When the motor is running, copper loss, iron loss and mechanical loss are all manifested in the form of heat. Part of this heat is absorbed by the motor and part is transmitted to the air. The heat absorbed by the motor causes the temperature inside the motor to gradually rise, and it stops rising when it reaches the equilibrium point.

The temperature rise of the motor refers to the difference between the temperature of each part of the motor and the ambient temperature.

Insulating materials are divided into 7 grades, namely Y, A, E, B, F, H and C, and their maximum allowable temperatures are 90℃, 105℃, 120℃, 130℃, 155℃, 180℃ and above 180℃. The commonly used insulating material for motors is grade F.

The temperature rise grade is divided into 5 grades, namely A, E, B, F and H, and the temperature rise limits of the resistance method are 60℃, 75℃, 80℃, 100℃ and 125℃ respectively.