An analysis measuring the phase impedance in the circuitry between the motor and the motor control center. The readings are compared to standards in order to detect imbalances in resistance or impedance. These imbalances may be caused by corrosion, mismatched cables, or current leakage in the circuit. Motor defects such as broken bars, shorts, and eccentricity can also be detected. 

Tip excerpted from: The Professional's Guide to Maintenance and Reliability Terminology by Ramesh Gulati, Jerry Kahn and Robert Baldwin