Reversing a three-phase motor requires swapping any two of the three power leads. That’s it. This changes the phase sequence of the power supply, which reverses the direction of the rotating magnetic field inside the motor, and the rotor follows. The principle is simple, but doing it safely and choosing the right method for your setup matters.
Why Swapping Two Leads Works
A three-phase motor creates a rotating magnetic field from three currents that peak one after another, each offset by 120 degrees. If the phase sequence is R-Y-B, the magnetic field rotates clockwise. Swap any two of those connections, and the sequence changes to something like R-B-Y. The magnetic field now rotates in the opposite direction, and the motor shaft follows.
It doesn’t matter which two leads you swap. You can exchange L1 and L2, L2 and L3, or L1 and L3. Any combination reverses the phase order. Swapping all three leads, on the other hand, restores the original sequence and changes nothing.
Manual Lead Swap at the Motor
For a motor that only needs to run in one direction and was wired incorrectly, physically swapping two leads is the most common fix. The process is straightforward:
- De-energize and lock out the circuit. Turn off the disconnect or breaker feeding the motor. Apply a lockout device so no one can re-energize it while you’re working. OSHA’s lockout/tagout standard (1910.147) requires you to verify isolation before touching any wiring, meaning you should confirm with a meter that no voltage is present.
- Identify the three power leads. At the motor terminal box, you’ll typically see terminals labeled U, V, and W (or T1, T2, T3). Note which supply conductor connects to which terminal.
- Swap any two connections. Disconnect two of the three leads and reconnect them to each other’s terminals. For example, move the wire on U to V and the wire on V to U. Leave the third wire where it is.
- Secure and test. Tighten all terminal connections, close the junction box, remove your lockout, and briefly bump the motor to confirm the new rotation direction.
If you’re not sure which direction the motor currently spins, or which direction it needs to spin, look at the driven equipment. Fans, pumps, and compressors almost always have a rotation arrow stamped on the housing or nameplate.
Checking Rotation Before Powering Up
A phase rotation meter lets you verify the direction a motor will spin without energizing it. You connect the meter’s leads to the motor terminals, then manually turn the shaft by hand in the direction you want it to rotate. The meter reads the small voltage the spinning rotor generates and tells you whether the current phase connection matches that direction.
If the meter shows the opposite direction, swap any two leads at the terminal box before you ever apply power. This is especially useful when installing a new motor or reconnecting one after maintenance, since running certain equipment backwards even briefly (scroll compressors, for example) can cause damage.
Forward/Reverse Starters
When a motor needs to run in both directions during normal operation, like a conveyor that loads and unloads, or a hoist that raises and lowers, the lead swap is built into the control circuit using a forward/reverse magnetic starter.
This starter uses two three-pole contactors instead of one. Each contactor connects the three-phase supply to the motor, but one of them has two leads crossed internally. When the “forward” contactor closes, the motor gets the normal phase sequence. When the “reverse” contactor closes, two phases are swapped and the motor runs the other way.
Because energizing both contactors at the same time would create a direct short circuit between two phases, forward/reverse starters include two layers of protection. Mechanical interlocks are physical barriers: when one contactor pulls in, a lever blocks the other contactor’s armature from moving. Electrical interlocks use a normally closed auxiliary contact from each contactor wired in series with the opposite contactor’s coil. If the forward contactor is energized, the reverse coil’s circuit is broken, and vice versa. Both interlocks work together so that a single failure doesn’t cause a short.
Only one set of overload relays is needed since both contactors feed the same motor. If an overload trips in either direction, both coils lose power and the motor stops.
Reversing With a VFD
If the motor is controlled by a variable frequency drive, you have two options. The first is the same physical lead swap at the motor terminals. The second is a software parameter inside the drive. Yaskawa drives, for example, use parameter b1-14, which toggles between standard and reversed phase order. Most other VFD manufacturers offer a similar setting.
There’s an important caveat: drive manufacturers generally recommend the software approach only for testing. If you initialize or factory-reset the drive, the parameter reverts to its default, and the motor goes back to its original direction without warning. For a permanent change, swap the physical motor leads and leave the drive parameter at its default. That way the correct rotation survives any future drive replacement or reset.
Many VFDs also accept a reverse command from an external signal (a switch, PLC output, or digital input) that tells the drive to reverse the output phase sequence on the fly. This is the cleanest approach for applications that need both directions during operation, since the drive handles acceleration, deceleration, and the transition between directions without mechanical contactors.
Common Mistakes to Avoid
Swapping leads on the supply side of a VFD instead of the motor side won’t reverse the motor. The drive rectifies incoming AC to DC internally, so input phase order doesn’t affect output rotation. Always make the swap between the drive’s output terminals and the motor.
On dual-voltage motors (those with multiple winding connections for 230V or 460V operation, for example), make sure you’re only swapping the main power leads, not rearranging the internal winding jumpers. The terminal diagram on the motor nameplate shows which terminals are supply connections and which are winding links.
Finally, if you reverse a motor that drives a pump, check that the system can handle reverse flow. Centrifugal pumps will spin backwards without mechanical damage in most cases, but positive displacement pumps can be destroyed or cause pipe failures if run in the wrong direction. Always verify what the driven equipment can tolerate before reversing rotation.