IEC 60364-4-43:2008

IEC 60364-4-43
Edition 3.0 2008-08
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Low-voltage electrical installations –
Part 4-43: Protection for safety – Protection against overcurrent

Installations électriques à basse tension –
Partie 4-43: Protection pour assurer la sécurité – Protection contre les
surintensités
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IEC 60364-4-43
Edition 3.0 2008-08
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Low-voltage electrical installations –
Part 4-43: Protection for safety – Protection against overcurrent

Installations électriques à basse tension –
Partie 4-43: Protection pour assurer la sécurité – Protection contre les
surintensités
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
PRICE CODE
INTERNATIONALE
V
CODE PRIX
ICS 29.120.50; 91.140.50 ISBN 2-8318- 8318-9922-2
– 2 – 60364-4-43 © IEC:2008
CONTENTS
FOREWORD.4

43 Protection against overcurrent.6
430.1 Scope.6
430.2 Normative references.6
430.3 General requirements.7
431 Requirements according to the nature of the circuits.7
431.1 Protection of line conductors .7
431.2 Protection of the neutral conductor .7
431.3 Disconnection and reconnection of the neutral conductor in multi-phase
systems .8
432 Nature of protective devices .8
432.1 Devices providing protection against both overload current and short-circuit
current.8
432.2 Devices ensuring protection against overload current only.9
432.3 Devices ensuring protection against short-circuit current only.9
432.4 Characteristics of protective devices.9
433 Protection against overload current .9
433.1 Coordination between conductors and overload protective devices.9
433.2 Position of devices for overload protection.10
433.3 Omission of devices for protection against overload .10
433.4 Overload protection of conductors in parallel .11
434 Protection against short-circuit currents .12
434.1 Determination of prospective short-circuit currents .12
434.2 Position of devices for short-circuit protection.12
434.3 Omission of devices for protection against short-circuit .12
434.4 Short-circuit protection of conductors in parallel .13
434.5 Characteristics of short-circuit protective devices .13
435 Coordination of overload and short-circuit protection .15
435.1 Protection afforded by one device.15
435.2 Protection afforded by separate devices .15
436 Limitation of overcurrent by characteristics of supply .15

Annex A (informative) Protection of conductors in parallel against overcurrent.16
Annex B (informative) Conditions 1 and 2 of 433.1.21
Annex C (informative) Position or omission of devices for overload protection .22
Annex D (informative) Position or omission of devices for short-circuit protection .25
Annex E (informative) List of notes concerning certain countries.28

Bibliography.30

Figure A.1 – Circuit in which an overload protective device is provided for each of the
m conductors in parallel.18
Figure A.2 – Circuit in which a single overload protective device is provided for the m
conductors in parallel.18

60364-4-43 © IEC:2008 – 3 –
Figure A.3 – Current flow at the beginning of the fault.19
Figure A.4 – Current flow after operation of the protective device cs.19
Figure A.5 – Illustration of linked protective device .20
Figure B.1 – Illustration of conditions 1 and 2 of 433.1.21
Figure C.1 – Overload protective device (P ) NOT at the origin of branch circuit (B)
(refer to 433.2.2a)).22
Figure C.2 – Overload protective device (P ) installed within 3 m of the origin of the
branch circuit (B) (refer to 433.2.2b)) .23
Figure C.3 – Illustration of cases where overload protection may be omitted (refer to
433.3.1a), b) and d)).23
Figure C.4 – Illustration of cases where overload protection may be omitted in an IT
system .24
Figure D.1 – Limited change of position of short-circuit protective device (P ) on a
branch circuit (refer to 434.2.1).25
Figure D.2 – Short-circuit protective device P installed at a point on the supply side of
the origin of a branch circuit (refer to 434.2.2) .26
Figure D.3 – Situation where the short-circuit protective device may be omitted for
some applications (refer to 434.3).27

Table 43A – Values of k for conductors.14

– 4 – 60364-4-43 © IEC:2008
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
LOW-VOLTAGE ELECTRICAL INSTALLATIONS –

Part 4-43: Protection for safety –
Protection against overcurrent

FOREWORD
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