IEC 60364-4-43

Low-voltage electrical installations - Part 4-43: Protection for safety - Protection against overcurrent

IEC 60364-4-43:2008 provides requirements for the protection of live conductors from the effects of overcurrents. IEC 60364-4-43:2008 describes how live conductors are protected by one or more devices for the automatic disconnection of the supply in the event of overload (Clause 433) and short-circuit (Clause 434) except in cases where the overcurrent is limited in accordance with Clause 436 or where the conditions described in 433.3 (omission of devices for protection against overload) or 434.3 (omission of devices for protection against short-circuit) are met. Coordination of overload protection and short-circuit protection is also covered (Clause 435). This third edition cancels and replaces the second edition, published in 2001, and constitutes a technical revision. The main changes with respect to the previous edition are:
- Introduction of new informative Annexes B, C and D.
- Information concerning flexible cables added to Scope.
  - Requirements added for overload detection for the neutral conductor for harmonic currents.
- Requirement that devices for protection against short-circuit current be capable of making as well as breaking short-circuit current added.
- Information added to clarify protection against overload current.
- Requirements where devices for protection against overload need not be provided expanded.
- Requirements where devices for protection against short-circuit need not be provided expanded.
- Requirements for short-circuit current ratings of busbar trunking systems added.[
]The contents of the corrigendum of October 2008 have been included in this copy.

Installations électriques à basse tension - Partie 4-43: Protection pour assurer la sécurité - Protection contre les surintensités

La CEI 60364-4-43:2008 donne les exigences pour les protections des conducteurs contre les effets des surintensités. Cette norme décrit comment protéger les conducteurs par un appareil ou plus de déconnexion automatique de l'alimentation en cas de surcharge (Article 433) et court-circuit (Article 434), à l'exception où les surintensités sont limitées conformément à l'Article 436 ou si les conditions décrites en 433.3 (omission d'appareils de protection contre les surcharges) ou 434.3 (omission d'appareils de protection contre les courts-circuits) sont remplies. La coordination entre les protections contre les surintensités et les courts-circuits est aussi incluse (Article 435). Cette troisième édition annule et remplace la seconde édition, publiée en 2001, et constitue une révision technique. Les principales modifications par rapport à l'édition précédente sont les suivantes:
- Introduction des nouvelles Annexes B, C et D informatives.
- Ajout d'information dans le domaine d'application concernant les câbles souples.
- Ajout d'exigence pour la détection de surcharge dans le conducteur neutre en cas de courants harmoniques.
- Ajout d'exigence pour que les dispositifs de protection contre les court-circuits soient capables d'opérer aussi bien à l'ouverture qu'à la fermeture sur un courant de court-circuit.
- Développement des exigences où des dispositifs de protection contre les surcharges ne sont pas nécessaire.
- Développement des exigences où des dispositifs de protection contre les courts-circuits ne sont pas nécessaires.
- Ajout d'exigences pour les courants de court-circuit assignés des systèmes de canalisations préfabriquées.[
]Le contenu du corrigendum d'octobre 2008 a été pris en considération dans cet exemplaire.

Nizkonapetostne električne inštalacije - 4-43. del: Zaščitni ukrepi - Zaščita pred nadtoki

General Information

• Status: Not Published
• ICS: 29.120.50 - Fuses and other overcurrent protection devices
• ICS: 91.140.50 - Electricity supply systems
• Technical Committee: TC 64 - Electrical installations and protection against electric shock
• Current Stage: PPUB - Publication issued
• Start Date: 13-Aug-2008
• Ref Project: SIST IEC 60364-4-43:2009 - Low-voltage electrical installations - Part 4-43: Protection for safety - Protection against overcurrent

Standards Content (Sample)

SLOVENSKI STANDARD
SIST IEC 60364-4-43:2009
01-junij-2009
1DGRPHãþD
SIST IEC 60364-4-43:2006
1L]NRQDSHWRVWQHHOHNWULþQHLQãWDODFLMHGHO=DãþLWQLXNUHSL=DãþLWDSUHG
QDGWRNL
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
Ta slovenski standard je istoveten z: IEC 60364-4-43
ICS:
29.120.50 9DURYDONHLQGUXJD Fuses and other overcurrent
PHGWRNRYQD]DãþLWD protection devices
91.140.50 Sistemi za oskrbo z elektriko Electricity supply systems
SIST IEC 60364-4-43:2009 en,fr,de
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

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SIST IEC 60364-4-43:2009

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SIST IEC 60364-4-43:2009
IEC 60364-4-43
Edition 3.0 2008-08
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
GROUP SAFETY PUBLICATION
PUBLICATION GROUPÉE DE SÉCURITÉ
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 2-8318-9922-2
® Registered trademark of the International Electrotechnical Commission
Marque déposée de la Commission Electrotechnique Internationale

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SIST IEC 60364-4-43:2009
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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

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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)
2
(refer to 433.2.2a)).22
Figure C.2 – Overload protective device (P ) installed within 3 m of the origin of the
2
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
2
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
2
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

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SIST IEC 60364-4-43:2009
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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, 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
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. 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 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
Committees in that sense. While all reasonable efforts are made to ensure that the technical content of IEC
Publications is accurate, IEC cannot be held responsible for the way in which they are used or for any
misinterpretation by any end user.
4) In order to promote international uniformity, IEC National Committees undertake to apply IEC Publications
transparently to the maximum extent possible in their national and regional publications. Any divergence
between any IEC Publication and the corresponding national or regional publication shall be clearly indicated in
the latter.
5) IEC provides no marking procedure to indicate its approval and cannot be rendered responsible for any
equipment declared to be in conformity with an IEC Publication.
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
Publications.
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) 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.
International Standard IEC 60364-4-43 has been prepared by IEC technical committee 64:
Electrical installations and protection against electric shock.
This third edition cancels and replaces the second edition, published in 2001, and constitutes
a technical revision.
The main changes with respect to the previous edition are listed below:
– Annex B “IEC 60364 – Parts 1 to 6: Restructuring” deleted.
– Introduction of new informative Annexes B, C and D.
– Information concerning flexible cables added to Scope.
– The word “phase” changed to “line” throughout the standard.
– Requirement not to distribute the neutral in IT systems changed to a NOTE.
– Requirements added for overload detection for the neutral conductor for harmonic
currents.

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SIST IEC 60364-4-43:2009
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– Requirement that devices for protection against short-circuit current be capable of making
as well as breaking short-circuit current added.
– Information added to clarify protection against overload current.
– Requirements where devices for protection against overload need not be provided
expanded.
– More examples given where omission of devices for protection against overload is
permitted.
– Requirements where devices for protection against short-circuit need not be provided
expanded.
– Requirements for short-circuit current ratings of busbar trunking systems added.
The text of this standard is based on the following documents:
FDIS Report on voting
64/1641/FDIS 64/1656/RVD

Full information on the voting for the approval of this standard can be found in the report on
voting indicated in the above table.
This publication has been drafted in accordance with the ISO/IEC Directives, Part 2.
The reader's attention is drawn to the fact that Annex E lists all of the "in-some-country"
clauses on differing practices of a less permanent nature relating to the subject of this
standard.
This International Standard has the status of a group safety publication in accordance with
IEC Guide 104.
A list of all parts in the IEC 60364 series, under the general title Low-voltage electrical
installations, can be found on the IEC website.
Future standards in this series will carry the new general title as cited above. Titles of existing
standards in this series will be updated at the time of the next edition.
The committee has decided that the contents of this publication will remain unchanged until
the maintenance result date indicated on the IEC web site under "http://webstore.iec.ch" in
the data related to the specific publication. At this date, the publication will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.

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LOW-VOLTAGE ELECTRICAL INSTALLATIONS –

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



43 Protection against overcurrent
430.1 Scope
This part of IEC 60364 provides requirements for the protection of live conductors from the
effects of overcurrents.
This standard describes how live conductors are protected by one or more devices for the
automatic disconnection of the supply in the event of overload (Clause 433) and short-circuit
(Clause 434) except in cases where the overcurrent is limited in accordance with Clause 436
or where the conditions described in 433.3 (omission of devices for protection against
overload) or 434.3 (omission of devices for protection against short-circuit) are met.
Coordination of overload protection and short-circuit protection is also covered (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.
NOTE 3 Protection of conductors according to this standard does not necessarily protect the equipment
connected to the conductors.
NOTE 4 Flexible cables connecting equipment by plugs and socket-outlet to fixed installations are not part of the
scope of this standard and for this reason are not necessarily protected against overcurrent.
NOTE 5 Disconnection does not mean isolation in this standard.
430.2 Normative references
The following referenced documents are indispensable for the application 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 60269-2, Low-voltage fuses – Part 2: Supplementary requirements for fuses for use by
authorized persons (fuses mainly for industrial application) – Examples of standardized
systems of fuses A to I
IEC 60269-3, Low-voltage fuses – Part 3: Supplementary requirements for fuses for use by
unskilled persons (fuses mainly for household and similar applications) – Examples of
standardized systems of fuses A to F
IEC 60269-4, Low-voltage fuses – Part 4: Supplementary requirements for fuse-links for the
protection of semiconductor devices
IEC 60364-4-41, Low-voltage electrical installations – Part 4-41: Protection for safety –
Protection against electric shock
IEC 60364-5-52:2001, Electrical installations of buildings – Part 5-52: Selection and erection
of electrical equipment – Wiring systems
IEC 60439-2, Low-voltage switchgear and controlgear assemblies – Part 2: Particular
requirements for busbar trunking systems (busways)

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SIST IEC 60364-4-43:2009
60364-4-43 © IEC:2008 – 7 –
IEC 60724, Short-circuit temperature limits of electric cables with rated voltages of 1 kV (U =
m
1,2 kV) and 3 kV (U = 3,6 kV)
m
IEC 60898 (all parts), Electrical accessories – Circuit-breakers for overcurrent protection for
household and similar installations
IEC 60947-2, Low-voltage switchgear and controlgear – Part 2: Circuit-breakers
IEC 60947-3, Low-voltage switchgear and controlgear – Part 3: Switches, disconnectors,
switch-disconnectors and fuse-combination units
IEC 60947-6-2, Low-voltage switchgear and controlgear – Part 6-2: Multiple function
equipment – Control and protective switching devices (or equipment) (CPS)
IEC 61009 (all parts), Residual current operated circuit-breakers with integral overcurrent
protection for household and similar uses (RCBOs)
IEC 61534 (all parts), Powertrack systems
IEC Guide 104, The preparation of safety publications and the use of basic safety publications
and group safety publications
430.3 General requirements
Protective devices shall be provided to disconnect any overcurrent in the circuit conductors
before such a current could cause danger due to thermal or mechanical effects detrimental to
insulation, joints, terminations or material surrounding the conductors.
431 Requirements according to the nature of the circuits
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 may cause danger, for example in the case of a three-
phase motor, appropriate precautions shall be taken.
431.1.2 In a TT or TN system, for a circuit supplied between line conductors and in which
the neutral conductor is not distributed, overcurrent detection need not be provided for one of
the line conductors, provided that the following conditions are simultaneously fulfilled:
a) there exists, in the same circuit or on the supply side, protection intended to detect
unbalanced loads and intended to cause disconnection of all the line conductors;
b) the neutral conductor is not distributed from an artificial neutral point of the circuits
situated on the load side of the protective device mentioned in a).
431.2 Protection of the neutral conductor
431.2.1 TT or TN systems
Where the cross-sectional area of the neutral conductor is at least equivalent to that of the
line conductors, and the current in the neutral is expected not to exceed the value in the line
conductors, it is not necessary to provide overcurrent detection for the neutral conductor or a
disconnecting device for that conductor.

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Where the cross-sectional area of the neutral conductor is less than that of the line
conductors, it is necessary to provide overcurrent detection for the neutral conductor,
appropriate to the cross-sectional area of that conductor; this detection shall cause the
disconnection of the line conductors, but not necessarily of the neutral conductor.
In both cases the neutral conductor shall be protected against short-circuit current.
NOTE This protection may be achieved by the overcurrent protective devices in the line conductors. In that case it
is not necessary to provide overcurrent protection for the neutral conductor or a disconnecting device for that
conductor.
Where the current in the neutral conductor is expected to exceed the value in the line
conductors, refer to 431.2.3.
Except for disconnection the requirements for a neutral conductor apply to a PEN conductor.
431.2.2 IT systems
Where the neutral conductor is distributed, it is necessary to provide overcurrent detection for
the neutral conductor of every circuit. The overcurrent detection shall cause the disconnection
of all the live conductors of the corresponding circuit, including the neutral conductor. This
measure is not necessary if
– the particular neutral conductor is effectively protected against overcurrent by a
protective device placed on the supply side, for example at the origin of the installation,
or if
– the particular circuit is protected by a residual current operated protective device with a
rated residual current not exceeding 0,20 times the current-carrying capacity of the
corresponding neutral conductor. This device shall disconnect all the live conductors of
the corresponding circuit, including the neutral conductor. The device shall have sufficient
breaking capacity for all poles.
NOTE In IT systems, it is strongly recommended that the neutral conductor should not be distributed.
431.2.3 Harmonic currents
Overload detection shall be provided for the neutral conductor in a multi-phase circuit where
the harmonic content of the line currents is such that the current in the neutral conductor is
expected to exceed the current-carrying capacity of that conductor. The overload detection
shall be compatible with the nature of the current through the neutral and shall cause the
disconnection of the line conductors but not necessarily the neutral conductor. Where the
neutral is disconnected, the requirements of 431.3 apply.
NOTE Further requirements regarding protection of neutral conductors are given in IEC 60364-5-52.
431.3 Disconnection and reconnection of the neutral conductor in multi-phase systems
Where disconnection of the neutral conductor is required, disconnection and reconnection
shall be such that the neutral conductor shall not be disconnected before the line conductors
and shall be reconnected at the same time as or before the line conductors.
432 Nature of protective devices
The protective devices shall be of the appropriate types indicated by 432.1 to 432.3.
432.1 Devices providing protection against both overload current and short-circuit
current
Except as stated in 434.5.1, a device providing protection against both overload and short-
circuit current shall be capable of breaking and, for a circuit-breaker, making any overcurrent

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up to and including the prospective short-circuit current at the point where the device is
installed. Such devices may be:
– circuit-breakers incorporating overload and short-circuit release;
– circuit-breakers in conjunction with fuses;
– fuses having fuse links with gG characteristics.
NOTE 1 The fuse comprises all the parts that form the complete protective device.
NOTE 2 This subclause does not exclude the use of other protective devices if the requirements in 433.1 and
434.5 are fulfilled.
432.2 Devices ensuring protection against overload current only
These protective devices shall satisfy the requirements of Clause 433 and may have an
interrupting capacity below the value of the prospective short-circuit current at the point where
the devices are installed.
NOTE 1 These devices are generally inverse time lag protective devices.
NOTE 2 Fuses type aM do not protect against overload.
432.3 Devices ensuring protection against short-circuit current only
A device providing protection against short-circuit current only shall be installed where
overload protection is achieved by other means or where Clause 433 permits overload
protection to be dispensed with. Such a device shall be capable of breaking, and for a circuit-
breaker making, the short-circuit current up to and including the prospective short-circuit
current. Such a device shall satisfy the requirements of Clause 434.
Such devices may be
− circuit-breakers with short-circuit release only,
− fuses with gM, aM type fuse links.
432.4 Characteristics of protective devices
The operating characteristics of overcurrent protective devices shall comply with those
specified in, for example, IEC 60898, IEC 60947-2, IEC 60947-6-2, IEC 61009, IEC 60269-2,
IEC 60269-3, IEC 60269-4 or IEC 60947-3.
NOTE The use of other devices is not excluded provided that their time/current characteristics provide an
equivalent level of protection to that specified in this clause.
433 Protection against overload current
433.1 Coordination between conductors and overload protective devices
The operating characteristics of a device protecting a cable against overload shall satisfy the
two following conditions:
I ≤ I ≤ I (1)

B n Z
≤ 1,45 × I (2)
I
2 Z
where
 is the design current for that circuit;
I
B
I is the continuous current-carrying capacity of the cable (see Clause 523);

Z
 is the rated current of the protective device;
I
n
NOTE 1 For adjustable protective devices, the rated current I is the current setting selected.
n

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SIST IEC 60364-4-43:2009
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I is the current ensuring effective operation in the conventional time of the protective
2
device.
The current I ensuring effective operation of the protective device shall be provided by the
2
manufacturer or as given in the product standard.
Protection in accordance with this clause may not ensure protection in certain cases, for
example where sustained overcurrents less than I occur. In such cases, consideration should

2
be given to selecting a cable with a larger cross-sectional area.
NOTE 2 I is the design current through the line or the permanent current through neutral in case of a high level
B
of the third harmonic
NOTE 3 The current ensuring effective operation in the conventional time of protective devices may also be
named I or I according to the product standards. Both I and I are multiples of I and attention should be given to

t f
t f n
the correct representation of values and indexes.
NOTE 4 See Annex B for an illustration of conditions (1) and (2) of 433.1.
NOTE 5 Design current I can be considered as an actual current I after applying correction factors. See Clause
B a
311.
433.2 Position of devices for overload protection
433.2.1 A device ensuring protection against overload shall be placed at the point where a
change, such as a change in cross-sectional area, nature, method of installation or in
constitution, causes a reduction in the value of current-carrying capacity of the conductors,
except where 433.2.2 and 433.3 apply.
433.2.2 The device protecting the conductor against overload may be placed along the run
of that conductor if the part of the run between the point where a change occurs (in cross-
sectional area, nature, method of installation or constitution) and the position of the protective
device has neither branch circuits nor socket-outlets and fulfils at least one of the following
two conditions:
a) it is protected against short-circuit current in accordance with the requirements stated in
Clause 434;
b) its length does not exceed 3 m, it is carried out in such a manner as to reduce the risk of
short-circuit to a minimum, and it is installed in such a manner as to reduce to a minimum
the risk of fire or danger to persons (see also 434.2.1).
NOTE For installation according to a) see Figure C.1. For installation according to b) see Figure C.2.
433.3 Omission of devices for protection against overload
The various cases stated in this subclause shall not be applied to installations situated in
locations presenting a fire risk or risk of explosion or where the requirements for special
installations and locations specify different conditions.
433.3.1 General
Devices for protection against overload need not be provided:
a) for a conductor situated on the load side of a change in cross-sectional area, nature,
method of installation or in constitution, that is effectively protected against overload by a
protective device placed on the supply side;
b) for a conductor that is not likely to carry overload current, provided that this conductor is
protected against short-circuit in accordance with the requirements of Clause 434 and that
it has neither branch circuits nor socket-outlets;
c) at the origin of an installation w
...

SLOVENSKI SIST IEC 60364-4-43


STANDARD junij 2009













Nizkonapetostne električne inštalacije – 4-43. del: Zaščitni ukrepi –
Zaščita pred nadtoki

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

















Referenčna oznaka
ICS 29.120.50; 91.140.50 SIST IEC 60364-4-43:2009 (sl)


 Nadaljevanje na straneh od 2 do 30


© 2009–09: Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov standarda ni dovoljeno.

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SIST IEC 60364-4-43 : 2009
NACIONALNI UVOD
Standard SIST IEC 60364-4-43 (sl), Nizkonapetostne električne inštalacije – 4-43. del: Zaščitni ukrepi
– Zaščita pred nadtoki, 2009, ima status slovenskega standarda in je istoveten mednarodnemu
standardu IEC 60364-4-43 (en), Low-voltage electrical installations – Part 4-43: Protection for safety –
Protection against overcurrent, 2008.
NACIONALNI PREDGOVOR
Mednarodni standard IEC 60364-4-43:2008 je pripravil tehnični odbor Mednarodne elektrotehniške
komisije IEC/TC 64 Električne inštalacije in zaščita pred električnim udarom.
Slovenski standard SIST IEC 60364-4-43:2009 je prevod mednarodnega standarda IEC 60364-4-
43:2008. V primeru spora glede besedila slovenskega prevoda v tem standardu je odločilen izvirni
evropski standard v angleškem jeziku. Slovensko izdajo standarda je pripravil tehnični odbor SIST/TC
ELI Nizkonapetostne in komunikacijske električne inštalacije.
Odločitev za privzem tega standarda po metodi ponatisa je dne 18. marca 2009 sprejel tehnični odbor
SIST/TC ELI. Hkrati je odbor tudi sklenil, da se pripravi prevod standarda.
OSNOVA ZA IZDAJO STANDARDA
Privzem standarda IEC 60364-4-43:2008.
ZVEZE S STANDARDI
S privzemom tega evropskega standarda veljajo za omenjeni namen referenčnih standardov vsi
standardi, navedeni v izvirniku, razen tistih, ki so že sprejeti v nacionalno standardizacijo:
SIST EN 60269-1:2007 Nizkonapetostne varovalke – 1. del: Splošne zahteve (IEC 60269-
1:2006)
SIST EN 60269-4:2007 Nizkonapetostne varovalke – 4. del: Dodatne zahteve za taljive
vložke za zaščito polprevodniških naprav (IEC 60269-4:2006)
SIST HD 60269-2:2008 Nizkonapetostne varovalke – 2. del: Dodatne zahteve za varovalke, ki
jih uporabljajo strokovne osebe (uporaba varovalk zlasti v industriji) –
Primeri tipov standardiziranih varovalk od A do I (IEC 60269-2:2006)
SIST HD 60269-3:2008 Nizkonapetostne varovalke – 3. del: Dodatne zahteve za varovalke, ki
jih uporabljajo nestrokovne osebe (uporaba varovalk zlasti v
gospodinjstvu in podobnih okoljih) – Razdelki od A do F: Primeri tipov
standardiziranih varovalk (IEC 60269-3:2006)
SIST IEC 60364-4-41:2006 Nizkonapetostne električne inštalacije – 4-41. del: Zaščitni ukrepi –
Zaščita pred električnim udarom
SIST IEC 60364-5-52:2006 Električne inštalacije zgradb – 5-52. del: Izbira in namestitev
električne opreme – Inštalacijski sistemi
SIST EN 60439-2:2000 Sestavi nizkonapetostnih stikalnih in krmilnih naprav – 2. del:
Posebne zahteve za zbiralčne razdelilne sisteme (zbiralčna vodila)
(IEC 60439-2:2000)
SIST EN 60898 (vsi deli) Električni pribor – Odklopniki za nadtokovno zaščito za gospodinjstvo
in podobne inštalacije
SIST EN 60947-2:2006 Nizkonapetostne stikalne naprave – 2. del: Odklopniki (IEC 60947-
2:2006)
SIST EN 60947-3:2000 Nizkonapetostne stikalne in krmilne naprave – 3. del: Stikala, ločilniki,
ločilna stikala in stikalni aparati z varovalkami
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SIST IEC 60364-4-43 : 2009
SIST EN 60947-6-2:2003 Nizkonapetostne stikalne naprave – 6. del: Večfunkcijska oprema –
2. oddelek: Krmilne in zaščitne stikalne naprave (ali oprema) (CPS)
(IEC 60947-6-2:2002)
SIST EN 61009 (vsi deli) Odklopniki na preostali (residualni) tok z vgrajeno nadtokovno zaščito
za gospodinjsko in podobno rabo (RCBO's)
SIST EN 61534 (vsi deli) Sistemi zbiralčnih vodnikov

OPOMBI
– Nacionalni uvod in nacionalni predgovor nista sestavni del standarda.
– Povsod, kjer se v besedilu standarda uporablja izraz “mednarodni standard”, v
SIST IEC 60364-4-43:2009 to pomeni “slovenski standard”.

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SIST IEC 60364-4-43 : 2009
VSEBINA Stran

Predgovor .5
43 Nadtokovna zaščita .7
430.1 Področje uporabe .7
430.2 Zveza s standardi .7
430.3 Splošne zahteve.8
431 Zahteve v zvezi z lastnostmi tokokrogov.8
431.1 Zaščita linijskih vodnikov .8
431.2 Zaščita nevtralnega vodnika.8
431.3 Odklop in ponovni vklop nevtralnega vodnika v večfaznih sistemih .9
432 Lastnosti zaščitnih naprav .9
432.1 Naprave, ki zagotavljajo zaščito pri preobremenitvenem toku in tudi pri kratkostičnem toku.9
432.2 Naprave, ki nudijo samo preobremenitveno zaščito .9
432.3 Naprave, ki nudijo samo kratkostično zaščito .10
432.4 Lastnosti zaščitnih naprav .10
433 Zaščita pri preobremenitvenem toku.10
433.1 Koordinacija med vodniki in preobremenitvenimi zaščitnimi napravami.10
433.2 Namestitev naprav za preobremenitveno zaščito .11
433.3 Opustitev naprav za zaščito pri preobremenitvi .11
433.4 Preobremenitvena zaščita vzporednih vodnikov.12
434 Zaščita pri kratkostičnih tokih .12
434.1 Določitev pričakovanih kratkostičnih tokov.12
434.2 Položaj naprav za kratkostično zaščito .12
434.3 Opustitev naprav za kratkostično zaščito.13
434.4 Kratkostična zaščita vzporednih vodnikov.13
434.5 Lastnosti kratkostičnih zaščitnih naprav .14
435 Koordinacija preobremenitvene in kratkostične zaščite .16
435.1 Zaščita, izvedena z eno napravo.16
435.2 Zaščita, izvedena z ločenima napravama .16
436 Omejitev nadtoka z lastnostmi napajanja.16
Dodatek A (informativni): Zaščita vzporednih vodnikov pri nadtoku .17
Dodatek B (informativni): Pogoja 1 in 2 iz točke 433.1 .21
Dodatek C (informativni): Namestitev ali opustitev naprav za preobremenitveno zaščito .22
Dodatek D (informativni): Namestitev ali opustitev kratkostične zaščite.25
Dodatek E (informativni): Seznam opomb, ki se nanašajo na določene države.28
Bibliografija .30




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SIST IEC 60364-4-43 : 2009
MEDNARODNA ELEKTROTEHNIŠKA KOMISIJA
-------------------------
NIZKONAPETOSTNE ELEKTRIČNE INŠTALACIJE –
– 4-43. del: Zaščitni ukrepi – Zaščita pred nadtoki
PREDGOVOR
1) IEC (Mednarodna elektrotehniška komisija) je svetovna organizacija za standardizacijo, ki
združuje vse nacionalne elektrotehnične komiteje (nacionalni komiteji IEC). Cilj IEC je
pospeševati mednarodno sodelovanje v vseh vprašanjih standardizacije s področja
elektrotehnike in elektronike. V ta namen poleg drugih aktivnosti izdaja mednarodne standarde,
tehnične specifikacije, tehnična poročila, javno dostopne specifikacije in vodila (v nadaljevanju:
publikacije IEC). Za njihovo pripravo so odgovorni tehnični odbori (TC). Vsak nacionalni komite
IEC, ki ga zanima obravnavana tema, lahko sodeluje v tem pripravljalnem delu. Prav tako lahko
v pripravi sodelujejo mednarodne organizacije ter vladne in nevladne ustanove, ki so povezane
z IEC. IEC deluje v tesni povezavi z mednarodno organizacijo za standardizacijo ISO skladno s
pogoji, določenimi v soglasju med obema organizacijama.
2) Uradne odločitve ali sporazumi IEC o tehničnih vprašanjih, pripravljeni v tehničnih odborih, kjer
so prisotni vsi nacionalni komiteji, ki jih tema zanima, izražajo, kolikor je mogoče, mednarodno
soglasje o obravnavani temi.
3) Publikacije IEC imajo obliko priporočil in so za mednarodno uporabo objavljeni v obliki
standardov, tehničnih poročil ali vodil ter jih kot takšne sprejmejo nacionalni komiteji. Čeprav
IEC skuša zagotavljati natančnost tehničnih vsebin v publikacijah IEC, IEC ni odgovoren za
način uporabe ali za možne napačne interpretacije končnih uporabnikov.
4) Da bi se pospeševalo mednarodno poenotenje, so nacionalni komiteji IEC v svojih nacionalnih
in regionalnih standardih dolžni čim pregledneje uporabljati mednarodne standarde. Vsako
odstopanje med standardom IEC in ustreznim nacionalnim ali regionalnim standardom je treba v
slednjem jasno označiti.
5) IEC ne predpisuje nobenega postopka označevanja, ki bi kazal na njegovo potrditev, in ne more
biti odgovoren za katero koli opremo, ki bi bila deklarirana kot skladna z eno od njegovih
publikacij.
6) Uporabniki naj bi si zagotovili zadnjo izdajo te publikacije.
7) IEC ali njegovi direktorji, zaposleni, uslužbenci ali zastopniki, vključno s samostojnimi
strokovnjaki ter člani tehničnih odborov in nacionalnih komitejev IEC, ne prevzemajo nobene
odgovornosti za kakršno koli osebno poškodbo, škodo na premoženju ali katerokoli drugo škodo
kakršnekoli vrste, bodisi neposredne ali posredne, ali za stroške (vključno s stroški za pravne
storitve) in izdatke, povezane s publikacijo, njeno uporabo ali zanašanjem na to publikacijo IEC
ali katerokoli drugo publikacijo IEC.
8) Posebno pozornost je treba posvetiti posvetiti normativnim virom, na katere se sklicuje ta
publikacija. Uporaba navedenih publikacij je nujna za pravilno uporabo te publikacije.
9) Opozoriti je treba na možnost, da so lahko nekateri elementi tega mednarodnega standarda
predmet patentnih pravic. IEC ni odgovoren za identificiranje nobene od teh patentnih pravic.
Mednarodni standard IEC 60364-4-43 je pripravil tehnični odbor IEC/TC 64 Električne inštalacije in
zaščita pred električnim udarom.
Ta tretja izdaja razveljavlja in nadomešča drugo izdajo iz leta 2001 in predstavlja tehnično revizijo.
Glede na prejšnjo izdajo so bile narejene naslednje bistvene spremembe:
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SIST IEC 60364-4-43 : 2009
– izbrisan je dodatek B v IEC 60364 – Deli 1–6: Prestrukturiranje;
– dodani so novi informativni dodatki B, C in D;
– v točko Področje uporabe so dodane informacije o zvijavih vodnikih;
– v celem standardu je izraz »fazni« zamenjan z »linijski«;
– zahteva, da nevtralni vodnik v sistemih IT ni razpeljan, je spremenjena v OPOMBO;
– dodana je zahteva za zaznavanje preobremenitve nevtralnega vodnika pri harmonskih tokovih;
– dodana je zahteva, da je naprava za zaščito pri kratkem stiku sposobna prenesti in tudi prekiniti
kratkostični tok;
– dodane so informacije, ki pojasnjujejo zaščito pred preobremenitvenim tokom;
– razširjene so zahteve za področja, kjer zaščita pri preobremenitvi ni potrebna;
– navedenih je več primerov, kjer je opustitev zaščite pri preobremenitvi dovoljena;
– razširjene so zahteve za področja, kjer zaščita pri kratkem stiku ni potrebna;
– dodane so zahteve za kratkostično zaščito zbiralčnih razdelilnikov.
Besedilo tega standarda temelji na naslednjih dokumentih:
Osnutek tehničnega Poročilo o glasovanju
odbora
64/1641/FDIS 64/1656/RVD

Vse informacije o glasovanju za potrditev tega tehničnega poročila lahko najdete v poročilu o
glasovanju, navedenem v gornji preglednici.
Ta publikacija je bila pripravljena v skladu z dokumentom Direktive ISO/IEC, 2. del.
Bralci naj bodo pozorni na dejstvo, da v seznamih v dodatku E izraz »v nekaterih državah« kaže na
različne prakse posameznih držav, zato tudi predmet tega standarda še ni ustaljen.
Ta mednarodni standard ima status varnostne publikacije v skladu z IEC Vodilom 104.
Celoten seznam standardov skupine IEC 60364 z naslovom »Nizkonapetostne električne inštalacije«
je na voljo na spletnih straneh IEC.
Vsi novi standardi v tej skupini bodo imeli nov splošni naslov, kot je naveden zgoraj. Naslovi
obstoječih standardov v tej skupini bodo popravljeni pri njihovi naslednji izdaji.
Tehnični odbor je sklenil, da bo vsebina tega standarda ostala nespremenjena do datuma, določenega
za zaključek periodičnega pregleda, ki je določen na spletni strani IEC "http://webstore.iec.ch" pri
podatkih za to publikacijo. Po tem datumu bo publikacija:
– ponovno potrjena,
– razveljavljena,
– zamenjana z novo izdajo ali
– dopolnjena.

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SIST IEC 60364-4-43 : 2009
43 Nadtokovna zaščita

430.1 Področje uporabe

Ta del IEC 60364 obravnava zahteve za zaščito vodnikov pod napetostjo pred učinki nadtokov.

Ta standard opisuje, kako so vodniki pod napetostjo zaščiteni z eno ali več napravami za samodejni
odklop napajanja v primeru preobremenitve (točka 433) in kratkega stika (točka 434), razen v primerih,
kjer je nadtok omejen skladno s točko 436 ali kjer so izpolnjeni pogoji, opisani v točkah 433.3 (opustitev
naprav za zaščito pri preobremenitvi) ali 434.3 (opustitev naprav za kratkostično zaščito). V standardu je
opisana tudi koordinacija preobremenitvene in kratkostične zaščite (točka 435).

OPOMBA 1: Za vodnike pod napetostjo, ki so zaščiteni pred preobremenitvijo skladno s točko 433, se šteje, da so
zaščiteni tudi pred okvarami, podobnimi tistim, ki jih povzročijo nadtoki v velikosti preobremenitvenih tokov.

OPOMBA 2: Zahteve tega standarda ne upoštevajo zunanjih vplivov.

OPOMBA 3: Zaščita vodnikov skladno s tem standardom ne pomeni sočasno tudi zaščite naprave, ki je nanje
priključena.

OPOMBA 4: Predmet tega standarda niso zvijavi kabli naprav, ki so preko vtiča in vtičnice priključeni na stalno
inštalacijo, in zato niso nujno zaščiteni pred nadtokom.

OPOMBA 5: V tem standardu odklop ne pomeni tudi ločitev.

430.2 Zveza s standardi

Pri uporabi tega dokumenta so nujno potrebni naslednji referenčni dokumenti. Pri datiranih
sklicevanjih velja le navedena izdaja dokumenta. Pri nedatiranih sklicevanjih se uporablja zadnja
izdaja publikacije (skupaj z dopolnili).

IEC 60269-2 Nizkonapetostne varovalke – 2. del: Dodatne zahteve za varovalke, ki jih
uporabljajo strokovne osebe (uporaba varovalk zlasti v industriji) – Primeri
tipov standardiziranih varovalk od A do I
IEC 60269-3 Nizkonapetostne varovalke – 3. del: Dodatne zahteve za varovalke, ki jih
uporabljajo nestrokovne osebe (uporaba varovalk zlasti v gospodinjstvu in
podobnih okoljih) – Razdelki od A do F: Primeri tipov standardiziranih varovalk
IEC 60269-4 Nizkonapetostne varovalke – 4. del: Dodatne zahteve za taljive vložke za
zaščito polprevodniških naprav
IEC 60364-4-41 Nizkonapetostne električne inštalacije – 4-41. del: Zaščitni ukrepi – Zaščita
pred električnim udarom
IEC 60364-5-52:2001 Električne inštalacije zgradb – 5-52. del: Izbira in namestitev električne opreme
– Inštalacijski sistemi
IEC 60439-2 Sestavi nizkonapetostnih stikalnih in krmilnih naprav – 2. del: Posebne zahteve
za zbiralčne razdelilne sisteme (zbiralčna vodila)
IEC 60724 Mejne vrednosti temperature zaradi kratkega stika pri električnih kablih z
nazivno napetostjo 1 kV (Um = 1,2 kV) in 3 kV (Um = 3,6 kV)
IEC 60898 (vsi deli) Električni pribor – Odklopniki za nadtokovno zaščito za gospodinjstvo in
podobne inštalacije
IEC 60947-2 Nizkonapetostne stikalne naprave – 2. del: Odklopniki
IEC 60947-3 Nizkonapetostne stikalne in krmilne naprave – 3. del: Stikala, ločilniki, ločilna
stikala in stikalni aparati z varovalkami
IEC 60947-6-2 Nizkonapetostne stikalne naprave – 6. del: Večfunkcijska oprema – 2. oddelek:
Krmilne in zaščitne stikalne naprave (ali oprema) (CPS)
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SIST IEC 60364-4-43 : 2009
IEC 61009 (vsi deli) Odklopniki na preostali (residualni) tok z vgrajeno nadtokovno zaščito za
gospodinjsko in podobno rabo (RCBO's)
IEC 61534 (vsi deli) Sistemi zbiralčnih vodnikov
IEC Guide 104 Priprava varnostnih publikacij in uporaba osnovnih ter skupinskih varnostnih
publikacij

430.3 Splošne zahteve

Zaščitne naprave morajo zagotoviti odklop kakršnegakoli nadtoka vodnikov tokokroga, preden bi tak
tok lahko povzročil nevarnost in bi zaradi toplotnih ali mehanskih učinkov škodil izolaciji, spojem,
končnikom ali materialu okoli vodnikov.

431  Zahteve v zvezi z lastnostmi tokokrogov

431.1 Zaščita linijskih vodnikov

431.1.1 Zaznavanje nadtokov je treba zagotoviti za vse linijske vodnike, razen tam, kjer se uporablja
431.1.2. Povzročiti mora odklop vodnika, v katerem je bil nadtok zaznan, ni pa potreben odklop drugih
vodnikov pod napetostjo.

Če odklop ene faze lahko povzroči nevarnost, na primer pri trifaznem motorju, je treba ustrezno
ukrepati.

431.1.2 V sistemu TT ali TN za tokokroge, ki so napajani medfazno in nevtralni vodnik ni voden,
zaznavanja nadtoka ni treba predvideti za enega od linijskih vodnikov, če sta hkrati izpolnjena
naslednja pogoja:
a) kjer v istem tokokrogu ali na strani napajanja obstaja zaščita, namenjena temu, da zaznava
nesimetrična bremena in da povzroči odklop vseh linijskih vodnikov;
b) nevtralni vodnik ni voden od umetne nevtralne točke tokokrogov na bremenski strani zaščitne
naprave, omenjene v točki a).

431.2 Zaščita nevtralnega vodnika

431.2.1 Sistemi TT ali TN

Kjer je prerez nevtralnega vodnika najmanj enak prerezu linijskih vodnikov in kjer pričakovani tok
nevtralnega vodnika ne presega vrednosti tokov v linijskih vodnikih, ni treba predvideti zaznave
nadtokov za nevtralni vodnik ali odklopne naprave za ta vodnik.

Kjer je prerez nevtralnega vodnika manjši od prereza linijskega vodnika, je treba izvesti zaznavanje
nadtoka nevtralnega vodnika skladno z njegovim prerezom. To zaznavanje mora povzročiti odklop
linijskega vodnika, ne pa nujno tudi nevtralnega.

V obeh primerih je treba nevtralni vodnik zaščititi pri kratkostičnem toku.

OPOMBA: Ta zaščita je lahko izpolnjena že z nadtokovnimi zaščitnimi napravami linijskih vodnikov. V tem primeru ni
treba predvideti nadtokovne zaščite nevtralnega vodnika ali odklopne naprave za ta vodnik.

Kjer pričakovani tok nevtralnega vodnika presega velikost toka linijskega vodnika, se upošteva
431.2.3.

Zahteve za nevtralni vodnik veljajo tudi za vodnik PEN, razen za odklop.

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SIST IEC 60364-4-43 : 2009
431.2.2 Sistemi IT

Kjer je nevtralni vodnik voden, je treba izvesti zaznavanje nadtoka nevtralnega vodnika vsakega
tokokroga. Zaznavanje nadtoka mora povzročiti odklop vseh vodnikov pod napetostjo ustreznega
tokokroga, vključno z nevtralnim vodnikom. Ta ukrep ni nujen, če:

– je obravnavani nevtralni vodnik učinkovito zaščiten pri nadtoku z zaščitno napravo, nameščeno
na strani napajanja, na primer na začetku inštalacije, ali
– je obravnavani tokokrog zaščiten z zaščitno napravo na diferenčni tok z naznačenim diferenčnim
tokom, ki ne presega 0,20-kratne tokovne obremenljivosti ustreznega nevtralnega vodnika. Ta
naprava mora odklopiti vse vodnike pod napetostjo ustreznega tokokroga, vključno z nevtralnim
vodnikom. Naprava mora imeti zadostno tokovno izklopno zmogljivost v vseh polih.

OPOMBA: V sistemih IT je zelo priporočljivo, da nevtralni vodnik ni voden.

431.2.3 Harmonski toki

Zaznavanje preobremenitve nevtralnega vodnika je treba izvesti v tistih večfaznih sistemih, kjer se
pričakuje prekoračitev harmoničnih tokovnih komponent, ki bi presegle tokovno obremenljivost
nevtralnih vodnikov. Zaznavanje preobremenitve mora biti v skladu z lastnostmi tokov skozi nevtralni
vodnik in mora povzročiti odklop linijskih vodnikov, vendar ne nujno nevtralnega vodnika. Kjer je
nevtralni vodnik odklopljen, je treba upoštevati 431.3.

OPOMBA: Podrobnejše zahteve za zaščito nevtralnih vodnikov so podane v IEC 60364-5-52.

431.3 Odklop in ponovni vklop nevtralnega vodnika v večfaznih sistemih

Kjer se zahteva odklop nevtralnega vodnika, je treba odklop in ponovni vklop nevtralnega vodnika
izvesti tako, da se odklop izvede za odklopom linijskih vodnikov in ponovni vklop sočasno ali pred
vklopom linijskih vodnikov.

432 Lastnosti zaščitnih naprav

Zaščitne naprave morajo ustrezati tipom, navedenim v 432.1 do 432.3.
432.1 Naprave, ki zagotavljajo zaščito pri preobremenitvenem toku in tudi pri kratkostičnem
toku

Razen v primeru, ki je podan v 434.5.1, morajo biti naprave, ki zagotavljajo preobremenitveno in
kratkostično zaščito, sposobne izklopiti in pri odklopnikih vklopiti vsak nadtok do vključno
pričakovanega kratkostičnega toka na točki, kjer je naprava nameščena. Take naprave so lahko:

– odklopniki s preobremenitvenim in kratkostičnim proženjem,
– odklopniki, kombinirani z varovalkami,
– varovalke s karakteristikami gG.

OPOMBA 1: Varovalka vsebuje vse dele, ki sestavljajo celotno zaščitno napravo.

OPOMBA 2: Ta točka ne izključuje uporabe drugih zaščitnih naprav, če so izpolnjene zahteve 433.1 in 434.5.

432.2 Naprave, ki nudijo samo preobremenitveno zaščito

Te zaščitne naprave morajo izpolnjevati zahteve točke 433 in imajo lahko izklopno zmogljivost pod
vrednostjo pričakovanega kratkostičnega toka na mestu, kjer so naprave nameščene.

OPOMBA 1: Te naprave so v splošnem zaščitne naprave z inverzno (obratno sorazmerno) časovno zakasnitvijo.

OPOMBA 2: Varovalke tipa aM ne ščitijo pred preobremenitvijo.
9

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SIST IEC 60364-4-43 : 2009
432.3 Naprave, ki nudijo samo kratkostično zaščito

Napravo, ki zagotavlja samo kratkostično zaščito, je treba namestiti samo tam, kjer je
preobremenitvena zaščita zagotovljena z drugimi ukrepi, ali tam, kjer jo je skladno s točko 433
dovoljeno opustiti. Taka naprava mora biti sposobna izklopiti in pri odklopnikih vklopiti kratkostični tok
do vključno pričakovanega kratkostičnega toka. Taka naprava mora zadostiti zahtevam točke 434.

Take naprave so lahko:
– odklopniki s samo kratkostičnim proženjem,
– varovalke tipov gM, aM.

432.4 Lastnosti zaščitnih naprav

Prožilne lastnosti nadtokovnih zaščitnih naprav morajo ustrezati tistim, ki so navedene na primer v
IEC 60898, IEC 60947-2, IEC 60947-6-2, IEC 61009, IEC 60269-2, IEC 60269-3, IEC 60269-4 ali
IEC 60947-3.

OPOMBA: Uporaba drugih naprav ni izključena, če njihova časovno-tokovna karakteristika ustreza stopnji zaščite,
specificirani v tej točki.

433 Zaščita pri preobremenitvenem toku

433.1 Koordinacija med vodniki in preobremenitvenimi zaščitnimi napravami

Prožilne lastnosti naprave za preobremenitveno zaščito kabla morajo ustrezati naslednjima
pogojema:

I ≤ I ≤ I (1)
B n Z

I ≤ 1,45 × I (2)
2 Z


kjer so:
I obratovalni tok za ta tokokrog
B
I trajni dopustni tok kabla (glej točko 523)
Z
I naznačeni tok zaščitne naprave
n

OPOMBA 1: Za nastavljive zaščitne naprave je naznačeni tok I nastavljen po izbiri.
n
I tok, ki zagotavlja učinkovito delovanje zaščitne naprave v določenem času
2

Tok I zagotavlja učinkovito delovanje zaščitne naprave in mora ustrezati proizvajalčevim zahtevam
2
ali zahtevam standarda za tovrstne naprave.

Zaščita, skladna s to točko, ne zagotavlja zaščite v določenih primerih, na primer pri dolgotrajnem
nadtoku, ki je manjši od I . V takih primerih naj se izbere kabel z večjim prerezom.
2

OPOMBA 2: I je tok skozi linijski vodnik ali stalni tok skozi nevtralni vodnik v primeru visokega nivoja tretjega
B
harmonika.

OPOMBA 3: Tok, ki zagotavlja učinkovito delovanje zaščitne naprave v določenem času, se lahko imenuje I ali I v
t f
skladu s standardi za posamezne proizvode. I in I sta oba večkratnika I in je treba paziti na pravilen
t f n
prikaz vrednosti in indeksov.

OPOMBA 4: Za predstavitev pogojev (1) in (2) v točki 433.1 glej dodatek B.

OPOMBA 5: Obratovalni tok I se lahko šteje za dejanski tok I po uporabi korekcijskih faktorjev. Glej točko 311.
B a

10

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SIST IEC 60364-4-43 : 2009
433.2 Namestitev naprav za preobremenitveno zaščito

433.2.1 Napravo, ki zagotavlja zaščito pred preobremenitvijo, je treba namestiti na mestu tako, da
spremembe, kot so sprememba prereza vodnika, okolja, načina polaganja ali konstitucije, povzročijo
zmanjšanje vrednosti tokovne obremenljivosti vodnikov, razen v primerih po 433.2 in 433.3.

433.2.2 Naprava, ki ščiti vodnik pred preobremenitvijo, je lahko nameščena vzdolž poteka tega vodnika,
če odsek med mestom spremembe (v prerezu, okolju, načinu polaganja in konstituciji) in položajem
zaščitne naprave nima niti odcepov niti vtičnic ter izpolnjuje najmanj enega od naslednjih dveh pogojev:
a) obravnavani odsek vodnika je zaščiten pri kratkostičnih tokih skladno z zahtevami, navedenimi v
točki 434;
b) njegova dolžina ne presega 3 m ter je izveden tako, da je nevarnost kratkega stika zmanjšana na
najmanjšo stopnjo, in nameščen tako, da je zmanjšana nevarnost pred požarom ali poškodbami
oseb (glej tudi 434.2.1).

OPOMBA: Za namestitev skladno z a) glej sliko C.1. Za namestitev skladno z b) glej sliko C.2.

433.3 Opustitev naprav za zaščito pri preobremenitvi

Različni primeri, ki so navedeni v tej točki, se ne smejo uporabljati v inštalacijah, ki predstavljajo nevarnost
požara ali eksplozije, ali kjer zahteve za posebne inštalacije in lokacije navajajo drugačne pogoje.

433.3.1 Splošno

Naprave za zaščito pri preobremenitvi niso potrebne:
a) za vodnik, ki se nahaja na bremenski strani spremembe v prerezu vodnika, načinu polaganja ali
v konstituciji in je učinkovito zaščiten pri preobremenitvi z zaščitno napravo na napajalni strani;
b) za vodnik, ki verjetno ne bo preobremenjen ter je zaščiten pred kratkim stikom skladno z
zahtevami točke 434 in nima niti odcepa niti vtičnice;
c) na začetku inštalacije, kjer je distributer predvidel preobremenitveno zaščitno napravo in soglaša,
da ta nudi zaščito med začetkom inštalacije in glavnim razdelilnikom, kjer je predvidena naslednja
preobremenitvena zaščita;
d) za tokokroge telekomunikacij, nadzora, signalizacije in podobnega.
OPOMBA: Za inštalacije iz a), b) in c) glej sliko C.3.
433.3.2 Namestitev ali opustitev naprav za zaščito pri preobremenitvi v sistemih IT

433.3.2.1 Določila 433.2.2 in 433.3.1 za drugačno namestitev ali opustitev naprav za zaščito pri
preobremenitvi niso uporabna v sistemih IT, razen če je vsak tokokrog, ki ni zaščiten pred
preobremenitvijo, zaščiten z enim od navedenih načinov:
a) uporaba zaščitnih ukrepov, opisanih v točki 412 standarda IEC 60364-4-41;
b) zaščita vsakega tokokroga z zaščitno napravo na diferenčni tok, ki deluje takoj na drugo okvaro;
c) za stalno nadzirane sisteme samo uporaba naprav za nadzor izolacije, ki:
– povzročijo odklop tokokroga ob prvi okvari ali
– javijo prisotnost okvare. Okvaro je treba odpraviti skladno z obratovalnimi zahtevami in ob
upoštevanju nevarnosti druge okvare.

OPOMBA: Priporoča se namestitev kontrolnika izolacije, skladnega z IEC 61557-9. Z njegovo uporabo je mogoče
zaznati in določiti mesto okvare izolacije brez prekinitve napajanja.

433.3.2.2 V sistemih IT brez nevtralnega vodnika je preobremenitvena zaščitna lahko opuščena v
enem od linijskih vodnikov, če je v vsakem tokokrogu nameščena naprava na difer
...

SLOVENSKI STANDARD
oSIST IEC 60364-4-43:2009
01-april-2009
1L]NRQDSHWRVWQHHOHNWULþQHLQãWDODFLMHGHO=DãþLWQLXNUHSL=DãþLWDSUHG
QDGWRNL
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
Ta slovenski standard je istoveten z: IEC 60364-4-43
ICS:
29.120.50 9DURYDONHLQGUXJD Fuses and other overcurrent
PHGWRNRYQD]DãþLWD protection devices
91.140.50 Sistemi za oskrbo z elektriko Electricity supply systems
oSIST IEC 60364-4-43:2009 en,fr,de
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

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SIST IEC 60364-4-43:2009

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SIST IEC 60364-4-43:2009
IEC 60364-4-43
Edition 3.0 2008-08
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
GROUP SAFETY PUBLICATION
PUBLICATION GROUPÉE DE SÉCURITÉ
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 2-8318-9922-2
® Registered trademark of the International Electrotechnical Commission
Marque déposée de la Commission Electrotechnique Internationale

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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

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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)
2
(refer to 433.2.2a)).22
Figure C.2 – Overload protective device (P ) installed within 3 m of the origin of the
2
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
2
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
2
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

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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, 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
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. 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 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
Committees in that sense. While all reasonable efforts are made to ensure that the technical content of IEC
Publications is accurate, IEC cannot be held responsible for the way in which they are used or for any
misinterpretation by any end user.
4) In order to promote international uniformity, IEC National Committees undertake to apply IEC Publications
transparently to the maximum extent possible in their national and regional publications. Any divergence
between any IEC Publication and the corresponding national or regional publication shall be clearly indicated in
the latter.
5) IEC provides no marking procedure to indicate its approval and cannot be rendered responsible for any
equipment declared to be in conformity with an IEC Publication.
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
Publications.
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) 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.
International Standard IEC 60364-4-43 has been prepared by IEC technical committee 64:
Electrical installations and protection against electric shock.
This third edition cancels and replaces the second edition, published in 2001, and constitutes
a technical revision.
The main changes with respect to the previous edition are listed below:
– Annex B “IEC 60364 – Parts 1 to 6: Restructuring” deleted.
– Introduction of new informative Annexes B, C and D.
– Information concerning flexible cables added to Scope.
– The word “phase” changed to “line” throughout the standard.
– Requirement not to distribute the neutral in IT systems changed to a NOTE.
– Requirements added for overload detection for the neutral conductor for harmonic
currents.

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– Requirement that devices for protection against short-circuit current be capable of making
as well as breaking short-circuit current added.
– Information added to clarify protection against overload current.
– Requirements where devices for protection against overload need not be provided
expanded.
– More examples given where omission of devices for protection against overload is
permitted.
– Requirements where devices for protection against short-circuit need not be provided
expanded.
– Requirements for short-circuit current ratings of busbar trunking systems added.
The text of this standard is based on the following documents:
FDIS Report on voting
64/1641/FDIS 64/1656/RVD

Full information on the voting for the approval of this standard can be found in the report on
voting indicated in the above table.
This publication has been drafted in accordance with the ISO/IEC Directives, Part 2.
The reader's attention is drawn to the fact that Annex E lists all of the "in-some-country"
clauses on differing practices of a less permanent nature relating to the subject of this
standard.
This International Standard has the status of a group safety publication in accordance with
IEC Guide 104.
A list of all parts in the IEC 60364 series, under the general title Low-voltage electrical
installations, can be found on the IEC website.
Future standards in this series will carry the new general title as cited above. Titles of existing
standards in this series will be updated at the time of the next edition.
The committee has decided that the contents of this publication will remain unchanged until
the maintenance result date indicated on the IEC web site under "http://webstore.iec.ch" in
the data related to the specific publication. At this date, the publication will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.

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LOW-VOLTAGE ELECTRICAL INSTALLATIONS –

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



43 Protection against overcurrent
430.1 Scope
This part of IEC 60364 provides requirements for the protection of live conductors from the
effects of overcurrents.
This standard describes how live conductors are protected by one or more devices for the
automatic disconnection of the supply in the event of overload (Clause 433) and short-circuit
(Clause 434) except in cases where the overcurrent is limited in accordance with Clause 436
or where the conditions described in 433.3 (omission of devices for protection against
overload) or 434.3 (omission of devices for protection against short-circuit) are met.
Coordination of overload protection and short-circuit protection is also covered (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.
NOTE 3 Protection of conductors according to this standard does not necessarily protect the equipment
connected to the conductors.
NOTE 4 Flexible cables connecting equipment by plugs and socket-outlet to fixed installations are not part of the
scope of this standard and for this reason are not necessarily protected against overcurrent.
NOTE 5 Disconnection does not mean isolation in this standard.
430.2 Normative references
The following referenced documents are indispensable for the application 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 60269-2, Low-voltage fuses – Part 2: Supplementary requirements for fuses for use by
authorized persons (fuses mainly for industrial application) – Examples of standardized
systems of fuses A to I
IEC 60269-3, Low-voltage fuses – Part 3: Supplementary requirements for fuses for use by
unskilled persons (fuses mainly for household and similar applications) – Examples of
standardized systems of fuses A to F
IEC 60269-4, Low-voltage fuses – Part 4: Supplementary requirements for fuse-links for the
protection of semiconductor devices
IEC 60364-4-41, Low-voltage electrical installations – Part 4-41: Protection for safety –
Protection against electric shock
IEC 60364-5-52:2001, Electrical installations of buildings – Part 5-52: Selection and erection
of electrical equipment – Wiring systems
IEC 60439-2, Low-voltage switchgear and controlgear assemblies – Part 2: Particular
requirements for busbar trunking systems (busways)

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IEC 60724, Short-circuit temperature limits of electric cables with rated voltages of 1 kV (U =
m
1,2 kV) and 3 kV (U = 3,6 kV)
m
IEC 60898 (all parts), Electrical accessories – Circuit-breakers for overcurrent protection for
household and similar installations
IEC 60947-2, Low-voltage switchgear and controlgear – Part 2: Circuit-breakers
IEC 60947-3, Low-voltage switchgear and controlgear – Part 3: Switches, disconnectors,
switch-disconnectors and fuse-combination units
IEC 60947-6-2, Low-voltage switchgear and controlgear – Part 6-2: Multiple function
equipment – Control and protective switching devices (or equipment) (CPS)
IEC 61009 (all parts), Residual current operated circuit-breakers with integral overcurrent
protection for household and similar uses (RCBOs)
IEC 61534 (all parts), Powertrack systems
IEC Guide 104, The preparation of safety publications and the use of basic safety publications
and group safety publications
430.3 General requirements
Protective devices shall be provided to disconnect any overcurrent in the circuit conductors
before such a current could cause danger due to thermal or mechanical effects detrimental to
insulation, joints, terminations or material surrounding the conductors.
431 Requirements according to the nature of the circuits
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 may cause danger, for example in the case of a three-
phase motor, appropriate precautions shall be taken.
431.1.2 In a TT or TN system, for a circuit supplied between line conductors and in which
the neutral conductor is not distributed, overcurrent detection need not be provided for one of
the line conductors, provided that the following conditions are simultaneously fulfilled:
a) there exists, in the same circuit or on the supply side, protection intended to detect
unbalanced loads and intended to cause disconnection of all the line conductors;
b) the neutral conductor is not distributed from an artificial neutral point of the circuits
situated on the load side of the protective device mentioned in a).
431.2 Protection of the neutral conductor
431.2.1 TT or TN systems
Where the cross-sectional area of the neutral conductor is at least equivalent to that of the
line conductors, and the current in the neutral is expected not to exceed the value in the line
conductors, it is not necessary to provide overcurrent detection for the neutral conductor or a
disconnecting device for that conductor.

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Where the cross-sectional area of the neutral conductor is less than that of the line
conductors, it is necessary to provide overcurrent detection for the neutral conductor,
appropriate to the cross-sectional area of that conductor; this detection shall cause the
disconnection of the line conductors, but not necessarily of the neutral conductor.
In both cases the neutral conductor shall be protected against short-circuit current.
NOTE This protection may be achieved by the overcurrent protective devices in the line conductors. In that case it
is not necessary to provide overcurrent protection for the neutral conductor or a disconnecting device for that
conductor.
Where the current in the neutral conductor is expected to exceed the value in the line
conductors, refer to 431.2.3.
Except for disconnection the requirements for a neutral conductor apply to a PEN conductor.
431.2.2 IT systems
Where the neutral conductor is distributed, it is necessary to provide overcurrent detection for
the neutral conductor of every circuit. The overcurrent detection shall cause the disconnection
of all the live conductors of the corresponding circuit, including the neutral conductor. This
measure is not necessary if
– the particular neutral conductor is effectively protected against overcurrent by a
protective device placed on the supply side, for example at the origin of the installation,
or if
– the particular circuit is protected by a residual current operated protective device with a
rated residual current not exceeding 0,20 times the current-carrying capacity of the
corresponding neutral conductor. This device shall disconnect all the live conductors of
the corresponding circuit, including the neutral conductor. The device shall have sufficient
breaking capacity for all poles.
NOTE In IT systems, it is strongly recommended that the neutral conductor should not be distributed.
431.2.3 Harmonic currents
Overload detection shall be provided for the neutral conductor in a multi-phase circuit where
the harmonic content of the line currents is such that the current in the neutral conductor is
expected to exceed the current-carrying capacity of that conductor. The overload detection
shall be compatible with the nature of the current through the neutral and shall cause the
disconnection of the line conductors but not necessarily the neutral conductor. Where the
neutral is disconnected, the requirements of 431.3 apply.
NOTE Further requirements regarding protection of neutral conductors are given in IEC 60364-5-52.
431.3 Disconnection and reconnection of the neutral conductor in multi-phase systems
Where disconnection of the neutral conductor is required, disconnection and reconnection
shall be such that the neutral conductor shall not be disconnected before the line conductors
and shall be reconnected at the same time as or before the line conductors.
432 Nature of protective devices
The protective devices shall be of the appropriate types indicated by 432.1 to 432.3.
432.1 Devices providing protection against both overload current and short-circuit
current
Except as stated in 434.5.1, a device providing protection against both overload and short-
circuit current shall be capable of breaking and, for a circuit-breaker, making any overcurrent

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up to and including the prospective short-circuit current at the point where the device is
installed. Such devices may be:
– circuit-breakers incorporating overload and short-circuit release;
– circuit-breakers in conjunction with fuses;
– fuses having fuse links with gG characteristics.
NOTE 1 The fuse comprises all the parts that form the complete protective device.
NOTE 2 This subclause does not exclude the use of other protective devices if the requirements in 433.1 and
434.5 are fulfilled.
432.2 Devices ensuring protection against overload current only
These protective devices shall satisfy the requirements of Clause 433 and may have an
interrupting capacity below the value of the prospective short-circuit current at the point where
the devices are installed.
NOTE 1 These devices are generally inverse time lag protective devices.
NOTE 2 Fuses type aM do not protect against overload.
432.3 Devices ensuring protection against short-circuit current only
A device providing protection against short-circuit current only shall be installed where
overload protection is achieved by other means or where Clause 433 permits overload
protection to be dispensed with. Such a device shall be capable of breaking, and for a circuit-
breaker making, the short-circuit current up to and including the prospective short-circuit
current. Such a device shall satisfy the requirements of Clause 434.
Such devices may be
− circuit-breakers with short-circuit release only,
− fuses with gM, aM type fuse links.
432.4 Characteristics of protective devices
The operating characteristics of overcurrent protective devices shall comply with those
specified in, for example, IEC 60898, IEC 60947-2, IEC 60947-6-2, IEC 61009, IEC 60269-2,
IEC 60269-3, IEC 60269-4 or IEC 60947-3.
NOTE The use of other devices is not excluded provided that their time/current characteristics provide an
equivalent level of protection to that specified in this clause.
433 Protection against overload current
433.1 Coordination between conductors and overload protective devices
The operating characteristics of a device protecting a cable against overload shall satisfy the
two following conditions:
I ≤ I ≤ I (1)

B n Z
≤ 1,45 × I (2)
I
2 Z
where
 is the design current for that circuit;
I
B
I is the continuous current-carrying capacity of the cable (see Clause 523);

Z
 is the rated current of the protective device;
I
n
NOTE 1 For adjustable protective devices, the rated current I is the current setting selected.
n

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SIST IEC 60364-4-43:2009
– 10 – 60364-4-43 © IEC:2008
I is the current ensuring effective operation in the conventional time of the protective
2
device.
The current I ensuring effective operation of the protective device shall be provided by the
2
manufacturer or as given in the product standard.
Protection in accordance with this clause may not ensure protection in certain cases, for
example where sustained overcurrents less than I occur. In such cases, consideration should

2
be given to selecting a cable with a larger cross-sectional area.
NOTE 2 I is the design current through the line or the permanent current through neutral in case of a high level
B
of the third harmonic
NOTE 3 The current ensuring effective operation in the conventional time of protective devices may also be
named I or I according to the product standards. Both I and I are multiples of I and attention should be given to

t f
t f n
the correct representation of values and indexes.
NOTE 4 See Annex B for an illustration of conditions (1) and (2) of 433.1.
NOTE 5 Design current I can be considered as an actual current I after applying correction factors. See Clause
B a
311.
433.2 Position of devices for overload protection
433.2.1 A device ensuring protection against overload shall be placed at the point where a
change, such as a change in cross-sectional area, nature, method of installation or in
constitution, causes a reduction in the value of current-carrying capacity of the conductors,
except where 433.2.2 and 433.3 apply.
433.2.2 The device protecting the conductor against overload may be placed along the run
of that conductor if the part of the run between the point where a change occurs (in cross-
sectional area, nature, method of installation or constitution) and the position of the protective
device has neither branch circuits nor socket-outlets and fulfils at least one of the following
two conditions:
a) it is protected against short-circuit current in accordance with the requirements stated in
Clause 434;
b) its length does not exceed 3 m, it is carried out in such a manner as to reduce the risk of
short-circuit to a minimum, and it is installed in such a manner as to reduce to a minimum
the risk of fire or danger to persons (see also 434.2.1).
NOTE For installation according to a) see Figure C.1. For installation according to b) see Figure C.2.
433.3 Omission of devices for protection against overload
The various cases stated in this subclause shall not be applied to installations situated in
locations presenting a fire risk or risk of explosion or where the requirements for special
installations and locations specify different conditions.
433.3.1 General
Devices for protection against overload need not be provided:
a) for a conductor situated on the load side of a change in cross-sectional area, nature,
method of installation or in constitution, that is effectively protected against overload by a
protective device placed on the supply side;
b) for a conductor that is not likely to carry overload current, provided that this conductor is
protected against short-circuit in accordance with the requirements of Clause 434 and that
it has neither branch circuits nor socket-outlets;
c) at the origin of an installation where the distributor provides an overload device and
ag
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