IEC 60112:2020
(Main)Method for the determination of the proof and the comparative tracking indices of solid insulating materials
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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IEC 60112 ®
Edition 5.0 2020-10
COMMENTED VERSION
INTERNATIONAL
STANDARD
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BASIC SAFETY PUBLICATION
Method for the determination of the proof and the comparative tracking indices
of solid insulating materials
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IEC 60112 ®
Edition 5.0 2020-10
COMMENTED VERSION
INTERNATIONAL
STANDARD
colour
inside
BASIC SAFETY PUBLICATION
Method for the determination of the proof and the comparative tracking indices
of solid insulating materials
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 19.080; 29.035.01 ISBN 978-2-8322-9013-2
– 2 – IEC 60112:2020 CMV © IEC 2020
CONTENTS
FOREWORD . 4
1 Scope . 6
2 Normative references. 6
3 Terms and definitions . 7
4 Principle . 8
5 Test specimen . 8
6 Test specimen conditioning . 9
6.1 Environmental conditioning . 9
6.2 Test specimen surface state . 9
7 Test apparatus . 9
7.1 Electrodes. 9
7.2 Test circuit . 10
7.3 Test solutions . 10
7.4 Dropping device . 11
7.5 Test specimen support platform . 11
7.6 Electrode assembly installation . 11
7.7 Conditioning chamber. 12
8 Basic test procedure . 12
8.1 General . 12
8.2 Preparation . 12
8.3 Test procedure . 13
9 Determination of erosion . 13
10 Determination of Proof tracking index test (PTI). 13
10.1 Procedure . 13
10.2 Report . 14
11 Determination of comparative tracking index (CTI) . 14
11.1 General . 14
11.2 Screening test . 15
11.3 Determination of the maximum 50 drop withstand voltage . 15
11.4 Determination of the 100 drop point . 16
11.5 Report . 17
Annex A (informative) List of factors that should be considered by product committees . 20
Annex B (informative) Solution B . 21
Annex C (informative) Electrode material selection . 22
C.1 Platinum electrodes . 22
C.2 Alternatives . 22
Bibliography . 23
List of comments . 24
Figure 1 – Electrode . 18
Figure 2 – Electrode/specimen arrangement . 18
Figure 3 – Example of typical electrode mounting and specimen support . 18
Figure 4 – Example of test circuit . 19
– 4 – IEC 60112:2020 CMV © IEC 2020
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
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8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is
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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.
This commented version (CMV) of the official standard IEC 60112:2020 edition 5.0
allows the user to identify the changes made to the previous edition IEC 60112:2003
+AMD1:2009 CSV edition 4.1. Futhermore, comments from IEC TC 112 experts are
provided to explain the reasons of the most relevant changes.
A vertical bar appears in the margin wherever a change has been made. Additions are in
green text, deletions are in strikethrough red text. Experts' comments are identified by
a blue-background number. Mouse over a number to display a pop-up note with the
comment.
This publication contains the CMV and the official standard. The full list of comments is
available at the end of the CMV.
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.
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.
– 6 – IEC 60112:2020 CMV © IEC 2020
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 1 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. 2
Test results cannot be used are not directly suitable 3 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. 4
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 required available 5 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 may can rank materials in a different order from the drop test given in this document. 6
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. 7
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 104:1997, The preparation of safety publications and the use of basic safety
publications and group safety publications 8
ISO 293:1986, Plastics – Compression moulding test specimens of thermoplastic materials 9
ISO 294-1:1996, Plastics – Injection moulding of test specimens of thermoplastic materials –
Part 1: General principles, and moulding of multi-purpose and bar test specimens 10
ISO 294-3:2002, Plastics – Injection moulding of test specimens of thermoplastic materials –
Part 3: Small plates 11
ISO 295:1991, Plastics – Compression moulding of test specimens of thermosetting materials 12
ISO 4287, Geometrical Product Specifications (GPS) – Surface texture: Profile method –
Terms, definitions and surface texture parameters 13
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 14
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 conducting conductive 15 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 of at least 0,5 A for at least 2 s 16 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) 17 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. 18
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. 19
3.6
persistent flame
in case of dispute – one flame 20 which burns for more than 2 s
– 8 – IEC 60112:2020 CMV © IEC 2020
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.
3.8
de-ionized water
water for analytical laboratory use in accordance with ISO 3696, grade 3, or equivalent quality 21
4 Principle
The upper surface of the test specimen is supported in a approximately 22 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. 23
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 over the edges of the test specimen away from the test
electrodes. 24
NOTE 1 In general flat surfaces of not less than 20 mm × 20 mm are recommended used to reduce the
probability of electrolyte loss over the specimen edge flows away from the test electrodes 25 although smaller
sizes may can 26 be used, subject to no electrolyte loss, e.g. ISO 3167, 15 mm × 15 mm multi-purpose test
specimens.
NOTE 2 It is preferable to use In general separate test specimens for each test are used. If several tests are to
be made on the same test piece, care should be taken to ensure that the testing points are 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. 27
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 may not 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 allowed possible. 28
Test specimens shall have nominally uniformly 29 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, 30 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.
NOTE 4 The use of different fabrication conditions/processes may can 31 lead to different levels of performance
in the PTI and CTI test.
NOTE 5 Parts moulded using different flow directions may can 32 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). 33
z
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. 34
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. 35
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 °C ± 5 K (23 ± 5) °C, 36 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. 37
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.
NOTE Dust, dirt, fingerprints, grease, oil, mould release or other contaminants may can
influence the results. Care should be taken When cleaning the test specimen to avoid,
swelling, softening, abrasion or other damage to the material shall be avoided. 38
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.
– 10 – IEC 60112:2020 CMV © IEC 2020
NOTE 2 It is recommended that In general, 39 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
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
100 V and 600 V at a frequency of 48 Hz to 62 Hz. The voltage measuring device shall
indicate a true RMS value and shall have a maximum error an accuracy 40 of 1,5 % or better
for the reading. The power of the source shall be not less than 0,6 kVA. An example of a
suitable test circuit is shown in Figure 4.
A variable resistor shall be capable of adjusting the current between the short-circuited
electrodes to (1,0 ± 0,1) A and the voltage indicated by the voltmeter shall not decrease by
more than 10 % when this current flows (see Figure 4). 41 The instrument used to measure
the value of the short-circuit current shall have a maximum error an accuracy 42 of ±3 % or
better for the reading.
The input supply voltage to the apparatus shall be adequately stable.
NOTE To achieve the tolerance requirement it may be necessary that the suppply voltage to the apparatus is
sufficiently stable. 43
The over-current device shall operate when a current with an RMS value of 0,50 A with
a relative tolerance of ±10 %, has persisted for 2,00 s with a relative tolerance of ±10 %
(0,50 ± 0,05) A has persisted for (2,00 ± 0,20) s. 44
7.3 Test solutions
Solution A:
Dissolve approximately 0,1 % by mass of analytical reagent grade anhydrous ammonium
chloride (NH Cl), of a purity of not less than 99,8 %, in de-ionized water, having a conductivity
of not greater than 1 mS/m 45 to give a resistivity of (3,95 ± 0,05) Ωm at (23 ± 1) °C.
NOTE 1 The quantity of ammonium chloride is selected to give a solution in the required range of resistivity.
NOTE 2 The conductivity of the solution A at 25°C is (3,75 ± 0,05) Ωm, and (4,25 ± 0,05) Ωm at 20 °C. 46
Solution B:
Description of this solution is given in Annex B (informative).
Solution C: 47
Dissolve approximately 0,12 % by mass of analytical reagent grade anhydrous ammonium
chloride (NH Cl), of a purity of not less than 99,8 %, and (0,5 ± 0,02) % by mass of sodium-di-
butyl naphthalene sulfonate a non-ionic surfactant (t-octylphenoxypolyethoxyethanol, CAS
Registry Number 9002-93-1) in de-ionized water, having a conductivity of not greater than
1 mS/m, to give a resistivity of (1,98 ± 0,05) Ωm at (23 ± 1) °C and a surface tension of
< 40 mN/m according to ISO 304.
NOTE 3 The quantity of ammonium chloride is selected to give a solution in the required range of resistivity, and
the quantity of the surfactant to give a surface tension of the solution in the required range. 48
Solution A is normally used, but where a more aggressive contaminant is required, solution B
C is recommended. To indicate that solution B C was used, the CTI or PTI value shall be
followed by the letter "MC". 49 The use of solution B may be stipulated for comparability with
prior results. 50
7.4 Dropping device
Drops of the test solution shall fall on to the specimen surface at intervals of (30 ± 5) s. The
drops shall fall approximately centrally between the two contact areas of 51 the electrodes
from a height of (35 ± 5) mm.
The time for 50 drops to fall on to the specimen shall be (24,5 ± 2) min.
The target time between single drops shall be 30 s. 52 The mass of a sequence of 50 drops
shall lie between 0,997 g and 1,147 g. The mass of a sequence of 20 drops shall lie between
0,380 g and 0,480 g.
NOTE 1 The mass of the drops may can 53 be determined by weighing with the appropriate laboratory balance.
NOTE 2 The target mass for 50 drops is 1,07 g and for 20 drops it is 0,43 g. 54
The mass of the drops shall be checked at appropriate time intervals.
NOTE 3 For solution A, a length of thin walled stainless steel tubing (e.g. hypodermic needle tubing), having an
outer diameter of between 0,9 mm and 1,2 mm, dependent upon the dropping system, has been found to be
suitable for the tip of the dropping device. For solution B and solution C, 55 tubes having outer diameters over the
range 0,9 mm to 3,45 mm have been found to be necessary with the different dropping systems in use.
NOTE 4 The use of A drop detector or counter is recommended can be used 56 to ascertain whether there are
any double drops or whether drops are missing.
7.5 Test specimen support platform
A glass plate or plates, having a total thickness of not less than 4 mm and of a suitable size
shall be used to support the test specimen during the test.
NOTE 1 In order to avoid the problem of cleaning the specimen support table, it is recommended common 57 that
a disposable glass microscope slide is placed on the specimen support table immediately under the test specimen.
NOTE 2 The use of thin metal foil conductors around the edge of the glass plate to detect electrolyte loss has
been found useful.
7.6 Electrode assembly installation
The specimen and its immediate the contacting electrodes shall be mounted in an essentially
draught-free space in an enclosure a chamber. 58
– 12 – IEC 60112:2020 CMV © IEC 2020
NOTE To keep the chamber reasonably free of fumes, it may can be necessary, for certain classes of materials,
to have a small air flow across the surface of the test specimen and between the electrodes. An air velocity of the
order of 0,2 m/s before the start of the test and as far as possible during the test has been found suitable. The air
velocity in other areas of the enclosure may chamber can be substantially higher to assist in fume removal. The air
velocity may can be measured with an appropriately scaled hot wire anemometer. 59
A suitable fume extraction system shall be provided to allow safe venting of the enclosure
chamber 60 after the test.
7.7 Conditioning chamber 61
The conditioning chamber shall be maintained at (23 ± 2) °C and a relative humidity of
(50 ± 10) %.
NOTE Standard conditions for use prior to and during the testing of solid electrical insulating materials are
specified in IEC 60212.
8 Basic test procedure
8.1 General
Where the material is substantially anisotropic, tests shall be made in the direction of the
features and orthogonal to them. Results from the direction giving the lower values shall be
used, unless otherwise specified.
Tests shall be made at an ambient temperature of (23 ± 5) °C.
Tests shall be made on uncontaminated test specimens, unless otherwise specified.
The result of a test where a hole is formed is considered to be valid, irrespective of the test
specimen thickness, but the formation of the hole shall be reported together with the depth of
the hole (the thickness of the test specimen or stack).
8.2 Preparation
After each test, clean the electrodes with an appropriate solvent and then rinse and dry them
with de-ionized water. If necessary, restore their shape, polish if necessary, and give a final
rinse and dry before the next test. 62
Immediately before the test ensure, if necessary by cooling the electrodes, that their
temperature is sufficiently low so that they have no adverse effect on the specimen
properties.
Ensure freedom from visual contamination and ensure that the solution to be used conforms
to the conductivity requirements either by regular testing, or by measurement immediately
before the test.
NOTE 1 Residues on the dropping device from an earlier test will probably contaminate the solution and
evaporation of the solution will increase its concentration – both of which may result in lower than true values. In
such cases it may be advisable to clean the outside of the dropping device can be cleaned 63 mechanically and/or
with a solvent and the inside by flushing through with conforming solution before each test. Flushing through some
10 to 20 drops depending upon the delay between tests will normally remove any non-conforming liquid.
In case of dispute, the cleaning procedures used for the electrodes and dropper tube shall be
agreed between purchaser and supplier.
Place the test specimen, with the test surface uppermost and horizontal on the specimen
support table. Adjust the relative height of the test specimen and electrode mounting
assembly, such that on lowering the electrodes on to the specimen, the correct orientation is
achieved with a separation of (4,0 ± 0,1) mm. Ensure that the chisel edges make contact with
the surface of the specimen with the required force and over the full width of the chisel. 64
NOTE 2 It may can 65 be helpful to place a light behind the electrodes when making this check visually.
The orientation of the specimen should ensure that the droplet stays between the electrodes. 66
Set the test voltage to the required value which shall be an integer multiple of 25 V, and
adjust the circuit parameters so that the short-circuit current is within the permitted tolerance.
8.3 Test procedure
Start the dropping system so that drops fall on to the test surface and continue the test until
one of the following occurs:
a) the over-current device operates;
b) a persistent flame occurs;
c) at least 25 s have elapsed after the fiftieth (hundredth) drop has fallen without a) or b)
occurring.
NOTE If there is no requirement for the determination of erosion, the 100 drop tests may can 67 be made ahead
of any 50 drop tests.
After completion of the test, vent the chamber of noxious fumes and remove the test
specimen.
9 Determination of erosion
When required, specimens which have not failed at the 50 drop point shall be cleaned of any
debris or loosely attached degradation products and placed on the platform of a depth gauge.
The maximum depth of erosion of each specimen shall be measured in millimetres to an
accuracy of 0,1 mm, using a 1,0 mm nominal diameter probe having a hemispherical end. The
result is the maximum of the five measured values.
Erosion depths of less than 1 mm are shall be 68 reported as <1 mm.
In the case of tests according to Clause 10, when required the erosion shall be measured on
the specimens which withstood 50 drops at the specified voltage.
In the case of tests according to Clause 11, when required the erosion shall be measured on
the five specimens tested at the maximum 50 drop voltage.
10 Determination of Proof tracking index test (PTI) 69
10.1 Procedure
Where, in IEC standards for material or for electrical equipment specifications, or in other
standards, a proof test only is required, 50 drop tests shall be made in accordance with
Clause 8 but at the single voltage specified. The required number of specimens shall
withstand the test period up to at least 25 s after the fiftieth drop has fallen without tracking
failure, and without a persistent flame occurring. 70
Operation of the over-current device by air arcs does not constitute a tracking failure.
NOTE The recommended minimum required number of specimens is five. If one of five
specimens fails at the certain test voltage, a new set of five samples may be tested unless
otherwise specified. If only one of the total of ten specimens fails, the result is "pass". 71
A different number of specimens may be agreed by manufacturer and user, or defined in
product standards.
– 14 – IEC 60112:2020 CMV © IEC 2020
The proof voltage shall be an integer multiple of 25 V.
10.2 Report
The report shall include the following information.
a) Identification of the material tested and details of any conditioning.
b) Thickness of the specimens and the number of layers used to achieve this thickness.
c) Nature of the test specimen surface where the original surface was not tested:
1) details of any cleaning process;
2) details of any machining processes, e.g. grinding;
3) details of any coating on the tested surface specimen. 72
d) State of the surface before testing, with regard to surface imperfections, e.g. surface
scratches, blemishes, impurities, etc.
e) The cleaning procedure used for the electrodes and dropper.
f) Where the measurements were not made in an essentially draught-free space, report on
the approximate air flow rate.
g) Orientation of the electrodes in relation to any known characteristics of the material.
h) Report on the result of the proof tracking index test where there is no requirement for the
determination of the degree of erosion as follows:
Pass or fail at the specified voltage with an indication of the type of solution if Type C
or Type B. 73
EXAMPLE for solution A 'Pass PTI 175', or 'Fail PTI 175 M'
EXAMPLE for solution B 'Pass PTI 225 M', or 'Fail PTI 225 M'
EXAMPLE for solution C 'Pass PTI 175 C', or 'Fail PTI 175 C'
Where there is an erosion requirement the result shall be reported as follows:
Pass or fail at the specified voltage with an indication of the type of solution if Type C,
or Type B, and the maximum depth of erosion. 74
PASS EXAMPLE for solution A 'Pass PTI 250 M – 3', or 'Fail PTI 250 – 3'
PASS EXAMPLE for solution B 'Pass PTI 375 M – 3', or 'Fail PTI 375 M – 3'
PASS EXAMPLE for solution C 'Pass PTI 250 C – 3' or 'Fail PTI 250 C – 3'.
Where the erosion cannot be reported because the specimen flamed, this both shall be
reported.
Where a hole developed through the specimen, its formation shall be reported together
with an indication of its depth (specimen thickness).
Where the tests were invalid due to air arcs, this shall be reported.
11 Determination of comparative tracking index (CTI)
11.1 General
Determination of the comparative tracking index requires the determination of the maximum
voltage at which five specimens withstand the test period for 50 drops without failure and
whether, at a voltage of 25 V lower than the maximum 50 drop figure, the specimen
withstands 100 drops. If this is not the case, the maximum 100 drop withstand voltage shall
be determined.
NOTE 1 The wording of the previous edition of this standard implied that determinations of the maximum 50 drop
withstand voltage had to be made before any 100 drop determinations.
NOTE 2 It is recognized that the cost of testing may be reduced by firstly determining the maximum 100 drop
withstand voltage and therefore this procedure is recommended in this standard. 75
If one of five specimens fails at a certain test voltage, a new set of five samples may be
tested. If only one of the total of ten specimens fails, this result qualifies for continuing the
procedure with the next higher voltage. 76
11.2 Screening test 77
If the behaviour of the material is unknown, a screening test shall start with at least
three specimens at a maximum starting voltage of 300 V with a minimum of 50 drops. If the
material withstands the initial test without tracking failure and without a persistent flame,
always using three specimens, increase the test voltage by 100 V steps until a tracking failure
or a persistent flame occurs. Then reduce the test voltage by 50 V, and finally increase or
reduce the test voltage by 25 V to identify the maximum test voltage for the determination of
the comparative tracking index.
If the materail fails at the initial test voltage, reduce the test voltage by 100 V and follow the
same iterative procedure for the determination of the comparative tracking index, always
using three specimens.
Complete the determination of the comparative tracking index according to the general
procedure, and procedures 11.1, 11.3 and 11.4.
NOTE Any result of the screening test can be used for completing the general procedure to evaluate the CTI
value.
This procedure is necessary because some materials can withstand high test voltages, but
fails at lower test voltages.
11.3 Determinati
...
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
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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
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
INTERNATIONALE
ICS 19.080; 29.035.01 ISBN 978-2-8322-8748-4
– 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
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
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
misinterpretation by any end user.
4) In order to promote international uniformity, IEC National Committees undertake to apply IEC Publications
transparently to the maximum extent possible in their national and regional publications. Any divergence
between any IEC Publication and the corresponding national or regional publication shall be clearly indicated in
the latter.
5) IEC itself does not provide any attestation of conformity. Independent certification bodies provide conformity
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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.
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.
– 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.
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
– 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.
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.
– 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).
z
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
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
100 V and 600 V at a frequency of 48 Hz to 62 Hz. The voltage measuring device shall
indicate a true RMS value and shall have an accuracy of 1,5 % or better for the reading. The
power of the source shall be not less than 0,6 kVA. An example of a suitable test circuit is
shown in Figure 4.
A variable resistor shall be capable of adjusting the current between the short-circuited
electrodes to (1,0 ± 0,1) A and the voltage indicated by the voltmeter shall not decrease by
more than 10 % when this current flows. The instrument used to measure the value of the
short-circuit current shall have an accuracy of ±3 % or better for the reading.
NOTE To achieve the tolerance requirement it may be necessary that the suppply voltage to the apparatus is
sufficiently stable.
The over-current device shall operate when a current with an RMS value of (0,50 ± 0,05) A
has persisted for (2,00 ± 0,20) s.
7.3 Test solutions
Solution A:
Dissolve approximately 0,1 % by mass of analytical reagent grade anhydrous ammonium
chloride (NH Cl), of a purity of not less than 99,8 %, in de-ionized water to give a resistivity of
(3,95 ± 0,05) Ωm at (23 ± 1) °C.
NOTE 1 The quantity of ammonium chloride is selected to give a solution in the required range of resistivity.
NOTE 2 The conductivity of the solution A at 25°C is (3,75 ± 0,05) Ωm, and (4,25 ± 0,05) Ωm at 20 °C.
Solution B:
Description of this solution is given in Annex B (informative).
Solution C:
Dissolve approximately 0,2 % by mass of analytical reagent grade anhydrous ammonium
chloride (NH Cl), of a purity of not less than 99,8 %, and (0,5 ± 0,02) % by mass of a non-
ionic surfactant (t-octylphenoxypolyethoxyethanol, CAS Registry Number 9002-93-1) in de-
ionized water to give a resistivity of (1,98 ± 0,05) Ωm at (23 ± 1) °C and a surface tension of
< 40 mN/m according to ISO 304.
NOTE 3 The quantity of ammonium chloride is selected to give a solution in the required range of resistivity, and
the quantity of the surfactant to give a surface tension of the solution in the required range.
– 10 – IEC 60112:2020 © IEC 2020
Solution A is normally used, but where a more aggressive contaminant is required, solution C
is recommended. To indicate that solution C was used, the CTI or PTI value shall be followed
by the letter "C". The use of solution B may be stipulated for comparability with prior results.
7.4 Dropping device
Drops of the test solution shall fall on to the specimen surface at intervals of (30 ± 5) s. The
drops shall fall approximately centrally between the two contact areas of the electrodes from a
height of (35 ± 5) mm.
The target time between single drops shall be 30 s. The mass of a sequence of 50 drops shall
lie between 0,997 g and 1,147 g. The mass of a sequence of 20 drops shall lie between
0,380 g and 0,480 g.
NOTE 1 The mass of the drops can be determined by weighing with the appropriate laboratory balance.
NOTE 2 The target mass for 50 drops is 1,07 g and for 20 drops it is 0,43 g.
The mass of the drops shall be checked at appropriate time intervals.
NOTE 3 For solution A, a length of thin walled stainless steel tubing (e.g. hypodermic needle tubing), having an
outer diameter of between 0,9 mm and 1,2 mm, dependent upon the dropping system, has been found to be
suitable for the tip of the dropping device. For solution B and solution C, tubes having outer diameters over the
range 0,9 mm to 3,45 mm have been found to be necessary with the different dropping systems in use.
NOTE 4 A drop detector or counter can be used to ascertain whether there are any double drops or whether drops
are missing.
7.5 Test specimen support platform
A glass plate or plates, having a total thickness of not less than 4 mm and of a suitable size
shall be used to support the test specimen during the test.
NOTE 1 In order to avoid the problem of cleaning the specimen support table, it is common that a disposable
glass microscope slide is placed on the specimen support table immediately under the test specimen.
NOTE 2 The use of thin metal foil conductors around the edge of the glass plate to detect electrolyte loss has
been found useful.
7.6 Electrode assembly installation
The specimen and the contacting electrodes shall be mounted in an essentially draught-free
space in a chamber.
NOTE To keep the chamber reasonably free of fumes, it can be necessary, for certain classes of materials, to
have a small air flow across the surface of the test specimen and between the electrodes. An air velocity of the
order of 0,2 m/s before the start of the test and as far as possible during the test has been found suitable. The air
velocity in other areas of the chamber can be substantially higher to assist in fume removal. The air velocity can be
measured with an appropriately scaled hot wire anemometer.
A suitable fume extraction system shall be provided to allow safe venting of the chamber after
the test.
7.7 Conditioning chamber
The conditioning chamber shall be maintained at (23 ± 2) °C and a relative humidity of
(50 ± 10) %.
NOTE Standard conditions for use prior to and during the testing of solid electrical insulating materials are
specified in IEC 60212.
8 Basic test procedure
8.1 General
Where the material is substantially anisotropic, tests shall be made in the direction of the
features and orthogonal to them. Results from the direction giving the lower values shall be
used, unless otherwise specified.
Tests shall be made at an ambient temperature of (23 ± 5) °C.
Tests shall be made on uncontaminated test specimens, unless otherwise specified.
The result of a test where a hole is formed is considered to be valid, irrespective of the test
specimen thickness, but the formation of the hole shall be reported together with the depth of
the hole (the thickness of the test specimen or stack).
8.2 Preparation
After each test, clean the electrodes with an appropriate solvent and then rinse and dry them
with de-ionized water. If necessary, restore their shape, polish if necessary, and give a final
rinse and dry before the next test.
Immediately before the test ensure, if necessary by cooling the electrodes, that their
temperature is sufficiently low so that they have no adverse effect on the specimen
properties.
Ensure freedom from visual contamination and ensure that the solution to be used conforms
to the conductivity requirements either by regular testing, or by measurement immediately
before the test.
NOTE 1 Residues on the dropping device from an earlier test will probably contaminate the solution and
evaporation of the solution will increase its concentration – both of which may result in lower than true values. In
such cases the outside of the dropping device can be cleaned mechanically and/or with a solvent and the inside by
flushing through with conforming solution before each test. Flushing through some 10 to 20 drops depending upon
the delay between tests will normally remove any non-conforming liquid.
In case of dispute, the cleaning procedures used for the electrodes and dropper tube shall be
agreed between purchaser and supplier.
Place the test specimen, with the test surface uppermost and horizontal on the specimen
support table. Adjust the relative height of the test specimen and electrode mounting
assembly, such that on lowering the electrodes on to the specimen, the correct orientation is
achieved with a separation of (4,0 ± 0,1) mm. Ensure that the chisel edges make contact with
the surface of the specimen with the required force and over the full width of the chisel.
NOTE 2 It can be helpful to place a light behind the electrodes when making this check visually.
The orientation of the specimen should ensure that the droplet stays between the electrodes.
Set the test voltage to the required value which shall be an integer multiple of 25 V, and
adjust the circuit parameters so that the short-circuit current is within the permitted tolerance.
8.3 Test procedure
Start the dropping system so that drops fall on to the test surface and continue the test until
one of the following occurs:
a) the over-current device operates;
b) a persistent flame occurs;
– 12 – IEC 60112:2020 © IEC 2020
c) at least 25 s have elapsed after the fiftieth (hundredth) drop has fallen without a) or b)
occurring.
NOTE If there is no requirement for the determination of erosion, the 100 drop tests can be made ahead of any
50 drop tests.
After completion of the test, vent the chamber of noxious fumes and remove the test
specimen.
9 Determination of erosion
When required, specimens which have not failed at the 50 drop point shall be cleaned of any
debris or loosely attached degradation products and placed on the platform of a depth gauge.
The maximum depth of erosion of each specimen shall be measured in millimetres to an
accuracy of 0,1 mm, using a 1,0 mm nominal diameter probe having a hemispherical end. The
result is the maximum of the five measured values.
Erosion depths of less than 1 mm shall be reported as < 1 mm.
In the case of tests according to Clause 10, when required the erosion shall be measured on
the specimens which withstood 50 drops at the specified voltage.
In the case of tests according to Clause 11, when required the erosion shall be measured on
the five specimens tested at the maximum 50 drop voltage.
10 Proof tracking index test (PTI)
10.1 Procedure
Where, in IEC standards for material or for electrical equipment specifications, or in other
standards, a proof test only is required, 50 drop tests shall be made in accordance with
Clause 8 but at the single voltage specified.
Operation of the over-current device by air arcs does not constitute a tracking failure.
The minimum required number of specimens is five. If one of five specimens fails at the
certain test voltage, a new set of five samples may be tested unless otherwise specified. If
only one of the total of ten specimens fails, the result is "pass".
A different number of specimens may be agreed by manufacturer and user, or defined in
product standards.
The proof voltage shall be an integer multiple of 25 V.
10.2 Report
The report shall include the following information.
a) Identification of the material tested and details of any conditioning.
b) Thickness of the specimens and the number of layers used to achieve this thickness.
c) Nature of the test specimen surface where the original surface was not tested:
1) details of any cleaning process;
2) details of any machining processes, e.g. grinding;
3) details of any coating on the tested specimen.
d) State of the surface before testing, with regard to surface imperfections, e.g. surface
scratches, blemishes, impurities, etc.
e) The cleaning procedure used for the electrodes and dropper.
f) Where the measurements were not made in an essentially draught-free space, report on
the approximate air flow rate.
g) Orientation of the electrodes in relation to any known characteristics of the material.
h) Report on the result of the proof tracking index test where there is no requirement for the
determination of the degree of erosion as follows:
• Pass or fail at the specified voltage with an indication of the type of solution if Type C
or Type B.
EXAMPLE for solution A 'Pass PTI 175', or 'Fail PTI 175'
EXAMPLE for solution B 'Pass PTI 225 M', or 'Fail PTI 225 M'
EXAMPLE for solution C 'Pass PTI 175 C', or 'Fail PTI 175 C'
Where there is an erosion requirement the result shall be reported as follows:
• Pass or fail at the specified voltage with an indication of the type of solution if Type C,
or Type B, and the maximum depth of erosion.
PASS EXAMPLE for solution A 'Pass PTI 250 – 3', or 'Fail PTI 250 – 3'
PASS EXAMPLE for solution B 'Pass PTI 375 M – 3', or 'Fail PTI 375 M – 3'
PASS EXAMPLE for solution C 'Pass PTI 250 C – 3' or 'Fail PTI 250 C – 3'.
Where the erosion cannot be reported because the specimen flamed, both shall be
reported.
Where a hole developed through the specimen, its formation shall be reported together
with an indication of its depth (specimen thickness).
Where the tests were invalid due to air arcs, this shall be reported.
11 Determination of comparative tracking index (CTI)
11.1 General
Determination of the comparative tracking index requires the determination of the maximum
voltage at which five specimens withstand the test period for 50 drops without failure and
whether, at a voltage of 25 V lower than the maximum 50 drop figure, the specimen
withstands 100 drops. If this is not the case, the maximum 100 drop withstand voltage shall
be determined.
If one of five specimens fails at a certain test voltage, a new set of five samples may be
tested. If only one of the total of ten specimens fails, this result qualifies for continuing the
procedure with the next higher voltage.
11.2 Screening test
If the behaviour of the material is unknown, a screening test shall start with at least
three specimens at a maximum starting voltage of 300 V with a minimum of 50 drops. If the
material withstands the initial test without tracking failure and without a persistent flame,
always using three specimens, increase the test voltage by 100 V steps until a tracking failure
or a persistent flame occurs. Then reduce the test voltage by 50 V, and finally increase or
reduce the test voltage by 25 V to identify the maximum test voltage for the determination of
the comparative tracking index.
If the materail fails at the initial test voltage, reduce the test voltage by 100 V and follow the
same iterative procedure for the determination of the comparative tracking index, always
using three specimens.
– 14 – IEC 60112:2020 © IEC 2020
Complete the determination of the comparative tracking index according to the general
procedure, and procedures 11.1, 11.3 and 11.4.
NOTE Any result of the screening test can be used for completing the general procedure to evaluate the CTI
value.
This procedure is necessary because some materials can withstand high test voltages, but
fails at lower test voltages.
11.3 Determination of the maximum 50 drop withstand voltage
By inference from the sceening data, repeat the test procedure at an appropriate test voltage,
using a new test specimen or site and determine whether the specimen withstands the test for
the period up to at least 25 s after the fiftieth drop has fallen.
If the over-current device operated due to the occurrence of an air arc above the test
specimen, the test was invalid. Repeat the test procedure at the same
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