NEMA Insulation Classes

Electrical insulation systems are rated by standard NEMA (National Electrical Manufacturers Association) classifications according to maximum allowable operating temperature.

Key Information:

Reference ambient temperature: 40°C
Operating temperature = Reference temperature + Allowable temperature rise + Hot spot allowance (typically 10°C)
Each 10°C rise above rating may reduce motor lifetime by one half
Class B is most common for U.S. 60-cycle motors
Class F is most common for international and 50-cycle motors

Temperature Class	Max Temp (°C)	Max Temp (°F)	Temp Rise @ 1.0 SF (°C)	Temp Rise @ 1.15 SF (°C)
A	105	221	60	70
B	130	266	80	90
F	155	311	105	115
H	180	356	125	-

NEMA Insulation Classes

NEMA Insulation Classes

Key Information:

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