Abstract: A motor heating control for retrofit applications has an enclosure with power supply terminals and motor heating output terminals. Inside an upper compartment is a first two-pole isolating switch which couples power from the supply terminals through a step-down transformer and a rectifier to one side of a motor heating contactor in the lower compartment. The other side of the motor heater contactor is coupled through fuses and a second two-pole isolating switch in the lower compartment to the motor heating output terminals. An operating handle outside the lower compartment is mechanically interlocked to both isolating switches so that the door of the enclosure cannot be opened without disconnecting both the motor heating power source and the electrical motor from the motor heating control. The motor heating contactor is also electromechanically interlocked to the door interlock mechanism so that the operating handle cannot be moved to its open position until the motor heating contacts are opened.