Temperature Classes Of Electrical Insulation

Thermal classifications for electrical insulation materials have been in existence since the 1930’s and became formalized by the International Electrotechnical Commission (IEC) in 1957. The system is effectively adopted world wide by various national and international bodies such as the National Electrical Manufacturers Association (NEMA) in the USA and the Japanese Industrial Standards (JIS) in Japan.

The classifications are as follows:

Insulation Class Code	Maximum Temperature °C
Y	90
A	105
E	120
B	130
F	155
H	180
C	Over 180

Here are some examples of materials in each category:

• Class Y includes natural materials such as cotton, paper and silk and some synthetics such as acetates, polyamide and PVC.
• Class A includes varnished cloth and again some acetates and polyamides.
• Class E includes phenolic products such as SRBP (synthetic resin bonded paper) and SRBF (synthetic resin bonded fabric)
• Class B includes polyester films and tapes, FR4 and epoxy glass sheets
• Class F includes acrylic coated glass products, NMN (Nomex Mylar Nomex), DMD (Dacron Mylar Dacron), Radox cables and GP03 glass sheets.
• Class H includes coated glass fibre products, Nomex © and tapes with a silicone adhesive.
• Class C includes PTFE (Polytetrafluoroethylene) Silicones, glass fibre, quartz and mica.