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Troubleshooting Common Motor Problems

Troubleshooting Common Motor Problems


Motor Repair Motor Repair

Electric motors run just about everything from small kitchen exhaust fans to commercial HVAC systems to large, industrial assembly lines. Every industry relies on electric motors to operate, sometimes running hundreds of motors non-stop. A widely cited 2011 study from the International Energy Agency determined that electric motors and related systems account for 40% of global energy use. With all of that motorized activity, maintaining motor efficiency is critical to managing your facility’s energy costs.

Troubleshooting Common Motor Problems

Common signs a motor’s efficiency has been compromised, or that it may be time for a replacement, include abnormal noises or vibration, below-normal performance of equipment or output, and overheating. If any of these signs are present, it might be possible to fix the problem with some troubleshooting. For example, if a unit stalls during operation, it could be due to low voltage, or it could be overloaded. The table below lists some common symptoms of motor operational problems, suggests some possible causes, and offers a corrective measure to consider. 


Possible Causes

Corrective Action

Unit Fails to Operate

No power

Consult local power company.

Blown fuse or open circuit breaker

• Replace fuse or reset circuit breaker.

• Check for grounded motor winding.

Voltage too low at motor terminals due to line drop

• Consult local power company.

• Check for poor connections Increase wire size.

Improper line connections

Check connections against diagram supplied with unit.

Defective motor

Repair or replace.

Defective control switch or starter

Repair or replace.

Overload, motor starter tripped

• Check and reset overload relay in starter.

• Check heater rating against gear motor nameplate current rating.

Gear motor may be overloaded

• Reduce load or increase gear motor size.

• Check load and alignment of coupling.

Unit Stalls During Operation



Determine cause of overload and either reduce load or increase gear motor size.

Low voltage

Verify that nameplate voltage is maintained

Unit Operational, No Output




Defective gear(s)

Check and replace if necessary.

Gear loose on shaft

Check and replace if necessary.

Loose coupling, sheave or sprocket

Check and tighten if necessary.

Sheared key on output shaft

Replace key and inspect keyway for damage.

Intermittent Rotation of Output Shaft

Damaged intermediate gear caused by shock load

Replace and if possible, avoid shock load.

Excessive Noise









Bearing worn or damaged


Belt or chain too tight

Adjust tension.

Overhung-load exceeds rating and causes bearing wear

Correct load and/or replace bearing.

Defective gear(s)


Output shaft misaligned


Loose sheave or sprocket or misaligned coupling

Tighten set screw(s) and realign coupling.

Defective motor winding

Repair or replace.

High or unbalanced voltage

Check wiring connections and consult local power company.

Three-phase motor running single-phase

Check for open circuit, blown fuse or unbalanced voltage.

Unit Overheats While Running Under Load

Overloaded, belts or chain too tight

Reduce load, increase gear motor size.

High or low voltage

Check voltage at motor connections, should not be more than 10% above or below.

Faulty connection

Check and tighten if necessary.

Dirt blocking ventilation openings

Clean motor.

If three-phase, one phase may be open

• Check lines for open phase.

• Check voltage with gear motor disconnected.

• One fuse may be blown.

If three-phase, unbalanced supply voltage

• Check for faulty connections.

• Voltage on all three lines should be balanced within 1%.

Defective motor

Repair or replace.

Unit Does Not Come Up to Speed or Takes Too Long to Accelerate

Voltage too low at motor terminals

• Check for poor connections.

• Increase wire size.

• If three-phase, check for voltage unbalance.

Starting load too high

• Unit may be under size to start load.

• Increase unit size.

Load contains a bound condition

Clear condition.

Excessive loading, tight belts or chain

• Reduce load and increase unit size.

• Adjust belt or chain tension.

Defective gearmotor

Repair or replace.

Inadequate starting torque

High inertia load

Replace with larger unit.

Once you've exhausted all of your troubleshooting options, and you've determined it's time for a motor replacement, this form can be a great tool to help narrow down your choices. You can also find some great guidance beginning on page 3 of the online Grainger Catalog.

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The information contained in this article is intended for general information purposes only and is based on information available as of the initial date of publication. No representation is made that the information or references are complete or remain current. This article is not a substitute for review of current applicable government regulations, industry standards, or other standards specific to your business and/or activities and should not be construed as legal advice or opinion. Readers with specific questions should refer to the applicable standards or consult with an attorney.