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Wireman · Motors troubleshooting · 2023 NEC ·

Motors

Won’t start, overheats, trips, noise, wrong rotation.

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Motor hums or won’t startCapacitors, lost phases, low voltage, open windings and seized loads.Up to 5 steps Motor overload trips or motor runs hotCompare current to nameplate, then find out whether it’s the load, the voltage or the overload setting.Up to 3 steps Motor runs backwardSwap two leads on three-phase, follow the nameplate on single-phase, and find out why the rotation changed.Up to 3 steps Noisy or vibrating motorSeparate electrical noise from mechanical with a coast-down test, then find the cause.Up to 3 steps Motor starts, then stopsFind out what opens: the seal-in, an overload, a protector, a control switch or the supply.Up to 5 steps Motor runs slow or won’t reach speedLow voltage, a lost phase, a wrong connection, overload or a weak capacitor.Up to 4 steps Capacitor keeps failingThe capacitor is usually the victim. Find the voltage, heat or start-circuit problem that keeps killing it.Up to 4 steps Motor trips the breaker on startFaults, jammed loads, long starts and breakers that are too small or set too low.Up to 4 steps Two-speed motor runs at the wrong speedCheck the speed contactor, its interlocks and the lead connections against the nameplate.Up to 3 steps Reading megger and winding test resultsWhat a spot reading, a polarization index and winding resistances tell you about a motor.Up to 4 steps