oSIST prEN IEC 61621:2026

• Status: Not Published
• Public Enquiry End Date: 31-Jul-2026
• ICS: 17.220.99 - Other standards related to electricity and magnetism
• ICS: 29.035.01 - Insulating materials in general
• Technical Committee: IIZS - Insulating materials and systems
• Current Stage: 4020 - Public enquire (PE) (Adopted Project)
• Start Date: 02-Jun-2026
• Due Date: 20-Oct-2026
• Completion Date: 03-Aug-2026
• Ref Project: prEN IEC 61621:2026 - Dry, solid insulating materials - Resistance test to high-voltage, low-current arc discharges

• Revises: SIST EN 61621:2001 - Dry, solid insulating materials - Resistance test to high-voltage, low-current arc discharges
• Effective Date: 01-Jul-2026

oSIST prEN IEC 61621:2026 is a CLC draft standard for testing dry, solid insulating materials against high-voltage, low-current arc discharges. It specifies a laboratory method for measuring arc resistance and classifying materials by time to failure, mainly for preliminary screening, formulation changes, and quality control.

What does oSIST prEN IEC 61621:2026 specify?

oSIST prEN IEC 61621:2026 specifies a test method for comparing similar insulating materials when arcs occur close to their surfaces. The method is meant to show how quickly a material is damaged by repeated arc exposure, and it is most useful for screening and quality control rather than predicting every service condition.

The scope also warns that the results are not a general ranking for all arc types. It notes that the behavior can differ from wet tracking tests and from service exposure, and it reports that the method has given acceptable reproducibility with thermoset materials while thermoplastics can show much larger scatter.

The document is organized into these main parts:

• Clause 1 - Scope
• Clause 2 - Normative references
• Clause 3 - Terms and definitions
• Clause 4 - Apparatus
• Clause 5 - Specimens
• Clause 6 - Procedure and failure recognition
• Clause 7 - Results
• Clause 8 - Report
• Annex A - Informative guidance on failure recognition by measurement

What are the key requirements of oSIST prEN IEC 61621:2026?

oSIST prEN IEC 61621:2026 requires a controlled arc test setup, defined specimen preparation, a staged increase in arc severity, and a result reported as time to failure in seconds. In practice, that means a laboratory cannot simply apply a spark and watch for damage - the spacing, current steps, specimen condition, and failure recognition all have to be controlled.

Apparatus and calibration

Clause 4 defines the test circuit, electrodes, chamber, and calibration checks. The circuit uses a transformer, variable autotransformer, voltmeter, milliammeter, current control resistors, suppressing resistor, air core inductors, breaker, and timer, and it calls for suppressing parasitic high-frequency effects so the arc remains stable.

The electrode system is tightly specified because the arc shape depends on it. The electrodes are tungsten rods with a defined tip geometry, mounted so both electrodes rest on the specimen with a set force and spacing; the practical effect is that the test measures material behavior, not accidental setup differences.

The chamber must prevent air drafts and allow safe observation and venting after the test. The document also requires calibration of the open-circuit operating voltage and adjustment of the secondary current before testing, so each test starts from a known electrical condition.

Specimens and conditioning

Clause 5 requires prepared specimens with a defined thickness for standard comparison, and it calls for at least five tests per material. Thin materials may be stacked to reach the target thickness, and any non-standard thickness has to be reported, which matters when comparing molded parts, laminates, or samples from different production lots.

Specimens must be clean, free from visible surface defects, and conditioned in a standard atmosphere based on IEC 60212:2010 before testing. In practice, this reduces the chance that moisture, fingerprints, or handling residue distort the arc resistance result.

Procedure and failure recognition

Clause 6 applies the test in stages. The early part of the test uses interrupted arcs, then the severity is increased step by step until failure occurs; this staged approach is what makes the method useful for comparing materials with different endurance levels.

Failure recognition is based mainly on visual and acoustic observation. A specimen fails when a conducting path forms and the arc disappears, or when burning continues after the arc is interrupted; this matters because the operator must distinguish true failure from glow, scintillation, or brief burning that does not persist.

The document also notes that failure often occurs just after a change in severity step, so time at the transition between steps is especially informative. For comparison work, that means small differences in elapsed time around a step change can be more significant than the same number of seconds inside one step.

Results and classification

Clause 7 states that the result is the time to failure, called arc resistance. The material is then classified using the lowest measured result from the five specimens, with an extension rule that allows five additional tests if only one of the first five falls into a class; this helps avoid over-interpreting one borderline specimen.

The classification runs from class 0 upward in bands of increasing arc resistance. For a buyer, engineer, or quality team, this means the document does not just give a pass/fail outcome - it provides a comparative class that can be used to distinguish candidate insulating materials.

Report content

Clause 8 requires the test report to identify the material, specimen thickness, fabrication, dimensions, cleaning and conditioning details, solvent used, any surface treatment, composite orientation, central/minimum/maximum arc resistance times, and notable observations such as burning or softening. That report content is important because arc resistance results can be strongly affected by preparation and specimen history.

What terms does oSIST prEN IEC 61621:2026 define?

• Failure - A specimen fails when a conducting path forms in the material, or when arc-related burning continues after the arc is interrupted.
• Arc resistance - The total elapsed time in seconds from the start of the test until specimen failure.
• Tracking - Progressive surface degradation caused by local discharges that form conducting or partially conducting paths.
• Conducting path - The continuous current-carrying route that marks specimen failure in this test method.

Who uses oSIST prEN IEC 61621:2026?

oSIST prEN IEC 61621:2026 is used by laboratories that test electrical insulating materials, by manufacturers developing or reformulating those materials, and by quality control teams that need a repeatable comparative arc test. It is also relevant to engineers and buyers evaluating dry, solid insulating materials for applications where surface arcing may be a concern.

The document is especially relevant to teams working on electrical insulation and systems qualification. Its scope also makes it useful where the aim is to detect changes in formulation or to compare similar materials during production control.

Which standards are used with oSIST prEN IEC 61621:2026?

The document cites several standards that support the test method:

• IEC 60112:2025 - Comparative tracking index testing for solid insulating materials, used as a comparison point for tracking behavior.
• IEC 60212:2010 - Standard conditioning atmosphere for solid electrical insulating materials before and during testing.
• IEC 60587:2022 - Test methods for tracking and erosion under severe ambient conditions, used for comparison with arc-related behavior.
• IEC 61302:1995 - Rotating wheel dip test for tracking and erosion resistance.
• EN 50191:2000 - Safety requirements for erection and operation of electrical test equipment.
• EN IEC 60112:2020 - European adoption of the comparative tracking index method, also used for comparison.

What does the oSIST prEN IEC 61621:2026 document contain?

oSIST prEN IEC 61621:2026 contains a complete laboratory test method, starting with the electrical apparatus and the electrode geometry, then moving to specimen preparation, test execution, failure recognition, and reporting. It includes an example electrical circuit, an example electrode mount, an example electrode assembly, and figures showing arc appearance before and after failure.

The document also includes a timing table for the staged current sequence used during the test and an informative annex on measurement-based approaches to failure recognition. Annex A discusses temperature, voltage, and current measurements as possible objective indicators, which can help laboratories develop or validate more consistent failure detection methods.

SLOVENSKI STANDARD
01-julij-2026
Suhi, trdni izolacijski materiali - Preskus odpornosti na visokonapetostne,
nizkotokovne obločne razelektritve
Dry, solid insulating materials - Resistance test to high-voltage, low-current arc
discharges
Trockene, feste Isolierstoffe - Prüfung der Lichtbogenbeständigkeit bei hoher Spannung
und niedrigem Strom
Matériaux isolants solides secs - Essai de résistance aux décharges à l'arc haute
tension, faible courant
Ta slovenski standard je istoveten z: prEN IEC 61621:2026
ICS:
17.220.99 Drugi standardi v zvezi z Other standards related to
elektriko in magnetizmom electricity and magnetism
29.035.01 Izolacijski materiali na Insulating materials in
splošno general
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

112/722/CDV
COMMITTEE DRAFT FOR VOTE (CDV)
PROJECT NUMBER:
IEC 61621 ED2
DATE OF CIRCULATION: CLOSING DATE FOR VOTING:
2026-05-29 2026-08-21
SUPERSEDES DOCUMENTS:
112/693/CD, 112/713/CC
IEC TC 112 : EVALUATION AND QUALIFICATION OF ELECTRICAL INSULATING MATERIALS AND SYSTEMS
SECRETARIAT: SECRETARY:
Germany Mr Bernd Komanschek
OF INTEREST TO THE FOLLOWING COMMITTEES: HORIZONTAL FUNCTION(S):

TC 15
ASPECTS CONCERNED:
Electricity transmission and distribution
SUBMITTED FOR CENELEC PARALLEL VOTING NOT SUBMITTED FOR CENELEC PARALLEL VOTING
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AC/22/2007 OR NEW GUIDANCE DOC).

TITLE:
Dry, solid insulating materials – Resistance test to high-voltage, low-current arc discharges

PROPOSED STABILITY DATE: 2030
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ii
IEC CDV 61621 © IEC 2026
CONTENTS
FOREWORD . 3
1 Scope . 5
2 Normative references . 5
3 Terms and definitions . 6
4 Apparatus . 6
4.1 Test circuit . 6
4.1.1 Transformer, T . 7
v
4.1.2 Variable autotransformer, T . 7
c
4.1.3 Voltmeter, V . 7
L
4.1.4 Milliammeter, A . 8
4.1.5 Current control resistors, R , R , R and R and switches S , S ,
10 20 30 40 2 3
S , S . 8
4 5
4.1.6 Suppressing resistor, R . 8
4.1.7 Air core inductors, Xs . 8
4.1.8 Breaker, B . 8
4.1.9 Timer, TT . 8
4.2 Electrodes and electrode assembly . 8
4.2.1 Electrode geometry . 8
4.2.2 Electrode assembly . 9
4.2.3 Cleaning and sharpening electrodes . 10
4.2.4 Specimen support . 10
4.3 Test chamber . 11
4.4 Calibration . 11
4.4.1 Open circuit operating voltage . 11
4.4.2 Adjustment of secondary current . 11
5 Specimens. 11
5.1 Specimen geometry . 11
5.2 Cleaning and conditioning . 11
6 Procedure and failure recognition . 11
6.1 Test procedure. 11
6.2 Failure and failure recognition . 12
7 Results . 14
8 Report . 14
Annex A (informative) Failure recognition by measurement . 15
Bibliography . 17

Figure 1 – Example for electrical circuit . 7
Figure 2 – Electrode mounted in a shank (example) . 9
Figure 3 – Electrode assembly (example) . 10
Figure 4 – Example of arc appearance on silicone elastomere . 13
Figure 5 – Example of arc appearance on resin material . 14
Figure A.1 – Schematic of characteristic temperature changes in the event of specimen
failure . 15
Figure A.2 – . 16
IEC CDV 61621 © IEC 2026
Table 1 – Sequence of 1 min steps . 12

IEC CDV 61621 © IEC 2026
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
Dry, solid insulating materials –
Resistance test to high-voltage, low-current arc discharges

FOREWORD
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However, implementers are cautioned that this may not represent the latest information, which
IEC CDV 61621 © IEC 2026
may be obtained from the patent database available at https://patents.iec.ch and
www.iso.org/patents . IEC shall not be held responsible for identifying any or all such patent
rights.
IEC 6XXXX has been prepared by subcommittee XX: [TITLE]:, of IEC technical committee XX:
[TITLE]. It is an International Standard.
In the case of a new edition replacing a previous edition, complete the following text. In the
case of a first edition, delete it, as it does not apply.
This second edition cancels and replaces the first edition published in XXXX, Amendment
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constitutes a technical revision.
This edition includes the following significant technical changes with respect to the previous
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a) [short description of the main changes]
b) .
The text of this International Standard is based on the following documents:
Draft Report on voting
Full information on the voting for its approval can be found in the report on voting indicated in
the above table.
The language used for the development of this International Standard is English [change
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This document was drafted in accordance with ISO/IEC Directives, Part 2, and developed in
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– reconfirmed,
– withdrawn, or
– revised.
IEC CDV 61621 © IEC 2026
1 Scope
This International Standard describes a test method which can provide preliminary
differentiation between similar insulating materials, with respect to their resistance to damage
when exposed to high-voltage, low-current arc discharges, occurring close to their surfaces.
The discharges cause localized thermal and chemical decomposition and erosion and
eventually a conductive path forms across the insulating material. The severity of the test
conditions is gradually increased: in the early stages a low-current arc discharge is repeatedly
interrupted, whereas in the later stages, the arc current is raised in successive steps.
Because of its convenience and because of the short time required for testing, the test method
is applicable for preliminary screening of materials, for detecting the effects of changes in
formulation and for quality control testing.
Previous experience with this test, showed acceptable reproducibility with thermoset materials.
Using thermoplastics, some testing laboratories report unacceptably large variation in test
results which lead to the recommendation not to use the test for thermoplastics.
NOTE Attempts are being made to reduce the variability of the results of tests on thermoplastics by controlling the
electrode pressure and depth of penetration into the material during the test. Without such electrode control, tests
on many thermoplastics may not be sufficiently meaningful to be performed.
This test method will not, in general, permit conclusions to be drawn concerning the relative arc
resistance rankings of materials which may be subjected to other types of arcs.
The ranking of materials may differ from what is found in wet tracking tests (e.g. IEC
60112:2025, IEC 60587:2022 and IEC 61302:1995) and from their performance in service,
where the intensity, recurrence frequency and time of exposure to arc discharges ar e very
different.Nevertheless, a certain correlation with the Inclined-Plane-Test according to IEC
60587:2022 was found within one material group (e.g. silicone elastomers). [1][2]
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 60112:2025, Method for the determination of the proof and the comparative tracking indices
of solid insulating materials
IEC 60212:2010, Standard conditions for use prior to and during the testing of solid electrical
insulating materials
IEC 60587:2022, Electrical insulating materials used under severe ambient conditions - Test
methods for evaluating resistance to tracking and erosion
IEC 61302:1995, Electrical insulating materials - Method to evaluate the resistance to tracking
and erosion - Rotating wheel dip test
EN 50191:2000, Erection and operation of electrical test equipment
EN IEC 60112:2020, Method for the determination of the proof and the comparative tracking
indices of solid insulating materials
IEC CDV 61621 © IEC 2026
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
failure
failure is considered to have occurred when a conducting path is formed in the material; failure
is also considered to have occurred if the arc causes a material to burn and the burning
continues when the arc is interrupted
3.2
arc resistance
total elapsed time in seconds from the start of test until specimen failure
3.3
tracking
the progressive degradation of the surface of a solid insulating material by local discharges to
form conducting or partially conducting paths

[SOURCE: EV ref 442-01-41 [IEC 60050-442-01-4]]
4 Apparatus
4.1 Test circuit
The principal components of the electrical circuit for the apparatus are shown in Figure 1.
IEC CDV 61621 © IEC 2026
Figure 1 – Example for electrical circuit
NOTE 1 In the secondary circuit wiring the stray capacitance should be less than 40 pF. Large stray capacitance
may disturb the arc shape and influence the test results.
NOTE 2 Due to electrical hazards, the appliance should be equipped with state-of-the-art safety technology to
prevent contact with live parts (e.g. EN 50191:2000)
4.1.1 Transformer, T
v
A transformer with a rated secondary potential (on open circuit) of 15 kV, and a rated secondary
current (on short circuit) of 60 mA, line frequency (48 Hz to 62 Hz).
4.1.2 Variable autotransformer, T
c
Rated 1 kVA and suitable for the line voltage.
NOTE A constant primary voltage supply ±2 % is recommended.
4.1.3 Voltmeter, V
L
AC voltmeter with an accuracy of ±0,5 %, capable of reading line voltage +10−20%.
Voltage on the secondary side shall be regularly controlled by a reference measurement.
Alternatively, measurement of th
...