Troubleshooting Electric Motors: 5 Common Problems and Solutions

1. What causes low resistance in an electric motor?

Low resistance (often found via insulation resistance testing) is a critical sign that the motor’s electrical system is deteriorating. Common triggers include:

1. Contamination
   Dust, oil, or moisture can create a conductive path across insulation.
2. Overheating
   High temperatures can “bake” varnish and crack protective insulation.
3. Insulation ageing
   Natural chemical degradation over years of service.
4. Physical stress
   Vibration or friction can cause windings to rub against the frame.

Below are the issues our technical team is asked about most often—along with typical remedies:

2. Why is my electric motor overheating?

Overheating is serious—it can reduce efficiency, shorten motor life, and lead to failure. The most common causes are:

1. Overloaded conditions
   If the motor is working beyond its rated capacity, it can overheat. Ensure the motor is not overloaded and consider installing overload protection.
2. Insufficient ventilation or cooling
   Motors rely on airflow. Blocked vents or a faulty cooling fan will prevent heat dissipation. Confirm adequate ventilation, clean air paths, and check fan operation.
3. Incorrect voltage or phase imbalance (AC motors)
   Wrong supply voltage or phase imbalance can increase current draw and heat. Verify supply matches the nameplate rating and check phase balance where applicable.
4. Electrical faults or short circuits
   Damaged insulation or winding faults can raise current and temperature. Test with appropriate instruments and repair/replace damaged components.
5. Incompatible motor size or type
   An undersized or unsuitable motor for the duty cycle will run hot. Re-check sizing, starting method, and duty rating; upgrade if necessary.

3. What causes an electric motor to lose power or slow down?

Loss of power or reduced speed can come from electrical supply issues, control issues, or mechanical drag. Common causes include:

1. Overloading the motor
   Excessive load can cause the motor to struggle to maintain speed. Reduce load, confirm correct sizing, and consider load/overload protection.
2. Voltage issues
   Low or fluctuating voltage can reduce torque and cause slow running. Verify the supply is stable and matches the motor’s rating; check wiring and connections.
3. Worn or damaged bearings
   Bearing wear creates drag and heat. Inspect, lubricate correctly, and replace bearings as part of planned maintenance.
4. Loss of supply phases (three-phase motors)
   Phase loss or imbalance can cause poor performance and overheating. Check with a phase monitor/voltmeter and rectify supply/wiring faults.
5. Capacitor failure (single-phase induction motors)
   A failed capacitor can reduce starting torque and running performance. Test and replace with the correct rating and type.
6. Dirt, dust, and contamination
   Debris can block ventilation and increase friction. Clean regularly and ensure appropriate sealing for the installation environment.

4. What should I do if my electric motor suddenly stops working?

When a motor stops suddenly, start by separating external causes (power/load) from internal causes (mechanical/electrical faults). Work through these checks in order:

1. Check the power supply
   Confirm the motor is receiving power. Check breakers/fuses. If using a VFD, confirm stable input supply and drive status.
2. Inspect electrical connections
   Loose or damaged wiring can stop a motor. Isolate power, then inspect for loose wires, burnt contacts, or broken connections.
3. Test for continuity
   Use a multimeter to test windings. No continuity (or resistance far from expected) can indicate winding damage.
4. Check overload protection
   If an overload has tripped, allow the motor to cool and reset. If it trips again, investigate load and mechanical resistance.
5. Examine the capacitor (single-phase motors)
   A failed capacitor can prevent starting/running. Test and replace with the correct specification.
6. Inspect bearings
   Grinding/squealing noises can indicate bearing failure. Address promptly to prevent further damage.

5. What causes an electric motor to trip a breaker?

A breaker trip usually indicates a fault or operating condition that is drawing excessive current. Breakers protect the motor and wiring from overloads, short circuits, and earth faults.

1. Overload
   The motor is being asked to do more than it’s rated for. Confirm correct motor sizing and check for jams/obstructions.
2. Short circuit
   A fault in wiring or windings can create a high-current path. Inspect for burnt wiring or damaged insulation; the motor may need rewinding or repair.
3. Ground (earth) fault
   A conductor contacting the casing or grounded surface can trip protection. Inspect insulation, cable condition, and grounding/earthing integrity.
4. Voltage imbalance (three-phase motors)
   Uneven phase voltage can increase current and heat. Check phase-to-phase voltages and correct supply/wiring issues.
5. Incorrect motor wiring
   Wrong voltage/connection configuration can cause overheating and high current. Verify wiring against the nameplate and manufacturer’s diagram.
6. Undervoltage
   Low supply voltage can force higher current draw to maintain load. Measure supply voltage under load and correct upstream issues.

How to stop an electric motor from constantly tripping the breaker

1. Proper sizing
   Ensure the motor is correctly sized for the load, and protection devices are rated correctly for the motor’s full-load current.
2. Routine maintenance
   Regularly inspect the motor, wiring, and electrical components to catch issues before trips occur.
3. Monitor operation
   Use temperature monitoring or condition monitoring where practical to spot overheating or degradation early.
4. Check the electrical system
   Confirm balanced voltage, correct wiring, and proper grounding/earthing.

Tip: If you’re unsure what to choose, note the motor nameplate details (kW/HP, RPM, frame size, voltage, mounting, shaft diameter) and match them when selecting a replacement.