Just because the three phase current data being returned by the installed relay is balanced, doesn’t clear the power circuit of possible anomalies. Remember from previous tips that the opposition to AC current is influenced by impedance, which is the combination of reactance and resistance. Not just resistance. A high resistance connection may be a small part of the overall impedance, but can still create a significant amount of localized heating. This localized heating can lead to big problems if not corrected. Waiting until the problem is severe enough that the resistance element dominates the total impedance and changes the AC current may be too late and risk a single-phase fault. Using the MCE® technology for precision resistance measurements will give an early indication of power circuit anomalies so they can be repaired before causing a high current imbalance.
Source PdMA
The five whys refers to the practice of asking five times why a motor failure occurred in order to get closer to the root cause of the problem. Failure to determine the root cause can result in treating the symptoms of the problem instead of its cause, in which case you will continue to have the same problems over and over again.