IEC 60092-202:2016

IEC 60092-202 ®
Edition 5.0 2016-09
REDLINE VERSION
INTERNATIONAL
STANDARD
colour
inside
Electrical installations in ships –
Part 202: System design – Protection

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IEC 60092-202 ®
Edition 5.0 2016-09
REDLINE VERSION
INTERNATIONAL
STANDARD
colour
inside
Electrical installations in ships –

Part 202: System design – Protection

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 47.020.60 ISBN 978-2-8322-3660-4

– 2 – IEC 60092-202:2016 RLV © IEC 2016
CONTENTS
FOREWORD . 4
INTRODUCTION . 7
1 Scope . 8
2 Normative references. 8
3 Terms and definitions . 8
4 General requirements . 10
4.1 General . 10
4.2 Basic protection . 11
4.3 Studies and calculations . 11
5 Electrical load study . 11
6 Short-circuit current calculations . 11
7 Protection discrimination study . 12
7.1 General . 12
7.2 Current selectivity . 12
7.3 Time-current selectivity . 13
7.4 Alternative protection schemes . 13
8 Characteristics and choice of protective devices with reference to short-circuit
rating . 13
8.1 General . 13
8.2 Protective devices . 13
8.3 Rated short-circuit breaking capacity . 14
8.4 Rated short-circuit making capacity . 15
8.5 Co-ordination of short-circuit ratings with regard to continuity of service
requirements Co-ordinated choice of protective devices with regard to
discrimination requirements . 15
9 Choice of protective devices with reference to overload . 16
9.1 Mechanical switching devices . 16
9.2 Fuses for overload protection . 17
9.3 Static or solid state switching devices . 17
10 Choice of protective devices with regard to their application . 17
10.1 General . 17
10.2 Generator protection . 17
10.2.1 General . 17
10.2.2 Protection against short-circuits and fault currents on the generator side . 18
10.3 Protection of essential services . 18
10.4 Protection of transformers . 18
10.5 Circuit protection . 19
10.6 Motor protection . 19
10.7 Accumulator (storage) battery protection . 19
10.8 Protection of meters, pilot lamps and control circuits . 20
10.9 Protection of static or solid-state devices . 20
11 Reverse power and reverse current protection for AC generators . 20
12 Undervoltage protection . 21
12.1 A.C. and d.c. DC generators . 21
12.2 A.C. and d.c. DC motors . 21

13 Overvoltage protection . 21
13.1 General . 21
13.2 Transformers . 21
13.3 AC machines . 21
14 Protection against under- and over-frequency . 21
Bibliography . 22

Figure 1– Continuity of supply and service . 16

– 4 – IEC 60092-202:2016 RLV © IEC 2016
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
ELECTRICAL INSTALLATIONS IN SHIPS –

Part 202: System design – Protection

FOREWORD
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International Standard IEC 60092-202 has been prepared by IEC technical
committee 18: Electrical installations of ships and of mobile and fixed offshore units.
This fifth edition cancels and replaces the fourth edition published in 1994 and
Amendment 1:1996. This edition constitutes a technical revision.
This edition includes the following significant technical changes with respect to the previous
edition:
This document: Previous document:
Clause/subclause No. and heading Corresponding clause/subclause No., remark
1 Scope 1, No change
2 Normative references 2, Updated
3 Definitions 3, Several definitions changed and added
4 General requirements 4, Text changed
4.1 General New clause/subclause
4.2 Basic protection New clause/subclause
4.3 Studies and calculations New clause/subclause
5 Electrical load study New clause/subclause
6 Short-circuit current calculations 5, Heading change
- 5.1, Text changed and moved to new Clause 6
- 5.2, Text deleted, for DC-Systems reference to
IEC 61660-1 added
7 Protection discrimination study New clause/subclause
7.1 General New clause/subclause
7.2 Current selectivity New clause/subclause
7.3 Time-current selectivity New clause/subclause
8 Characteristics and choice of protective devices 6, Text completely revised and extended
with reference to short-circuit rating
8.1 General 6.1
8.2 Protective devices New clause/subclause
8.3 Rated short-circuit breaking capacity 6.2
8.4 Rated short-circuit making capacity 6.3
8.5 Co-ordinated choice of protective devices with 6.4, Heading changed, new text
regard to discrimination requirements
9 Choice of protective devices with reference to 7
overload
9.1 Mechanical switching devices 7.1
9.2 Fuses for overload protection 7.2
10 Choice of protective devices with regard to their 8
application
10.1 General 8.1
10.2 Generator protection 8.2
10.3 Protection of essential services 8.3
10.4 Protection of transformers 8.4
10.5 Circuit protection 8.5
10.6 Motor protection 8.6
10.7 Accumulator (storage) battery protection 8.9
10.8 Protection of meters, pilot lamps and control 8.10
circuits
– 6 – IEC 60092-202:2016 RLV © IEC 2016
This document: Previous document:
Clause/subclause No. and heading Corresponding clause/subclause No., remark
10.9 Protection of static or solid-state devices 8.11
11 Reverse power and reverse current protection for 9
AC generators
11 Reverse power and reverse current protection for 9.1
AC generators
- 9.2
12 Undervoltage protection 10
12.1 AC and DC generators 10.1
12.2 AC and DC motors 10.2
13 Overvoltage protection 11
13.1 General New clause/subclause
13.2 Transformers 11.1
13.3 AC machines 11.2
14 Protection against under- and over-frequency New clause/subclause

The text of this standard is based on the following documents:
FDIS Report on voting
18/1538/FDIS 18/1542/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.
A list of all parts of the IEC 60092 series, published under the general title Electrical
installations in ships, can be found on the IEC website.
The committee has decided that the contents of this publication will remain unchanged until
the stability date indicated on the IEC website 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.
IMPORTANT – The “colour inside” logo on the cover page of this publication
indicates that it contains colours which are considered to be useful for the
correct understanding of its contents. Users should therefore print this
publication using a colour printer.

INTRODUCTION
The IEC 60092 series: Electrical installations in ships includes international standards for
electrical installations in sea-going ships, incorporating good practice and co-ordinating as far
as possible existing rules.
These standards form a code of practical interpretation and amplification of the requirements
of the International Convention on for the safety of life at sea, a guide for future regulations
which may be prepared and a statement of practice for use by ship owners, ship builders and
appropriate organizations.
– 8 – IEC 60092-202:2016 RLV © IEC 2016
ELECTRICAL INSTALLATIONS IN SHIPS –

Part 202: System design – Protection

1 Scope
This part of IEC 60092 is applicable to the main features of the electrical protective system to
be applied to electrical installations for use in ships.
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 92-301:1980, Electrical installations in ships - Part 301: Equipment - Generators and
motors
IEC 363:1972, Short-circuit current evaluation with special regard to rated short-circuit
capacity of circuit-breakers in installations in ships
IEC 60909 (all parts), Short-circuit currents in three-phase a.c. systems
IEC 60909-0, Short-circuit currents in three-phase a.c. systems – Part 0: Calculation of
currents
IEC TR 60909-1, Short-circuit currents in three-phase a.c. systems – Part 1: Factors for the
calculation of short-circuit currents according to IEC 60909-0
IEC 60947-2:1989 2006, Low-voltage switchgear and controlgear – Part 2: Circuit-breakers
IEC 60947-2:2006/AMD1:2009
IEC 60947-2:2006/AMD2:2013
IEC 61140, Protection against electric shock – Common aspects for installation and
equipment
IEC 61363-1, Electrical installations of ships and mobile and fixed offshore units – Part 1:
Procedures for calculating short-circuit currents in three-phase a.c.
IEC 61660-1, Short-circuit currents in d.c. auxiliary installations in power plants and
substations – Part 1: Calculation of short-circuit currents
IEC 62271-100, High-voltage switchgear and controlgear – Part 100: Alternating-current
circuit-breakers
3 Terms and definitions
1)
For the purposes of this document, the following terms and definitions apply .
ISO and IEC maintain terminological databases for use in standardization at the following
addresses:
• IEC Electropedia: available at http://www.electropedia.org/
—————————
1)
The International Electrotechnical Vocabulary (IEV) definitions for these four terms are not applicable to this
standard.
• ISO Online browsing platform: available at http://www.iso.org/obp
3.1
rated load
the highest value of load specified for rated conditions
3.2
overload
Excess of the actual load over the nominal load.
operating conditions in an electrically undamaged circuit, which cause an overload above the
rated load
[SOURCE: IEC 60050-441:1984, 441-11-08, modified — The words "which cause an over-
current" has been replaced with "which cause an overload above the rated load".]
3.3
nominal load, full load
Power for which a machine has been designed.
3.3
over-current
Abnormal current greater than the full load
current exceeding the rated current
[SOURCE IEC 60050-441:1984, 441-11-06]
3.4
short-circuit
Intentional or accidental connection of two points of a circuit through a negligible impedance.
The term is often applied to the group of phenomena which accompany a short circuit
between points at different potentials.
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 60050-195:1998, 195-04-11]
3.5
backup protection
protection equipment or system which is intended to operate when a system fault is not
cleared in due time because of:
– failure or inability of a protective device closest to the fault to operate or
– failure of a protective device other than the protective device closest to the fault to operate
Note 1 to entry: This definition differs from the one given in IEC 60050-448:1995, 448-11-14.
3.6
over-current discrimination
selectivity
co-ordination of the operating characteristics of two or more over-current protective devices
such that, on the incidence of over-currents within stated limits, the device intended to
operate within these limits does so, while the other(s) does (do) not
Note 1 to entry: Distinction is made between series discrimination, involving different over-current protective
devices passing substantially the same over-current, and network discrimination involving identical protective
devices passing different proportions of the over-current.
[SOURCE 60050-441:1984, 441-17-15, modified — The term "selectivity" has been added as
an equivalent term.]
3.7
total discrimination
total selectivity
selectivity (over-current discrimination) where, in the presence of two over-current protective
devices in series, the protective device on the load side effects the protection without causing
the other protective device to operate

– 10 – IEC 60092-202:2016 RLV © IEC 2016
[SOURCE IEC 60947-2:2006/AMD2:2013, 2.17.2, modified — The term "total discrimination"
has been added as an equivalent term and the term "over-current discrimination" has been
replaced by "selectivity (over-current discrimination)" in the definition.]
3.8
partial discrimination
partial selectivity
selectivity (over-current discrimination) where, in the presence of two or more over-current
protective devices in series, the protective device closest to the fault at the load side effects
the protection up to a given level of short-circuit current without causing the other protective
devices to operate
[SOURCE IEC 60947-2:2006/AMD2:2013, 2.17.3, modified —The term "partial discrimination"
has been added as an equivalent term and the definition has been rephrased.]
3.9
continuity of service
condition where, after a fault in a circuit has been cleared, the supply to the healthy circuits is
re-established
3.10
continuity of supply
condition where during and after a fault in a circuit, the supply to the healthy circuits is
permanently ensured
Note 1 to entry: This definition is different from that given in IEC 60050-614:2016, 614-01-22.
3.11
basic protection
minimum required protection for equipment
3.12
electrical load study
study reflecting the different operational modes and their respective load requirements
Note 1 to entry: Typical examples of operational modes are harbour, manoeuvre, seagoing mode.
4 General requirements
4.1 General
Electrical installations shall be protected against accidental over-currents, up to and including
short-circuit, by appropriate devices. Choice, arrangement and performance of the various
protective devices shall provide complete and co-ordinated automatic protection in order to
ensure as far as possible obtain
– elimination of the effects of faults to reduce damage to the system and the hazard of fire
as much as possible, and
– continuity of service through discrimination or another system of co-ordinated action of the
protective devices to maintain supply to healthy circuits in the event of a fault elsewhere
supply.
Under these conditions, the elements of the healthy system shall be designed and
constructed to withstand the thermal and electrodynamic stresses caused by the possible
over-current, including short-circuit, for the admissible durations.
4.2 Basic protection
Devices provided for overcurrent basic protection shall be chosen according to the
requirements suitable for the equipment they are protecting, especially with regard to
– overload;
– over-current,
– short-circuit, and
– earth fault, as appropriate.
The complexity of the protections is driven by a number of factors such as improved system
performance, reliability, and reduction of the damage to the equipment for economical reason.
Additional protection features shall not interfere with the basic protection requirements of this
standard.
Electrical installation shall be provided with protections against electric shock in accordance
with IEC 61140.
4.3 Studies and calculations
Studies and calculations shall demonstrate the proper coordination of power ratings, load
requirements, system dynamics and protection.
In order to confirm the design of the electrical system and to confirm the ratings of the
equipment selected, system studies shall be carried out. The system studies and calculation
shall include
– an electrical load study (see Clause 5),
– short-circuit current calculations (see Clause 6), and
– a protection discrimination study (see Clause 7).
5 Electrical load study
An electrical load list shall be prepared to establish the electrical power requirements
throughout the installation.
Based on analysis, load shedding shall be applied when required in order to avoid a blackout.
Load shedding can be implemented by shedding of individual/groups of consumers or by
appropriate separation of switchboard busbars.
Care should be taken to ensure that the response time is sufficient to enable the load
shedding system to perform its function and maintain a stable electrical system.
Load estimates should be carried out for all operational conditions, for example
– navigation at sea,
– estuary trading and navigation close to port, and
– emergency power supply.
6 Short-circuit current calculations
An example of the short-circuit calculation in both a.c. and d.c. systems is given in IEC 363.
5.1 Short-circuit current in a.c. systems
5.1.1 For the evaluation of the prospective short-circuit current, the equivalent system
impedance shall be considered seen from the point of fault.
5.1.2 The source of current shall include the maximum number of generators which can be
simultaneously connected, and the maximum number of motors which are normally
simultaneously connected in the system. The contribution of generators and motors shall be
calculated on the basis of their characteristics.
The fault currents that flow as a result of short-circuits shall be calculated at each system
voltage under three-phase fault conditions. These calculated currents shall be used to select
suitably rated equipment and to allow the selection and setting of protective devices to ensure
that successful discriminatory fault clearance is achieved.
The fault current shall be calculated for maximum and minimum system supply. The
contribution of induction motors should be included in the study.

– 12 – IEC 60092-202:2016 RLV © IEC 2016
For general information regarding short-circuit calculations, reference shall be made to
IEC 61363-1, IEC 60909-0 and IEC TR 60909-1 for AC systems, and IEC 61660-1 for DC
systems.
IEC 60909 (all parts) is written for installations in which the short-circuit behaviour is
predominantly ruled by passive elements (e.g. transformers, cables). It shall therefore only be
applied for small transformer-fed low voltage installations. In all other cases, IEC 61363-1,
which takes generator short-circuit behaviour into account, shall be applied.
NOTE Where precise information of their characteristics is lacking, the contribution of induction
motors for determining the maximum peak value attainable by the short-circuit current (i.e. the
value of the current to be added to the maximum peak value of the short-circuit due to the
generators) can be taken as equal to 8 I where I is the sum of the rated currents of the
n n
motors estimated normally when simultaneously in service (I is an r.m.s. RMS value).
n
For more precise calculation, the following r.m.s. RMS values may be used:
– at the instant of short-circuit occurrence (sub-transient value): 6,25 I
n
– at the instant T, i.e. after one cycle from short-circuit inception: 2,5 I
n
– at the instant 2T, i.e. after two cycles from short-circuit inception: 1,0 I
n
5.2 Short-circuit current in d.c. systems
5.2.1 The prospective short-circuit current at a definite point of the system shall be evaluated
by considering the equivalent system resistance seen from the point of fault.
5.2.2 The source of a short-circuit current shall include the maximum number of generators
which can be simultaneously connected, and the maximum number of motors which are
normally simultaneously connected in the system. The contribution of each rotating machine
shall be evaluated as a function of its characteristics.
In the absence of precise information, the contribution of motors in the determination of the
maximum value reached by the short-circuit current can be taken as equal to six times the
sum of the rated currents of the motors estimated to be normally in se rvice simultaneously.
7 Protection discrimination study
7.1 General
A coordination study shall be carried out to determine the setting of the protective relays and
direct acting circuit-breakers (see Clause 4).
In general, the two protection schemes described in 7.2 and 7.3 are possible.
7.2 Current selectivity
This type of selectivity is based on the observation that the closer the fault point is to the
power supply of the installation, the higher the short-circuit current is. It is therefore possible
to discriminate the zone the fault occurred in by setting the instantaneous protections to
different current values.
The coordination of protection devices shall consider tolerances and accuracies.
Because of the large variation in short currents due to different operational conditions, current
selectivity shall be used with caution and may not be achievable in all instances.
7.3 Time-current selectivity
Time-current selectivity makes trip selectivity by adjusting the protections so that the load-
side protection, for all possible over-current values, trips more rapidly than the supply-side
circuit-breaker. When the trip times of the two circuit-breakers are analysed, it is necessary to
consider
– the tolerances over the thresholds and trip times, and

– the real currents circulating in the circuit-breakers.
7.4 Alternative protection schemes
Alternative protection schemes are permissible provided that the same level of protection is
achieved.
8 Characteristics and choice of protective devices with reference to short-
circuit rating
8.1 General
Protection against short-circuit shall be provided by circuit-breakers or fuses. For AC systems
with a voltage higher than 1 kV, special consideration of fuses shall be made regarding their
characteristics.
The use of a protective device not having a short-circuit breaking or making capacity at least
equal to the maximum prospective short-circuit current at the point where it is installed is
allowed, provided that it is backed-up by a fuse or by a circuit-breaker on the generator side,
having at least the necessary short-circuit rating and not being the generator circuit-breaker.
The same fuse or circuit-breaker may back up more than one circuit-breaker when essential
services are not involved.
A separate current limiter to increase the short-circuit breaking capacity of a circuit-breaker
may be used according to the manufacturer’s instructions. The same current limiter can back
up more than one circuit-breaker. The connection between current limiter and circuit-
breaker(s) shall be made in such a way as to minimize the risk of short-circuit.
For low voltage systems, the short-circuit performance of the arrangement shall at least be
equal to the requirements of IEC 60947-2.
NOTE For low voltage switchgear, further information can be found in IEC 60947-2:2006/AMD2:2013, Annex A.
For high voltage systems, the short-circuit performance of the arrangement shall at least be
equal to the requirements of IEC 62271-100.
8.2 Protective devices
6.1.1 Protective devices for short-circuit protection shall conform to the requirements of the
IEC standards concerning circuit-breakers and fuses, but it shall be taken into account that
the conditions of the ship’s installations may differ from the conditions foreseen in those
publications, in particular with reference to the following.
– The short-circuit power factor in an a.c. AC systems in a ships, which may be lower than
that assumed as a basis for short-circuit rating of normal distribution circuit-breakers.
Where no data are available, a short-circuit power factor of 0,2 shall be assumed.
– The sub-transient and transient component of the a.c. AC short-circuit current.
– The AC and DC decrement of short-circuit current.
As a consequence, the ratio between rated breaking capacity and the correlated making
capacity of circuit-breakers corresponding to the normal conditions of distribution systems
(see IEC 947-2), may be substantially inadequate.
In such cases, the circuit-breakers shall be chosen with regard to their short-circuit making
capacity, even though their available short-circuit breaking capacity, which complies with
normal conditions, may be in excess of the one required for the actual application.
P2 category circuit-breakers shall be used for generator circuits and preferably for other
circuits.
P1 category circuit-breakers may be used where the system arrangements are such, for
example by duplication and separation of supplies, that failure of the circuit-breakers will not
jeopardize the safety of the vessel.
6.1.2 Protection against short circuit shall be provided by circuit-breakers or fuses

– 14 – IEC 60092-202:2016 RLV © IEC 2016
In some cases, and particularly for high-voltage a.c. systems, it shall be noted that certain
types of fuses have such characteristics for ce rtain overcurrents that they shall be arranged
to cause an associated switch to trip for these overcurrents.
6.1.3 The use of a circuit-breaker not having a short-circuit breaking and/or making capacity
at least equal to the maximum prospective short-circuit current at the point where it is
installed is allowed, provided that it is backed up by a fuse or by a circuit-breaker on the
generator side, having at least the necessary short-circuit rating and not being the generator
circuit-breaker.
The same fuse or circuit-breaker may back up more than one circuit-breaker when essential
services are not involved.
The short-circuit performance of the arrangement shall at least be equal to the requirements
of IEC 947-2 for a single circuit-breaker having the same short-circuit performance category
as the backed-up circuit-breaker and rated for the maximum prospective short-circuit level at
the supply terminals of the arrangement.
Circuit-breakers with fuses connected to the load side may be used, provided the back-up
fuses and the circuit-breakers are of co-ordinated design, in order to ensure that the operation
of the fuses takes place in due time so as to prevent arcing between poles or against metal
parts of the circuit-breakers when they are submitted to overcurrents involving the operation
of the fuse.
When determining the performance requirements for the above-mentioned back-up protection
arrangement, it is permitted to take into account the impedance of the various circuit elements
of the arrangement, such as the impedance of a cable connection when the backed-up circuit-
breaker is located away from the back-up breaker or fuse.
When current selectivity according to 7.2 is chosen, circuit-breakers with utilisation category A
according to IEC 60947-2:2006 are acceptable.
When time current selectivity according to 7.3 is chosen, circuit-breakers shall be selected
according to their rated short-time withstand current capacity I .
CW
Utilisation category B according to IEC 60947-2:2006 shall be used for all low voltage circuit-
breakers with delayed tripping during short-circuit conditions.
High voltage circuit-breakers shall comply with IEC 62271-100.
8.3 Rated short-circuit breaking capacity
The rated short-circuit breaking capacity of every device intended for short-circuit protection
shall be not less than the maximum prospective current to be broken at that point in the
installation, unless a method according to 8.1 is used.
For a.c., the rated short-circuit breaking capacity shall be not less than the r.m.s. value of the
a.c. component of the prospective short-circuit current at the point of application (for
exceptions, see 6.1.3).
This implies the ability of the circuit-breaker to break any current having an a.c. component
not exceeding its rated breaking capacity, whatever may be the possible value of the inherent
d.c. component at the beginning of the interruption.
The conditions of the circuit which determine the inherent d.c. component may be more
severe in systems on board than those assumed as normal (see IEC 947-2) for distribution
circuit-breakers. In such an event, the ability of the circuit-breaker to break the current
corresponding to its rated breaking capacity, irrespective of the possible value of the d.c.
component, shall be ascertained under the conditions of the actual installation.
Circuit-breakers with breaking capacity identified by rated service short-circuit breaking
capacity I (IEC 60947-2:2006(AMD1:2009/AMD2:2013 4.3.5.2.2) shall be used for all
CS
generator circuits and preferably for other circuits.

Circuit-breakers with breaking capacity identified by rated ultimate service short-circuit
breaking capacity I (IEC 60947-2:2006/AMD1:2009/AMD2:2013 4.3.5.2.1) may be used
CU
where the system arrangements are such, for example by duplication and separation of
supplies, that failure of the circuit-breakers will not jeopardize the safety of the vessel.
When circuit-breakers with rated ultimate short-circuit breaking capacity I are used on main
CU
or emergency switchboards, they are to be of plug-in type.
8.4 Rated short-circuit making capacity
The rated short-circuit making capacity of every mechanical switching device intended to be
closed on a short-circuit shall be adequate for the maximum peak value of the prospective
short-circuit current at the point of installation (for exceptions, see 8.1).
When closing on a short-circuit, the circuit breaker shall be able to withstand the short-circuit
current during the time delay required due to selectivity/discrimination reasons.
NOTE The circuit-breaker should be able to make the current corresponding to its making capacity without
opening within a time corresponding to the maximum time delay required.
8.5 Co-ordination of short-circuit ratings with regard to continuity of service
requirements
Co-ordinated choice of protective devices with regard to discrimination
requirements
8.5.1 Continuity of service supply of healthy circuits under short-circuit conditions may
shall be achieved by total discrimination or by a different system of co-ordinated action of the
protective devices.
All systems require:
– the tripping characteristics of protective devices in series to be properly co-ordinated;
– all protective devices carrying the fault current shall withstand, without damage, currents up
to the maximum level at the point of application in the relevant installation, until complete fault
clearance.
Discrimination requires in addition
– only the protective device nearest to the fault shall open the faulty circuit;
– the protective devices shall be capable of carrying, without opening, a current not mless
than the short-circuit current at the point of application for a time corresponding to the
opening of the breaker, increased by the time delay required for discrimination.
Other systems require:
– the tripping characteristics as well as the short-circuit capacities of the protective devices in
series to be properly co-ordinated and, unless already proven to conform with an IEC
standard, tested according to a testing method agreed between manufacturer and purchaser.
6.4.2 The tripping characteristics of protective devices in series shall be properly co-
ordinated.
6.4.3 The protective devices shall be capable of carrying, without opening, a current not less
than the short-circuit current at the point of application for a time corresponding to the
opening of the breaker increased by the time delay required for discrimination.
The requirement of total discrimination versus backup protection has to be decided as a part
of the system study. The requirement will, among others, depend on the criticality of the
individual consumer.
The protective devices shall be capable of carrying, without opening, a current no less than
the short-circuit current at the point of application for a time required by total discrimination,
and, by partial discrimination, up to the given short-circuit current level (see Figure 1).

– 16 – IEC 60092-202:2016 RLV © IEC 2016
Before a fault During a fault After a fault

IEC
Figure 1– Continuity of supply and service
8.5.2 The preferred power supply method is continuity of supply. Where continuity of
service is allowed, the operating characteristic of protective devices and of the user
equipment shall be co-ordinated and verified.
9 Choice of protective devices with reference to overload
9.1 Mechanical switching devices
Mechanical switching devices provided for overload protection should shall have a tripping
characteristic (over-current trip time) adequate for the overload ability of the elements of the
system to be protected and for any discrimination requirements.
9.2 Fuses for overload protection
The use of fuses for overload protection is admissible permitted up to 320 A, provided they
have suitable characteristics, but the use of circuit-breakers or similar devices is
recommended above 200 A. For high-voltage a.c. AC systems, the use of fuses for overload
protection is not admissible acceptable.
9.3 Static or solid state switching devices
Static or solid state switching devices do not provide isolation for personal protection. Static
or solid state devices provided for overload protection should have a tripping characteristic
(over-current trip time) adequ
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