Intermittent Motor Stopping: Causes, Troubleshooting & Solutions

Intermittent motor stopping is one of the most challenging issues in industrial plants. A motor that stops unexpectedly and then resumes operation can disrupt production, reduce efficiency, and even damage connected equipment. Understanding the root causes and implementing effective troubleshooting and preventive measures is crucial for industrial engineers and maintenance teams. This article covers all the common questions asked by engineers and provides detailed practical solutions.

1. Why does the motor stop occasionally and then start again?

Cause:

• Thermal overload protection activation due to short-term overcurrent.

• Loose electrical connections causing intermittent contact.

• Momentary voltage drops or fluctuations in the power supply.

Solution:

1. Inspect and tighten all motor terminals and connections.

2. Check for proper torque on terminal screws.

3. Use voltage monitoring equipment to detect dips and spikes.

4. Ensure thermal overload relay settings match motor specifications.

Practical Tip: Installing continuous motor monitoring can alert engineers to transient conditions before a stop occurs.

Read About: Motor Vibration Excessive: Causes, Diagnosis & Solutions

2. Is the issue from the VFD or the motor itself?

Cause:

• Incorrect VFD programming can lead to overcurrent, under-voltage, or thermal trips.

• VFD hardware faults such as damaged IGBTs or poor cooling.

Solution:

1. Check the VFD fault logs and alarm history.

2. Verify that all VFD parameters (acceleration, deceleration, current limits) match motor ratings.

3. Inspect the VFD cooling system; clean filters and fans regularly.

4. Test the motor directly on line voltage (bypassing VFD if safe) to see if the issue persists.

3. How to check the electrical circuit if the motor stops without reason?

Diagnostic Steps:

• Use a multimeter to verify voltage at the motor terminals.

• Use a clamp meter to monitor current fluctuations.

• Perform insulation resistance testing (Megger test) to check for degraded insulation.

• Inspect fuses, circuit breakers, and contactors for intermittent faults.

4. Could the problem be caused by mechanical load on the shaft?

Cause:

• Sudden load changes on connected machinery can temporarily stall the motor.

• Misalignment of couplings or worn belts increases torque beyond motor capacity.

Solution:

1. Check alignment using laser alignment tools or dial indicators.

2. Inspect belts, pulleys, and couplings for wear or slippage.

3. Ensure the driven load does not exceed motor rated torque.

5. Is it possible that bearings or cooling issues are causing this?

Cause:

• Worn or poorly lubricated bearings can cause friction spikes.

• Blocked ventilation or dust accumulation can cause localized overheating.

Solution:

1. Conduct vibration analysis to detect bearing wear.

2. Inspect and lubricate bearings according to manufacturer recommendations.

3. Clean motor cooling vents and ensure fans are operational.

6. How to monitor the motor to prevent unplanned stops?

Monitoring Tools:

• Temperature sensors on stator windings and bearings.

• Vibration sensors for early detection of imbalance or bearing wear.

• Voltage and current loggers for detecting fluctuations.

7. Is this issue harmful to the motor’s lifespan?

Cause:

• Repeated intermittent stops can stress windings, bearings, and the rotor.

• Frequent starts increase thermal and mechanical stress.

Solution:

• Reduce the number of starts per hour by adjusting control logic.

• Ensure proper thermal protection and use soft starters if needed.

• Monitor motor operating temperature continuously.

8. If the problem is in external connections, can it happen again after repair?

Cause:

• Loose or oxidized connections may not be fixed permanently if not treated properly.

Solution:

1. Clean contacts with anti-oxidation compounds.

2. Use torque wrenches to secure connections accurately.

3. Inspect connections periodically, especially in high-vibration environments.

9. Can environmental factors (humidity, dust) cause intermittent motor stopping?

Cause:

• Moisture ingress can cause insulation failure.

• Dust can block cooling or create partial shorts.

Solution:

1. Install IP-rated enclosures for harsh environments.

2. Use filtered cooling air or positive pressure systems.

3. Clean motors regularly and inspect for moisture or dust accumulation.

10. Can using a soft starter reduce intermittent stopping issues?

Benefit:

• Soft starters reduce inrush current during startup, preventing unnecessary trips.

• Reduces mechanical stress on the shaft and connected equipment.

Implementation:

1. Select a soft starter compatible with motor voltage and current.

2. Set ramp-up time according to motor and load requirements.

3. Monitor motor performance during initial operation to adjust parameters.

Conclusion

Intermittent motor stopping is a complex issue caused by a combination of electrical, mechanical, and environmental factors. Understanding each potential cause and implementing preventive measures can save industrial plants significant downtime and maintenance costs. Regular inspections, proper motor and VFD configuration, real-time monitoring, and predictive maintenance are key to keeping motors running efficiently.

By addressing all potential issues—from loose connections and bearing wear to VFD settings and environmental protection—engineers can minimize unplanned stops, extend motor life, and improve overall plant reliability.