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

Written by eric w. thompson
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How to Run a Three-Phase Motor on a Single Phase
Three-phase motors can only be run on a single phase when a rotary or static converter is employed. (macro of meter housing image by jimcox40 from

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.

Skill level:

Things you need

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

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  1. 1

    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.

  2. 2

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

  3. 3

    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.

  4. 4

    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.

  5. 5

    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.

  6. 6

    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.

  7. 7

    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 start-up. However, if it stays on too long, there is a problem with the motor.

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