Method for the determination of the proof and the comparative tracking indices of solid insulating materials

IEC 60112:2020 specifies the method of test for the determination of the proof and comparative tracking indices of solid insulating materials on pieces taken from parts of equipment and on plaques of material using alternating voltage. This document provides a procedure for the determination of erosion when required.
This test method evaluates the composition of the material as well as the surface of the material being evaluated. Both the composition and surface condition directly influence the results of the evaluation and are considered when using the results in material selection process.
Test results are not directly suitable for the evaluation of safe creepage distances when designing electrical apparatus.
This basic safety publication focusing on a safety test method is primarily intended for use by technical committees in the preparation of safety publications in accordance with the principles laid down in IEC Guide 104 and lSO/lEC Guide 51.
This edition includes the following significant technical changes with respect to the previous edition:
Introduction of a new contaminant, solution C with a surfactant aligned with the test method of IEC 60587. The definition of the solution B was transferred to Annex B for backward reference.
Introduction of a screening test, considering the fact that some materials can withstand high test voltages, but fail at lower test voltages.  It has the status of a basic safety publication in accordance with IEC Guide 104.

Méthode de détermination des indices de résistance et de tenue au cheminement des matériaux isolants solides

L'IEC 60112:2020 spécifie la méthode d’essai pour la détermination des indices de résistance et de tenue au cheminement des matériaux isolants solides sur des échantillons prélevés sur des parties d'équipement et des plaques de matériau en utilisant une tension alternative. Le présent document fournit une procédure pour la détermination de la valeur de l’érosion quand cela est exigé.
Cette méthode d’essai évalue la composition et la surface du matériau soumis à l’essai. La composition et les conditions de surface influencent directement les résultats de l’évaluation et sont prises en considération lors de l’utilisation des résultats au moment de la sélection des matériaux.
Les résultats d’essais tels quels ne sont pas adaptés à l’évaluation des lignes de fuite de sécurité lors de la conception des appareils électriques.
La présente publication fondamentale de sécurité portant sur une méthode d’essai de sécurité est avant tout destinée à être utilisée par les comités d’études dans le cadre de l’élaboration de publications de sécurité, conformément aux principes établis dans le Guide IEC 104 et le Guide lSO/lEC 51.
Cette édition inclut les modifications techniques majeures suivantes par rapport à l'édition précédente:
Introduction d’un nouveau contaminant, la solution C, avec un tensioactif aligné sur la méthode d’essai de l’IEC 60587. Transfert à l’Annexe B de la définition de la solution B pour référence arrière.
Introduction d’un essai de déverminage, en tenant compte du fait que certains matériaux peuvent supporter des tensions d’essai élevées, mais pas des tensions d’essai plus basses.  Elle a le statut de publication fondamentale de sécurité, conformément au Guide IEC 104.

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Publication Date
27-Oct-2020
Current Stage
PPUB - Publication issued
Completion Date
28-Oct-2020
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IEC 60112
Edition 5.0 2020-10
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
BASIC SAFETY PUBLICATION
PUBLICATION FONDAMENTALE DE SÉCURITÉ
Method for the determination of the proof and the comparative tracking indices
of solid insulating materials
Méthode de détermination des indices de résistance et de tenue
au cheminement des matériaux isolants solides
IEC 60112:2020-10(en-fr)
---------------------- Page: 1 ----------------------
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---------------------- Page: 2 ----------------------
IEC 60112
Edition 5.0 2020-10
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
BASIC SAFETY PUBLICATION
PUBLICATION FONDAMENTALE DE SÉCURITÉ
Method for the determination of the proof and the comparative tracking indices
of solid insulating materials
Méthode de détermination des indices de résistance et de tenue
au cheminement des matériaux isolants solides
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
INTERNATIONALE
ICS 19.080; 29.035.01 ISBN 978-2-8322-8748-4

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 60112:2020 © IEC 2020
CONTENTS

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

1 Scope .............................................................................................................................. 5

2 Normative references ...................................................................................................... 5

3 Terms and definitions ...................................................................................................... 6

4 Principle .......................................................................................................................... 7

5 Test specimen ................................................................................................................. 7

6 Test specimen conditioning ............................................................................................. 8

6.1 Environmental conditioning ..................................................................................... 8

6.2 Test specimen surface state ................................................................................... 8

7 Test apparatus ................................................................................................................ 8

7.1 Electrodes .............................................................................................................. 8

7.2 Test circuit .............................................................................................................. 9

7.3 Test solutions ......................................................................................................... 9

7.4 Dropping device .................................................................................................... 10

7.5 Test specimen support platform ............................................................................ 10

7.6 Electrode assembly installation ............................................................................. 10

7.7 Conditioning chamber ........................................................................................... 10

8 Basic test procedure ...................................................................................................... 11

8.1 General ................................................................................................................. 11

8.2 Preparation ........................................................................................................... 11

8.3 Test procedure ...................................................................................................... 11

9 Determination of erosion ................................................................................................ 12

10 Proof tracking index test (PTI) ....................................................................................... 12

10.1 Procedure ............................................................................................................. 12

10.2 Report................................................................................................................... 12

11 Determination of comparative tracking index (CTI) ......................................................... 13

11.1 General ................................................................................................................. 13

11.2 Screening test ....................................................................................................... 13

11.3 Determination of the maximum 50 drop withstand voltage ..................................... 14

11.4 Determination of the 100 drop point ...................................................................... 15

11.5 Report................................................................................................................... 15

Annex A (informative) List of factors that should be considered by product committees ....... 19

Annex B (informative) Solution B ......................................................................................... 20

Annex C (informative) Electrode material selection .............................................................. 21

C.1 Platinum electrodes .............................................................................................. 21

C.2 Alternatives ........................................................................................................... 21

Bibliography .......................................................................................................................... 22

Figure 1 – Electrode ............................................................................................................. 17

Figure 2 – Electrode/specimen arrangement ......................................................................... 17

Figure 3 – Example of typical electrode mounting and specimen support .............................. 17

Figure 4 – Example of test circuit .......................................................................................... 18

---------------------- Page: 4 ----------------------
IEC 60112:2020 © IEC 2020 – 3 –
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
METHOD FOR THE DETERMINATION OF THE PROOF AND THE
COMPARATIVE TRACKING INDICES OF SOLID INSULATING MATERIALS
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

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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

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services carried out by independent certification bodies.

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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.

International Standard IEC 60112 has been prepared by IEC technical committee 112:

Evaluation and qualification of electrical insulating materials and systems.
This fifth edition cancels and replaces the fourth edition published in 2003 and
Amendment 1:2009. This edition constitutes a technical revision.

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

edition:

• Introduction of a new contaminant, solution C with a surfactant aligned with the test

method of IEC 60587. The definition of the solution B was transferred to Annex B for

backward reference.

• Introduction of a screening test, considering the fact that some materials can withstand

high test voltages, but fail at lower test voltages.

It has the status of a basic safety publication in accordance with IEC Guide 104.

---------------------- Page: 5 ----------------------
– 4 – IEC 60112:2020 © IEC 2020
The text of this International Standard is based on the following documents:
FDIS Report on voting
112/479/FDIS 112/484/RVD

Full information on the voting for the approval of this International Standard can be found in

the report on voting indicated in the above table.

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.
---------------------- Page: 6 ----------------------
IEC 60112:2020 © IEC 2020 – 5 –
METHOD FOR THE DETERMINATION OF THE PROOF AND THE
COMPARATIVE TRACKING INDICES OF SOLID INSULATING MATERIALS
1 Scope

This document specifies the method of test for the determination of the proof and comparative

tracking indices of solid insulating materials on pieces taken from parts of equipment and on

plaques of material using alternating voltage.

This document provides a procedure for the determination of erosion when required.

NOTE 1 The proof tracking index is used as an acceptance criterion as well as a means for the quality control of

materials and fabricated parts. The comparative tracking index is mainly used for the basic characterization and

comparison of the properties of materials.

This test method evaluates the composition of the material as well as the surface of the

material being evaluated. Both the composition and surface condition directly influence the

results of the evaluation and are considered when using the results in material selection

process.

Test results are not directly suitable for the evaluation of safe creepage distances when

designing electrical apparatus.

NOTE 2 This is in compliance with IEC 60664-1, Insulation coordination for equipment within low-voltage

systems – Part 1: Principles, requirements and tests.

NOTE 3 This test discriminates between materials with relatively poor resistance to tracking, and those with

moderate or good resistance, for use in equipment which can be used under moist conditions. More severe tests of

longer duration are available for the assessment of performance of materials for outdoor use, utilizing higher

voltages and larger test specimens (see the inclined plane test of IEC 60587). Other test methods such as the

inclined method can rank materials in a different order from the drop test given in this document.

This basic safety publication focusing on a safety test method is primarily intended for use by

technical committees in the preparation of safety publications in accordance with the

principles laid down in IEC Guide 104 and lSO/lEC 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.
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.

ISO 4287, Geometrical Product Specifications (GPS) – Surface texture: Profile method –

Terms, definitions and surface texture parameters
---------------------- Page: 7 ----------------------
– 6 – IEC 60112:2020 © IEC 2020
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
tracking

progressive formation of conducting paths, which are produced on the surface and/or within a

solid insulating material, due to the combined effects of electric stress and electrolytic

contamination
3.2
tracking failure
failure of insulation due to tracking between conductive parts

Note 1 to entry: In the present test, tracking is indicated by operation of an over-current device due to the

passage of a current across the test surface and/or within the specimen.
3.3
electrical erosion
wearing away of insulating material by the action of electrical discharges
3.4
air arc
arc between the electrodes above the surface of the specimen
3.5
comparative tracking index
CTI

numerical value of the maximum voltage (in V) at which five test specimens withstand the test

period for 50 drops without tracking failure and without a persistent flame occurring and

including also a statement relating to the behaviour of the material when tested using

100 drops (see 11.3)

Note 1 to entry: No tracking failure and no persistant flame are allowed at any lower test voltage.

Note 2 to entry: The criteria for CTI may also require a statement concerning the degree of erosion.

Note 3 to entry: Although a non-persistent flame is allowed in the test without constituting failure, materials which

generate no flame at all are preferred unless other factors are considered to be more important. See also Annex A.

Note 4 to entry: Some materials can withstand high test voltages, but fail at lower test voltages. See also 11.2.

3.6
persistent flame
flame which burns for more than 2 s
3.7
proof tracking index
PTI

numerical value of the proof voltage (in V) at which five test specimens withstand the test

period for 50 drops without tracking failure and without a persistent flame occurring

Note 1 to entry: Although a non-persistent flame is allowed in the test without constituting failure, materials which

generate no flame at all are preferred unless other factors are considered to be more important. See also Annex A.

---------------------- Page: 8 ----------------------
IEC 60112:2020 © IEC 2020 – 7 –
3.8
de-ionized water

water for analytical laboratory use in accordance with ISO 3696, grade 3, or equivalent quality

4 Principle

The upper surface of the test specimen is supported in a horizontal plane and subjected to an

electrical stress via two electrodes. The surface between the electrodes is subjected to a

succession of drops of electrolyte either until the over-current device operates, or until a

persistent flame occurs, or until the test period has elapsed.

The individual tests are of short duration (less than 1 h) with up to 50 or 100 drops of about

20 mg of electrolyte falling at 30 s intervals between platinum electrodes, 4 mm apart on the

test specimen surface.

An AC voltage between 100 V and 600 V is applied to the electrodes during the test.

During the test, specimens may also erode or soften, thereby allowing the electrodes to

penetrate them. The formation of a hole through the test specimen during a test is to be

reported together with the hole depth (test specimen thickness). Retests may be made using

thicker test specimens, up to a maximum of 10 mm.

NOTE The number of drops needed to cause failure by tracking usually increases with decreasing applied voltage

and, below a critical value, tracking ceases to occur. For some materials, tracking also ceases to occur above an

upper critical value.
5 Test specimen

Any approximately flat surface may be used, provided that the area is sufficient to ensure that

during the test no liquid flows away from the test electrodes.

NOTE 1 In general flat surfaces of not less than 20 mm × 20 mm are used to reduce the probability of electrolyte

flows away from the test electrodes although smaller sizes can be used, subject to no electrolyte loss,

e.g. ISO 3167, 15 mm × 15 mm multi-purpose test specimens.

NOTE 2 In general separate test specimens for each test are used. If several tests are to be made on the same

test piece, testing points can be sufficiently far from each other so that splashes, fumes, or erosion, from the

testing point will not contaminate or influence the other areas to be tested.

The thickness of the test specimen shall be 3 mm or more. Individual pieces of material may

be stacked to obtain the required thickness of at least 3 mm.

NOTE 3 The values of the CTI obtained on specimens with a thickness below 3 mm cannot be comparable with

those obtained on thicker specimens because of greater heat transmission to the glass support through thinner test

specimens. For this reason, stacked specimens are possible.

Test specimens shall have uniformly smooth and untextured surfaces which are free from

surface imperfections such as scratches, blemishes, impurities, etc, unless otherwise stated

in the product standard. If this is impossible, the results shall be reported together with a

statement describing the surface of the specimen because certain characteristics on the

surface of the specimen could add to the dispersion of the results.

For tests on parts of products, where it is impossible to cut a suitable test specimen from a

part of a product, specimens cut from moulded plaques of the same insulating material may

be used. In these cases, care should be taken to ensure that both the part and the plaque are

produced by the same fabrication process, resulting in the same surface texture, wherever

possible. Where the details of the final fabrication process are unknown, methods given in

ISO 293, ISO 294-1 and ISO 294-3 and ISO 295 may be appropriate.
---------------------- Page: 9 ----------------------
– 8 – IEC 60112:2020 © IEC 2020

NOTE 4 The use of different fabrication conditions/processes can lead to different levels of performance in the

PTI and CTI test.

NOTE 5 Parts moulded using different flow directions can also exhibit different levels of performance in the PTI

and CTI test.

In special cases, the test specimen may be ground to obtain a flat surface. In this case, the

surface texture according ISO 4287 (e.g. R values) shall be reported (see 10.2 and 11.5).

NOTE 6 Any grinding can damage the specimen. In this case, material surface made by grinding has higher or

lower tracking value than the original surface.

Where the direction of the electrodes relative to any feature of the material is significant,

measurements shall be made in the direction of the feature and orthogonal to it. The direction

giving the lower CTI shall be reported, unless otherwise specified.

NOTE 7 Use of an aggressive electrolyte, such as solution C, is common, when the material has a hydrophobic

surface.
6 Test specimen conditioning
6.1 Environmental conditioning

Unless otherwise specified, the test specimens shall be conditioned for a minimum of 24 h at

(23 ± 5) °C, with (50 ± 10) % RH. Once the test specimen has been removed from the

conditioning chamber (see 7.7) the test shall be started within 30 minutes.
6.2 Test specimen surface state
Unless otherwise specified,
a) tests shall be made on clean surfaces;

b) any cleaning procedure used shall be reported. Wherever possible, the details shall be

agreed between supplier and customer.

Dust, dirt, fingerprints, grease, oil, mould release or other contaminants can influence the

results. When cleaning the test specimen, swelling, softening, abrasion or other damage to

the material shall be avoided.
7 Test apparatus
7.1 Electrodes

Two electrodes of platinum with a minimum purity of 99 % shall be used (see Annex C). The

two electrodes shall have a rectangular cross-section of (5 ± 0,1) mm × (2 ± 0,1) mm, with

one end chisel-edged with an angle of (30 ± 2)° (see Figure 1). The sharp edge shall be

removed to produce an approximately flat surface, 0,01 mm to 0,1 mm wide.

NOTE 1 A microscope with a calibrated eyepiece has been found suitable for checking the size of the end

surface.

NOTE 2 In general, mechanical means are used to re-furbish the electrode shape after a test to ensure that the

electrodes maintain the required tolerances, especially with respect to the edges and corners.

At the start of the test, the electrodes shall be symmetrically arranged in a vertical plane, the

total angle between them being (60 ± 5)° and with opposing electrode faces approximately

vertical on a flat horizontal surface of the test specimen (see Figure 2). Their separation along

the surface of the test specimen at the start of the test shall be (4,0 ± 0,1) mm.

A thin metal rectangular slip gauge shall be used to check the electrode separation. The

electrodes shall move freely and the force exerted by each electrode on the surface of the

---------------------- Page: 10 ----------------------
IEC 60112:2020 © IEC 2020 – 9 –

test specimen at the start of the test shall be (1,00 ± 0,05) N. The design shall be such that

the force can be expected to remain at the initial level during the test.

One typical type of arrangement for applying the electrodes to the test specimen is shown in

Figure 3. The force shall be verified at appropriate intervals.

Where tests are made solely on those materials where the degree of electrode penetration is

small, the electrode force may be generated by the use of springs. However, gravity should be

used to generate the force on general purpose equipment (see Figure 3).

NOTE 3 With most, but not all designs of apparatus, if the electrodes move during a test due to softening or

erosion of the specimen, their tips will prescribe an arc and the electrode gap will change. The magnitude and

direction of the gap change will depend on the relative positions of the electrode pivots and the electrode/specimen

contact points. The significance of these changes will probably be material dependent and has not been

determined. Differences in design could give rise to differences in inter-apparatus results.

7.2 Test circuit

The electrodes shall be supplied with a substantially sinusoidal voltage, variable between

...

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