Fire hazard testing - Part 2-20: Glowing/hot-wire based test methods - Hot wire coil test method - Apparatus, verification, test method and guidance

IEC TS 60695-2-20:2021 describes a test method that applies to solid electrical insulating materials of which test specimens can be provided. The test measures the time required to ignite a test specimen when it is affected by heat from an electrically heated wire wound around the test specimen. If the test specimen drips, the time at which this occurs is also recorded.
The test method can be used to provide classifications which can be used for quality assurance, the preselection of materials of products as described in IEC 60695-1-30, or to verify the required minimum classification of materials used in end products.
This basic safety publication is intended for use by technical committees in the preparation of standards in accordance with the principles laid down in IEC Guide 104 and ISO/IEC Guide 51.
One of the responsibilities of a technical committee is, wherever applicable, to make use of basic safety publications in the preparation of its publications. The requirements, test methods or test conditions of this basic safety publication will not apply unless specifically referred to or included in the relevant publications.
This third edition of IEC TS 60695-2-20 cancels and replaces the second edition of IEC TS 60695-2-20 published in 2004. This edition constitutes a technical revision.
This edition includes the following significant technical changes with respect to the previous edition:
– Contents page added
– Updated Scope (Clause 1)
– Updated Terms and Definitions, added new relevant terms (Clause 3)
– Updated Principle (Clause 4)
– Updated Apparatus (Clause 5; recommendation to change the power source from a.c. to d.c. with a constant current output. Reason for this recommendation: d.c. technology is easier to obtain and to handle, which has been found to improve the Repeatability and Reproducibility of the test.
– Updated Test specimen dimensions (6.2)
– Revised Test procedure (Clause 8)
– Revised Observations and measurements (Clause 9)
– Revised Evaluation of test results (Clause 10)
– Revised Test report (Clause 11)
– Revised Annex A: Deletion of conformational test; Guidance on verification of the heater wire winding before testing
– Addition of normative Annex B: HWCT PLC Classes
– Addition of informative Annex C: Calibration curve to determine test current (Ic) in a spreadsheet program
– Addition of informative Annex D: Precision data
It has the status of a basic safety publication in accordance with IEC Guide 104 and ISO/IEC Guide 51.
This basic safety publication is intended for use by technical committees in the preparation of standards in accordance with the principles laid down in IEC Guide 104 and ISO/IEC Guide 51.

General Information

Status
Published
Publication Date
26-Apr-2021
Technical Committee
Current Stage
PPUB - Publication issued
Completion Date
27-Apr-2021
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IEC TS 60695-2-20:2021 - Fire hazard testing - Part 2-20: Glowing/hot-wire based test methods - Hot wire coil test method - Apparatus, verification, test method and guidance
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IEC TS 60695-2-20
Edition 3.0 2021-04
TECHNICAL
SPECIFICATION
colour
inside
Fire hazard testing –
Part 2-20: Glowing/hot wire based test methods – Hot-wire coil test method –
Apparatus, verification, test method and guidance
IEC TS 60695-2-20:2021-04(en)
---------------------- Page: 1 ----------------------
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---------------------- Page: 2 ----------------------
IEC TS 60695-2-20
Edition 3.0 2021-04
TECHNICAL
SPECIFICATION
colour
inside
Fire hazard testing –
Part 2-20: Glowing/hot wire based test methods – Hot-wire coil test method –
Apparatus, verification, test method and guidance
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 13.220.40, 29.020 ISBN 978-2-8322-9707-0

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

® Registered trademark of the International Electrotechnical Commission
---------------------- Page: 3 ----------------------
– 2 – IEC TS 60695-2-20:2021 © IEC 2021
CONTENTS

FOREWORD ........................................................................................................................... 4

INTRODUCTION ..................................................................................................................... 7

1 Scope .............................................................................................................................. 8

2 Normative references ...................................................................................................... 8

3 Terms and definitions ...................................................................................................... 9

4 Principle ........................................................................................................................ 11

5 Apparatus ...................................................................................................................... 12

5.1 Test chamber ........................................................................................................ 12

5.2 Heater wire ........................................................................................................... 12

5.3 Power supply and test circuit ................................................................................ 13

5.4 Test specimen fixture ............................................................................................ 13

5.5 Test specimen winding and pressing ..................................................................... 13

5.6 Conditioning chamber ........................................................................................... 14

5.7 Timing device ....................................................................................................... 15

5.8 Micrometer ............................................................................................................ 15

5.9 Measuring scale .................................................................................................... 15

6 Test specimens ............................................................................................................. 15

6.1 Test specimen preparation .................................................................................... 15

6.2 Test specimen dimensions .................................................................................... 15

7 Conditioning .................................................................................................................. 16

7.1 Requirements ....................................................................................................... 16

7.2 Test specimen conditioning ................................................................................... 16

7.3 Heater wire conditioning ....................................................................................... 16

7.4 Test conditions ..................................................................................................... 16

8 Test procedure .............................................................................................................. 17

8.1 General ................................................................................................................. 17

8.2 Apparatus ............................................................................................................. 17

8.3 Determination of the test current, I ...................................................................... 17

8.4 Calculation of test current, I ................................................................................ 18

8.5 Determination of time to ignite, IT and/or time to drip, DT ..................................... 18

9 Observations and measurement .................................................................................... 20

10 Evaluation of test results ............................................................................................... 21

10.1 Assigning a HWCT PLC classification ................................................................... 21

10.2 Precision data ....................................................................................................... 21

11 Test report ..................................................................................................................... 21

Annex A (informative) Guidance on how to effectively wind the heater wire on to the

test specimen ....................................................................................................................... 22

Annex B (normative) Hot wire coil test (HWCT) – Performance level category (PLC)

classes ................................................................................................................................. 23

B.1 General ................................................................................................................. 23

B.2 Reporting a classification ...................................................................................... 23

Annex C (informative) Calibration curve to determine test current (I ) in a spreadsheet

program ................................................................................................................................ 24

Annex D (informative) Precision data ................................................................................... 25

D.1 General ................................................................................................................. 25

---------------------- Page: 4 ----------------------
IEC TS 60695-2-20:2021 © IEC 2021 – 3 –

D.2 Results of preliminary inter-laboratory round robin ................................................ 25

D.3 Evaluation of test results ....................................................................................... 28

Bibliography .......................................................................................................................... 30

Figure 1 – Test fixture arrangement (example) ...................................................................... 11

Figure 2 – Test specimen winding pattern ............................................................................. 12

Figure 3 – Test specimen fixture (example) .......................................................................... 13

Figure 4 – Heater wire winding device (Example) .................................................................. 14

Figure 5 – Test circuit arrangement for heater wire calibration .............................................. 17

Figure 6 – Calibration curve .................................................................................................. 18

Figure 7 – Decision tree ........................................................................................................ 20

Figure A.1 – Illustration of type a) behaviour ......................................................................... 22

Figure A.2 – Illustration of type b) behaviour ......................................................................... 22

Figure C.1 – Calibration curve in a spreadsheet program used to determine I ..................... 24

Table 1 – Nominal thickness tolerances ................................................................................ 16

Table B.1 – Hot wire coil test (HWCT) – Performance level category (PLC) classes .............. 23

Table D.1 – Results for material 1A ...................................................................................... 26

Table D.2 – Results for material 1B ...................................................................................... 26

Table D.3 – Results for material 2A ...................................................................................... 26

Table D.4 – Results for material 2B ...................................................................................... 27

Table D.5 – Results for material 3 ......................................................................................... 27

Table D.6 – Results for material 4 ......................................................................................... 28

Table D.7 – Occurrence of PLC classes in the round robin ................................................... 29

---------------------- Page: 5 ----------------------
– 4 – IEC TS 60695-2-20:2021 © IEC 2021
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
FIRE HAZARD TESTING –
Part 2-20: Glowing/hot wire based test methods –
Hot-wire coil test method –
Apparatus, verification, test method and guidance
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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4) In order to promote international uniformity, IEC National Committees undertake to apply IEC Publications

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

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expenses arising out of the publication, use of, or reliance upon, this IEC Publication or any other IEC

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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 TS 60695-2-20 has been prepared by IEC technical committee 89: Fire hazard testing. It is

a Technical Specification.

This third edition of IEC TS 60695-2-20 replaces the second edition of IEC TS 60695-2-20

published in 2004. This edition constitutes a technical revision.

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

edition:
– Contents page added
– Updated Scope (Clause 1)
– Updated Terms and Definitions, added new relevant terms (Clause 3)
– Updated Principle (Clause 4)
---------------------- Page: 6 ----------------------
IEC TS 60695-2-20:2021 © IEC 2021 – 5 –

– Updated Apparatus (Clause 5; recommendation to change the power source from a.c. to

d.c. with a constant current output. Reason for this recommendation: D.c. technology is

easier to obtain and to handle, which has been found to improve the Repeatability and

Reproducibility of the test.
– Updated Test specimen dimensions (6.2)
– Revised Test procedure (Clause 8)
– Revised Observations and measurements (Clause 9)
– Revised Evaluation of test results (Clause 10)
– Revised Test report (Clause 11)

– Revised Annex A: Deletion of conformational test; Guidance on verification of the heater

wire winding before testing
– Addition of normative Annex B: HWCT PLC Classes

– Addition of informative Annex C: Calibration curve to determine test current (I ) in a

spreadsheet program
– Addition of informative Annex D: Precision data
The text of this Technical Specification is based on the following documents:
DTS Report on voting
89/1465/DTS 89/1488/RVDTS

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 Technical Specification 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.

It has the status of a basic safety publication in accordance with IEC Guide 104 and ISO/IEC

Guide 51.
Part 2 of IEC 60695 consists of the following parts:

Part 2-10: Glowing/hot-wire based test methods – Glow-wire apparatus and common test

procedure

Part 2-11: Glowing/hot-wire based test methods – Glow-wire flammability test method for end

products

Part 2-12: Glowing/hot-wire based test methods – Glow-wire flammability index (GWFI) test

method for materials

Part 2-13: Glowing/hot-wire based test methods – Glow-wire ignition temperature (GWIT) test

method for materials

Part 2-20: Glowing/hot-wire based test methods – Hot-wire coil test method – Apparatus,

verification, test method and guidance

A list of all parts in the IEC 60695 series, published under the general title Fire hazard testing,

can be found on the IEC website.
Words in bold in the text are defined in Clause 3.
---------------------- Page: 7 ----------------------
– 6 – IEC TS 60695-2-20:2021 © IEC 2021

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

stability date indicated on the IEC website under 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 document 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.
---------------------- Page: 8 ----------------------
IEC TS 60695-2-20:2021 © IEC 2021 – 7 –
INTRODUCTION

In the design of any electrotechnical product, the risk of abnormal heat and the potential

hazards associated with abnormal heat need to be considered. In this respect the objective of

component, circuit, and product design, as well as the choice of materials, is to reduce to

acceptable levels the potential risks during normal operating conditions, reasonably foreseeable

abnormal use, malfunction and/or failure. IEC/TC 89 has developed IEC 60695-1-10 [1] ,

together with its companion IEC 60695-1-11 [2], to provide guidance on how this is to be

accomplished.

The primary aims of IEC 60695-1-10 [1] and IEC 60695-1-11 [2] are to provide guidance on

how:
a) to prevent ignition caused by an electrically energized component part, and

b) to confine any resulting fire within the bounds of the enclosure of the electro technical

product in the event of ignition.

Secondary aims of IEC 60695-1-10 [1] and IEC 60695-1-11 [2] include the minimization of any

flame spread beyond the product’s enclosure and the minimization of the harmful effects of fire

effluents such as heat, smoke, toxicity and/or corrosivity.

This test method applies to solid electrical insulating materials which can provide test

specimens. It applies to materials for which the test specimen does not deform during

preparation, especially during the winding of the test specimen with the heater wire as described

in 5.5.
Examples of deformation that render this test method inapplicable include:

a) bowing, in either a transverse or a longitudinal direction, or twisting of the test specimen

during the winding of the test specimen with the heater wire, to a degree visible to the eye,

b) visible indentation of the test specimen by the heater wire.

An informative classification system described in Annex B can be used for the preselection of

materials.
_____________
Numbers in square brackets refer to the bibliography.
---------------------- Page: 9 ----------------------
– 8 – IEC TS 60695-2-20:2021 © IEC 2021
FIRE HAZARD TESTING –
Part 2-20: Glowing/hot wire based test methods –
Hot-wire coil test method –
Apparatus, verification, test method and guidance
1 Scope

This part of IEC 60695, which is a technical specification, describes a test method that applies

to solid electrical insulating materials of which test specimens can be provided. The test

measures the time required to ignite a test specimen when it is affected by heat from an

electrically heated wire wound around the test specimen. If the test specimen drips, the time at

which this occurs is also recorded.

The test method can be used to provide classifications which can be used for quality assurance,

the preselection of materials of products as described in IEC 60695-1-30, or to verify the

required minimum classification of materials used in end products.

This basic safety publication is intended for use by technical committees in the preparation of

standards in accordance with the principles laid down in IEC Guide 104 and ISO/IEC Guide 51.

One of the responsibilities of a technical committee is, wherever applicable, to make use of

basic safety publications in the preparation of its publications. The requirements, test methods

or test conditions of this basic safety publication will not apply unless specifically referred to or

included in the relevant publications.
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 60695-1-30, Fire hazard testing - Part 1-30: Guidance for assessing the fire hazard of

electrotechnical products - Preselection testing process - General guidelines

IEC 60695-4:2012, Fire hazard testing - Part 4: Terminology concerning fire tests for

electrotechnical products

IEC GUIDE 104:2019, The preparation of safety publications and the use of basic safety

publications and group safety publications

ISO/IEC Guide 51:2014, Safety aspects – Guidelines for their inclusion in standards

ISO 291:2008, Plastics – Standard atmospheres for conditioning and testing

ISO 293, Plastics – Compression moulding test specimens of thermoplastic materials

ISO 294 (all parts), Plastics – Injection moulding of test specimens of thermoplastic materials

ISO 295, Plastics – Compression moulding of test specimens of thermosetting materials

---------------------- Page: 10 ----------------------
IEC TS 60695-2-20:2021 © IEC 2021 – 9 –
ISO 13943:2008, Fire safety - Vocabulary
ISO 16012:2004, Plastics – Determination of linear dimensions of test specimens
JIS C 2520:1999, Wires and rolled wires for electrical heating
3 Terms and definitions

For the purposes of this document, the terms and definitions given in ISO 13943:2017, some of

which are reproduced below for the user’s convenience, as well as the following 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
abnormal heat

heat that is additional to that resulting from use under normal conditions, up

to and including that which causes a fire
[SOURCE: ISO 13943:2017, definition 3.1]
3.2
classification time, t

arithmetic mean of relevant times to ignite, IT and times to drip, DT, used for the purpose of

classification
3.3
combustion
exothermic reaction of a substance with an oxidizing agent

Note 1 to entry: Combustion generally emits fire effluent accompanied by flames and/or glowing.

[SOURCE: ISO 13943:2017, definition 3.55]
3.4
draught-free environment

space in which the results of experiments are not significantly affected by the local air speed

Note 1 to entry: A qualitative example is a space in which a wax candle flame remains essentially undisturbed.

-1 -1

Quantitative examples are small-scale fire tests in which a maximum air speed of 0,1 m⋅s or 0,2 m⋅s is sometimes

specified
[SOURCE: ISO 13943:2017, definition 3.83]
3.5
end product
product which is ready for use
Note 1 to entry: An end product can be a component of another end product.
[SOURCE: IEC 60695-4:2012, definition 3.2.7]
---------------------- Page: 11 ----------------------
– 10 – IEC TS 60695-2-20:2021 © IEC 2021
3.6
fire effluent

all gases and aerosols, including suspended particles, created by combustion or pyrolysis and

emitted to the environment
[SOURCE: ISO 13943:2017, definition 3.123]
3.7
fire hazard
potential for harm associated with fire

Note 1 to entry: Alternatively, fire hazard can be a physical object or condition with a potential for an undesirable

consequence from fire.
[SOURCE: ISO 13943:2017, definition 3.131]
3.8
ignitability
ease of ignition

measure of the ease with which a test specimen can be ignited, under specified conditions

Note 1 to entry: Modified, notes to entry have been deleted
[SOURCE: ISO 13943:2017, definition 3.212]
3.9
ignition
sustained ignition (deprecated)
initiation of combustion
[SOURCE: ISO 13943:2017, definition 3.217]
3.10
molten drip
falling droplet of material which has been softened or liquefied by heat
Note 1 to entry: The droplets can be flaming or not flaming.
[SOURCE: ISO 13943:2017, definition 3.275]
3.11
preselection

process of assessing and choosing candidate materials, components or sub-assemblies for

making an end product
[SOURCE: IEC 60695-1-30, definition 3.5]
3.12
time to drip, DT

time elapsed after the start of a test when molten drips are first observed to fall from the test

specimen
3.13
time to ignite, IT

time elapsed after the start of a test when ignition of the test specimen is observed to occur

---------------------- Page: 12 ----------------------
IEC TS 60695-2-20:2021 © IEC 2021 – 11 –
4 Principle

A rectangular bar-shaped test specimen is supported horizontally on a test fixture (an example

of a test fixture is shown in Figure 1 and Figure 3). The centre portion is wound with a coil of

heater wire as shown in Figure 2. A constant current is applied to the coil, which rapidly heats

up and the behaviour of the test specimen is observed. The time to ignite, IT and/or the time

to drip, DT shall be recorded.
Figure 1 – Test fixture arrangement (example)
---------------------- Page: 13 ----------------------
– 12 – IEC TS 60695-2-20:2021 © IEC 2021
Dimension in millimetres
Key
1 Test specimen
2 Heater wire
3 Electrical connection point
4 Distance to electrical connection points
5 Distance between all 5 windings (31,5 – 32,0 mm)
Figure 2 – Test specimen winding pattern
5 Apparatus
5.1 Test chamber

The laboratory fume hood/chamber shall have an inside volume of at least 0,5 m . The chamber

shall provide a draught-free environment whilst allowing normal thermal circulation of air past

the test specimen. The chamber shall permit observation of the test in progress. The inside

surfaces of the walls shall be a dark colour. The test chamber shall have an ambient light level

not exceeding 20 lux. For safety and convenience, it is desirable that this enclosure (which can

be completely closed) is fitted with an extraction device, such as an exhaust fan, to remove the

fire effluent which may be toxic. The extraction device, if fitted, shall be turned off during the

test and turned on immediately after the test. A positive closing damper may be needed.

5.2 Heater wire

The heater wire shall be a Nickel/Chromium wire (NCHW1 according to JIS C 2520), having a

nominal composition of > 77 % Ni and 20 ± 1 % Cr, having a nominal diameter of 0,5 ± 0,016 mm

and a length of 260 mm (+ 10 mm, – 0 mm).

NOTE 1 NiCr (> 77 % Ni / 20 ± 1 % Cr) heater wire has a nominal cold resistivity of (1,08 ± 0,05) × 10 Ω⋅m.

NOTE 2 NCHW1 according to JIS C 2520 is also known as NiCr8020 according to DIN 17470 Werkstoffnummer

2.4869.

NOTE 3 The length of wire may need to be adapted as follows: 280 mm (+10 mm, -0 mm) for specimens with

thicknesses between >3 mm and ≤8 mm; and 350 mm (+10 mm, -0 mm) for specimens with thicknesses between

>8 mm and ≤13 mm.
---------------------- Page: 14 ----------------------
IEC TS 60695-2-20:2021 © IEC 2021 – 13 –
5.3 Power supply and test circuit

A constant current DC power supply which can provide a constant current of at least 8 A and a

power of at least 150 W shall be used to energize the heater wire. The suppl
...

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