Question

Illustrate the difference between different types of insulation and enumerate the various classes of electrical equipment. Give examples for each class.

Answer 1

Class A

Class A insulation consists of materials such as cotton, silk and paper when suitably impregnated or coated or when immersed in a dielectric liquid such as oil. Other materials or combinations of materials may be included in this class if by experience or tests they can be shown to be capable of operation at the Class A temperature.

Maximum allowed temperature: (IEC60034-1 & NEMA MG1-12.43): 105C, 221F.

Class B

Class B insulation consists of materials or combinations of materials such as mica, glass fibre, asbestos, etc., with suitable bonding, impregnating or coating substances (beware a few older applications used asbestos). Other materials or combination of materials, not necessarily inorganic, may be included in this class, if by experience or tests they can be shown to be capable of operation at the class B temperature.

Maximum allowed temperature: (IEC60034-1 & NEMA MG1-12.43): 130C, 266F.

Class C

Class C insulation consists of materials or combinations of materials such as mica, porcelain, glass, quartz with or without an inorganic binder (beware a few older applications used asbestos). Other materials or combinations of materials may be included in this class, if by experience or tests they can be shown to be capable of operation at temperatures above the Class H limit. Specific materials or combinations of materials in this class will have a temperature limit, which is dependent upon their physical, chemical and electrical properties.

Maximum allowed temperature: (IEC60034-1 only): >180C, 356F.

Class E

Class E insulation consists of materials or combinations of materials, which by experience or tests can be shown to be capable of operation at Class E temperature (materials possessing a degree of thermal stability allowing them to be operated at a temperature 15 Centigrade degrees higher than Class A materials).

Maximum allowed temperature: (IEC60034-1 only): 120C, 248F.

Class F

Class F insulation consists of materials or combinations of materials such as mica, glass fibre, asbestos, etc., with suitable bonding, impregnating or coating substances, as well as other materials or combinations of materials, not necessarily inorganic, which by experience or tests can be shown to be capable of operation at the Class F temperature (materials possessing a degree of thermal stability allowing them to be operated at a temperature 25 Centigrade degrees higher than Class B materials).

Maximum allowed temperature: (IEC60034-1 & NEMA MG1-12.43): 155C, 311F.

Class H

Class H insulation consists of materials such as silicone elastomer and combinations of materials such as mica, glass fibre, asbestos etc., with suitable bonding, impregnating or coating substances such as appropriate silicone resins. Other materials or combinations of materials may be included in this class if by experience or tests they can be shown to be capable of operation at the Class H temperature.

Maximum allowed temperature: (IEC60034-1 & NEMA MG1-12.43): 180C, 356F.