Electrical Insulation Classes | Classification of Insulating Materials

Life of electrical insulating materials gets adversely affected with rise in temperature.

Average insulation life gets halved for every 10° C increase in temperature. Therefore, the classification of insulating materials is done on the basis of maximum temperature that insulating material can withstand.

The insulating materials are grouped in the following categories.

Insulation Class	Max Permissible temperature (° C)
Y	90
A	105
E	120
B	130
F	155
H	180
C	Above 180

Class-Y Insulation

The insulating materials of class-Y insulation can withstand temperature up to 90° C.

Examples of Class-Y insulating materials is made of cotton, silk, paper, wood, press wood.

Class-A Insulation

The temperature withstand capacity of class-Y insulation can be improved by impregnation of class-Y insulation with varnish or insulating oil. The class-A insulating material can withstand temperature up to 105° C. Class-A insulation is used in oil filled transformer.Examples of class-A insulating materials are impregnated cotton, paper, oil, enamels, laminated wood etc.

Class-E Insulation

The maximum temperature capacity of class-E insulating materials is 120° C.

Class-B Insulation

The maximum temperature withstand capacity of class-B insulating material is 130° C.Examples of class-B insulating materials are wire enamel based on polyvinyl formal, polyurethane or epoxy resin, phenol-formaldehyde moldings of cotton, paper etc, cellulose triacetate film etc.

Class-F Insulation

The maximum temperature withstand capacity of class-F insulation is 155° C. Examples of class-F insulating materials are alkyd, epoxy polyester, silicon alkyd and siliconphenoilc resin, impregnated glass fiber cloth, built up mica with alkyd, epoxy cross linked polyester and polyurethane resins with superior thermal stability silicone alkyd resins.

Class-H insulation

The temperature withstand capacity of class-H insulating materials is 180° C. Examples of class H insulating material are silicon varnished impregnated glass fiber cloth, mica, silicon. Resin bonded up mica.

Class-C Insulation

Class-C insulating materials can withstand temperature above 180° C.Examples of class-C insulating materials are mica, porcelain glass quartz and asbestos, built-up mica treated Glass fiber cloth.