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Why Does My Motor Keep Tripping? 5 Causes & Fixes

Release Date ：2026-10-14

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"My motor keeps tripping the breaker" is one of the most common calls we get from plant engineers. A tripping motor is rarely just "a bad motor" - it is usually an electrical, mechanical or load-side problem. This guide breaks the causes into five groups with a fault table and a three-step diagnosis you can run in minutes.

Electrician checking motor circuit breaker in panel

1. Which Device Is Tripping? Identify It First

Different protective devices trip for different reasons: a circuit breaker (short circuit / overload), a thermal overload relay (overload), an RCD (earth leakage), a VFD fault code (overcurrent / overload), or a contactor drop-out (undervoltage). Step one is to identify which device tripped and what happened just before - do not just reset and restart.

2. Five Common Trip Causes at a Glance

Trip type	Common causes	Check / fix
Trips instantly at start (short circuit)	Winding earth fault or phase-to-phase fault, damaged cable, wrong wiring	Disconnect motor, measure insulation resistance with a megohmmeter, inspect cable and connections
Overload trip while running	Jammed load, failing bearing, low voltage, voltage unbalance, undersized motor	Measure three-phase current vs nameplate, check load and voltage, inspect bearings
Thermal relay trips repeatedly	Setting too low, high ambient temperature, poor ventilation, frequent starting	Reset to actual running current, improve cooling, review duty cycle
RCD trips	Moisture in winding, damaged cable, water in terminal box	Measure earth insulation, dry the winding, reseal the terminal box
VFD fault trip	Wrong parameters, acceleration too short, overcurrent, IGBT over-temperature	Read fault code, extend ramp times, clean cooling ducts

3. A Three-Step Diagnosis (Narrow It Down in 5 Minutes)

Step 1: Identify the tripping device and its fault indication (breaker / relay / VFD code);
Step 2: Run the motor uncoupled with no load - if it still trips the problem is in the motor or wiring; if not, the load is the cause;
Step 3: Measure three-phase current, voltage and insulation resistance and compare with the nameplate.

4. Three Causes People Most Often Overlook

Low voltage or voltage unbalance: unbalance above 2% noticeably raises winding losses and pushes current up, causing overload trips. Measure voltage before replacing the motor; see our pre-start checklist after long shutdown for related checks;
Frequent starting / jogging: starting current is 5-7 times rated current, so rapid restarts can falsely trip thermal protection. Review motor starting methods for better options;
Moisture in the winding: starting a motor after a long idle period without an insulation check is a common cause of winding failure.

5. Do You Need a New Motor?

If insulation, bearings and current are all normal, the trip is usually a protection-setting or load-matching problem and the motor does not need replacing. But if repeated overloads have discoloured the winding or reduced insulation resistance, a rewind or replacement is the safer call. When re-selecting, give the manufacturer the real load profile and starting duty. At SHANGDIAN (Shanghai Electric Motor Factory) we help customers pick the right low-voltage three-phase induction motors and VFD-duty motors so power and starting capability match the site conditions.

If you are troubleshooting a repeated trip, send us the current, voltage and insulation readings and our engineers will help you locate the root cause quickly.