If these readings vary by a few volts, it may be possible to equalize them by rolling the connections, taking care not to reverse rotation. In a three-phase hookup, all legs should have substantially equal voltage readings, with no dropped phase. When the circuit electrical load is close to the circuit capacity, the voltage drop should not exceed 3% for optimum motor efficiency. When there is no electrical load, the same voltage should appear at both ends of the branch circuit conductors. What you are looking for is essentially the same voltage level as measured at the entrance panel main breaker. Take readings at accessible points including disconnect(s), the motor controller, any fuses or junction boxes, and so on, back to the over-current device output at the entrance panel. If there is no voltage or reduced voltage, work back upstream. If the motor is completely unresponsive, no ac humming or false starts, take a reading at the motor terminals. This tester is capable of providing diagnostic information for all sorts of motors. Preliminary (often definitive) tests generally take place using the ubiquitous multimeter. A hand-held multimeterĪ number of diagnostic tools – a clamp-on ammeter, temperature sensor, Megger, or oscilloscope – may help illuminate the problem. If the motor itself has developed a fault, the fault may be a burnt wire or connection, a winding failure including insulation deterioration, or a deteriorating bearing. Another possibility is that the driven load is jammed, binding or mismatched. Sometimes the trouble lies within the power supply, including branch circuit conductors or motor controller. When an electric motor fails to start, runs intermittently, runs hot, or continually trips its overcurrent device, there my be a variety of causes.
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