National foreword

This British Standard is the UK implementation of EN IEC 60947‑9‑2:2025. It is identical to IEC 60947‑9‑2:2021.

The UK participation in its preparation was entrusted to Technical Committee PEL/121/1, Low voltage switchgear and controlgear.

A list of organizations represented on this committee can be obtained on request to its committee manager.

Contractual and legal considerations

This publication has been prepared in good faith, however no representation, warranty, assurance or undertaking (express or implied) is or will be made, and no responsibility or liability is or will be accepted by BSI in relation to the adequacy, accuracy, completeness or reasonableness of this publication. All and any such responsibility and liability is expressly disclaimed to the full extent permitted by the law.

This publication is provided as is, and is to be used at the recipient’s own risk.

The recipient is advised to consider seeking professional guidance with respect to its use of this publication.

This publication is not intended to constitute a contract. Users are responsible for its correct application.

This publication has been prepared under a mandate given to the European Standards Organizations by the European Commission and the European Free Trade Association. It is intended to support requirements of the EU legislation detailed in the European Foreword. A European Annex, usually Annex ZA or ZZ, describes how this publication relates to that EU legislation.

For the Great Britain market (England, Scotland and Wales), if UK Government has designated this publication for conformity with UKCA marking (or similar) legislation, it may contain an additional National Annex. Where such a National Annex exists, it shows the correlation between this publication and the relevant UK legislation. If there is no National Annex of this kind, the relevant Annex ZA or ZZ in the body of the European text will indicate the relationship to UK regulation applicable in Great Britain. References to EU legislation may need to be read in accordance with the UK designation and the applicable UK law. Further information on designated standards can be found at www.bsigroup.com/standardsandregulation.

For the Northern Ireland market, UK law will continue to implement relevant EU law subject to periodic confirmation. Therefore Annex ZA/ZZ in the European text, and references to EU legislation, are still valid for this market.

UK Government is responsible for legislation. For information on legislation and policies relating to that legislation, consult the relevant pages of www.gov.uk.

Compliance with a British Standard cannot confer immunity from legal obligations.

This British Standard was published under the authority of the Standards Policy and Strategy Committee on 31 July 2025.

This European Standard was approved by CENELEC on 31 May 2021. 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, Czechia, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Republic of North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Türkiye and United Kingdom.

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 EN IEC 60947‑9‑2:2025.

The following dates are fixed:

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:

FOREWORD

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.
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.
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.
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.
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.
All users should ensure that they have the latest edition of this publication.
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.
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.
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:

Full information on the voting for its approval can be found in the report on voting indicated in the above table.

The language used for the development of this International Standard is English.

This document was drafted in accordance with ISO/IEC Directives, Part 2, and developed in accordance with ISO/IEC Directives, Part 1 and ISO/IEC Directives, IEC Supplement, available at www.iec.ch/members_experts/refdocs. The main document types developed by IEC are described in greater detail at www.iec.ch/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.

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 continuously increasing density of installed apparatus.

This document is intended to cover devices and functions dedicated to:

detect an arc-fault internal to an assembly by processing optical effects of an internal arc-fault, and to signal and trigger devices intended to mitigate the internal arc-fault, and
detect by processing optical effects of an internal arc-fault and mitigate the impact of the internal arc-fault by its extinction.

NOTE Even when both terms are related to assemblies in which an arc occurs between conductors, arc-flash is terminology mainly used in NFPA 70E, CSA Z462 and IEEE 1584, which usually describes effects of direct exposure of workers to thermal energy emitted, whereas the term "internal arc-fault" as used in this document describes the hot-gas flow phenomena which can injure people in the vicinity of the arcing current.

1 Scope

This document covers internal arc-fault control devices, hereinafter referred to as IACD, which are intended to:

detect internal arc-faults in low-voltage switchgear and controlgear assemblies, by processing (at a minimum) the optical effect of an internal arc-fault, and
operate mitigation device (either external or combined)

in order to minimize the effects of the internal arc-fault (see Figure 1).

For the purpose of this document the terms "light" or "optical" covers more than visible spectra. They may cover also, for example, infrared or ultraviolet electromagnetic radiations (see Annex D).

For combined-type IACD, this document is considered in addition to the relevant product standard for internal arc-fault mitigation devices (IARD per IEC TS 63107:2020). Compliance to the relevant product standard is mandatory and cannot be claimed by testing to this document alone.

NOTE 1 Low-voltage switchgear and controlgear assemblies are usually described by IEC 61439 series.

Therefore, this document covers the following:

internal arc-fault control device (stand-alone, multifunction or combined);
one or more associated sensor(s) used to detect optical effect of the internal arc-fault;
sensor(s), sensing another physical effect, to confirm the fault;
associated or combined mitigation device.

An IACD is not intended to trigger under normal operation of low-voltage switchgear and controlgear (i.e. absence of internal arc-fault), including normal arcing associated with operation of disconnecting and switching devices.

This document only covers the following methods:

optical detection of the light caused by an internal arc-fault;
optional confirmation of internal arc-fault by line current measurement.

Many different conductive materials could be used in LV assemblies (e.g. steel, copper, aluminium). Nevertheless, tests specified in this document are deemed to represent the most critical and challenging conditions for arc-detection and cover all combinations of conductive materials.

NOTE 2 Compared to other materials (e.g. steel, aluminium), copper leads to a lower optical radiation energy.

The rated voltage of the assembly in which an IACD is installed does not exceed 1 000 V AC.

Such devices are designed to be operated and maintained by skilled persons only.

This document does not cover:

DC internal arc-fault detection and control;
overcurrent relays;
AFDD (arc-fault detection devices) as defined by IEC 62606;
guidance on installation within assemblies;
NOTE 3 The integration of an IACD into an assembly is described in IEC TS 63107.
use with additional measures needed for installation and operation within explosive atmospheres. These are given in IEC 60079 series documents;
requirements for embedded software and firmware design rules; for this subject, the manufacturer is responsible for taking additional safety measures;
NOTE 4 IEC TR 63201 describes rules for firmware and embedded software development preventing errors in software.
cybersecurity aspects; for this subject, the manufacturer is responsible for taking additional safety measures;
NOTE 5 See IEC TS 63208.
mobile applications.

NOTE 6 Even when addressing internal arc-fault mitigation devices, this document does not supersede any other relevant product standard (e.g. IEC 60947‑2 or IEC 60947‑9‑1).

NOTE 7 DC arcing fault phenomena are under consideration. Further investigation is needed to comprehend DC arcing phenomena and required sensing.

2 Normative references

3 Terms and definitions

4 Classification

4.1 IACD type

4.2 Combination of sensors

4.3 Binary output types

5 Characteristics

5.1 Maximum arc-fault detection time

5.2 Maximum arc-fault extinction time

5.3 Minimum arc-fault detection current value

5.4 Maximum prospective short-circuit current value

6 Product information

6.1 Nature of information

6.2 Markings

6.3 Instructions for installation, operation, maintenance, decommissioning and dismantling

7 Normal service, mounting and transport conditions

8 Constructional and performance requirements

8.1 Constructional requirements

8.2 Performance requirements

8.3 Electromagnetic compatibility (EMC)

9 Tests

9.1 General – Kind of tests

9.2 Compliance with constructional requirements

9.3 Type tests

9.4 Routine tests

10 Test report

Bibliography

BS EN IEC 60947-9-2:2025

Low-voltage switchgear and controlgear - Active arc-fault mitigation systems. Optical-based internal arc-detection and mitigation devices

Current

Published:

31 Jul 2025