The temperature grade of FR-4 epoxy insulation sheet is generally divided into A grade, E grade, B grade, F grade, H grade, C grade, N grade, R grade.Generally, the insulation grades of motors are mostly E-class and B-class insulation. The thermal classification of the machine refers to the heat resistance grade of the insulating material used, which is divided into A, E, B, F, H, C, N, R grades.The allowable temperature rise refers to the limit at which the temperature of the motor increases compared to the ambient temperature.

FR-4 epoxy sheet temperature grade: insulation temperature grade A grade E grade B grade F grade H grade C grade N grade R grade;
Maximum allowable temperature (℃) 105 120 130 155 180 200 220 240;
Winding temperature rise limit (K) 60 75 80 105 125 135 150 170;
Performance reference temperature (℃) 80 95 100 120 145 155 170 190.

FR-4 epoxy sheet is processed in electrical equipment such as generators, and the insulating material is the weakest link. Insulating materials are particularly susceptible to accelerated aging and damage from high temperatures.Different insulating materials have different heat resistance properties, Electrical equipment with different insulating materials has different ability to withstand high temperature Therefore, general electrical equipment stipulates the maximum temperature for its operation.