Insulation class overview
The electrical insulating materials can be divided into the following recognized classes:
Insulation class A
Class A insulation consists of materials such as cotton, silk and paper when appropriately impregnated or coated or immersed in a dielectric liquid such as oil. Other materials or combinations of materials may be included in this class if experience or testing shows that they can be operated at the Class A temperature.
Maximum allowable temperature: (IEC60034-1 & NEMA MG1-12.43): 105C, 221F.
Insulation class E
Class E insulation consists of materials or combinations of materials which experience or tests have shown to be capable of operating at a class E temperature (materials exhibiting a degree of thermal stability which allows them to be operated at a temperature closer to 15 degrees higher than class A materials).
Maximum allowable temperature: (IEC60034-1 only): 120C, 248F.
Class B insulation consists of materials or combinations of materials such as mica, fiberglass, asbestos, etc. with appropriate bonding, impregnating or coating materials (note some older applications used asbestos). Other materials or combinations of materials, not necessarily inorganic, may be included in this class if experience or testing can show that they can be operated at the class B temperature.
Maximum allowable temperature: (IEC60034-1 & NEMA MG1-12.43): 130C, 266F.
Class F insulation consists of materials or material combinations such as mica, glass fiber, asbestos, etc. with suitable binders, impregnating or coating materials and other materials or material combinations which are not necessarily inorganic and which experience or tests have proven to operate at class F temperatures (materials that exhibit a degree of thermal stability that allows them to be operated at a temperature 25 degrees higher than Class B materials).
Maximum allowable temperature: (IEC60034-1 & NEMA MG1-12.43): 155°C, 311°F.
Class H insulation consists of materials such as silicone elastomer and material combinations such as mica, fiberglass, etc. with suitable adhesives, impregnating or coating materials such as suitable silicone resins. Other materials or combinations of materials may be included in this class if it can be demonstrated by experience or testing that they can be operated at the H-class temperature.
Maximum allowable temperature: (IEC60034-1 & NEMA MG1-12.43): 180C, 356F.
Insulation class C
Class C insulation consists of materials or combinations of materials such as mica, porcelain, glass, quartz with or without an inorganic binder (note, some older applications used asbestos, which is now banned). Other materials or combinations of materials may be included in this class if it can be demonstrated by experience or testing that they can be operated at temperatures above the Class H limit. Certain materials or combinations of materials in this class have a temperature limit that depends on their physical, chemical and electrical properties.
Maximum allowable temperature: (IEC60034-1 only): >180C, 356F.
Insulation class, thermal class, ISO class
