The inspection and maintenance of ac motors is very simple. The bearings may or may not need frequent lubrication. If they are the sealed type, lubricated at the factory, they require no further attention. Be sure the coils are kept dry and free from oil or other abuse.

The temperature of a motor is usually its only limiting operating factor. A good rule of thumb is that a temperature too hot for the hand is too high for safety.

Next to the temperature, the sound of a motor or generator is the best trouble indicator. When operating properly, it should hum evenly. If it is overloaded it will "grunt." A three phase motor with one lead disconnected will refuse to turn and will "growl." A knocking sound generally indicates a loose armature coil, a shaft out of alignment, or armature dragging because of worn bearings.

The inspection and maintenance of all ac motors should be performed in accordance with the applicable manufacturer's instructions.

Troubleshooting

The following troubleshooting procedures are not applicable to a particular ac motor, but are included as examples of the general troubleshooting procedures provided by various manufacturers of ac motors.

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TROUBLE: Motor speed slow.

POSSIBLE CAUSE: No lubrication. Applied voltage low. Motor wiring defective.
CORRECTION: Lubricate as necessary. Check motor source voltage. Perform voltage continuity test of motor wiring.

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TROUBLE: Motor speed fast.

POSSIBLE CAUSE: Excessive supply voltage. Motor field windings shorted.
CORRECTION: Check and adjust level of motor supply voltage. Repair shorted windings or replace or overhaul motor.

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TROUBLE: Motor will not operate. No voltage applied to motor.

POSSIBLE CAUSE: Loose or broken wiring inside motor.
CORRECTION: Perform continuity test of motor circuit.

POSSIBLE CAUSE: Defective motor switch.
CORRECTION: Check switch and switch wiring using a continuity tester.

POSSIBLE CAUSE: Armature or field winding open circuited.
CORRECTION: Repair open winding or replace motor.

POSSIBLE CAUSE: Brushes worn excessively.
CORRECTION: Replace brushes.

POSSIBLE CAUSE: Brush springs broken or too weak.
CORRECTION: Replace brush springs.

POSSIBLE CAUSE: Brushes sticking in brush holders.
CORRECTION: Replace or clean and adjust brushes.

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TROUBLE: Motor vibrates.

POSSIBLE CAUSE: Loose or broken motor mountings.
CORRECTION: Repair or replace motor mountings.

POSSIBLE CAUSE: Motor shaft bent.
CORRECTION: Replace shaft or overhaul or replace motor.

POSSIBLE CAUSE: Motor bearings worn excessively.
CORRECTION: Replace bearings or overhaul motor.

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TROUBLE: Motor arcing excessively at brushes.

POSSIBLE CAUSE: Brushes worn excessively.
CORRECTION: Replace brushes.

POSSIBLE CAUSE: Brush springs weak.
CORRECTION: Replace brush springs.

POSSIBLE CAUSE: Brushes sticking in holders.
CORRECTION: Replace or clean brushes.

POSSIBLE CAUSE: Brushes incorrectly located.
CORRECTION: Position brushes properly.

POSSIBLE CAUSE: Commutator dirty or excessively worn or pitted.
CORRECTION: Clean or repair commutator as necessary.

POSSIBLE CAUSE: Open circuited armature coil.
CORRECTION: Repair open circuit or overhaul or replace motor.

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TROUBLE: Motor runs but overheats.

POSSIBLE CAUSE: Motor bearings improperly lubricated.
CORRECTION: Lubricate bearings.

POSSIBLE CAUSE: Excessive applied voltage.
CORRECTION: Check voltage and adjust to proper level.

POSSIBLE CAUSE: Field windings short circuited.
CORRECTION: Repair short circuit or overhaul or replace.

POSSIBLE CAUSE: Excessive brush arcing.
CORRECTION: Replace and adjust brushes.

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TROUBLE: Motor will not operate but draws high current.

POSSIBLE CAUSE: Shorted circuit to motor.
CORRECTION: Locate and repair short circuit.

POSSIBLE CAUSE: Open field winding in shunt motor.
CORRECTION: Repair or overhaul or replace motor.

POSSIBLE CAUSE: Motor internal circuit shorted.
CORRECTION: Repair short circuit or overhaul or replace motor.

POSSIBLE CAUSE: Mechanical stoppage.
CORRECTION: Check for seized motor bearings or binding of mechanism driven by motor. Repair or replace seized components.

POSSIBLE CAUSE: Excessive load on motor.
CORRECTION: Reduce load or install motor capable of carrying greater load.

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