An on-line testing regime for electric motors that is extremely useful in assessing rotor condition in induction motors as tested under normal operating conditions. This is accomplished through spectral analysis at the first and fifth harmonics of line frequency. This testing also yields current imbalance expressed as a percentage under load, and impedance imbalance as a trendable measure of stator condition. Power quality assessment, including measures of total harmonic distortion and crest factor, is performed in those cases where voltage and current signals (PTs and CTs on any testing over 600 volts) are both available. This type of testing also offers the advantage of being non-intrusive to production operations.