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How to Run a Three-Phase Motor on a Single Phase

By Eric W. Thompson
Three-phase motors can only be run on a single phase when a rotary or static converter is employed.

Although three-phase motors run on alternating current just as single-phase motors do, they are usually powered by a polyphase system that supplies continuous current in a way unavailable for single-phase motors. As such, it is generally impossible to run a three-phase motor on a single phase unless you employ a converter to transform the three-phase current down to a single phase. As long as you have access to either a rotary converter or a static converter, you can perform the job quite easily yourself.

Shut off the motor breaker in the breaker box and lock the breaker shut with a padlock to prevent anyone from turning the breaker on.

Pick a dry and stable location for the converter in relation to the motor, then bolt it in place using a ratchet and socket.

Ground the converter by running a green grounding cable from the converter to a grounding screw on the motor, apply a metal terminal to one end of the wire for the converter grounding screw and apply a terminal to the other end for the motor grounding screw, then crimp the terminals with wire crimpers and screw both terminals in using a flathead screwdriver.

Connect the two leads of the incoming circuit to their corresponding inputs on the converter. Phase one goes to input A and phase two goes to input C. Leave the B input open.

Place a wire nut on the neutral cable, wind up any excess wire into a loose coil, then tape the cable to the motor in a safe place where it will not be damaged.

Attach three output wires to the converter using a flathead screwdriver, then run them to the motor. Run the converter output B to the L2 input on the motor, then run the converter output C to the L3 input on the motor.

Meg the motor to test for proper ground and insulation, then turn the power on to test the motor. The converter’s red light will come on for a few seconds during startup. However, if it stays on too long, there is a problem with the motor.


Things You Will Need

  • Phase converter
  • Wire terminals
  • Wire crimpers
  • Ratchet and socket
  • Flathead screwdriver
  • Padlock

About the Author


Eric W. Thompson began his writing career in 1996 and is now a member of the All-USA Academic Team, having been featured in "USA Today" as one of the top 20 community college students in the country. He is currently taking a break from earning an undergraduate degree in contemplative psychology at Naropa University.