On a 3 phase motor a megger test between any connection point and the chassis will give the reading of the worst set of windings, as they’re all connected together. If its above the minimum go ahead and use the motor. If not, disconnect all the coils in the connector box and determine which one is down. Also, ensure that the megger is on the correct voltage setting for the motor. Its no use testing a 3000 volt motor using a 500 volt megger.
Motors also require a vibration analysis test prior to being sent to a system to determine bearing faults, rotor/shaft imbalances and end plate misalignment. The rotor should turn freely by hand as well. A test run should have been conducted to determine amperage drawn is not excessive and overheating of any components is not present.
Transformers require megger testing at the right megger settings for primary and secondary to chassis and between primary and secondary. A load test should be applied before sending it to the system to check for current draw, overheating and excessive humming which could mean loose windings which will cause it to vibrate to pieces eventually.
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