Reversing Single-Phase Motor Wiring Diagram

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Reversing a single-phase induction motor requires swapping the start-winding connections relative to the run winding — achieved with a DPDT switch or a pair of contactors before energising the motor.

A single-phase induction motor produces rotation using two windings: the main (run) winding and the auxiliary (start) winding. The start winding is connected in parallel with the run winding but is electrically phase-shifted — either by a capacitor (capacitor-start or capacitor-run motor) or by resistance differences — so the resulting two-phase field produces starting torque in one direction.

To reverse the direction of rotation, you reverse the current direction through one winding relative to the other. You cannot reverse rotation by simply swapping the two supply leads — that reverses both windings simultaneously and the direction of rotation remains unchanged.

The correct method is to reverse the connections to either the start winding OR the run winding, but not both. The start winding leads on most motors are brought out separately to the terminal block, typically marked as T5 and T8 (NEMA) or as the auxiliary winding terminals in IEC notation. By swapping these two leads, you reverse the phase relationship between windings and therefore reverse rotation.

In practice this is done with a DPDT (double-pole double-throw) switch or relay wired in a specific cross-over configuration on the start-winding leads. The line-side (run winding) connections remain undisturbed. For automated or remote reversal, two contactors are interlocked — both mechanically and electrically — so that both cannot be energised simultaneously.

Important: the motor must come to a complete stop before reversing. Attempting to reverse a motor while it is still spinning in the original direction produces high inrush currents and severe mechanical shock that can damage windings, centrifugal switch contacts, and the driven machinery. For applications requiring frequent or on-the-fly reversal, a dedicated reversing motor or a variable-frequency drive (VFD) with single-phase input should be considered.

The centrifugal switch — which disconnects the start winding once the motor reaches approximately 75–80% of synchronous speed — must be fully closed (returned to start position) before the reversed start sequence can work correctly.

How to wire reversing single phase motor wiring diagram

Confirm the motor is suitable for field reversal Check the motor nameplate and the wiring diagram inside the terminal cover. Verify the motor type (capacitor-start, permanent-split capacitor, or resistance-split-phase). Confirm that both start-winding leads are brought out to accessible terminals. Shaded-pole motors cannot be reversed by this method.
Isolate, lock out, and verify dead Switch off and lock out the supply at the circuit breaker or isolator. Use a calibrated voltage tester to confirm zero voltage at the motor terminal block on all terminals before touching any wiring. Do not rely on the motor switch alone as the means of isolation.
Identify and label the start winding terminals Using the motor's wiring diagram, identify the start (auxiliary) winding terminals. On NEMA motors, these are typically T5 and T8. Photograph the original wiring before disturbing any connections. Label each lead with tape markers so the original configuration can be restored if required.
Install or wire the DPDT switch in cross-over configuration Wire the DPDT switch so that in one position, T5 connects to supply L1 and T8 connects to the capacitor or the other start-circuit conductor; in the opposite position, T8 connects to supply L1 and T5 connects to the capacitor conductor. This cross-over reverses current through the start winding. The run winding connections are not changed. Refer to a verified wiring diagram for your specific motor type.
Check for mechanical interlock if using contactors If using two contactors (KM-Forward and KM-Reverse) instead of a manual DPDT switch, fit a mechanical interlock between the contactors so both cannot close simultaneously. Add electrical interlocking using normally-closed auxiliary contacts from each contactor in series with the opposite contactor's coil circuit.
Allow the motor to stop completely before switching direction Verify the motor has come to a complete stop before operating the reversing switch. Fit a time-delay relay or mechanical brake if the application requires rapid reversal. Never attempt plug reversal (switching direction on a spinning motor) with a standard single-phase induction motor.
Test rotation in both directions under no-load conditions Restore supply and test rotation in both switch positions with the motor uncoupled from the load if possible. Confirm correct direction, listen for abnormal noise, and measure running current in both directions. Current should be within 10% of nameplate full-load current. Couple the load only after confirming both directions function correctly.

Specifications

Typical rotation reversal method	Swap start (auxiliary) winding leads only; do not swap run winding leads or main supply leads
Centrifugal switch opening speed (typical)	75–80% of synchronous speed (e.g., approx. 1 350–1 440 RPM for a 4-pole, 50 Hz motor)
Start capacitor typical capacitance range	50 µF to 500 µF depending on motor power; rated 250 V AC or higher
Run capacitor typical capacitance range (PSC motors)	2 µF to 50 µF; rated 370 V AC or 440 V AC for continuous duty
Minimum stop time before reversal	Motor must reach zero speed; time varies by inertia — verify by observation or tachometer
Motor terminal designation (NEMA, reversible type)	T1, T3 (run winding); T5, T8 (start winding); T4 (common)

Safety warnings

All motor wiring must be performed by a licensed or qualified electrician in accordance with applicable wiring regulations: NEC / NFPA 70 (USA), BS 7671 (UK), AS/NZS 3000 (Australia/New Zealand), or IEC 60364 (international). This content is for reference and educational purposes only.
Isolate, lock out, and verify dead using a calibrated voltage tester before working on any motor terminals. Residual charge on run capacitors can persist after disconnection — discharge capacitors through a resistor (typically 10 kΩ to 25 kΩ, rated for the capacitor voltage) before touching capacitor terminals.
Never switch a running motor directly into the reverse direction unless the motor is specifically designed and rated for plug reversal (plugging). Attempting to reverse a running standard single-phase induction motor causes very high inrush currents and mechanical shock that can damage the motor and driven equipment.
Verify that the mechanical interlock between forward and reverse contactors is correctly installed and functioning before commissioning. Simultaneous energisation of both contactors creates a direct short-circuit across the supply.
After any reversal modification, verify the earth (ground) continuity between the motor frame and the main earthing terminal before re-energising. Motor frame earthing is a safety-critical requirement under all applicable wiring regulations.

Tools needed

Calibrated voltage tester or multimeter (for isolation verification)
Insulation resistance tester (megohmmeter)
Capacitor discharge resistor (10 kΩ to 25 kΩ, rated voltage)
Screwdrivers (flathead and Phillips, insulated handles)
Clamp-on ammeter (to verify running current after modification)
Lockout/tagout (LOTO) equipment
Wire ferrule crimping tool and ferrules
Cable labels and marker

Common mistakes

Swapping the main supply leads instead of the start-winding leads — this does not reverse rotation on a single-phase induction motor and is a very common error.
Reversing a running motor without first allowing it to stop completely — causes high inrush current, possible winding damage, and mechanical shock to the driven load.
Not discharging the start capacitor before working on the terminal block — charged electrolytic capacitors can deliver a painful or dangerous electric shock even with supply disconnected.
Omitting the mechanical and electrical interlock between forward and reverse contactors in contactor-based reversal circuits — a single contact failure can then result in both contactors closing simultaneously, creating a short circuit.
Failing to re-verify motor earth continuity after rewiring — any wiring disturbance at the terminal block can inadvertently loosen the earth terminal if it shares the terminal cover mounting.
Not testing rotation direction under no-load conditions before coupling the driven equipment — reversing the driven load while coupled can cause immediate mechanical damage if the load has a preferred rotation direction (e.g., a fan, pump, or conveyor).

Troubleshooting

Motor rotates in the same direction regardless of switch position: Cause: DPDT switch is wired incorrectly — both positions connect the start winding in the same polarity, or the switch is actually wired in the run winding instead of the start winding Fix: With supply isolated and locked out, verify which terminals at the motor terminal block are the start-winding leads using the motor's own wiring diagram and a continuity test. Confirm that the DPDT switch performs a cross-over (the two leads are swapped relative to each other) rather than a simple changeover.
Motor hums but does not start in one direction after reversal wiring: Cause: Start winding circuit is open in that switch position — a loose terminal, broken switch contact, or incorrect connection means the start winding is not energised and no starting torque is produced Fix: With supply isolated and locked out, use a continuity tester to trace the start winding circuit through the switch in the non-starting position. Check all terminal tightness and switch contact continuity. Repair the open connection.
Motor overload relay trips shortly after start in reversed direction: Cause: Motor has not fully stopped before reversal was attempted, causing high inrush; or a start capacitor fault is causing the motor to draw high current during the start phase Fix: Allow the motor to fully stop before reversing. If tripping persists after a full stop, test the start capacitor with a capacitance meter — a capacitor with significantly reduced capacitance or open-circuit failure will prevent correct start-winding operation and cause excessive current draw.

Frequently asked questions

Can I reverse a single-phase motor by swapping the two main supply leads?

No. Swapping both supply leads reverses current through both the run winding and the start winding simultaneously. Because the relative phase relationship between the two windings is unchanged, the motor continues to rotate in the same direction. To reverse rotation, you must swap the connections to one winding only — typically the start winding leads.

Which winding leads do I swap to reverse a capacitor-start motor?

Swap the two start-winding leads at the terminal block. On NEMA-coded motors these are typically marked T5 and T8. On IEC motors, the manufacturer's wiring diagram inside the terminal cover shows the auxiliary winding terminals. Always confirm with the motor's own nameplate diagram before making any changes, as terminal numbering varies between manufacturers and motor types.

Does the capacitor need to be rewired when reversing direction?

No. The run capacitor (in a permanent-split capacitor motor) or the start capacitor remains connected between its existing terminals. When you swap the start winding leads, the capacitor's phase-shift effect is automatically reversed relative to the run winding, producing the reversed rotation. The capacitor wiring itself does not change.

Why must the motor stop completely before reversing?

When a running motor is reversed, the voltage across the start winding momentarily approaches twice the supply voltage because the back-EMF adds to the supply. This produces very high inrush current (often 5–7 times full-load current) and severe mechanical shock. Repeated plug reversal without allowing the motor to stop will overheat the windings and damage the centrifugal switch.

Can all single-phase motors be reversed in the field?

Most capacitor-start, capacitor-run, and resistance-split-phase motors can be reversed by swapping start winding leads, provided the leads are accessible at the terminal block. Shaded-pole motors cannot be reversed by rewiring — reversal requires physically rotating the stator. Some sealed single-phase motors have internal connections that do not allow field reversal. Check the motor nameplate and manufacturer documentation.

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