To reverse a single phase motor, you swap the connections of either the start winding or the main winding relative to the other, but not both at the same time. This reverses the magnetic field relationship that determines rotation direction. The exact process depends on your motor type, how many wires it has, and whether you want to switch direction on the fly or just rewire it once.
Why Swapping One Winding Works
Single phase motors use two sets of windings to create a rotating magnetic field: a main (run) winding and a start (auxiliary) winding. The interaction between these two windings determines which way the rotor spins. When you reverse the electrical polarity of just one winding, you flip the direction of the rotating field, and the motor turns the opposite way. If you reverse both windings simultaneously, the phase relationship stays the same and the motor continues spinning in the original direction.
Reversing a Capacitor Start or Capacitor Run Motor
Most capacitor start and capacitor run motors bring out four or more color-coded leads from the windings. Two leads connect to the main winding and two to the start winding (which runs through the capacitor). To reverse direction, you swap the two start winding leads while leaving the main winding connections unchanged. Alternatively, you can swap the main winding leads while leaving the start winding alone. Either approach works, as long as you only reverse one pair.
On dual voltage motors (those rated for both 115V and 230V), the same principle applies regardless of which voltage configuration you’re using. The key difference is the wiring complexity: at 230V the windings are typically connected in series, while at 115V they’re in parallel. In both cases, reversing is handled by an external reversing switch or contactor. For applications that require frequent direction changes, two mechanically interlocked contactors prevent both from energizing at the same time, which would short the motor.
Three-Wire PSC Motors
Permanent split capacitor (PSC) motors often have just three external wires, typically black, red, and blue. These motors are common in fans, blowers, and small gear motors. With only three wires, you can’t simply “swap two leads” the way you would on a four-wire motor. Instead, you change which colored wire connects to the capacitor and the hot line.
For clockwise rotation on a typical Bodine-style PSC motor: connect the black wire and the hot line lead to one terminal of the capacitor, the red wire to the other capacitor terminal, and the blue wire to the neutral side of the AC line. For counterclockwise rotation: connect the red wire and the hot line lead to one capacitor terminal, the black wire to the other capacitor terminal, and leave the blue wire on neutral. The blue wire and ground connection stay the same in both cases.
If you want to switch directions with a physical toggle, use a single pole, double throw (SPDT) switch with a center-off position. Wire the black motor lead to one outer terminal of the switch and one capacitor lead. Wire the red motor lead to the other outer terminal and the other capacitor lead. Connect the hot line to the center (pole) terminal. The blue wire goes straight to neutral. Flipping the switch routes power through either the black or red lead first, reversing the capacitor’s relationship to the windings and changing rotation.
Reversing a Universal Motor
Universal motors, found in power tools, vacuum cleaners, and small appliances, work on both AC and DC. They use carbon brushes pressing against a spinning commutator. Each brush connects to one of the two field coils inside the motor housing.
To reverse a universal motor, you change which brush connects to which field coil. The simplest method is to remove the brushes and the internal wiring board, rotate the board 180 degrees, and reinstall everything. Before the swap, each brush is wired to the field coil nearest to it. After rotating the board, each brush connects to the opposite field coil. That phase shift between the field windings and rotor windings is all it takes to flip the direction. No other wiring changes are needed.
Some universal motors have their field coils and brush connections soldered or hardwired in ways that make this difficult without cutting and resoldering wires. If the motor has accessible external leads for the field and armature circuits, you can swap the two field coil leads instead of physically moving brushes.
Shaded Pole Motors: A Special Case
Shaded pole motors are the simplest and cheapest single phase motors, commonly found in small fans and low-torque applications. They don’t use a capacitor or start winding. Instead, a copper “shading” ring on one side of each pole piece creates a slight delay in the magnetic field, which nudges the rotor in one direction. The rotor always turns from the center of the pole toward the shaded side.
You cannot reverse a shaded pole motor by swapping wires. The direction is physically built into the stator. To reverse one, you need to disassemble the motor, remove the rotor, flip the stator 180 degrees so the shading rings end up on the opposite side relative to the rotor, and reassemble. This is a mechanical modification, not an electrical one, and it only works if the motor housing is symmetrical enough to allow the stator to be flipped. Many cheap shaded pole motors aren’t designed for this, and the effort often isn’t worth it compared to buying a motor that already spins the direction you need.
Safety Before You Start
Always disconnect the motor from power before touching any wiring. If the motor has a capacitor (start capacitor, run capacitor, or both), it can hold a dangerous charge even after the power is off. Before handling capacitor terminals, place a resistor across the two terminals to drain the stored energy safely. A resistor with a value between 10,000 and 20,000 ohms rated for the voltage works well. After a few seconds, use a multimeter set to DC voltage to confirm the reading across the capacitor terminals is zero before proceeding. Skipping this step risks a painful or dangerous shock.
Take a photo of the original wiring before you disconnect anything. Single phase motors can have anywhere from three to eight leads depending on the type, voltage rating, and whether they have thermal protection. A photo makes it easy to return to the original configuration if something doesn’t work as expected.
Quick Reference by Motor Type
- Capacitor start / capacitor run (4+ wires): Swap the two start winding leads, or swap the two main winding leads. Never swap both pairs.
- PSC motor (3 wires): Reroute which colored lead connects to the capacitor and hot line, following the manufacturer’s wiring diagram for your specific model.
- Universal motor: Swap which brush connects to which field coil, either by rotating the wiring board or resoldering leads.
- Shaded pole motor: Physically flip the stator so the shading rings face the opposite direction. No wiring change will reverse this type.
- Split phase motor (no capacitor): Same principle as capacitor motors. Swap either the start or main winding leads, not both.
Some motors are labeled “non-reversible” by the manufacturer. This usually means the start and main windings share internal connections that aren’t brought out as separate leads, making it impossible to reverse one winding independently. If your motor has only two external wires (besides ground) and no capacitor, it’s likely non-reversible without internal modification.