Engineering · Electrical — Motors
A three-phase induction motor that hums but will not start, or runs at reduced torque and overheats, may be suffering from:
- ASingle-phasing (loss of one phase)✓ Correct
- BToo high a power factor
- CExcess lube oil
- DReverse osmosis
Explanation
If one phase is lost (blown fuse, open contact), a running motor continues on two phases but draws high current and overheats; a stopped motor only hums and won't start. Overload/single-phase protection is fitted to trip the motor.
Authority: Modern Marine Engineer's Manual; AC motors
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