This Standard is applicable to the cases where the thermal factor is the dominant ageing factor.

NOTE 1 A thermal class of a certain electrical insulation system cannot be assigned to the electrical insulating material which is used therein solely because of its use in the electrical insulation system.

NOTE 2 The International Standard corresponding to this Standard and the symbol of degree of correspondence are as follows.

IEC 60085 : 2007 Electrical insulation – Thermal evaluation and designation (MOD)

The symbols which denote the degree of correspondence in the contents between the relevant International Standard and JIS are IDT (identical), MOD (modified), and NEQ (not equivalent) according to ISO/IEC Guide 21-1.

The range is sufficiently wide to enable suitable conditions to be selected so that either of the primary objects of conditioning can be achieved.

These objects are:

a) To obtain greater reproducibility of test results by:

1) partly counteracting the variations of the properties of the material due to the past history of the test specimens, and

2) ensuring uniformity of conditions during the testing.

b) To determine the influence of exposure to certain temperatures and humidities, or immersions in liquids, on the properties of a material by subjecting specimens to specified conditions before or during the test or both.

NOTE : The International Standard corresponding to this Standard and the symbol of degree of correspondence are as follows.

IEC 60212 : 1971 Standard conditions for use prior to and during the testing of solid electrical insulating materials (MOD)

The symbols which denote the degree of correspondence in the contents between JIS and the corresponding International Standard are IDT (identical), MOD (modified) and NEQ (not equivalent) according to ISO/ IEC Guide 21.

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 of 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 1 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 material may differ from that found in wet tracking tests (for example, JIS C 2134, JIS C 2136 and JIS C 2137) and from their performance in service, where the intensity, recurrence frequency and time of exposure to arc discharges are very different.

NOTE 2 The International Standard corresponding to this Standard and the symbol of degree of correspondence are as follows.

IEC 61621 : 1997 Dry, solid insulating material~Resistance test to high-voltage) low-current arc discharges (MOD)

In addition, symbols which denote the degree of correspondence in the contents between the relevant International Standard and JIS are IDT (identical), MOD (modified), and NEQ (not equivalent) according to ISO/IEC Guide 21-1.

Because the test specimens are simply and easily prepared, these methods are particularly useful for rapidly determining values which will give a general indication of quality when great accuracy is not required.

NOTE: The International Standard corresponding to this Standard and the symbol of degree of correspondence are as follows.

IEC 60167: 1964 Methods of test for the determination of the insulation resistance of solid insulating materials (MOD)

The symbols which denote the degree of correspondence in the contents between JIS and the corresponding International Standard are IDT (identical), MOD (modified) and NEQ (not equivalent) according to ISO/IEC Guide 21.