Single phase troubleshooting guide
 
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3 Phase Motors
Single Phase Motors
Single Phase Continued
 
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 Last Updated: Wednesday June 17, 2009

 

Single Phase Continued
   
 
                                                                             
 
Troubleshooting Guide For Single-Phase
(Split-Phase) Motors
Problem Possible Cause Suggested Test Tool   Corrective Action
Motor will not start

 Thermal cutout switch is open   Reset the thermal switch. Caution: Resetting the thermal switch may automatically start the motor.
Blown fuse or open CB Basic electrical tester, DMM,
clamp meter,
megohmmeter		 Test the OCPD. If voltage is present at the input, but not the output of the OCPD, the fuse is blown or the CB is open. Check the number of the OCPD. It should be at least 125 % of the motor's FLC.
Motor overload on starter tripped   Allow overloads to cool. Reset overloads. If reset overloads do not start the motor, test the starter.
Low or no voltage applied to motor Basic electrical tester, DMM,
clamp meter		 Check the voltage at the motor terminals. The voltage must be present and within 10 % of the motor nameplate voltage. If voltage is present at the motor but the motor is not operating, remove the motor from the load the motor is driving. Reapply power to the motor. If the motor runs, the problem is with the load. If the motor does not run, the problem is with the motor. Replace or service the motor.
Open control circuit between incoming power and motor Basic electrical tester, DMM
clamp meter		 Check for cleanliness, tightness, and breaks. Test the circuit starting with the incoming power and moving to the motor terminals. Voltage generally stops at the problem area.
Starting winding not receiving power Basic electrical tester, DMM
clamp meter		 Check the centrifugal switch to make sure it connects the starting winding when the motor is OFF.
Fuse, CB, or overloads retrip after service

 Blown fuse or open CB Basic electrical tester, DMM,
clamp meter,
megohmmeter		 Test the OCPD. If voltage is present at the input, but not the output of the OCPD, the fuse is blown or the CB is open. Check the rating of the OCPD. It should be at least 125 % of the motor's FLC.
Motor overload on starter tripped   Allow overloads to cool. Reset overloads. If reset overloads do not start the motor, test the starter.
Low or no voltage applied to motor Basic electrical tester, DMM,
clamp meter		 Check the voltage at the motor terminals. The voltage must be present and within 10 % of the motor nameplate voltage. If voltage is present at the motor but the motor is not operating, remove the motor from the load the motor is driving. Reapply power to the motor. If the motor runs, the problem is with the load. If the motor does not run, the problem is with the motor. Replace or service the motor.
Open control circuit between incoming power and motor Basic electrical tester, DMM,
clamp meter		 Check for cleanliness, tightness, and breaks. Test the circuit starting with the incoming power and moving to the motor terminals. Voltage generally stops at the problem area.
Motor shaft does not turn   Disconnect the motor from the load. If the motor shaft still does not turn, the bearings are frozen. Replace or service the motor.
Motor produces electric shock


 Broken or disconnected ground strap   Connect or replace ground strap. Test for proper ground.
Hot power lead at motor connecting terminals is touching motor frame   Disconnect the motor. Open the motor terminal box and check for poor connections, damaged insulation, or leads touching the frame. Service and test motor for ground.
Motor winding shorted to frame   Remove, service, and test motor.
Motor overheats

 Starting windings are not being removed from circuit as motor accelerates   When the motor is turned OFF, a distinct click should be heard as the centrifugal switch closes as the motor slows down
Improper ventilation Infrared thermometer Clean all ventilation openings. Vacuum or blow dirt out of motor with low-pressure, dry, compressed air.
Motor is overloaded Basic electrical tester, clamp meter or DMM
with clamp accessory		 Check the load for binding. Check shaft straightness. Measure motor current under operating conditions. If the current is above the listed current rating, remove the motor. Remeasure the current under no-load conditions. If the current is excessive under load but not when unloaded, check the load. If the motor draws excessive current when disconnected, replace or service the motor.
Dry or worn bearings   Dry or worn bearings cause noise. The bearings may be dry due to dirty oil, oil not reaching the shaft, or motor overheating. Oil the bearings as recommended. If noise remains, replace the bearings or the motor.
Dirty bearings   Clean or replace bearings.
Excessive Noise

 Excessive end play   Check end play by trying to move the motor shaft in and out. Add end-play washers as required.
Unbalanced motor or load   An unbalanced motor or load causes vibration, which causes noise. Realign the motor and load. Check for excessive end play or loose parts. If the shaft is bent, replace the rotor or motor.
Dry or worn bearings   Dry or worn bearings cause noise. The bearings may be dry due to dirty oil, oil not reaching the shaft, or motor overheating. Oil the bearings as recommended. If noise remains, replace the bearings or the motor.
Excessive grease   Ball bearings that have excessive grease may cause the bearings to overheat. Overheated bearings cause noise. Remove any excess grease.