3-Phase Forward/Reverse Motor Control Circuit Diagram

3-Phase Forward/Reverse Motor Control Circuit Diagram — interactive diagram. Open it in the editor to customise components and wiring.

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A three-phase forward/reverse motor control circuit uses two interlocked contactors that reverse any two of the three supply phases to the motor terminals, changing the direction of rotation of the motor shaft.

Reversing a three-phase induction motor is achieved by swapping any two of the three phase connections to the motor's stator terminals. The forward/reverse control circuit implements this through two main contactors — Forward contactor (KM1) and Reverse contactor (KM2) — wired so they can never close simultaneously, which would create a three-phase short circuit.

CIRCUIT STRUCTURE: The power (main) circuit carries the three-phase supply (L1, L2, L3) through a main isolator and motor overload protection relay (thermal overload or electronic relay) before reaching the two contactors. KM1 passes phases in the order L1-L2-L3 to motor terminals U-V-W (forward rotation). KM2 swaps two phases — typically L1 and L3 are exchanged, so the motor receives L3-L2-L1 to U-V-W — reversing the rotating magnetic field and thus the shaft direction.

The control (auxiliary) circuit operates at a lower voltage — typically 24 V AC, 110 V AC, or 230 V AC drawn from the supply through a control transformer — and contains: - A Forward pushbutton (NO contact) - A Reverse pushbutton (NO contact) - A Stop pushbutton (NC contact) - Overload relay auxiliary contacts (NC) - Auxiliary contacts of each contactor used for self-hold (seal-in) and interlock functions

INTERLOCKING: Both mechanical and electrical interlocking are mandatory: 1. Electrical interlock: An NC auxiliary contact of KM1 is wired in series with the KM2 coil circuit, and vice versa. If KM1 is energised, its NC auxiliary contact opens and prevents KM2 from energising — even if the Reverse button is pressed simultaneously. 2. Mechanical interlock: A physical linkage mechanism between the two contactors — often a separate mechanical interlock accessory — provides a second, independent layer of protection. If an electrical contact welds, the mechanical interlock still prevents simultaneous closure.

OPERATION SEQUENCE: To reverse the motor, the operator must first press Stop (to de-energise the running contactor and allow the motor to decelerate) before pressing the opposite direction button. Some circuits include a timing relay to enforce a minimum stop time before reversing direction, protecting the motor from switching stress.

How to wire 3 phase forward reverse motor control circuit diagram

Isolate and lock out the three-phase supply Switch off and lock the main isolator. Use a suitable voltage tester to confirm all three phases are dead at the contactor input terminals before any wiring work begins. Follow lockout/tagout (LOTO) procedures.
Wire the main (power) circuit Connect L1, L2, L3 from the main isolator through the overload relay and then to the input terminals of both KM1 and KM2. The output terminals of KM1 connect to motor terminals U-V-W in phase order L1-L2-L3. The output terminals of KM2 connect to U-V-W with L1 and L3 swapped (L3-L2-L1 to U-V-W).
Install the mechanical interlock between contactors Mount KM1 and KM2 adjacent to each other and fit the mechanical interlock accessory specified by the contactor manufacturer. The interlock must physically prevent both contactors from closing simultaneously. Follow the manufacturer's installation instructions precisely.
Wire the electrical interlock in the control circuit In series with the KM2 coil circuit, insert an NC auxiliary contact of KM1. In series with the KM1 coil circuit, insert an NC auxiliary contact of KM2. These cross-interlocks mean each contactor's coil can only energise when the other is de-energised.
Wire the control circuit pushbuttons and overload contacts Connect the Stop button (NC) in series with the main control supply. Connect the Forward button (NO) in parallel with KM1's NO self-hold auxiliary contact, feeding KM1's coil. Connect the Reverse button (NO) in parallel with KM2's NO self-hold auxiliary contact, feeding KM2's coil. Wire the overload relay NC auxiliary contact in series with the common control supply.
Set the overload relay to motor full-load current Read the motor's full-load current (FLC) from the nameplate. Set the thermal overload relay adjustment dial to this value. If the overload has a separate setting for service factor, consult the motor nameplate.
Test under no load before connecting the motor to its driven load Restore supply and test control circuit function: press Forward, confirm KM1 energises and KM2 cannot be energised. Press Stop, then press Reverse, confirm KM2 energises and KM1 cannot be energised. Verify motor rotation direction in both modes before connecting to the load.

Specifications

Supply voltage (typical)	400 V AC three-phase, 50 Hz (IEC); 480 V AC three-phase, 60 Hz (NEMA)
Control circuit voltage (typical)	24 V AC, 110 V AC, or 230 V AC (via control transformer)
Phase reversal method	Swap any two of three phases — conventionally L1 and L3 exchanged to motor terminals U and W
Interlock requirement	Both electrical (NC auxiliary contacts) AND mechanical interlock mandatory
Overload relay setting	Motor nameplate full-load current (FLC)
Contactor duty class	AC3 (squirrel-cage motor starting and stopping)
Standards applicable	IEC 60947-4-1 (contactors), IEC 60947-5-1 (control devices), NEC Article 430 (US)
Minimum stop time before reversing (recommended)	Allow motor to decelerate to standstill — use anti-plugging timer if required

Safety warnings

A forward/reverse circuit without both mechanical and electrical interlocks creates a risk of three-phase short circuit with potentially catastrophic arc flash energy. Both interlock types are mandatory — do not omit either.
This circuit involves three-phase mains voltage. Work must only be performed by a qualified electrician in compliance with local regulations (IEC 60364, BS 7671, NEC Article 430, AS/NZS 3000 as applicable). Always apply lockout/tagout before working on the panel.
Arc flash hazard exists at the main isolator and contactor terminals. Determine the incident energy level for the panel before working inside it and use appropriate arc-rated PPE (face shield, gloves, arc suit rated to the calculated incident energy).
Set the overload relay to the motor's full-load current nameplate value. Incorrect overload settings allow a motor to overheat silently without tripping — leading to insulation failure and potential fire.
Do not attempt to reverse the motor direction while it is running unless the circuit includes verified anti-plugging protection. Plugging a loaded motor can mechanically damage couplings, gearboxes, and driven equipment, and will cause significant overcurrent in the motor windings.

Tools needed

Lockout/tagout equipment (padlock, tags, multi-lock hasp)
Three-phase voltage tester or multimeter (CAT III or CAT IV rated)
Insulated screwdrivers and nut drivers
Torque screwdriver (terminal torque values specified by contactor manufacturer)
Continuity tester / multimeter for control circuit testing
Wire strippers and ferrule crimping tool (for panel wiring)
Ferrules and terminal markers for control wiring identification
Arc-rated PPE (face shield, gloves, arc-rated jacket)

Common mistakes

Omitting the mechanical interlock and relying on electrical interlock alone — contact welding under fault conditions can defeat a purely electrical interlock, causing a three-phase short.
Swapping all three phases for reverse instead of only two — swapping all three phases gives the same phase sequence and the same rotation direction. Only two phases must be exchanged.
Wiring KM2's output in the same phase order as KM1 — if both contactors pass L1-L2-L3 to the motor in the same order, pressing Reverse produces the same rotation as Forward. Verify phase order with a phase rotation meter.
Setting the overload relay to a higher current than the motor nameplate FLC to prevent nuisance trips — this defeats the motor's only thermal protection. Investigate the root cause of nuisance trips instead.
Not providing a separate self-hold (seal-in) contact for each contactor coil — without self-hold, the motor only runs while the pushbutton is held pressed.

Troubleshooting

Motor runs in Forward but not in Reverse (or vice versa): Cause: KM2 coil circuit is open — check the KM1 electrical interlock NC contact in series with the KM2 coil, or the KM2 coil fuse or overload trip. Fix: With KM1 de-energised, measure voltage across the KM2 coil terminals while pressing Reverse. If 0 V, trace the control circuit upstream — check KM1's NC auxiliary contact continuity, the Stop button, and the overload relay contacts.
Motor does not stop when Stop button is pressed: Cause: Stop button NC contacts are failed open (making the button appear pressed at all times, which would stop the motor) — if the motor continues to run, the self-hold contacts of the contactor are bypassing the Stop button or the Stop button is wired incorrectly in parallel rather than series. Fix: Isolate and check Stop button wiring. The NC Stop button must be in series with the coil circuit so that opening the contact interrupts coil supply. Wiring it in parallel creates a permanent bypass.
Overload relay trips shortly after motor starts: Cause: Overload set too low, motor is mechanically overloaded, or the motor is single-phasing (one phase lost). Fix: Check overload setting against motor nameplate FLC. Measure all three supply phase voltages — confirm all three are present and balanced. Check motor current on all three phases using clamp meter. Investigate mechanical load if current is excessive on all three phases.
Both contactors energise simultaneously despite interlocks: Cause: Electrical interlock auxiliary contacts have failed (welded or missing), and mechanical interlock is absent or incorrectly installed. Fix: Immediately isolate the supply. Inspect auxiliary contact blocks on both contactors — replace any failed contacts. Verify mechanical interlock installation. Do not restore power until both interlock types are confirmed functional.

Frequently asked questions

Why must both mechanical and electrical interlocks be used?

Electrical contacts can weld closed under overload or fault conditions. If KM1's contacts are welded and only an electrical interlock is used, pressing Reverse would energise KM2 while KM1 is still conducting — creating a direct three-phase short circuit. Mechanical interlocking provides an independent physical barrier that remains effective even with welded contacts.

Which two phases are swapped to reverse a three-phase motor?

Any two of the three phases can be swapped — the result is the same. Convention dictates swapping L1 and L3, leaving L2 in the middle position unchanged. The motor receives L3-L2-L1 at terminals U-V-W in reverse, instead of L1-L2-L3 in forward. Never swap all three phases — that produces the same rotation as the original.

Can a variable-frequency drive (VFD) replace the forward/reverse contactor circuit?

Yes, a VFD can reverse motor direction by changing its internal output phase sequence via a control signal, eliminating the need for contactors. A VFD also provides soft start and overload protection. However, the forward/reverse contactor circuit remains the standard for simple, cost-sensitive applications where variable speed is not required.

What does the thermal overload relay protect against?

The thermal overload relay protects the motor windings against sustained overcurrent caused by overloading, stalled rotor, or single-phasing (loss of one phase). It does not protect against short circuits — that is the function of the main fuses or circuit breaker upstream. The overload relay is set to the motor's full-load current (FLC) as shown on the nameplate.

Why should a timer be used when reversing direction?

Switching a running motor directly to the opposite direction (plugging) subjects the stator windings and driven machinery to high current and mechanical shock. An anti-plugging timer (or a plugging relay sensing back-EMF) ensures the motor decelerates to near zero speed before the reverse contactor energises, protecting the motor and connected equipment.

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