To confidently report the electrical condition of a motor, there are six areas of interest known as Fault Zones that must be looked at during the troubleshooting effort.
These Fault Zones are Power Quality, Power Circuit, Stator, Insulation, Rotor, and Air Gap.
Quality of the voltage and current
Turn-to-turn insulation and internal coil connections
Quality of the air gap between the rotor and the stator
Winding to ground insulation
Health of the rotor cage and laminations
Circuit supplying power to the motor
This insightful white paper by PdMA's David L. McKinnon will provide a brief introduction to a Six Fault Zone approach for predictive maintenance on motors.