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 some of those tests. One of the tests 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 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 training courses.