IEC 60364-4-43

NORME CEI
INTERNATIONALE IEC
60364-4-43
INTERNATIONAL
Deuxième édition
STANDARD
Second edition
2001-08
Installations électriques des bâtiments –
Partie 4-43:
Protection pour assurer la sécurité –
Protection contre les surintensités
Electrical installations of buildings –
Part 4-43:
Protection for safety –
Protection against overcurrent
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60364-4-43 © IEC:2001 – 3 –
CONTENTS
FOREWORD . 5
430 Introduction.7
430.1 Scope . 7
430.2 Normative references . 7
431 Requirements according to the nature of the circuits. 9
431.1 Protection of phase conductors . 9
431.2 Protection of the neutral conductor . 9
431.3 Disconnection and reconnection of the neutral conductor. 11
432 Nature of protective devices . 11
432.1 Devices ensuring protection against both overload current and
short-circuit current . 11
432.2 Devices ensuring protection against overload current only . 11
432.3 Devices ensuring protection against short-circuit current only . 11
433 Protection against overload current . 13
433.1 Co-ordination between conductors and overload protective devices . 13
433.2 Position of devices for overload protection. 13
433.3 Omission of devices for protection against overload. 15
433.4 Position or omission of devices for protection against overload in IT systems. 15
433.5 Cases where omission of devices for overload protection is recommended
for safety reasons . 15
433.6 Overload protection of conductors in parallel . 17
434 Protection against short-circuit currents . 17
434.1 Determination of prospective short-circuit currents . 17
434.2 Position of devices for short-circuit protection . 17
434.3 Omission of devices for short-circuit protection . 19
434.4 Short-circuit protection of conductors in parallel. 19
434.5 Characteristics of short-circuit protective devices . 19
435 Co-ordination of overload and short-circuit protection . 23
435.1 Protection afforded by one device . 23
435.2 Protection afforded by separate devices . 23
436 Limitation of overcurrent by characteristics of supply . 23
Annex A (informative) Protection of conductors in parallel against overcurrent. 25
Annex B (informative) IEC 60364 – Parts 1 to 6: Restructuring . 33
Bibliography . 41
Figure A.1 – Circuit in which an overload protective device is provided for each of
the m conductors in parallel . 27
Figure A.2 – Circuit in which a single overload protective device is provided for
the m conductors in parallel . 29
Figure A.3 – Current flow at the beginning of the fault . 31
Figure A.4 – Current flow after operation of the protective device cs. 31
Table 43A – Values of k for phase conductor . 21
Table B.1 – Relationship between restructured and original parts . 33
Table B.2 – Relationship between new and old clause numbering. 37

60364-4-43 © IEC:2001 – 5 –
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
ELECTRICAL INSTALLATIONS OF BUILDINGS –
Part 4-43: Protection for safety –
Protection against overcurrent
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 specifications, 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.
International Standard IEC 60364-4-43 has been prepared by IEC technical committee 64:
Electrical installations and protection against electric shock.
The IEC 60364 series (parts 1 to 6), is currently being restructured, without any technical
changes, into a more simple form (see annex B).
According to a unanimous decision by the Committee of Action (CA/1720/RV (2000-03-21)),
the restructured parts of IEC 60364 have not been submitted to National Committees for
approval.
The text of this second edition of IEC 60364-4-43 is compiled from and replaces
– part 4-43, first edition (1977) and its amendment 1 (1997),
– part 4-473, first edition (1977) and its amendment 1 (1998).
This publication has been drafted, as close as possible, in accordance with the ISO/IEC
Directives, Part 3.
Annexes A and B are for information only.
The committee has decided that the contents of this publication will remain unchanged
until 2006. At this date, the publication will be
• reconfirmed;
• withdrawn;
• replaced by a revised edition, or
• amended.
The contents of the corrigendum of August 2002 have been included in this copy.

60364-4-43 © IEC:2001 – 7 –
ELECTRICAL INSTALLATIONS OF BUILDINGS –
Part 4-43: Protection for safety –
Protection against overcurrent
430 Introduction
430.1 (431) Scope
Part 4-43 of IEC 60364 describes how live conductors are protected by one or more devices for
automatic interruption of the supply in the event of overload (see clause 433) and short-circuits
(see clause 434) except in cases where the overcurrent is limited in accordance with
clause 436 or by the conditions described in 433.3, 433.5 or 434.3 are met. Further, protection
against overload and against short-circuits shall be co-ordinated in accordance with
clause 435.
NOTE 1 Live conductors protected against overload in accordance with clause 433 are considered to be protected
also against faults likely to cause overcurrents of a magnitude similar to overload currents.
NOTE 2 The requirements of this standard do not take account of external influences. For the application of
protective measures in relation to conditions of external influences, see 410.3.4 of IEC 60364-4-41 and clause 422
of IEC 60364-4-42.
NOTE 3 Protection of conductors according to this standard does not necessarily protect the equipment connected
to the conductors.
(433.1 and 434.1)
Protective devices shall be provided to break any overcurrent flowing in the circuit conductors
before such a current could cause a danger due to thermal and mechanical effects or a
temperature rise detrimental to insulation, joints, terminations, or surroundings of the conductors.
430.2 Normative references
The following normative documents contain provisions which, through reference in this text,
constitute provisions of this part of IEC 60364. For dated references, subsequent amendments
to, or revisions of, any of these publications do not apply. However, parties to agreements
based on this part of IEC 60364 are encouraged to investigate the possibility of applying the
most recent editions of the normative documents indicated below. For undated references, the
latest edition of the normative document referred to applies. Members of IEC and ISO maintain
registers of currently valid International Standards.
IEC 60269-1:1998, Low-voltage fuses – Part 1: General requirements
IEC 60269-2:1986, Low-voltage fuses – Part 2: Supplementary requirements for fuses for use
by authorized persons (fuses mainly for industrial application)
IEC 60269-3:1987, Low-voltage fuses – Part 3: Supplementary requirements for fuses used by
unskilled persons (fuses mainly for household and similar applications)
IEC 60364-4-41: Electrical installations of buildings – Part 4-41: Protection for safety –
Protection against electric shock
IEC 60364-5-52: Electrical installations of buildings – Part 5-52: Selection and erection of
electrical equipment – Wiring systems
________
In this standard, references in brackets refer to the previous numbering system.

60364-4-43 © IEC:2001 – 9 –
IEC 60724:1984, Guide to the short-circuit temperature limits of electric cables with a rated
voltage not exceeding 0,6/1,0 kV
IEC 60898:1995, Electrical accessories – Circuit-breakers for overcurrent protection for
household and similar installations
IEC 60947-1:1999, Low-voltage switchgear and controlgear – Part 1: General rules
IEC 60947-2:1995, Low-voltage switchgear and controlgear – Part 2: Circuit-breakers
IEC 60947-4-1:1990, Low-voltage switchgear and controlgear – Part 4-1: Contactors and
motor-starters – Electromechanical contactors and motor-starters
IEC 61009 (all parts), Residual current operated circuit-breakers with integral overcurrent
protection for household and similar uses (RCBOs)
431 (473.3) Requirements according to the nature of the circuits
431.1 (473.3.1) Protection of phase conductors
431.1.1 (473.3.1.1) Detection of overcurrent shall be provided for all phase conductors; it
shall cause the disconnection of the conductor in which the overcurrent is detected, but not
necessarily the disconnection of other live conductors, except where 431.1.2 applies.
431.1.2 (473.3.1.2) In TT systems, for circuits supplied between phases and in which the
neutral conductor is not distributed, overcurrent detection need not be provided for one of
the phase conductors, provided that the following conditions are simultaneously fulfilled:
a) there exists, in the same circuit or on the supply side, differential protection intended to
cause disconnection of all the phase conductors;
b) the neutral conductor is not distributed from an artificial neutral point of the circuits situated
on the load side of the differential protective device mentioned in a).
NOTE If disconnection of a single phase may cause danger, for example in the case of three-phase motors,
appropriate precautions should be taken.
431.2 (473.3.2) Protection of the neutral conductor
431.2.1 (473.3.2.1) TT or TN systems
Where the cross-sectional area of the neutral conductor is at least equal or equivalent to that
of the phase conductors, it is not necessary to provide overcurrent detection for the neutral
conductor or a disconnecting device for that conductor.
Where the cross-sectional area of the neutral conductor is less than that of the phase
con
...