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Insulation Resistance

Testing of all electrical equipment before any high voltage testing is commenced. The test voltage will depend on the equipment to be tested. If a polarisation index is required the duration of the test will be over in a ten minute period. The polarisation index is the ratio of the DC resistances after one-minute and ten-minute periods have passed.
Insulation Temperature Classification for MachinesTemperature IndexSome Insulation Combinations
Class O (Obsolete)90°COleo, Resinous, Cotton, Wood
Class A105°CCotton, Vinyl Acetate
Class E120°CPhenolics, Alkyds, Leatheroid
Class B130°CShellac/Bitumen, Silk, Mica, Polyesters
Class F155°CEpoxy/Polyesters, Silicone, Mica, Glass
Class H180°CEpoxy/ Polymides/ Silicone/ Mica/ Glass
Class C220°CGlass/ Silicone/ Mica/ Nomex/ Silicates
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