5.2.3.2) which specifies the
values of the coefficient of filling to be used in several practical cases.

60943 © IEC:1998 – 13 –
The quantities involved in calculating contact constriction resistance are subject to wide
variations due to the physical conditions and degree of contamination of the surface in
contact. By calculation alone, therefore, the contact resistance can be estimated to an
accuracy of no
...