Enclosed low-voltage switchgear and controlgear assemblies - Guide for testing under conditions of arcing due to internal fault

IEC TR 61641:2014 gives guidance on the method of testing of ASSEMBLIES under conditions of arcing in air due to an internal fault. The purpose of this test is to assess the ability of the ASSEMBLY to limit the risk of personal injury, damage of ASSEMBLIES and its suitability for further service as a result of an internal arcing fault. This third edition cancels and replaces the second edition published in 2008. It constitutes a technical revision. This third edition includes the following significant technical changes with respect to the previous edition:
- arcing classes to define the different forms of protection provided against arcing faults; (i) personnel protection, (ii) damage restricted to part of the ASSEMBLY, and (iii) ASSEMBLY suitable for limited further service.;
- two levels of personnel protection afforded by ASSEMBLIES under arcing fault conditions; (i) for ASSEMBLIES installed in areas where access to the ASSEMBLY is restricted to skilled persons, and (ii) for ASSEMBLIES installed in areas where the area is accessible to ordinary persons;
- option of individually insulating all live conductors to make the complete ASSEMBLY an arc ignition protected zone (referred to as an 'arc free zone' in previous editions of the Technical report);
- arc fault protection front, back and sides of an ASSEMBLY as the normal requirement;
- minimum performance requirements for arc ignition protected zone.

Ensembles d'appareillage à basse tension sous enveloppe - Guide pour l'essai en conditions d'arc dues à un défaut interne

L'IEC TR 61641:2014 donne des lignes directrices sur les méthodes d'essai des ENSEMBLES d'appareillage en conditions d'arc dus à un défaut interne se développant dans l'air. Le but de cet essai est d'évaluer l'aptitude de l'ENSEMBLE à limiter le risque de blessure corporelle et les dommages aux ENSEMBLES, ainsi que l'adaptabilité au service consécutif et postérieur à un arc dû à un défaut interne. Cette troisième édition annule et remplace la deuxième édition publiée en 2008. Cette édition constitue une révision technique. Cette troisième édition inclut les modifications techniques majeures suivantes par rapport à l'édition précédente:
- les classes d'arc pour définir les différentes formes de protection fournies contre les défauts d'arc; (i) protection individuelle, (ii) dommage limité à une partie de l'ENSEMBLE et (iii) ENSEMBLE adapté à un service postérieur au défaut limité;
- deux niveaux de protection individuelle offerts par les ENSEMBLES dans des conditions de défaut d'arc; (i) pour les ENSEMBLES installés dans des zones où l'accès à l'ENSEMBLE est limité aux personnes formées et (ii) pour les ENSEMBLES installés dans des zones où l'accès est possible pour les personnes ordinaires;
- l'option d'isolation individuelle de tous les conducteurs sous tension afin de faire de l'ENSEMBLE complet une zone protégée à la création d'arc de défaut (désignée comme une "zone exempte d'arc" dans les éditions précédentes du rapport technique);
- la protection contre le défaut d'arc à l'avant, à l'arrière et sur les côtés d'un ENSEMBLE comme exigence normale;
- les exigences de performances minimales pour la zone à probabilité marginale de création d'arc.

General Information

Status
Published
Publication Date
08-Sep-2014
Current Stage
PPUB - Publication issued
Start Date
09-Sep-2014
Completion Date
09-Sep-2014
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IEC TR 61641
Edition 3.0 2014-09
TECHNICAL
REPORT
RAPPORT
TECHNIQUE
Enclosed low-voltage switchgear and controlgear assemblies – Guide for
testing under conditions of arcing due to internal fault
Ensembles d'appareillage à basse tension sous enveloppe – Guide pour l'essai
en conditions d'arc dues à un défaut interne
IEC TR 61641:2014-09(en-fr)
---------------------- Page: 1 ----------------------
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---------------------- Page: 2 ----------------------
IEC TR 61641
Edition 3.0 2014-09
TECHNICAL
REPORT
RAPPORT
TECHNIQUE
Enclosed low-voltage switchgear and controlgear assemblies – Guide for
testing under conditions of arcing due to internal fault
Ensembles d'appareillage à basse tension sous enveloppe – Guide pour l'essai
en conditions d'arc dues à un défaut interne
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
PRICE CODE
INTERNATIONALE
CODE PRIX T
ICS 29.130.20 ISBN 978-2-8322-1855-6

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

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

® Registered trademark of the International Electrotechnical Commission
Marque déposée de la Commission Electrotechnique Internationale
---------------------- Page: 3 ----------------------
– 2 – IEC TR 61641:2014 © IEC 2014
CONTENTS

FOREWORD ........................................................................................................................... 3

INTRODUCTION ..................................................................................................................... 5

1 Scope .............................................................................................................................. 6

2 Normative references ...................................................................................................... 6

3 Terms and definitions ...................................................................................................... 7

4 Classification of low-voltage switchgear and controlgear assemblies ............................... 9

4.1 Classification with regard to the protection characteristic ........................................ 9

4.2 Classification with regard to persons who have access ........................................... 9

5 ASSEMBLY characteristics ............................................................................................... 10

6 Requirements and tests for an arc ignition protected zone ............................................. 10

6.1 Constructional requirements of an arc ignition protected zone .............................. 10

6.2 Dielectric test of arc ignition protected zones ........................................................ 11

6.3 IP test of arc ignition protected zones ................................................................... 11

7 Selection of test specimen and validity of tests for similar designs (possibilities for

derivation) ..................................................................................................................... 11

8 Testing – Arc fault tests ................................................................................................. 12

8.1 General ................................................................................................................. 12

8.2 Voltage ................................................................................................................. 12

8.3 Current ................................................................................................................. 13

8.4 Frequency ............................................................................................................. 13

8.5 Duration of the test ............................................................................................... 13

8.6 Test procedure ...................................................................................................... 13

8.6.1 Supply circuit ................................................................................................. 13

8.6.2 Arc initiation .................................................................................................. 13

8.6.3 Repetition of the test ..................................................................................... 15

8.6.4 Indicators (for observing the thermal effects of gases) ................................... 15

8.7 Assessment of the test .......................................................................................... 16

9 Test report ..................................................................................................................... 16

Annex A (informative) User guide to arc fault mitigation ....................................................... 19

A.1 General ................................................................................................................. 19

A.2 Arc ignition protected zones .................................................................................. 20

A.3 Items for classification .......................................................................................... 20

A.4 Use of this technical report ................................................................................... 21

Annex B (informative) List of notes concerning certain countries .......................................... 22

Bibliography .......................................................................................................................... 23

Figure 1 – Mounting frame for indicators ............................................................................... 18

Figure 2 – Examples of installation positions of the indicators ............................................... 18

Table 1 – Sizes of the copper ignition wire without current-limiting protection device ............ 14

Table 2 – Sizes of the copper ignition wire with current-limiting protection device ................. 14

Table A.1 – Options for classification .................................................................................... 20

---------------------- Page: 4 ----------------------
IEC TR 61641:2014 © IEC 2014 – 3 –
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
ENCLOSED LOW-VOLTAGE SWITCHGEAR
AND CONTROLGEAR ASSEMBLIES –
GUIDE FOR TESTING UNDER CONDITIONS
OF ARCING DUE TO INTERNAL FAULT
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

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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

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5) IEC itself does not provide any attestation of conformity. Independent certification bodies provide conformity

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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

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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.

The main task of IEC technical committees is to prepare International Standards. However, a

technical committee may propose the publication of a technical report when it has collected

data of a different kind from that which is normally published as an International Standard, for

example "state of the art".

IEC/TR 61641, which is a technical report, has been prepared by subcommittee SC 121B:

Low-voltage switchgear and controlgear assemblies, of IEC technical committee 121:

Switchgear and controlgear and their assemblies for low voltage.

This third edition cancels and replaces the second edition published in 2008. It constitutes a

technical revision.

This third edition includes the following significant technical changes with respect to the

previous edition:
---------------------- Page: 5 ----------------------
– 4 – IEC TR 61641:2014 © IEC 2014

– arcing classes to define the different forms of protection provided against arcing faults; (i)

personnel protection, (ii) damage restricted to part of the ASSEMBLY, and (iii) ASSEMBLY

suitable for limited further service.;

– two levels of personnel protection afforded by ASSEMBLIES under arcing fault conditions; (i)

for ASSEMBLIES installed in areas where access to the ASSEMBLY is restricted to skilled

persons, and (ii) for ASSEMBLIES installed in areas where the area is accessible to ordinary

persons;

– option of individually insulating all live conductors to make the complete ASSEMBLY an arc

ignition protected zone (referred to as an ‘arc free zone’ in previous editions of the

Technical report);

– arc fault protection front, back and sides of an ASSEMBLY as the normal requirement;

– minimum performance requirements for arc ignition protected zone.
The text of this technical report is based on the following documents:
Enquiry draft Report on voting
121B/4/DTR 121B/14/RVC

Full information on the voting for the approval of this technical report 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 B lists all of the “in-some-country”

clauses on differing practices of a less permanent nature relating to the subject of this

Technical Report.

The committee has decided that the contents of this publication will remain unchanged until

the stability 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.
---------------------- Page: 6 ----------------------
IEC TR 61641:2014 © IEC 2014 – 5 –
INTRODUCTION

The IEC 61439 series of standards gives rules and requirements for interface characteristics,

service conditions, construction, performance and verification of low-voltage switchgear and

controlgear assemblies, hereafter called ASSEMBLIES.

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 overvoltages, overload or short-circuit

currents. Therefore no characteristics, design and verification requirements are given dealing

with the case of an arc fault inside the ASSEMBLY.

Nevertheless the occurrence of an internal arc cannot completely be excluded. On the rare

occasions that they do occur, typically internal arc faults result from:

– conducting materials inadvertently left in ASSEMBLIES during manufacture, installation or

maintenance;
– faults in materials or workmanship;
– entry of small animals such as mice, snakes, etc.;

– use of an incorrect ASSEMBLY for the application resulting in overheating and subsequently

an internal arcing fault;
– inappropriate operating conditions;
– incorrect operation; or,
– lack of maintenance.

The occurrence of arcs inside enclosed ASSEMBLIES is coupled 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 or vapours,

which may be discharged to the outside of the enclosure.

Due to the risk of personal injury, damage and loss of energy supply as consequences of arc

faults there is a demand for arc fault tested ASSEMBLIES, even though an arc fault in an

ASSEMBLY is considered as an unlikely event. The purpose of this technical report is to give

guidance on the method of testing of ASSEMBLIES under conditions of arcing in air due to an

internal failure.

The ability of an ASSEMBLY to pass tests according to this technical report is only one aspect

when assessing the potential risk due to an arc fault within an ASSEMBLY. The skill of

personnel having access to the ASSEMBLY, the personal protective equipment (PPE) used, the

working procedures applied and the conditions in the location where the ASSEMBLY is installed,

are other aspects that need to be taken into account.

The possibility of an arc fault within an ASSEMBLY can be reduced by the addition of suitable

solid insulation of all conductors. Such ASSEMBLIES are categorised as arcing class I. This

technical report does not provide any indication of performance in the unlikely event of an

arcing fault within an arcing class I ASSEMBLY (see 4.1).

General information about arc fault behaviour and possible protective measures from the

perspective of the user of an ASSEMBLY is given in IEC/TR 61439-0:2013, C.3 and Annex A of

this technical report.
---------------------- Page: 7 ----------------------
– 6 – IEC TR 61641:2014 © IEC 2014
ENCLOSED LOW-VOLTAGE SWITCHGEAR
AND CONTROLGEAR ASSEMBLIES –
GUIDE FOR TESTING UNDER CONDITIONS
OF ARCING DUE TO INTERNAL FAULT
1 Scope

This technical report gives guidance on the method of testing of ASSEMBLIES under conditions

of arcing in air due to an internal fault.

The purpose of this test is to assess the ability of the ASSEMBLY to limit the risk of personal

injury, damage of ASSEMBLIES and its suitability for further service as a result of an internal

arcing fault.
The test procedure given in this technical report applies only:

– to enclosed, floor-standing or wall-mounted low-voltage switchgear and controlgear

assemblies according to IEC 61439-2 (power switchgear and controlgear assemblies –

PSC ASSEMBLIES);

NOTE This technical report can be used as a reference for arc fault tests of other products, but adaptations of the

test procedures and acceptance criteria can apply taking into account the specifics of such other ASSEMBLIES or

products.

– to situations when doors and covers of the ASSEMBLY are closed and correctly secured.

When tests under different or more severe conditions are agreed between the user and the

manufacturer, this technical report can be used as a guide.
The test procedure given in this technical report takes into consideration:
– the effects of the internal overpressure acting on covers, doors, etc.;

– the thermal effects of the arc or its roots on the enclosures and of ejected hot gases and

glowing particles.
The test procedure given in this technical report does not cover:

– other effects which can constitute a risk, such as toxic gases and loud noises;

– conditions during maintenance work, open doors or similar;
– access to the top and bottom of the ASSEMBLY.
This is a voluntary test made at the discretion of the manufacturer.
2 Normative references

The following documents, in whole or in part, are normatively referenced in this document and

are indispensable for its application. For dated references, only the edition cited applies. For

undated references, the latest edition of the referenced document (including any
amendments) applies.
IEC 60529:1989, Degrees of protection provided by enclosures (IP Code)
IEC 60529:1989/AMD 1:1999
IEC 60529:1989/AMD 2:2013
---------------------- Page: 8 ----------------------
IEC TR 61641:2014 © IEC 2014 – 7 –

IEC 61439-1:2011, Low-voltage switchgear and controlgear assemblies – Part 1: General

rules

IEC 61439-2:2011, Low-voltage switchgear and controlgear assemblies – Part 2: Power

switchgear and controlgear assemblies
3 Terms and definitions

For the purposes of this document, the terms and definitions given in IEC 61439-2, as well as

the following, apply.
3.1
permissible short-circuit current under self-extinguishing arcing conditions
ps arc

r.m.s. value of the maximum permissible prospective short circuit current at the incoming

ASSEMBLY, as declared by the manufacturer, for a given rated operational
terminals of the

voltage U , for which the ASSEMBLY is able to satisfy the requirements of this technical report

by means of a self-extinguishing arc and without the operation of any protection devices

3.2
permissible short-circuit current under arcing conditions
p arc

r.m.s. value of the maximum permissible prospective short circuit current at the incoming

terminals of the ASSEMBLY, as declared by the manufacturer for a given rated operational

voltage U , and arc duration (see 3.3) for which the ASSEMBLY is able to satisfy the

requirements of this technical report
3.3
permissible arc duration
arc

value of the maximum arc duration which is not self-extinguishing and which is not limited by

any current-limiting device, as declared by the manufacturer, for a given prospective short

circuit current and rated operational voltage U at the incoming terminals of the ASSEMBLY and

for which the requirements of this technical report are satisfied
Note 1 to entry: The value can be different for different parts of the ASSEMBLY.
3.4
permissible conditional short-circuit current under arcing conditions
pc arc

r.m.s value of maximum permissible prospective short circuit current at the incoming terminals

of the ASSEMBLY, as declared by the manufacturer, for a given rated operational voltage U ,

for a circuit of an ASSEMBLY which satisfies the requirements of this technical report when the

circuit is protected by a current-limiting device or by an arcing fault mitigation device with arc

current-limiting function
3.5
arc

free burning short-circuit through air arising from a fault between live parts of different

potential and/or between live parts and other conductive parts within an ASSEMBLY

3.6
personnel protection under arcing conditions

ability of an ASSEMBLY to limit the risk of personnel injury caused by the mechanical and

thermal effects of an internal arcing fault
---------------------- Page: 9 ----------------------
– 8 – IEC TR 61641:2014 © IEC 2014
3.7
ASSEMBLY protection under arcing conditions

ability of an ASSEMBLY to limit the effects of an internal arcing fault inside the ASSEMBLY to an

area as defined by the manufacturer
3.8
ASSEMBLY protection under arcing conditions with limited operation

ability of an ASSEMBLY to limit the effects of an internal arcing fault inside the ASSEMBLY to an

area as defined by the manufacturer and to allow limited continued operation after such a

fault
3.9
arc ignition protected zone

part of a circuit within an ASSEMBLY where specific measures are provided to ensure the

initiation of an arcing fault is a remote possibility

Note 1 to entry: Arc ignition protected zones were previously referred to as “arc free zones”.

Note 2 to entry: The concept of an arc ignition protected zone takes into account that insulation is an important

means to reduce the probability of an arc ignition and the possibility of an arc propagating within the ASSEMBLY.

When adopting the concept of arc ignition protected zones it should be recognized that also within an arc ignition

protected zone there is a residual risk of an arc ignition, either due to damage of the insulation itself or due to

failure of the insulated conductor or its connections. The quality and reliability of the conductor, its connections and

its insulation within an arc ignition protected zone is crucial for the additional arc fault protection offered by the so

called arc ignition protected zone.

Note 3 to entry: See 6.1 for constructional requirements of an arc ignition protected zone.

3.10
arc tested zone

part of a circuit or compartment where the ignition of an arc is made and all selected criteria

for the assessment of the test(s) are fulfilled
3.11
current-limiting device

device that, within a specified range of current, prevents the let-through current reaching the

prospective peak value and which limits the let-through energy (I
3.12
arcing fault mitigation device

device that operates only in case of an arc fault to reduce the duration of burning

Note 1 to entry: Arc mitigation devices use effects of an arc, e.g. light, gas pressure, harmonics in the current or

voltage etc, and possibly the magnitude of the current to detect an arc inside the ASSEMBLY. They can comprise

special components for reduction, fast interruption or transfer of the fault current to a bolted short circuit link,

and/or they can instantaneously trip an upstream circuit breaker irrespective of its settings.

3.13
arcing fault mitigation device with arc current-limiting function

arcing fault mitigation device with an operation time short enough to prevent the arc current

reaching its otherwise attainable peak value

Note 1 to entry: The arc current can be limited by fast interruption of the fault current or by transfer of the fault

current to another current path. In the first case the arc current-limiting arc mitigation device acts as a current-

limiting device, whereas in the latter case the fault current continues to flow, can increase if the impedance of the

new current path is lower (e.g. in the case of a bolted short circuit link) and needs to be interrupted by another

protection device.
3.14
access (to an ASSEMBLY)

ability of a person to be in close proximity to an ASSEMBLY with all its doors and covers closed

and secured as in normal service and to operate devices such as switches and circuit

breakers that have external operating handles, buttons etc.
---------------------- Page: 10 ----------------------
IEC TR 61641:2014 © IEC 2014 – 9 –
3.15
restricted access
access to the location of the ASSEMBLY limited to authorized personnel only
Note 1 to entry: Technical m
...

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