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Motor will not start Power not available at motor terminals Check power at starter. Correct any bad  connections between the control     apparatus and the motor.
    Check starter contacts and control circuit. Rest overloads.
    If power is not on all leads at starter make sure overload and short-circuit devices are in proper condition.
  Wrong connections Check motor and control  Connections against wiring diagrams.
  Low Voltage Check nameplate voltage against power supply. Check voltage at motor terminals.
  Open circuit in motor winding Check stator windings for open circuit.
  Motor or fan drive stuck Disconnect motor from load and check motor and Gear reducer for cause of problem.
  Rotor defective Look for broken bars or rings.
Unusual motor noise  Motor running single phase Stop motor and attempt to start it. Motor will not start if single phased. Check wiring, controls and motor.

Motor leads connected incorrectly

Check motor connections against wiring diagram on motor.
  Ball bearings Check lubrication, replace bad bearings.
  Electrical unbalance Check voltages and currents of all three lines. Correct if required.

Air gap uniform

Check and correct bracket fits or bearing.

Rotor unbalance


  Cooling fan hitting guard Reinstall or replace fan.
Motor runs hot

Wrong voltage or unbalanced voltage

Check voltage and current of all three lines against nameplate value.


Check fan blade pitch. Check for drag in fan drive train as from damaged bearings.

Wrong motor rpm

Check nameplate against power supply. Check rpm of motor and gear ratio.
  Bearings overgreased Remove grease reliefs. Run motor up to speed to purge excessive grease.
  Rotor rubs stator bore

If not poor machining, replace worn bearings.

  Wrong lubricant in bearings Change to proper lubricant. See motor manufacturer’s instructions.

One phase open

Stop motor and attempt to start it. Motor will not start if single phased. Check wiring, controls and motor.

Poor ventilation

Clean motor and check ventilation openings. Allow ample ventilation around motor.

Winding fault

Check with ohmmeter.


Bent motor shaft

Straighten or replace shaft.


Insufficient grease

Remove plugs and replace bearings.
  Deterioration of or foreign material on grease Flush bearings and Re lubricate.

Bearings damaged

Replace bearings.


Incorrect fan blade pitch

See fan service manual for blade pitching instructions.

Gear reducer bearings

If new, see if noise disappears after one week of operation. Drain, flush and refill Gear reducer. See Gear reducer service manual, if noisy, replace.

  Gears Correct tooth engagement. Replace badly worn gears and imperfect tooth spacing or form.