IEC 60364-4-43:2023

IEC 60364-4-43
®

Edition 4.0 2023-07
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

IEC 60364-4-43:2023-07(en-fr)

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IEC 60364-4-43

®


Edition 4.0 2023-07




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


INTERNATIONALE




ICS 29.120.50; 91.140.50 ISBN 978-2-8322-7031-8




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

Attention! Veuillez vous assurer que vous avez obtenu cette publication via un distributeur agréé.

® Registered trademark of the International Electrotechnical Commission
Marque déposée de la Commission Electrotechnique Internationale

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– 2 – IEC 60364-4-43:2023 © IEC 2023
CONTENTS
FOREWORD . 4
430 Protection against overcurrent . 8
430.1 Scope . 8
430.2 Normative references . 8
430.3 Terms and definitions . 8
430.4 General requirements . 10
431 Protection against overcurrent by automatic disconnection of supply . 10
431.1 Protection of line conductors . 10
431.2 Protection of neutral or mid-point conductor . 10
431.2.1 AC circuits without triplen harmonics and DC circuits . 10
431.2.2 Additional requirements for IT systems . 11
431.2.3 AC system with triplen harmonics . 11
431.3 Protection against overcurrent . 12
431.3.1 Protection against both overload current and short-circuit current . 12
431.3.2 Protection against overload current only . 12
431.3.3 Protection against short-circuit current only . 12
431.4 Protection against overload current . 12
431.4.1 General . 12
431.4.2 Coordination between conductors and overload protective devices . 12
431.4.3 Protection against overload current of conductors connected in parallel . 13
431.5 Protection against short-circuit currents . 14
431.5.1 General . 14
431.5.2 Determination of prospective short-circuit currents . 14
431.5.3 Protection against short-circuit current of conductors connected in
parallel . 14
431.5.4 Requirements for protection against short-circuit current . 15
431.6 Coordination of protection against overload current and protection against
short-circuit current . 17
431.6.1 Protection afforded by one device . 17
431.6.2 Protection afforded by separate devices . 17
431.6.3 Coordination for selectivity and combined short-circuit protection . 17
Annex A (normative) Protection against overcurrent by other means . 19
A.1 General . 19
A.2 Protection against overload . 19
A.3 Protection against short-circuits . 19
Annex B (normative) Protection against overcurrent by limitation of the characteristics
of supply . 20
Annex C (informative) Protection of conductors in parallel against overcurrent . 21
C.1 General . 21
C.2 Protection against overload current of conductors connected in parallel . 21
C.3 Protection against short-circuit current of conductors connected in parallel . 24
Annex D (informative) Design current . 27
Annex E (normative) Cases where automatic disconnection of supply for protection
against overcurrent can cause an increased risk . 28
Annex F (informative) List of notes concerning certain countries . 29
Bibliography . 32

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IEC 60364-4-43:2023 © IEC 2023 – 3 –
Figure 1 – Coordination between conductor and protective device (conditions 1 and 2) . 13
Figure C.1 – Circuit in which an overload protective device is provided for each of the
m conductors in parallel . 23
Figure C.2 – Circuit in which a single overload protective device is provided for the m
conductors in parallel . 24
Figure C.3 – Current flow at the beginning of the short-circuit . 25
Figure C.4 – Current flow after operation of the protective device D3 . 25
Figure C.5 – Illustration of linked protective device . 26

Table 1 – Correspondence between IEC 60364-4-43:2008 and this document . 6
Table 2 – Values of k for conductors . 16

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– 4 – IEC 60364-4-43:2023 © IEC 2023
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________

LOW-VOLTAGE ELECTRICAL INSTALLATIONS –

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

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,
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Standardization (ISO) in accordance with conditions determined by agreement between the two organizations.
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9) Attention is drawn to the possibility that some of the elements of this IEC Publication may be the subject of patent
rights. IEC shall not be held responsible for identifying any or all such patent rights.
IEC 60364-4-43 has been prepared by IEC technical committee 64: Electrical installations and
protection against electric shock. It is an International Standard.
This fourth edition cancels and replaces the third edition published in 2008. This edition
constitutes a technical revision.
This edition includes the following significant technical changes with respect to the previous
edition:
a) the standard has been restructured, see Table 1 (Correspondence between
IEC 60364‑4‑43:2008 and this document) below;
b) the measure "automatic disconnection of supply" has been designated as the preferred
measure for protection against overcurrent;
c) all measures except the measure "automatic disconnection of supply" have been transferred
into new normative annexes to indicate that these measures are usable in certain
applications and under certain restricted conditions only (see Annex A, Annex B and
Annex E);

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IEC 60364-4-43:2023 © IEC 2023 – 5 –
d) a new clause "Terms and definitions" has been added;
e) new requirements have been added for the protection of the neutral or mid-point conductor
(with and without triplen harmonics).
The text of this International Standard is based on the following documents:
Draft Report on voting
64/2591/FDIS 64/2618/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 parts in the IEC 60364 series, published under the general title Low-voltage electrical
installations, can be found on the IEC website.
The reader's attention is drawn to the fact that Annex F lists all of the "in-some-country" clauses
on differing practices of a less permanent nature relating to the subject of this document.
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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– 6 – IEC 60364-4-43:2023 © IEC 2023
Correspondence between IEC 60364-4-43:2008 and this document
Table 1 provides a list of contents of both the previous edition and the current edition of
IEC 60364-4-43, indicating the new structure of the standard.
Table 1 also indicates which clauses of IEC 60364-4-43:2008 have been transferred to
IEC 60364-5-53:2019.
Table 1 – Correspondence between IEC 60364-4-43:2008 and this document
IEC 60364-4-43:2008 IEC 60364-4-43:2023
Low-voltage electrical installations – Low-voltage electrical installations –
Part 4-43: Protection for safety – Protection Part 4-43: Protection for safety – Protection
against overcurrent against overcurrent
43 Protection against overcurrent 430 Protection against overcurrent
430.1 Scope 430.1 Scope
430.2 Normative references 430.2 Normative references
 430.3 Terms and definitions
430.3 General requirements 430.4 General requirements
431 Requirements according to the nature of the 431 Protection against overcurrent by automatic
circuits disconnection of supply
431.1 Protection of line conductors 431.1 Protection of line conductors
431.2 Protection of the neutral conductor 431.2 Protection of neutral or mid-point conductor
431.3 Disconnection and reconnection of the neutral Deleted
conductor in multi-phase systems
Covered by product standards and 530.4.2
432 Nature of protective devices 431.3 Protection against overcurrent
Partly covered by Clause 533
432.1 Devices providing protection against both 431.3.1 Protection against both overload current
overload current and short-circuit current and short-circuit current
432.2 Devices ensuring protection against overload 431.3.2 Protection against overload current only
current only
432.3 Devices ensuring protection against 431.3.3 Protection against short-circuit current only
short‑circuit current only
432.4 Characteristics of protective devices Deleted
Covered by Clause 533
433 Protection against overload current 431.4 Protection against overload current
Coordination between conductors and Coordination between conductors and
433.1 431.4.2
overload protective devices overload protective devices

433.2 Position of devices for overload protection Deleted
Covered by 533.4.2
433.3 Omission of devices for protection against Annex A Protection against overcurrent by other
overload means, Clause A.2 Protection against overload
except 433.3.2.1 which was initially transferred to
IEC 60364-5-53:2019, 533.4.2.4 but was then
deleted at CDV stage from IEC 60364-5-53:2019
433.4 Overload protection of conductors in parallel 431.4.3 Protection against overload current of
conductors connected in parallel
434 Protection against short-circuit currents 431.5 Protection against short-circuit currents
434.1 Determination of prospective short-circuit 431.5.2 Determination of prospective short-circuit
currents currents

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IEC 60364-4-43:2023 © IEC 2023 – 7 –
IEC 60364-4-43:2008 IEC 60364-4-43:2023
Low-voltage electrical installations – Low-voltage electrical installations –
Part 4-43: Protection for safety – Protection Part 4-43: Protection for safety – Protection
against overcurrent against overcurrent
434.2 Position of devices for short-circuit protection Deleted
Covered by 533.4.3
434.3 Omission of devices for protection against Annex A Protection against overcurrent by other
short-circuit means, Clause A.3 Protection against short-circuits
434.4 Short-circuit protection of conductors in 431.5.3 Protection against short-circuit current of
parallel conductors connected in parallel
434.5 Characteristics of short-circuit protective 431.5.4 Requirements for protection against short-
devices circuit current
435 Coordination of overload and short-circuit 431.6 Coordination of protection against overload
protection current and protection against short-circuit
current
435.1 Protection afforded by one device 431.6.1 Protection afforded by one device
435.2 Protection afforded by separate devices 431.6.2 Protection afforded by separate devices
Coordination for selectivity and combined
 431.6.3
short-circuit protection
 Annex A (normative) Protection against overcurrent by
other means
436 Limitation of overcurrent by characteristics of Annex B (normative) Protection against overcurrent by
supply limitation of the characteristics of supply
Annex A (informative) Protection of conductors in Annex C (informative) Protection of conductors in
parallel against overcurrent. parallel against overcurrent
Annex B (informative) Conditions 1 and 2 of 433.1 Deleted
Covered by Figure 1 in 431.4.2
Annex C (informative) Position or omission of devices Moved to IEC 60364-5-53:2019, Annex A
for overload protection (Position of devices for overload protection)
Annex D (informative) Position or omission of devices Moved to IEC 60364-5-53:2019, Annex B
for short-circuit protection (Position of devices for short-circuit
protection)
Annex D (informative) Design current
Annex E (normative) Cases where automatic
disconnection of supply for protection against
overcurrent can cause an increased risk
Annex E (informative) List of notes concerning certain Annex F (informative) List of notes concerning certain
countries countries

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LOW-VOLTAGE ELECTRICAL INSTALLATIONS –

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



430 Protection against overcurrent
430.1 Scope
This part of IEC 60364 provides requirements for:
– protection of live conductors, PEN conductors, PEM conductors, and PEL conductors
against the harmful effects caused by overcurrent;
– coordination of measures for protection against overcurrent.
NOTE 1 The requirements of this document do not take account of external influences.
NOTE 2 Protection of conductors according to this document does not necessarily protect the equipment
connected to the conductors.
NOTE 3 Flexible cables connecting equipment by plugs and socket-outlet to fixed installations are not part of
the scope of this document and for this reason are not necessarily protected against the harmful effects caused
by overcurrent.
430.2 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 60364-5-52:2009, Low-voltage electrical installations – Part 5-52: Selection and erection
of electrical equipment – Wiring systems
430.3 Terms and definitions
For the purposes of this document, the following terms and definitions 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
430.3.1
overcurrent
electric current the value of which exceeds a specified limiting value
Note 1 to entry: For conductors, the specified limiting value is equal to the current-carrying capacity.
Note 2 to entry: An overcurrent is an overload current or a short-circuit current.
[SOURCE: IEC 60050-151:2001, 151-15-28, modified – The Notes to entry have been added.]

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IEC 60364-4-43:2023 © IEC 2023 – 9 –
430.3.2
overload current
overcurrent occurring in an electric circuit, which is not caused by a
short-circuit or an earth fault
[SOURCE: IEC 60050-826:2022, 826-11-15]
430.3.3
short-circuit current
electric current in a given short-circuit
[SOURCE: IEC 60050-195:2021, 195-05-18]
430.3.4
short-circuit
accidental or intentional conductive path between two or more conductive parts forcing the
electric potential differences between these conductive parts to be equal to or close to zero
[SOURCE: IEC 60050-151:2001, 151-12-04]
430.3.5
overload
operating conditions in an electrically undamaged circuit, which cause an overcurrent
[SOURCE: IEC 60050-441:1984, 441-11-08]
430.3.6
design current
electric current intended to be carried by an electric circuit in normal
operation
[SOURCE: IEC 60050-826:2022, 826-11-10]
430.3.7
rated conditional short-circuit current

I
cc
value of prospective short-circuit current, declared by the busbar trunking or powertrack system
manufacturer, that can be withstood for the disconnection time of the overcurrent protective
device under specified conditions
[SOURCE: IEC 61439-1:2020, 3.8.10.4, modified – The definition has been adapted to busbar
trunking or powertrack system.]
430.3.8
combined short-circuit protection
coordination of two overcurrent protective devices in series, capable of breaking short-circuit
currents higher than the breaking capacity of one of the devices alone
430.3.9
diversity
prospective simultaneous demand of a group of electrical loads.
[SOURCE: IEC 60364-1:—, 1.3.1]

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430.4 General requirements
Electric circuits shall be protected so as to eliminate the harmful effects caused by
overcurrent in live conductors, PEN conductors, PEM conductors, and PEL conductors.
This protection shall be achieved by the use of a protective device to disconnect any
overcurrent in the circuit conductors in accordance with Clause 431.
However, in certain cases, where automatic disconnection of the supply can be inappropriate,
protection may be achieved by other means as given in Annex A or by limitation of overcurrent
by the characteristics of supply as given in Annex B. In those cases where automatic
disconnection of supply can cause a danger or an increased risk, Annex E applies.
NOTE 1 Disconnection does not mean isolation in this document.
NOTE 2 Harmful effects include: thermal or mechanical effects detrimental to insulation, joints, terminations or
material surrounding the conductors.
NOTE 3 Conductors protected against overload in accordance with 431.4 are considered to be protected also
against faults likely to cause short-circuit currents of a magnitude similar to overload currents.
431 Protection against overcurrent by automatic disconnection of supply
431.1 Protection of line conductors
431.1.1 Detection of overcurrent shall be provided for all line conductors, except
where 431.1.2 applies. It shall cause the disconnection of the conductor in which the
overcurrent is detected but not necessarily the disconnection of the other live conductors.
If disconnection of a single phase can cause danger, for example in the case of a
three-phase motor, appropriate precautions shall be taken.
431.1.2 Detection of overcurrent is not required for a PEL conductor in DC circuits.
431.2 Protection of neutral or mid-point conductor
431.2.1 AC circuits without triplen harmonics and DC circuits
NOTE 1 AC circuits with triplen harmonics THD < 5 % are considered to be AC circuits without triplen harm
...