9 common faults of electric motors and their troubleshooting methods

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1. Fault symptom: The motor will not start. Causes: 1) The power supply is not connected； 2) Winding open circuit ； 3) Winding grounding or inter-phase short circuit ； 4) Incorrect winding wiring ； 5) Melt burnout ； 6) Incorrect wiring of control equipment. Troubleshooting method: 1) Check the switch, fuses, all contact points, and motor lead terminals ； 2) Heat the broken section to a temperature permitted by the insulation rating to soften the paint; then lift the wire. Use wire of the same specifications to reweld the broken part, cover it with insulation, and finally apply paint and dry it ； 3) The treatment method is the same as above; simply insulate the grounded or short-circuited area, then paint it and dry it ； 4) Verify the wiring diagram; after heating the ends, rewire them according to the correct connections (including bundling, insulation treatment, and painting) ； 5) Identify the cause, resolve the fault, and install a new fuse matching the motor specifications ； 6) Correct wiring. 2. Fault symptoms: After the motor is connected to the power supply, the fuse blows. Causes: 1) Single-phase starting ； 2) The motor is under excessive load or stuck ； 3) The melt cross-sectional area is too small ； 4) The connection wire between the power supply and the motor is short-circuited. Troubleshooting method: 1) Check all contact points of the power cable, motor leads, fuses, and switches; upon identifying any broken wires or poor connections, make the necessary repairs ； 2) Adjust the load to the rated value and eliminate faults in the driven mechanism ； 3) The fuse does not provide protection against motor overload; the fuse should generally be selected using the following formula ； Melting current rating = Starting current / (2~3) ； 4) Check for the short circuit point and then repair it. 3. Fault symptoms: The motor does not start after being powered on but emits a humming sound. Causes: 1) The motor is under excessive load or stuck ； 2) The power supply has not been fully connected ； 3) Voltage is too low ； 4) For small electric motors, the grease is too hard or the assembly is too tight. Exclusion method 1) Check the equipment to eliminate faults ； 2) Replace the fuse element ； Tighten the screws that hold the terminal posts in place ； Use a multimeter to check for broken wires or incorrect connections in the power cable, and then repair them ； 3) If the motor connected in delta is mistakenly connected in star configuration, it should be changed back to delta connection. When the supply voltage is too low, contact the power supply provider to resolve the issue ； When the voltage drops too low due to excessive voltage drop in the power cable, the cable should be made thicker ； 4) Select the appropriate grease to improve assembly quality. 4. Fault symptoms: The motor housing is electrified. Causes: 1) The power cable and ground cable have been mixed up ； 2) The motor windings are damp, and the insulation is severely aged ； 3) The lead wires and the junction box are grounded. Exclusion method 1) Correct the error ； 2) Motor drying treatment; aged insulation needs to be replaced ； 3) Wrap or renew the insulation of the lead wires; repair the junction box. 5. Fault symptoms: The motor has difficulty starting, and when a rated load is applied, its speed is lower than the rated speed. Causes: 1) The supply voltage is too low ； 2) The △-connected windings are incorrectly connected in Y configuration ； 3) Welding failure or fracture of the cage rotor ； 4) Too many turns during rewinding. Troubleshooting method: 1) Use a voltmeter or multimeter to check the magnitude of the input power voltage to the motor, and then take appropriate actions ； 2) Change the Y connection back to a Δ connection ； 3) Inspect for weld cracks or breaks and carry out repairs ； 4) Rewind with the correct number of winding turns. 6. Fault phenomenon: Low insulation resistance. Causes: 1) The windings are damp or wetted by water ； 2) Aging of winding insulation. Exclusion method 1) Perform heating and drying treatment ； 2) Having been evaluated as still usable, it can be cleaned, dried, and repainted ； If the insulation ages and cannot operate safely, it needs to be replaced. 7. Fault symptoms: Abnormal noise is heard during the operation of the motor. Causes: 1) Bearing wear, resulting in a fault ； 2) Loose stator and rotor cores ； 3) Voltage is too high or unbalanced ； 4) Lack of grease in the bearing ； 5) Fan hitting the air shroud or air duct obstruction ； 6) The air gap is uneven, causing the stator and rotor to rub against each other. Exclusion method 1) Overhaul or replace with a new bearing ； 2) Check the cause of vibration and re-tighten the core for treatment ； 3) Measure the supply voltage, identify the causes of excessive voltage and imbalance, and take corrective actions ； 4) Clean the bearing and fill it with grease to occupy 1/2 to 2/3 of the bearing chamber volume ； 5) Repair the fan and shroud to ensure their dimensions are correct ； Clean the ventilation ducts ； 6) Adjust the air gap to improve assembly quality. 8. Fault symptoms: The motor overheats or starts to smoke. Causes: 1) Excessively high supply voltage, which leads to oversaturation of the magnetic flux density in the core, resulting in an increase in the motor’s temperature ； 2) The supply voltage is too low, resulting in excessive temperature rise of the motor under rated load ； 3) Rubbing between the stator and rotor cores ； 4) The motor is overloaded or the resistance encountered by the machinery it drives is too high, causing the motor to overheat ； 5) Frequent starting of the motor or excessive number of forward/reverse rotations ； 6) Fan failure, poor ventilation. Exclusion method 1) If the power supply voltage is significantly above the standard, contact the power supply provider to resolve the issue ； 2) If it is caused by excessive voltage drop in the power cable, a thicker power cable can be used ； If the power supply voltage is too low, you can contact the power supply authority to increase it ； 3) Check the cause of the fault; if the bearing clearance is out of limit, the bearing should be replaced ； If the rotating shaft is bent, it needs to be straightened ； When the core is loose or deformed, it should be repaired to eliminate the fault ； 4) Eliminate mechanical faults in the dragging mechanism to reduce resistance ； According to the current indication, if it exceeds the rated current, the load must be reduced, a motor with a higher capacity must be installed, or measures to increase capacity should be taken ； 5) Reduce the number of motor starts and forward/reverse rotations, or replace with a suitable motor ； 6) Check whether the motor fan is damaged, and whether the fan blades are deformed or not properly secured; replace the fan if necessary. 9. Fault symptoms: The current is unbalanced when the motor operates under no-load conditions, with a significant difference between the currents. Causes: 1) Unbalanced supply voltage ； 2) There is a fault in the winding, such as inter-turn short circuit or reversed connection of a certain set of coils ； 3) During rewinding, the number of turns per phase winding is uneven. Exclusion method 1) Measure the power supply voltage to identify the cause ； 2) Disassemble the motor to check the winding polarity and identify any faults, then correct or eliminate them ； 3) Winding rewinding.