Insulation testing is by far the most important testing that you may perform on electric motor and motor circuits. There are several different tests and variations of those tests. One of the best instruments available for fully evaluating insulation is High Potential testing.

High Potential testing, commonly referred to as Hi-Pot, is the most effective insulation test, to ensure that an insulation system will withstand operating potential. It is also called a Dielectric Withstanding Voltage test, DWV. It is essentially an insulation system “Stress Test.” It tests insulation to a maximum value that is determined by the line voltage. The instruments can be Alternating Current, AC or Direct Current, DC. DC testing is the most common for motor testing. AC is more frequently used for cabling.

Some High Potential testers can be destructive.  Many new units have sensitive triggering circuitry, that will interrupt testing with any ramp-up in current. This prevents destroying the insulation.

The table below provides the recommended test voltages for DC Hi-Pot Testing. AC Hi-Pot values are 2 x line voltage plus 1000V.

Another valuable test that is available is Step Voltage testing. Step Voltage testing can be classified as a type of timed resistance test.  Instead of observing resistance to ground values, it provides visual indication of how return current reacts to increased stepping of voltage.

Voltage is stepped in user-defined increments and duration. As each step-in voltage occurs, if the resistance remains the same then a proportional increase in current should be observed. If a symmetrical response is not observed, an insulation anomaly may exist or may be developing.

For more information on insulation testing or motor testing consider attending one of the Snell Groups Electric Motor Testing and Certification training courses.