IEC TR 63054:2017

IEC TR 63054 ®
Edition 1.0 2017-07
TECHNICAL
REPORT
colour
inside
Low-voltage switchgear and controlgear – Fire risk analysis and risk reduction
measures
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IEC TR 63054 ®
Edition 1.0 2017-07
TECHNICAL
REPORT
colour
inside
Low-voltage switchgear and controlgear – Fire risk analysis and risk reduction

measures
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 29.130.20 ISBN 978-2-8322-4622-1

– 2 – IEC TR 63054:2017 © IEC 2017
CONTENTS
FOREWORD . 3
INTRODUCTION . 5
1 Scope . 6
2 Normative references . 6
3 Terms and definitions . 7
4 Ignition modes for electrical fires . 8
4.1 General . 8
4.2 Overheating at the connection point due to loose connections . 10
4.2.1 General . 10
4.2.2 Ignition mechanisms . 11
4.2.3 Loose connections mitigation measures . 11
4.3 Overheating of internal power conductors . 14
4.4 Arcs . 14
4.4.1 General . 14
4.4.2 Breaking and making arcs . 15
4.4.3 Arcs occurring at loose connections . 15
4.4.4 Arcing through char and tracking arcs . 16
4.4.5 Sparks . 16
4.4.6 Arcs due to excessive overvoltage . 16
4.5 Failure of electronic components . 16
4.5.1 Basic description of the ignition mechanism . 16
4.5.2 Mitigation measures. 17
5 Conclusion . 17
Bibliography . 19

Figure 1 – Voltage drop and power dissipation versus current values (schematic) [5]. 11
Figure 2 – Current and voltage conditions for switching arcs (schematic) [10] . 15

Table 1 – Ignition phenomena in electrotechnical products . 9
Table 2 – Root causes of electrical fires according to [6] . 10
Table 3 – Potential failure modes for low-voltage switchgear and controlgear . 10
Table 4 – Function of the equipment and glow-wire test temperatures . 13
Table 5 – Relevant source ignition modes for low-voltage switchgear and controlgear . 18

INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
LOW-VOLTAGE SWITCHGEAR AND CONTROLGEAR –
FIRE RISK ANALYSIS AND RISK REDUCTION MEASURES

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
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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 63054, which is a technical report, 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.
The text of this technical report is based on the following documents:
Enquiry draft Report on voting
121A/115/DTR 121A/155/RVDTR
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.

– 4 – IEC TR 63054:2017 © IEC 2017
This document has been drafted in accordance with the ISO/IEC Directives, Part 2.
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.
A bilingual version of this publication may be issued at a later date.

IMPORTANT – The 'colour inside' logo on the cover page of this publication indicates
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INTRODUCTION
As fire-ignition hazards are inherent with electricity, installation rules and product standards
for electrical equipment are aimed at providing risk reduction measures and minimizing
residual risk without compromising product safety and function.
Residual risk of low-voltage switchgear and controlgear compliant with IEC 60947 relevant
publications is generally low and, when selected, installed and used according to
manufacturer instruction and installation rules, do not ignite fire in normal operation or
reasonably foreseeable fault conditions.
This document, in accordance to ISO/IEC Guide 51 and IEC Guide 116, describes the fire risk
analysis of electrical equipment and risk reduction measures in IEC 60947 relevant
publications. While intended to apply specifically to low voltage switchgear and controlgear, it
is suggested that other product committees may find this information useful.
The fire hazards, namely the flame ignition mechanisms, relevant for low-voltage switchgear
and controlgear are reviewed and discussed. The related risk reduction measures included in
IEC 60947 relevant publications are subsequently reported for each of those mechanisms.
These measures are based on a system approach, not limited to construction materials
requirements and include design rules and type testing to ensure equipment do not cause
fires in normal operation or due to reasonably foreseeable faulty conditions.

– 6 – IEC TR 63054:2017 © IEC 2017
LOW-VOLTAGE SWITCHGEAR AND CONTROLGEAR –
FIRE RISK ANALYSIS AND RISK REDUCTION MEASURES

1 Scope
This document applies to the fire risk analysis of low-voltage switchgear and controlgear
(hereinafter referred to as "equipment") referring to the IEC 60947 relevant publications,
where the following applies:
– only the case where a fire originates (typically under fault or misuse conditions) within the
equipment;
– only equipment installed in normal environments. Hazardous environments, for example in
presence of combustible materials, is not to be considered;
– only the case of products selected, installed and used according to the manufacturer
instructions and installation rules.
In addition, the following cases are not considered:
– faults addressed by IEC TR 61641;
– risks due to smoke emissions;
– double faults, i.e. multiple phenomenon, potentially combined.
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 Guide 116:2010, Guidelines for safety related risk assessment and risk reduction for low
voltage equipment
IEC 60695-1-10:2015, Fire hazard testing – Guidance for assessing the fire hazard of
electrotechnical products – General guidelines
IEC 60947-1:2007, Low-voltage switchgear and controlgear – Part 1: General rules
IEC 60947-1:2007/AMD1:2010
IEC 60947-1:2007/AMD2:2014
IEC 60947-2, Low-voltage switchgear and controlgear – Part 2: Circuit-breakers
IEC 60947-3, Low-voltage switchgear and controlgear – Part 3: Switches, disconnectors,
switch-disconnectors and fuse-combination units
IEC 60947-5-1, Low-voltage switchgear and controlgear – Part 5-1: Control circuit devices
and switching elements – Electromechanical control circuit devices
IEC 60947-6-1, Low-voltage switchgear and controlgear – Part 6-1: Multiple function
equipment – Transfer switching equipment
IEC 60947-7-1:2009, Low-voltage switchgear and controlgear – Part 7-1: Ancillary
equipment – Terminal blocks for copper conductors

IEC 60999-1, Connecting devices – Electrical copper conductors – Safety requirements for
screw-type and screwless-type clamping units – Part 1: General requirements and particular
2 2
requirements for clamping units for conductors from 0,2 mm up to 35 mm (included)
IEC 60999-2, Connecting devices – Electrical copper conductors – Safety requirements for
screw-type and screwless-type clamping units – Part 2: Particular requirements for clamping
2 2
units for conductors above 35 mm up to 300 mm (included)
IEC 62477-1:2012, Safety requirements for power electronic converter systems and
equipment – Part 1: General
3 Terms and definitions
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/
• ISO Online browsing platform: available at http://www.iso.org/obp
3.1
fire risk
probability of a fire combined with a quantified measure of its consequence
[SOURCE: IEC 60695-1-10:2016, 3.5, modified – Note 1 to entry deleted.]
3.2
electrical fire
fire caused by electrical equipment or installation
3.3
spark
electric spark
small luminous electric arc of short duration
[SOURCE: IEC 60050-121:1998, 121-13-16]
3.4
electric arc
high-temperature luminous electric discharge across a gap or through a medium such as
charred insulation
[SOURCE: NFPA 921:2014]
3.5
discharge
electric discharge
discontinuous movement of charge carriers through part of an otherwise insulating medium,
initiated by electronic avalanche and supplemented by secondary processes
[SOURCE: IEC 60050-121:1998, 121-13-11]

– 8 – IEC TR 63054:2017 © IEC 2017
3.6
tracking
progressive formation of conductive paths, which are produced on the surface or within a solid
insulating material, due to the combined effects of electric stress and electrolytic
contamination
[SOURCE: IEC 60050-212:2010, 212-11-56, modified – Note deleted.]
4 Ignition modes for electrical fires
4.1 General
Physical effects occurring in electrical equipment that can potentially cause fires are listed in
Table 1 below, inspired by Table 1 of IEC 60695-1-10:2016.

Table 1 – Ignition phenomena in electrotechnical products
a
Phenomenon Origin Consequential effects
Abnormal temperature rises Overcurrent in a conductor The temperature rises are gradual
b
and at times very slow . Therefore
Defective contacts
a significant accumulation of heat
and effluent in the vicinity of the
Leakage currents (insulation loss and
product may result, sufficient to
heating)
support fire as soon as ignition
Failure of a component, an internal occurs
part or an associated system (for
Accumulation and diffusion of
example, ventilation)
flammable gases in air may give
Mechanical distortions which modify rise to ignition or an explosion,
electrical contacts or the insulation especially inside hermetically
system sealed products
Seizure of a motor shaft (locked
rotor)
Premature thermal ageing
Short-circuit Direct contact between conductive The rise in temperature is
c
live parts at different potentials (stray significant after a very short time
conductors from loose terminals, and is quite localized
ingress of conducting foreign bodies,
Possible arc-flash and emission of
etc.)
smoke and flammable gases
Gradual degradation of some
Release of glowing materials or
components causing changes in their
substances
insulation impedances
After sudden failure of a component
or an internal part
e
Accidental sparks and arcs Cause external to the product Possible emission and ignition of
d
(overvoltage of the system network, flammable gases , with
accidental mechanical action consequent flames
exposing live parts or bringing them
Ignition may occur locally in
together, etc.)
surrounding components
Internal cause (switching operations
with gradual degradation of internal
components and/or ingress of
moisture)
After sudden failure of a component
or an internal part
High transient peak current Defect in the electrical circuit The rise in temperature is
d
significant after a very short time
and is quite localized
However ignition or explosion are
unlikely
NOTE The protective devices can include thermal, mechanical, electrical or electronic types.
a
Mechanical distortions and structural changes induced by anyone phenomenon may result in the
occurrence of one or more of the others.
b
At start, protective devices may interrupt the current after a variable length of time according to a
predefined tripping curve.
c
The protective devices are activated.
d
The protective devices may not always be activated.
e
Some products produce arcs and sparks in normal operation.

A quantitative analysis of the probability of those phenomena and the severity of their
consequences is overwhelming. An alternative approach is using fire statistics.

– 10 – IEC TR 63054:2017 © IEC 2017
Even though fire statistics usually do not report the physical mechanism that caused the fire,
some authors [6] have classified and ranked those mechanisms according to common field
experience (see Table 2 below).
Table 2 – Root causes of electrical fires according to [6]
Mechanism Frequency
Poor connections most
Arcing across a carbonized path
Arcing in air
Excessive thermal insulation
Overload
Ejection of hot particles
Dielectric breakdown in solid or liquid insulators

Miscellaneous phenomena
least
NOTE Other possible miscellaneous phenomena are incompatible metals (e.g.
Cu/Al), worn plating, ionic conduction, fungus and water treeing.

Table 3 below lists the possible ignition modes from Table 1 that are relevant for low-voltage
switchgear and controlgear, ordered according to the frequency ranking of Table 2.
Table 3 – Potential failure modes for low-voltage
switchgear and controlgear
Potential ignition modes and effects
1 Overheating at the connection point resulting in ignition of the insulation
supporting or adjacent to the terminals (termination)
2 Overheating of a power conductor creating ignition of a component supporting
a current carrying part
3 Operational and fault arcs (e.g. between the terminals), including ejection of
hot particles
4 Ignition starting from an electronic component

All these ignition modes will be discussed in the following subclauses together with the most
relevant mitigation measures.
4.2 Overheating at the connection point due to loose connections
4.2.1 General
Terminals (terminations) and internal connections are those points in electrical equipment
where two different conducting materials are in close contact to provide electrical conductivity.
As the heat dissipated at the connection depends on the contact resistance, which is a
function of the normal mechanical load applied across the mated contact surfaces, a loose
connection may result in overheating, glowing, arcing and/or potential fire ignition [8].
According to Table 2, "loose connections" or "poor terminations" seem the most usual cause
of overheating, even more critical than "overloads" and electric arcs. In the case of low-
voltage switchgear and controlgear, there are two possible explanations:
___________
Numbers in square brackets refer to the Bibliography

– power dissipation and local temperature-rise are typically larger for poor connections
than for overloads;
– protection devices (e.g. those integrated in the equipment) are designed in such a way
that they provide protection against overloads, in particular severe overloads, whereas
poor connections are typically not cleared by such protection devices and may result
in long-term heating.
4.2.2 Ignition mechanisms
Babrauskas [5] reviewed scientific investigations about power dissipation, glowing and ignition
from high-resistance loose connections. Even though there are quite a few studies and the
phenomenon is not completely understood yet, the following conclusions can be drawn:
– wire-glowing can occur for quite low currents (< 1 A) and voltages (3 V to 4 V);
– for low values of current in the order of 1 A, in the vicinity of the glowing tip (at a
distance of 10 mm), the wire temperature can be 200 °C to 350 °C;
– typical temperature on the glowing region can exceed 1 200 °C;
– power dissipation magnitude is of the order of 15 W for 1 A and 25 W for 2,5 A and
depends on contact materials but not on supply voltage;
– the voltage drop across poor connections decreases as the current increases, so that
the power dissipation trend versus the current is illustrated in Figure 1, and not
quadratic as in normal connections with low and constant contact resistance value, it
is not dependent of the supply voltage value;
0 0
Current  (A)
IEC
NOTE a more detailed chart describing g
...