WiremanWireman · Motor overload trips or motor runs hot: troubleshooting for electricians · 2023 NEC ·
Motor overload trips or motor runs hot
Compare current to nameplate, then find out whether it’s the load, the voltage or the overload setting.
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How it works
An overload relay is a heat model of the motor. It trips when current stays above its setting long enough to overheat the windings. So a tripping overload means the motor really is drawing too much (bad load, low or unbalanced voltage) or the overload is set or sized wrong.
Every question and answer in this guide. Tap “Step by step” to walk through it.
- Test: Measure running current on every lineExpect: Each line at or below FLA (up to FLA × SF briefly), and the three within about 10% of each other.
- All lines above FLATest: Measure the voltage at the motor while it runsExpect: Within 10% of nameplate voltage.
- Low (more than 10% under)Low voltage at the motor
- NormalToo much mechanical load
- Lines unbalanced by more than 10%Current unbalance
- At or below FLAIs the overload set (or the heater sized) for this motor’s FLA?
- Set too lowOverload set too low
- Set correctlyIs the starter in a hot location, or are its terminals discolored?
- Hot locationHigh temperature around the starter
- Discolored or loose terminalsA loose or overheated connection
- NeitherPossible bad overload relay
- All lines above FLATest: Measure the voltage at the motor while it runsExpect: Within 10% of nameplate voltage.