scope:

This Standard describes a test method which can provide preliminary differentiation between similar insulating materials (hereafter referred to as "materials"), with respect to their resistance to damage when exposed to high-voltage, low-current arc discharges, occurring close to their surface.

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.