While the PI Test has been considered the primary test when evaluating the condition of a motor’s insulation, its process has become outdated compared with newer testing methods that provide a more comprehensive diagnostic evaluation of a motor’s overall health.

This article provides a practical understanding of a motor’s insulation system, a basic understanding of polarization index testing, and how modern motor testing methods provide more comprehensive results in less time.

POLARIZATION INDEX (PI)

The polarization index (PI) test is a standard electric motor testing method developed in the 1800s that attempts to determine the health of a motor’s winding insulation.

While the PI test provides information on ground wall insulation (GWI) systems typically installed prior to the 1970s, it fails to provide an accurate condition of the winding insulation in modern motors.