Motor Keeps Tripping the MCB: Causes & Solutions

A motor that keeps tripping the MCB (Miniature Circuit Breaker) is telling you something is wrong — either with the motor, the load, or the protection setup. Repeatedly resetting without finding the cause risks a burnt motor. Here is how to diagnose it.

1. Motor Overload

The motor is drawing more current than rated — usually because the driven load is too heavy, jammed, or the pump/machine is binding. Fix: Check the load turns freely; verify the motor is not undersized for the job.

2. Short Circuit or Earth Fault

Damaged winding insulation or a cable fault causes a sudden high current. Fix: Megger-test the motor windings to earth. Low insulation resistance means the motor needs rewinding or replacement.

3. Wrong MCB Rating or Type

A standard MCB may nuisance-trip on normal motor starting inrush (6-8× running current). Fix: Use a motor-rated MCB or MPCB with a suitable curve (Type C or D), correctly sized to the motor.

4. Low Voltage

Under-voltage makes the motor draw more current to maintain torque, tripping the MCB. Fix: Check supply voltage; add a stabiliser if the supply is weak.

5. Single Phasing

Loss of one phase on a three-phase supply causes the remaining phases to overload. Fix: Check all three phases; add single-phasing preventer protection.

6. Frequent Starting

Starting a motor too often overheats it and trips protection. Fix: Reduce start frequency or use a soft starter/VFD for high-cycle applications.

Persistent tripping usually points to a winding or sizing issue. Bring the motor to us for an insulation test and honest diagnosis. Contact us or send a pump inquiry for free sizing guidance.