Troubleshooting
Motor hums but will not start
Work from mechanical load and supply condition to starting components.
A humming motor has energy but insufficient starting torque or an obstructed mechanical path. Limit energization time to avoid damage.
Likely causes
- Lost phase or low voltage.
- Seized load, bearings, or rotor.
- Failed capacitor or starting switch on single-phase equipment.
- Incorrect connection or contactor pole failure.
Safe tests
- De-energize, lock out, verify absence of voltage, and check shaft/load freedom where appropriate.
- Inspect connections, contactor poles, overloads, capacitors, and evidence of heat.
- Qualified persons may compare phase voltages under an approved energized-work procedure.
Expected evidence
- Balanced supply close to nameplate range.
- Low, similar winding resistances without a ground path.
- Free mechanical rotation and intact starting components.
Correct & verify
- Repair the confirmed supply, connection, starting-component, motor, or load fault.
- Verify rotation, acceleration time, running current balance, temperature, and operation under representative load.