An overheating motor is more than a maintenance inconvenience. Excessive heat can shorten motor life, damage insulation, cause unexpected downtime, and eventually lead to motor failure.
If an industrial motor is running hotter than normal, the cause may be electrical, mechanical, environmental, or related to the motor’s load.
Quick answer: Common causes of motor overheating include overloading, low or high voltage, voltage imbalance, phase loss, poor ventilation, incorrect motor settings, frequent starting and stopping, bearing problems, mechanical misalignment, and operating conditions outside the motor’s design.
Quick Troubleshooting Guide
| If your motor is… | Check for… |
|---|---|
| Running hot under normal load | Overload, voltage problems, ventilation |
| Hot even when lightly loaded | Voltage, bearings, ventilation, motor settings |
| Tripping a VFD or overload | Overload, phase loss, voltage imbalance |
| Hot on one side | Cooling problems, bearings, alignment |
| Getting hotter over time | Bearing wear, dirt buildup, changing load |
| Hot immediately after startup | Incorrect settings, wiring, phase loss |
| Overheating only during heavy production | Overloading or mechanical problems |
Detailed Troubleshooting Guide
The Motor Is Overloaded
One of the most common reasons a motor overheats is that it is working harder than it was designed to.
When a motor operates above its rated load, it draws more current. That additional current generates heat in the motor windings.
Signs of an overloaded motor:
- Motor current is above the nameplate rating
- Motor temperature increases during heavy production
- Overload protection frequently trips
- The motor slows down under load
- The motor runs normally when the equipment is unloaded
What to check
Measure the motor’s current while it is operating under normal conditions and compare it with the motor nameplate rating.
Also check whether the driven equipment is experiencing increased resistance or load.
Possible solutions: Reduce the mechanical load, correct the mechanical problem, or determine whether the motor is properly sized for the application.
Incorrect Voltage
Motors are designed to operate within a specific voltage range. Voltage that is too high or too low can cause excessive heating and poor motor performance.
Low voltage can cause a motor to draw additional current to produce the required torque, increasing heat in the windings.
Check:
- Voltage at the motor terminals
- Motor nameplate voltage
- Voltage supplied by the electrical system
- Voltage drop in the wiring
- Connections and terminals
If the voltage at the motor differs significantly from the required operating voltage, investigate the electrical supply before continuing to operate the motor.
Voltage Imbalance
Three-phase motors are particularly sensitive to voltage imbalance.
Even a relatively small voltage imbalance can produce a much larger current imbalance in the motor windings, resulting in excessive heat.
Symptoms can include:
- Uneven phase currents
- Excessive motor temperature
- Reduced motor efficiency
- Vibration
- Premature motor failure
- Overload or drive faults
Measure voltage between each phase and compare the readings. If the phases aren’t balanced, investigate the incoming power supply, connections, transformers, or other electrical equipment.
Phase Loss
A three-phase motor can also overheat when one phase is lost.
This condition is sometimes called single-phasing. Depending on the motor and protection equipment, the motor may continue running while drawing excessive current through the remaining phases.
Potential causes include:
- Blown fuse
- Tripped circuit breaker
- Loose connection
- Damaged wiring
- Failed contactor
- Electrical connection failure
Do not continue operating a motor suspected of single-phasing. Find and correct the electrical problem before returning the motor to service.
Poor Ventilation or Cooling
Motors need to dissipate the heat they generate during operation. If airflow around the motor is restricted, heat can build up.
This is especially common in dusty, dirty, or confined industrial environments.
Check for:
- Dirt or debris covering cooling fins
- Blocked ventilation openings
- Damaged cooling fans
- Excessive dust buildup
- Equipment installed too close to the motor
- High ambient temperatures
A motor that operates in a hot environment may also require additional consideration when selecting the motor and cooling method.
Keep the motor clean and make sure air can circulate around it.
Incorrect VFD Settings
If the motor is controlled by a variable frequency drive (VFD), incorrect drive settings can contribute to overheating.
The VFD needs accurate motor information to properly control and protect the motor.
Check the VFD parameters against the motor nameplate:
- Motor voltage
- Motor current
- Motor frequency
- Motor horsepower
- Motor speed
- Motor configuration
Also consider the motor’s operating speed.
A standard motor may not provide adequate cooling when operated continuously at very low speeds because its shaft-mounted cooling fan may also be turning slowly.
If a motor is frequently operating at low speed, verify that the motor and cooling system are appropriate for the application.
Frequent Starting and Stopping
Starting a motor requires significantly more current than normal running conditions.
If a motor starts and stops frequently, the repeated starting cycles can cause heat to build faster than the motor can dissipate it.
This can occur in applications with:
- Frequent cycling
- Short operating periods
- Repeated starts
- Conveyor systems
- Pumps
- Compressors
- Automated machinery
Check the motor manufacturer’s specifications for the appropriate starting frequency and duty cycle.
If the application requires frequent starts and stops, a different motor, control strategy, or application-specific solution may be necessary
Bearing Problems
Not every overheating problem is electrical.
Worn, damaged, or improperly lubricated bearings can create mechanical resistance that makes the motor work harder.
Signs of a bearing problem may include:
- Unusual noise
- Vibration
- Excessive bearing temperature
- Grinding or squealing
- Increased motor current
- Visible shaft movement
Inspect the bearings according to the motor manufacturer’s maintenance recommendations.
Avoid adding lubricant simply because a bearing is hot. Over-lubrication can also cause problems. Follow the manufacturer’s lubrication specifications.
Misalignment or Mechanical Problems
The motor may be perfectly healthy while the equipment connected to it is creating excessive resistance.
Misalignment between the motor and driven equipment can increase mechanical load, vibration, and bearing stress.
Other potential mechanical causes include:
- Bent shafts
- Tight or damaged belts
- Coupling problems
- Pump problems
- Gearbox problems
- Excessive friction
- Mechanical binding
A useful troubleshooting step
If it is safe and appropriate to do so, determine whether the motor overheats when operating independently from the driven equipment.
If the motor runs normally without the mechanical load, the problem may be downstream of the motor.
The Motor Is Not Designed for the Application
Sometimes the motor isn’t failing the application simply isn’t a good match for the motor.
Factors that can affect motor temperature include:
- Ambient temperature
- Altitude
- Duty cycle
- Operating speed
- Load profile
- Enclosure type
- Installation location
- Starting frequency
- Continuous vs. intermittent operation
A motor selected for one application may not be suitable for another, even if the horsepower and voltage appear to match.
Motor selection should consider the complete application, not just horsepower.
How to Troubleshoot an Overheating Motor
When a motor is running hot, don’t immediately assume the motor itself needs to be replaced.
A systematic approach can help identify the underlying problem.
Start with these checks:
1. Check the motor nameplate.
Record the rated voltage, current, horsepower, frequency, and speed.
2. Measure operating current.
Compare the measured current on each phase with the motor’s rated current.
3. Check voltage.
Measure the voltage at the motor and look for voltage imbalance.
4. Inspect the motor.
Look for dirt, blocked ventilation, damaged cooling fans, loose connections, and visible damage.
5. Check the mechanical load.
Inspect bearings, couplings, belts, gearboxes, pumps, and other connected equipment.
6. Check VFD settings.
If the motor is VFD-controlled, verify that the programmed motor parameters match the nameplate.
7. Consider the operating environment.
Check ambient temperature, airflow, duty cycle, and operating speed.
When Should You Replace the Motor?
Motor overheating does not automatically mean the motor needs to be replaced.
If the underlying problem is an overloaded machine, voltage imbalance, poor ventilation, misalignment, or incorrect VFD settings, replacing the motor may not solve the problem.
Before replacing a motor, determine why it is overheating.
If the motor has damaged windings, failed bearings, insulation damage, or other significant internal problems, replacement or professional repair may be appropriate.
Need Help Troubleshooting an Industrial Motor?
Motor problems can have multiple causes, and finding the right solution often requires looking at the entire electrical and mechanical system.
Lakeland Engineering Equipment Company supplies motors, drives, motor controls, sensors, electrical components, and test equipment used for industrial troubleshooting and automation applications.
Our team can help you identify the right components and equipment for your application; from VFDs and motor controls to electrical test equipment for diagnosing power and equipment problems.
Having trouble with an overheating motor or another industrial electrical problem? Contact Lakeland Engineering to discuss your application and find the right solution.