Several motors supplied by the same MCC blow their overloads regularly. The loss of production is making this problem a priority.
The MCC consists of multiple sections. The plant manager said if the problem for one motor originates there it would have to exist in each section so don’t waste time troubleshooting at the MCC. The production superintendent mentioned that the MCC is a long way from the motors and so it’s probably voltage drop. But the actual voltages are close to nominal.
Where should you look?
The plant manager may have put his thumb on the problem without realizing it. The MCC sections must be connected with an equipment grounding conductor (EGC) [430.96]. If they aren’t, there may be differences of potential. This can cause all sorts of malfunctions. So visually inspect the EGC and check the integrity of EGC connections with an AC resistance tester. Finally, make sure the EGC is big enough to do the job (it should be sized per Table 250.122).
The reason to check the EGC first is it’s a “common link” sort of issue. Another issue like that is any sort of power quality problem. You need a power analyzer to identify those.
