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Electric Power & Utilities/star delta motor troubleshooting


I have a 30 hp ac motor. we sent it out for repair. when it came back it was a different motor. same voltage and amp rating. I wired it in using the original diagrams. now when in starting it runs fine at 23 amps on 3 phases 480 AC. when it switches to high it stops. no current on any of 6 power wires. 480vac on all 6 wires. Our original control wiring is still as it was when the motor was sent out for rewind. If this motor is phased differently than the original would this cause this problem? We also sent it back to see if it was rewound properly. checked by repair company. all good. what can i do now to troubleshoot this problem?

Not much I can help you with here. It would appear there is something wired incorrectly in the run starters.

For wye start, lines should be 1,2,3, 4-5-6 joined.

For delta run, lines will be 1-6, 2-4, 3-5.

Phasing of the motor would need to be done at your location, for correct rotation. Checking voltage should be done with lines disconnected from the motor, as you could get a feedback reading through the windings.

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Charles C. Jones


Let Me help you with your problems with single phase and three phase electric motors. I can tell you how to troubleshoot your motor problems. From simple testing of capacitors, how to test your windings, replacing bearings, and general maintenance. Before we go any further, remember these words of advice: Disconnect the power before you do anything! Please limit your questions to electric motors and there immediate components. I review each question, and if I can answer or help, then I will. If you receive a rejection, it means it is out of my expertise, and just do not have the answer. I'll be waiting for your question.


I have 40 years experience in the repair of electric motors and related equipment. I am a master machinist in the field of motor repair. I was employed with my company for 35 years, but retired in May of 2013. The downside to that is I lost access to a lot of technical data. I will still try to give you the most accurate advice that I can.

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