What does class F insulation mean?

The insulation class defines the highest temperature that winding materials such as varnish, slot liners and phase separators can withstand continuously. Class F sets this limit at 155 °C; HEM motors have class F insulation as standard.

This does not mean the motor runs at 155 °C. According to the catalogue references, winding temperature is targeted at about 110 °C maximum and temperature rise below 75 K. The margin between the insulation limit and the actual operating temperature protects the winding during short overloads, high ambient temperatures and voltage fluctuations, and slows the ageing of the insulation.

Exact values are given in the model test report. For an application that will run continuously at high temperature, insulation class and power rating should be assessed together.