Motor will not start or the overload keeps tripping
Symptom
A motor does not start, hums without turning, trips at start or after running, runs hot, or a drive shows an overcurrent or overtemperature fault.
Likely causes
- An E-stop, interlock or control fuse is open, so the contactor never pulls in.
- One phase missing, or low or unbalanced supply voltage.
- The machine is jammed or starting loaded (mixer with a trapped batch, screw full of cement).
- Overload relay set below the motor nameplate, or a contactor with burnt contacts.
- Dirt on the motor fins, a failed drive fan, or a hot cabinet.
Most likely and cheapest to check first.
Checks
- Read the alarm and the PLC output lamp; check the safety relay status.
- Have an electrician measure all three phases and the running current on each.
- Lock out and turn the driven machine by hand.
- Compare the overload setting with the nameplate full-load current.
Fix
- Find and fix the open interlock; never bridge it.
- Restore the missing phase; correct the supply.
- Empty and free the machine before restarting.
- Set the overload to the nameplate, never higher; replace worn contactors with the same type and coil voltage.
- Clean motor fins and drive heatsinks; replace failed fans.
Stop the equipment if
The breaker trips instantly, or a motor hums without turning. Do not keep resetting it.
Parts you may need
A tripping overload is telling you something
Raising the overload setting to stop nuisance trips burns motors. First look for the mechanical cause - a seized bearing, build-up, a slipping belt, a trapped batch.
DANGERElectrical work is for qualified electricians, with the circuit isolated and tested dead. Operators read indicators, do visual checks and report faults clearly.
FIELD TIPThermograph the panels during a busy production morning. A panel scanned with the plant idle always looks perfect.
⚠ Every check inside a machine starts with full lockout. Safety disclaimer