Shaft voltage

Shaft voltage occurs in electric motors and generators due to leakage, induction, or capacitive coupling with the windings of the motor. It can occur in motors powered by variable-frequency drives, as often used in heating, ventilation, air conditioning and refrigeration systems. DC machines may have leakage current from the armature windings that energizes the shaft. Currents due to shaft voltage causes deterioration of motor bearings, but can be prevented with a grounding brush on the shaft, grounding of the motor frame, insulation of the bearing supports, or shielding.