3 phase electric motor fails to start. It's magnetic contactor has power on all 3 lines. When contractor engaged manually el. motor attempts to turn and sounds like transformer but seems to lack of torq. Motor shaft can be easily turned by hand when power disconnected and bearings seem to operate good .

asked 05 Jun '17, 22:44

June 5, 2017, 10:44 p.m.
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Most likely 1 phase of motor is not energized or burnt.

1) Check magnetic contactor for loosen or broken wires. Check it for proper functioning i.e. closing all 3 lines when energized. Check contactor control coil.

2) Conduct resistance and insulation check of motor winding.

3) If motor itself and magnetic contactor has proven to be operational trace down all 3 phase lines from magnetic contactor down to electric motor. Inspect junction boxes if any for loosen or broken wires. Often copper wiring gets broken at terminal connection because of vibration.

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answered 05 Jun '17, 22:47

June 5, 2017, 10:47 p.m.
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