Electric Motor Troubleshooting: Causes & Fixes

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Problems on this page:

Motor won't start Overheating Trips the breaker / overload Excessive vibration / bearing noise Single-phasing / runs noisy under load Running hot on a variable speed drive Bearing damage from shaft currents Moisture getting into the motor Motor running at the wrong speed Electrical noise from the motor

Motor won't start

Hits OEE: Availability

Symptoms: Hums but doesn't turn, or completely dead on start.

Tripped overload / blown fuse

Reset overload, replace fuses; investigate the trip cause.

Loss of a phase (3-phase)

Check all three phases at the motor; fix the open phase/connection.

Failed start capacitor (1-phase)

Test and replace the start/run capacitor.

Mechanical seizure

Try turning by hand; clear the seized load or replace bearings.

Prevention: Thermographic/connection checks, overload sizing, lubrication.

Overheating

Hits OEE: Availability

Symptoms: Hot frame, burning smell, thermal trips, short insulation life.

Overload

Measure running current vs nameplate; reduce load or upsize.

Blocked cooling / dirty fins

Clean the fan cover and frame; restore airflow.

Voltage imbalance/under-voltage

Check supply balance and voltage; correct supply issues.

Bearing failure adding drag

Replace bearings; check alignment.

Prevention: Load/current monitoring, keep cooling clear, supply quality checks.

Trips the breaker / overload

Hits OEE: Availability

Symptoms: Repeated overload or breaker trips shortly after start/run.

Mechanical overload/jam

Inspect the driven load for binding; clear it.

Short or ground fault in windings

Megger-test windings; rewind/replace if failed.

Incorrect overload setting

Set overload to motor FLA per nameplate.

Prevention: Insulation resistance testing, correct protection settings, load checks.

Excessive vibration / bearing noise

Hits OEE: Performance

Symptoms: Vibration, rumble or whine from bearings, rising temperature.

Worn bearings

Replace bearings; use correct fit and lubrication.

Misalignment / soft foot

Align to coupling spec; correct soft foot.

Imbalance

Balance the rotor/fan; remove build-up.

Prevention: Vibration trending, precision alignment, greasing schedule.

Single-phasing / runs noisy under load

Hits OEE: Availability

Symptoms: Motor hums, struggles under load, overheats, may trip; one phase suspect.

Lost phase (blown fuse/loose connection)

Check all three phases and connections; fix the open phase.

Voltage imbalance

Measure phase balance; correct the supply issue.

Winding fault

Megger the windings; rewind/replace if failed.

Prevention: Connection thermography, phase-balance checks, protection settings.

Running hot on a variable speed drive

Hits OEE: Availability

Symptoms: A motor on a drive runs hot at low speed, insulation ages early.

Shaft fan too slow at low speed

Add forced cooling or avoid long running at low speed.

Drive settings not matched to the motor

Set the drive with the motor's data.

Motor not rated for drive duty

Use a motor rated for inverter duty.

Prevention: Check motor temperature at the lowest running speed.

Bearing damage from shaft currents

Hits OEE: Availability

Symptoms: Repeated bearing failures on drive-fed motors, frosted or fluted bearing races.

Drive-induced shaft currents

Fit a shaft grounding device or insulated bearings.

Poor grounding between motor and drive

Improve grounding and use suitable motor cable.

Wrong bearing for the duty

Check bearing choice with the motor maker.

Prevention: Inspect removed bearings for fluting.

Moisture getting into the motor

Hits OEE: Availability

Symptoms: Insulation faults after washdown or a long stop, water in the terminal box.

Washdown water entering

Use motors and glands suited to washdown and keep covers sealed.

Condensation during stops

Use anti-condensation heaters where the maker recommends.

Damaged seals or glands

Replace damaged seals and cable glands.

Prevention: Insulation resistance tests on a schedule.

Motor running at the wrong speed

Hits OEE: Performance

Symptoms: The driven machine runs slower or faster than it should.

Supply voltage low

Measure the voltage at the motor terminals under load.

Motor overloaded and slipping

Check the load and the motor current.

Wrong motor or wrong winding connection

Check the rating plate and the connection for the supply.

Drive setpoint wrong on a VFD motor

Check the speed reference and the drive parameters.

Prevention: Running speed checked after any motor change.

Electrical noise from the motor

Hits OEE: Availability

Symptoms: A hum or growl that changes with load or supply, without a mechanical cause.

Unbalanced supply voltage

Measure the three phase voltages and fix the imbalance.

Broken rotor bars

Have the motor tested with current analysis.

Loose stator laminations

Send the motor for repair.

Drive switching frequency

Check the switching frequency setting on VFD motors.

Prevention: Motor current analysis on critical motors at planned intervals.

Guidance only. Always follow lockout/tagout and your site's safe-work procedures, and verify against OEM manuals before acting.

Alarm codes: Siemens SINAMICS G120 fault codes · Yaskawa V1000 alarm codes · Siemens MICROMASTER 440 fault codes

Stop the same fault coming back

Recurring electric motor stops usually trace to a cause you cannot see by hand. The partner we recommend is Fabrico: it tracks OEE and downtime live from PLCs, IoT sensors or AI cameras; where cameras are fitted, the video of a stop sits next to its machine data so the cause can be reviewed; and a technician opens the work order from the stop in the same system. Data is hosted in the AWS EU region, and Fabrico and the company behind it hold ISO/IEC 27001, ISO/IEC 20000-1 and ISO 9001.

Book a Fabrico demo

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Methods that cut recurring stops: the six big losses · root cause analysis · preventive vs predictive maintenance · TPM · SMED & changeover