It can occur in motors powered by variable-frequency drives, as often used in heating, ventilation, air conditioning and refrigeration systems.
External sources of shaft voltage include other coupled machines, and electrostatic charging due to rubber belts rubbing on drive pulleys.
[4] The presence of high frequency ground currents can cause sparks, arcing and electrical shocks and can damage bearings.
An electrostatic shielded induction motor (ESIM) is one approach to the shaft-voltage problem, as the insulation reduces voltage levels below the dielectric breakdown.
High frequency grounding can be significantly improved by installing shielded cable with an extremely low impedance path between the VFD and the motor.