What motor insulation class is required in combination with a fan speed controller or VFD?
The insulation of the motor windings prevents short circuits in the windings or connection of the winding to the protective earth. The class of insulation of a motor winding defines the strength of insulation required with respect to maximum temperature rise of the motor. Different motor types have different temperature rise characteristics in function of the duty cycle and the size of the motor enclosure.
Usually class F insulation or class H insulation is suitable for VFD use.