SIST EN IEC 60947-9-2:2025

SLOVENSKI STANDARD
01-september-2025
Nizkonapetostne stikalne in krmilne naprave - 9-2. del: Aktivni sistemi za blažitev
učinkov okvarnega obloka - Naprave za odkrivanje in ublažitev lokov, ki temeljijo
na optičnem sistemu (IEC 60947-9-2:2021)
Low-voltage switchgear and controlgear - Part 9-2: Active arc-fault mitigation systems -
Optical-based internal arc-detection and mitigation devices (IEC 60947-9-2:2021)
Niederspannungsschaltgeräte - Aktive Systeme zur Abschwächung von Störlichtbögen -
Teil 9-2: Optische Geräte zur Erfassung und Abschwächung innerer Lichtbögen (IEC
60947-9-2:2021)
Appareillage à basse tension - Partie 9-2: Systèmes actifs de limitation des défauts d'arc
- Dispositifs optiques de détection et de limitation d'arcs internes (IEC 60947-9-2:2021)
Ta slovenski standard je istoveten z: EN IEC 60947-9-2:2025
ICS:
29.120.40 Stikala Switches
29.130.20 Nizkonapetostne stikalne in Low voltage switchgear and
krmilne naprave controlgear
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EUROPEAN STANDARD EN IEC 60947-9-2

NORME EUROPÉENNE
EUROPÄISCHE NORM July 2025
ICS 29.120.40; 29.130.20
English Version
Low-voltage switchgear and controlgear - Part 9-2: Active arc-
fault mitigation systems - Optical-based internal arc-detection
and mitigation devices
(IEC 60947-9-2:2021)
Appareillage à basse tension - Partie 9-2: Systèmes actifs Niederspannungsschaltgeräte - Aktive Systeme zur
de limitation des défauts d'arc - Dispositifs optiques de Abschwächung von Störlichtbögen - Teil 9-2: Optische
détection et de limitation d'arcs internes Geräte zur Erfassung und Abschwächung innerer
(IEC 60947-9-2:2021) Lichtbögen
(IEC 60947-9-2:2021)
This European Standard was approved by CENELEC on 2021-05-31. CENELEC members are bound to comply with the CEN/CENELEC
Internal Regulations which stipulate the conditions for giving this European Standard the status of a national standard without any alteration.
Up-to-date lists and bibliographical references concerning such national standards may be obtained on application to the CEN-CENELEC
Management Centre or to any CENELEC member.
This European Standard exists in three official versions (English, French, German). A version in any other language made by translation
under the responsibility of a CENELEC member into its own language and notified to the CEN-CENELEC Management Centre has the
same status as the official versions.
CENELEC members are the national electrotechnical committees of Austria, Belgium, Bulgaria, Croatia, Cyprus, the Czech Republic,
Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, the
Netherlands, Norway, Poland, Portugal, Republic of North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland,
Türkiye and the United Kingdom.

European Committee for Electrotechnical Standardization
Comité Européen de Normalisation Electrotechnique
Europäisches Komitee für Elektrotechnische Normung
CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels
© 2025 CENELEC All rights of exploitation in any form and by any means reserved worldwide for CENELEC Members.
Ref. No. EN IEC 60947-9-2:2025 E

European foreword
The text of document 121A/406/FDIS, future edition 1 of IEC 60947-9-2, prepared by SC 121A "Low-
voltage switchgear and controlgear" of IEC/TC 121 "Switchgear and controlgear and their assemblies
for low voltage" was submitted to the IEC-CENELEC parallel vote and approved by CENELEC as
The following dates are fixed:
• latest date by which the document has to be implemented at national (dop) 2026-07-31
level by publication of an identical national standard or by endorsement
• latest date by which the national standards conflicting with the (dow) 2028-07-31
document have to be withdrawn
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. CENELEC shall not be held responsible for identifying any or all such patent rights.
This document has been prepared under a standardization request addressed to CENELEC by the
European Commission. The Standing Committee of the EFTA States subsequently approves these
requests for its Member States.
For the relationship with EU Legislation, see informative Annex ZZ, which is an integral part of this
document.
Any feedback and questions on this document should be directed to the users’ national committee. A
complete listing of these bodies can be found on the CENELEC website.
Endorsement notice
The text of the International Standard IEC 60947-9-2:2021 was approved by CENELEC as a
European Standard without any modification.
In the official version, for Bibliography, the following notes have to be added for the standard indicated:
IEC 60079 (series) NOTE Approved as EN IEC 60079 (series)
IEC 60269 (series) NOTE Approved as EN 60269 (series)
IEC 60664-1:2020 NOTE Approved as EN IEC 60664-1:2020 (not modified)
IEC 60947-3 NOTE Approved as EN IEC 60947-3
IEC 61439 (series) NOTE Approved as EN IEC 61439 (series)
IEC 61439-1:2020 NOTE Approved as EN IEC 61439-1:2021 (not modified)
IEC 61439-2:2020 NOTE Approved as EN IEC 61439-2:2021 (not modified)
IEC 62474 NOTE Approved as EN IEC 62474
IEC 62606 NOTE Approved as EN 62606
IEC/TR 63201 NOTE Approved as CLC IEC/TR 63201
Annex ZA
(normative)
Normative references to international publications
with their corresponding European publications
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.
NOTE 1  Where an International Publication has been modified by common modifications, indicated by (mod),
the relevant EN/HD applies.
NOTE 2  Up-to-date information on the latest versions of the European Standards listed in this annex is available
here: www.cencenelec.eu.
Publication Year Title EN/HD Year
IEC 60068-2-6 2007 Environmental testing - Part 2-6: Tests - EN 60068-2-6 2008
Test Fc: Vibration (sinusoidal)
IEC 60068-2-27 2008 Environmental testing - Part 2-27: Tests - EN 60068-2-27 2009
Test Ea and guidance: Shock
IEC 60068-2-30 2005 Environmental testing - Part 2-30: Tests - EN 60068-2-30 2005
Test Db: Damp heat, cyclic (12 h + 12 h
cycle)
IEC 60255-27 2013 Measuring relays and protection EN 60255-27 2014
equipment - Part 27: Product safety
requirements
IEC 60695-2-10 - Fire hazard testing - Part 2-10: EN IEC 60695-2-10 2021
Glowing/hot-wire based test methods -
Glow-wire apparatus and common test
procedure
IEC 60695-2-11 2014 Fire hazard testing - Part 2-11: EN IEC 60695-2-11 2021
Glowing/hot-wire based test methods -
Glow-wire flammability test method for
end-products (GWEPT)
IEC 60695-2-12 - Fire hazard testing - Part 2-12: EN IEC 60695-2-12 2021
Glowing/hot-wire based test methods -
Glow-wire flammability index (GWFI) test
method for materials
IEC 60715 2017 Dimensions of low-voltage switchgear and EN 60715 2017
controlgear - Standardized mounting on
rails for mechanical support of switchgear,
controlgear and accessories
IEC 60947-1 2020 Low-voltage switchgear and controlgear - EN IEC 60947-1 2021
Part 1: General rules
IEC 60947-2 2016 Low-voltage switchgear and controlgear - EN 60947-2 2017
Part 2: Circuit-breakers
+ A1 2019 + A1 2020
Publication Year Title EN/HD Year
IEC 60947-9-1 2019 Low-voltage switchgear and controlgear - EN IEC 60947-9-1 2019
Part 9-1: Active arc-fault mitigation
systems - Arc quenching devices
IEC 60990 2016 Methods of measurement of touch current EN 60990 2016
and protective conductor current
IEC 61482-1-2 2014 Live working - Protective clothing against EN 61482-1-2 2014
the thermal hazards of an electric arc -
Part 1-2: Test methods - Method 2:
Determination of arc protection class of
material and clothing by using a
constrained and directed arc (box test)
IEC 61557-2 - Electrical safety in low voltage distribution EN IEC 61557-2 2021
systems up to 1 000 V a.c. and 1 500 V
d.c. - Equipment for testing, measuring or
monitoring of protective measures - Part 2:
Insulation resistance
CISPR 11 (mod) 2015 Industrial, scientific and medical equipment EN 55011 2016
- Radio-frequency disturbance
characteristics - Limits and methods of
measurement
+ A1 2016 + A1 2017
+ A11 2020
CISPR 32 2015 Electromagnetic compatibility of EN 55032 2015
multimedia equipment - Emission
requirements
+ AC 2016
+ A11 2020
ISO 3864-1 2011 Graphical symbols - Safety colours and - -
safety signs – Part 1: Design principles for
safety signs and safety markings
ISO 3864-2 2016 Graphical symbols - Safety colours and - -
safety signs – Part 2: Design principles for
product safety labels
Annex ZZ
(informative)
Relationship between this European standard and the safety
objectives of Directive 2014/35/EU [2014 OJ L96] aimed to be
covered
This European standard has been prepared under a Commission’s standardisation request relating to
harmonised standards in the field of the Low Voltage Directive, M/511, to provide one voluntary means
of conforming to safety objectives of Directive 2014/35/EU of the European Parliament and of the
Council of 26 February 2014 on the harmonisation of the laws of the Member States relating to the
making available on the market of electrical equipment designed for use within certain voltage limits
[2014 OJ L96].
Once this standard is cited in the Official Journal of the European Union under that Directive,
compliance with the normative clauses of this standard given in Table ZZ.1 confers, within the limits of
the scope of this standard, a presumption of conformity with the corresponding safety objectives of
that Directive, and associated EFTA regulations.
Table ZZ.1 — Correspondence between this European standard and the Annex I of Directive
2014/35/EU [2014 OJ L96]
Safety objectives of Clause(s) / sub-clause(s) Remarks/note
Directive 2014/35/EU of this EN
1 a) 4, 6.1, 6.2, 6.3
4, 6.1, 6.3, 9.3.3, 9.3.4, A.5, B.5,
1 b)
E.2.7
see 2 a) to 2 d) and 3 a) to 3 c)
1 c) 4, 6, B.5
in this table
2 a) 4, 5, 6, 7, 8.1, 8.2, 9.2, 9.3, 9.4
2 b) 4, 6, 8.1, 8.2, 9.3
2 c) 4, 5, 8.1, 9
2 d) 4, 5, 8.1, 9.1, 9.3, 9.4
3 a) 4, 6.3, 7, 8.1, 9
3 b) 4, 6, 8.3, 9.1, 9.3, 9.4
3 c) 4, 5, 9.3
WARNING 1 — Presumption of conformity stays valid only as long as a reference to this European
standard is maintained in the list published in the Official Journal of the European Union. Users of this
standard should consult frequently the latest list published in the Official Journal of the European
Union.
WARNING 2 — Other Union legislation may be applicable to the product(s) falling within the scope of
this standard.
IEC 60947-9-2 ®
Edition 1.0 2021-04
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Low-voltage switchgear and controlgear –

Part 9-2: Active arc-fault mitigation systems – Optical-based internal

arc‑detection and mitigation devices

Appareillage à basse tension –

Partie 9-2: Systèmes actifs de limitation des défauts d'arc – Dispositifs optiques

de détection et de limitation d’arcs internes

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
INTERNATIONALE
ICS 29.120.40; 29.130.20 ISBN 978-2-8322-9606-6

– 2 – IEC 60947-9-2:2021 © IEC 2021
CONTENTS
FOREWORD . 7
INTRODUCTION . 9
1 Scope . 11
2 Normative references . 12
3 Terms and definitions . 13
4 Classification . 16
4.1 IACD type . 16
4.1.1 Stand-alone type IACD . 16
4.1.2 Multifunction-type IACD . 17
4.1.3 Combined-type IACD . 17
4.2 Combination of sensors . 18
4.2.1 Optical sensors-only type . 18
4.2.2 Optical sensors and secondary sensors type . 18
4.3 Binary output types . 19
4.3.1 Operate output . 19
4.3.2 Auxiliary binary output . 19
5 Characteristics . 19
5.1 Maximum arc-fault detection time . 19
5.2 Maximum arc-fault extinction time . 19
5.3 Minimum arc-fault detection current value . 19
5.4 Maximum prospective short-circuit current value . 19
6 Product information . 20
6.1 Nature of information . 20
6.2 Markings . 20
6.3 Instructions for installation, operation, maintenance, decommissioning and
dismantling . 21
7 Normal service, mounting and transport conditions . 22
8 Constructional and performance requirements . 22
8.1 Constructional requirements . 22
8.1.1 General . 22
8.1.2 Creepages and clearances . 22
8.1.3 Material requirement . 22
8.2 Performance requirements . 23
8.2.1 General . 23
8.2.2 Operating conditions . 23
8.2.3 Temperature-rise . 23
8.3 Electromagnetic compatibility (EMC) . 24
9 Tests . 24
9.1 General – Kind of tests . 24
9.2 Compliance with constructional requirements . 24
9.3 Type tests . 24
9.3.1 General . 24
9.3.2 Guidance on sample selection . 26
9.3.3 Light-immunity tests . 29
9.3.4 Detection and extinction tests . 31
9.3.5 Dielectric properties . 37

IEC 60947-9-2:2021 © IEC 2021 – 3 –
9.3.6 EMC tests . 38
9.3.7 Environmental tests . 39
9.3.8 Temperature-rise tests . 41
9.3.9 Functional tests . 41
9.4 Routine tests. 41
9.4.1 General . 41
9.4.2 Functional requirements . 42
9.4.3 Safety requirements. 42
10 Test report . 43
Annex A (normative) Detection tests under reduced energy arcs . 44
A.1 General . 44
A.2 Electrical test circuit, electrodes and arc parameters . 45
A.2.1 Electrical test circuit . 45
A.2.2 Calibration of test circuit . 45
A.2.3 Electrodes . 45
A.2.4 Ignition wire . 45
A.2.5 Arc electrical values . 45
A.2.6 Environmental conditions . 46
A.2.7 Conditioning of test objects . 46
A.3 Preparation and maintenance . 46
A.3.1 Preparation and conditioning of the test box . 46
A.3.2 Care and maintenance of the test equipment . 47
A.4 Optical sensors conditioning and positioning . 47
A.5 Instructions for IACD maintenance during test sequence . 49
Annex B (normative) Detection and extinction tests for high energy arcs . 50
B.1 General . 50
B.2 Test specimen, electrical test circuit, arc parameters . 50
B.2.1 Test specimen (stand-alone or multifunction-type IACD) . 50
B.2.2 Test specimen (combined-type IACD) . 51
B.2.3 Electrical test circuit . 55
B.2.4 IACD configuration . 56
B.2.5 Arc parameters . 56
B.3 Environmental conditions . 56
B.4 Optical sensors conditioning and positioning . 57
B.5 Instructions for maintenance . 58
Annex C (normative) Arcing current parameters . 59
C.1 Preamble . 59
C.2 The different phases of an arc . 59
C.3 Detection of arc initiation (t ) . 60
C.4 Arc continuity . 62
C.5 Detection of arc-extinction . 62
C.5.1 General . 62
C.5.2 Quenching device . 62
C.5.3 Current-switching device . 62
C.6 Measurement means . 62
C.7 Waveform consistency . 62
Annex D (informative) IACD optical measurements . 64
D.1 Preamble . 64

– 4 – IEC 60947-9-2:2021 © IEC 2021
D.1.1 General . 64
D.1.2 Photometry – The appearance point of view . 64
D.1.3 Radiometry – The technical point of view . 64
D.2 The different optical units . 64
D.2.1 General . 64
D.2.2 The luminosity function . 65
D.2.3 How to use the luminosity function . 66
D.3 Light measurement . 68
D.3.1 Use of a luxmeter . 68
D.3.2 Use of a spectrometer . 69
D.3.3 Spectrometer operation . 70
D.3.4 Calibration . 71
D.3.5 Absolute irradiance calibration . 73
D.3.6 Luxmeter operation . 73
D.3.7 Luxmeter calibration . 74
D.3.8 Luxmeter to spectrometer comparison . 75
D.4 Measuring the sensitivity and bandwidth of the optical sensors of an IACD . 75
Annex E (normative) Ambient light immunity tests . 77
E.1 General . 77
E.2 Test method . 78
E.2.1 Principle . 78
E.2.2 IACD installation and setup. 78
E.2.3 Environmental conditions . 79
E.2.4 Requirements for light source . 79
E.2.5 Requirements for luxmeter . 79
E.2.6 Calibration and testing method . 80
E.2.7 Test report . 82
Annex F (informative) Items subject to agreement between manufacturer and user . 83
Bibliography . 84

Figure 1 – Optical-based IACD schematic (stand-alone type and no secondary sensor) . 11
Figure 2 – Stand-alone type IACD architecture overview . 17
Figure 3 – Multifunction-type IACD architecture overview . 17
Figure 4 – Combined-type IACD architecture overview. 18
Figure 5 – Stand-alone IACD (hardware) architecture . 27
Figure 6 – Multifunction-type IACD (hardware) architecture . 28
Figure 7 – Reduced energy detection tests – Arrangement principle . 33
Figure 8 – Method of test . 35
Figure 9 – High energy detection and extinction tests – Arrangement principle . 36
Figure A.1 – Arc-test box outline . 44
Figure A.2 – Positioning principle (point-sensor test case) . 48
Figure A.3 – Positioning principle (optical fibre test case) . 49
Figure B.1 – Three-phase edge-to-edge arrangement principle (stand-alone or
multifunction-type, top view) . 50
Figure B.2 – Three-phase face-to-face arrangement principle (stand-alone or
multifunction-type, top view) . 51

IEC 60947-9-2:2021 © IEC 2021 – 5 –
Figure B.3 – Three-phase edge-to-edge arrangement principle (line combined-type, top
view) . 52
Figure B.4 – Three-phase face-to-face arrangement principle (line combined-type, top

view) . 53
Figure B.5 – Three-phase test edge-to-edge arrangement principle (parallel combined-
type, top view) . 54
Figure B.6 – Three-phase test face-to-face arrangement principle (parallel combined-
type, top view) . 55
Figure B.7 – Positioning of optical sensor vs arc . 57
Figure C.1 – Detection of arc ignition . 61
Figure C.2 – Example of invalid test due to unintended arcing caused by incorrect

connection of ignition wire . 63
Figure D.1 – The luminosity function, also known as υ(λ) curve, describes the
sensitivity of the human eye . 66
Figure D.2 – Example of a measured absolute irradiance spectrum from an arc formed
across two copper busbars at 5 kA (RMS) 60 Hz . 67
Figure D.3 – Resulting integrals of the illuminance, Φ , and irradiance, Φ , produced
v e
from the measured arc data taken from Figure D.2 . 68
Figure D.4 – Block diagram of typical luxmeter circuit . 69
Figure D.5 – Example of spectral irradiance measurement from a compact
fluorescent light . 69
Figure D.6 – Basic components of a spectrometer . 71
Figure D.7 – Calculated emission of a Planck’s emitter at 2 500 K, υ(λ) curve and
resulting overlap . 73
Figure D.8 – Calibration bench for luxmeters . 74
Figure D.9 – Examples of spectral irradiance measured at 50 cm distance between
spectrometer and light source . 76
Figure D.10 – Spectral irradiance examples comparing a continuous xenon light source
to a pulsed xenon light source . 76
Figure E.1 – Calibrating the system for 2 000 lx . 78
Figure E.2 – Luxmeter readings for QTH at 207 W (6,50 A at 31,8 V) at various
distances between the luxmeter and the light source . 80
Figure E.3 – Test setup for an IACD fitted with point-sensor . 81
Figure E.4 – Test setup for an IACD fitted with optical fibre sensor . 81

d
Table 1 – Markings and indications for an IACD . 20
Table 2 – Test conditions for glow-wire test . 23
Table 3 – Tests sequences for standalone-type or multifunction-type IACD . 25
Table 4 – Tests sequences for combined-type IACD . 26
Table 5 – General conditions of tests under high energy . 37
Table 6 − EMC − Emission tests . 39
Table 7 – Insulation test parameters . 40
Table 8 – Vibration test parameters . 40
Table A.1 – Test circuit conditions . 45
Table A.2 – Ignition wire specifications . 45
Table A.3 – Arc parameters . 46
Table A.4 – Environmental conditions . 46

– 6 – IEC 60947-9-2:2021 © IEC 2021
Table A.5 – Point-sensor positioning values . 47
Table A.6 – Optical fibre sensor positioning values . 48
Table B.1 – Test circuit conditions . 56
Table B.2 – Arc values . 56
Table B.3 – Environmental conditions . 57
Table B.4 – Point-sensor positioning values . 58
Table B.5 – Optical fibre sensor positioning values . 58
Table B.6 – Authorized maintenance . 58
Table C.1 – Main phases of an arc-fault . 59
Table D.1 – Selected photometric and radiometric definitions and units . 65
Table E.1 – Minimum ambient light values regarding specific workplaces . 77

IEC 60947-9-2:2021 © IEC 2021 – 7 –
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
LOW-VOLTAGE SWITCHGEAR AND CONTROLGEAR –

Part 9-2: Active arc-fault mitigation systems –
Optical-based internal arc-detection and mitigation devices

FOREWORD
1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising
all national electrotechnical committees (IEC National Committees). The object of IEC is to promote international
co-operation on all questions concerning standardization in the electrical and electronic fields. To this end and
in addition to other activities, IEC publishes International Standards, Technical Specifications, Technical Reports,
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preparation is entrusted to technical committees; any IEC National Committee interested in the subject dealt with
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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.
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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 itself does not provide any attestation of conformity. Independent certification bodies provide conformity
assessment services and, in some areas, access to IEC marks of conformity. IEC is not responsible for any
services carried out by independent certification bodies.
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
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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.
IEC 60947-9-2 has been prepared by subcommittee 121A: Low-voltage switchgear and
controlgear, of IEC technical committee 121: Switchgear and controlgear and their assemblies
for low voltage. It is an International Standard.
The text of this International Standard is based on the following documents:
Draft Report on voting
121A/406/FDIS 121A/417/RVD
Full information on the voting for its approval can be found in the report on voting indicated in
the above table.
The language used for the development of this International Standard is English.

– 8 – IEC 60947-9-2:2021 © IEC 2021
This document was drafted in accordance with ISO/IEC Directives, Part 2, and developed in
accordance with ISO/IEC Directives, Part 1 and ISO/IEC Directives, IEC Supplement, available
at www.iec.ch/members_experts/refdocs. The main document types developed by IEC are
described in greater detail at www.iec.ch/standardsdev/publications.
The committee has decided that the contents of this document will remain unchanged until the
stability date indicated on the IEC website under "http://webstore.iec.ch" in the data related to
the specific document. At this date, the document will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
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 document using a colour printer.

IEC 60947-9-2:2021 © IEC 2021 – 9 –
INTRODUCTION
Low-voltage switchgear and controlgear, as well as complementary protective and measuring
devices, are installed in assemblies according to IEC 61439 series standards and/or others,
which provide rules and requirements for interface characteristics, service conditions,
construction, performance and verification.
The main objective of these standards is to achieve the safe operation of low-voltage switchgear
and controlgear assemblies under normal operating conditions as well as under abnormal
operating conditions, e.g. occurrence of overvoltage, overload or short-circuit currents.
The case of an arc-fault inside a LV assembly is considered by the following publications:
– IEC TR 61641, which specify tests requirements for assemblies under internal arc-fault;
– IEC TR 61439-0:2013, which identifies arc-fault containment in its Annex C;
– IEC TS 63107, which specifies tests to verify correct integration of internal arc-fault
mitigation systems in power switchgear and controlgear assemblies (PSC assemblies)
according to IEC 61439-2.
Even in a Class I assembly according to IEC TR 61641, the occurrence of an internal arc cannot
be completely excluded. Typically, internal arc-faults result from:
– conducting materials inadvertently left inside equipment during manufacture, installation or
maintenance;
– failures in materials or workmanship;
– inadvertent contact with a live conductor;
– entry of small animals such as mice, snakes, ants, etc.;
– use of an incorrect assembly for the application resulting in overheating and subsequently
an internal arcing fault;
– inappropriate operating conditions (for example water, fungus, or dust);
– incorrect operation; or,
– lack of maintenance or inappropriate maintenance (loose parts, paint, etc.).
The occurrence of arcs inside enclosed assemblies is associated with various physical
phenomena. For example, the arc energy resulting from an arc developed in air at atmospheric
pressure within the enclosure will cause an internal overpressure and local overheating which
will result in mechanical and thermal stressing of the assembly. Moreover, the materials
involved may produce hot decomposition products, either gases, metals or vapours, which may
be discharged outside of the enclosure.
Due to the risk of personal injury, damage and loss of energy supply as consequences of
internal arc-faults there is a growing demand for internal arc-fault sensing and mitigation. This
is the reason why some standards have been drafted to give specifications including test
protocol and acceptance criteria for corresponding devices. Arc-fault effects can be dramatically
reduced by active arc-fault mitigation systems, combining fast detection of the internal arc-fault,
and related actions on short-circuit protection devices and/or additional quenching devices.
Therefore, the application of such devices can result in:
– reduction of incident/released energy;
– shortening of power outage/downtime (by minimizing damage to the enclosed equipment,
switchgear and controlgear as well as other measuring and protective devices);
– limitation of side-effects to other systems, due to high and conti
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