Your plant has a high rate of motor failure. You find voltage imbalances on several feeders and branch circuits. Meeting with the plant engineer, you identify the imbalances as the cause of the motor failures. He looks over the measurements you took on one feeder picked at random. The average voltage is 479V. Two of the phases are pretty close to that, but C Phase is 467V. That makes for a voltage imbalance of about 2.5%. Because the deviation is toward lower voltage, the plant engineer instructs you to look for insulation leakage or something similar on that phase.
Is this approach correct, or should you look at something else first?
This isn’t the best place to start, because you will need to schedule a downtime window to perform these tests. It’s amazing how many facilities will do this kind of testing ad hoc when there’s a problem but not do it as part of a cable maintenance program to prevent problems. Use the current crisis to establish such a program.
Lighting is usually the single largest single phase load in an industrial or commercial facility, so examine the power distribution that supplies the lighting. You may find that some rewiring at the lighting supply panels solves the imbalance problem.
While you’re waiting for that area shutdown, perform relevant tests on conductors (.e.g., insulation resistance) and connections (e.g., AC resistance) on the load side of motor disconnects.
