When taking voltage or resistance measurements, it is important to take into consideration the connection point of your test equipment. Voltage readings will indicate power circuit anomalies upstream of where the voltage test leads are connected. Any power circuit anomaly occurring downstream of the voltage test leads toward the motor will not be seen. The opposite is true for the resistance measurements. Power circuit anomalies occurring downstream of the resistance test lead connections will be identified by a resistance imbalance. However, all power circuit anomalies that exist upstream of the resistance test leads towards the power supply or transformer will not be seen. Knowing this warrants both a voltage and a resistance measurement when trying to troubleshoot or determine the health of your power circuit.
For more information on testing and troubleshooting the power circuit, go to:
http://www.pdma.com/webinars/Power_Circuit_Fault_Zone/powercircuit.html