WiremanWireman · Motor runs backward: troubleshooting for electricians · 2023 NEC ·
Motor runs backward
Swap two leads on three-phase, follow the nameplate on single-phase, and find out why the rotation changed.
Before you start
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How it works
A three-phase motor turns in the direction its rotating magnetic field turns, and that is set by the order the phases arrive (the phase sequence). Swapping any two line leads reverses the sequence and the motor. A single-phase motor’s direction is set by how its start or auxiliary winding is connected relative to the main winding, so reversing it depends on which leads the manufacturer brought out, and some motors can’t be reversed at all.
Every question and answer in this guide. Tap “Step by step” to walk through it.
- What kind of motor and how is it fed?
- Three phase, on a starter or contactorIs it just this motor, or did several motors reverse at once?
- Just this motor (new or rewired)Phase order at this motor
- Several, after utility work, a generator or a service changeTest: Check phase sequence at the sourceExpect: The same sequence (ABC) at every source, matching what it was before.
- Utility and generator sequences differGenerator sequence doesn’t match utility
- Utility sequence changedUtility phase sequence changed
- Three phase, on a VFDDrive output sets the rotation
- Single phaseDoes the nameplate or lead tag show a reversing connection?
- Yes, there’s a diagram for both directionsReversible single-phase motor
- No reversing leads (shaded pole, sealed PSC)Motor isn’t field reversible
- Diagram missing or leads unmarkedCan’t confirm the leads
- Three phase, on a starter or contactorIs it just this motor, or did several motors reverse at once?