How to Reverse an AC Motor

Written by josh turner
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How to Reverse an AC Motor
AC motors are more complex than DC motors. (Jupiterimages/Photos.com/Getty Images)

AC or alternating current motors rotate by way of an alternating electromagnetic field, while DC motors rotate via a direct current of electricity transferring through copper brushes. The most common AC motors come in two different classifications-single-phase and three-phase. Although AC motors are more complex than DC motors, learning how to reverse an AC motor's direction can be a useful bit of information for any motor enthusiast. By acquiring a little wiring knowledge and understanding how the motor operates, you can make an AC motor rotate in any direction you please.

Skill level:
Moderately Challenging

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Things you need

  • Flathead screwdriver
  • Cross-head screwdriver
  • Needle-nose pliers
  • Socket wrench
  • Various sockets
  • Wiring diagrams
  • Operator's manual

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Instructions

    Basic Preparation

  1. 1

    Disconnect all sources of input power and do not open the motor for at least twenty-four hours.

    How to Reverse an AC Motor
    Disconnect any power to avoid risk of electrocution. (Jupiterimages/Photos.com/Getty Images)
  2. 2

    Determine the motor type. Look in the operator's manual or on the back cover of the motor to determine the motor type-single-phase or three-phase.

    How to Reverse an AC Motor
    Look at the operator's manual to determine the motor type. (Keith Brofsky/Stockbyte/Getty Images)
  3. 3

    Take off the back cover of the motor with a flathead screwdriver, a crosshead screwdriver or the appropriate size socket, back cover mounting hardware will vary with motor type.

    How to Reverse an AC Motor
    Remove the back cover using the appropriate tool. (Jupiterimages/Photos.com/Getty Images)

    Single-Phase Motors

  1. 1

    Find the starter winding leads, using a wiring diagram or the instruction manual. The winding leads start the motor and cause it to go in a set direction, usually counter-clockwise. Look for engraved numbers, 1 through 8, or letters, A through H.

  2. 2

    Pull out the first and last wires with a pair of needle-nose pliers. Reconnect the first wire to the last wire's lead port and the last wire to the first wire's lead port.

    How to Reverse an AC Motor
    Remove the wires from their leads with a pair of needle-nose pliers. (Medioimages/Photodisc/Photodisc/Getty Images)
  3. 3

    Pull out the middle two wires and reconnect them to their opposite lead ports.

    Three Phase Motors

  1. 1

    Find the stator or main winding wiring dock using the motor's wiring diagram or the operator's manual. Once the starter windings cause the motor to rotate in a certain direction, the main windings keep the motor going in that same direction. You will need to switch the stator wires to change the direction of a three-phase motor.

    How to Reverse an AC Motor
    The main winding keeps three-phase AC motors rotating in a set direction. (Jupiterimages/Photos.com/Getty Images)
  2. 2

    Look for the main winding poles labelled "T1" and "T3." Pull out the two wires from their respective pole ports with a pair of needle-nose pliers.

  3. 3

    Hook up the "T1" wire to the "T3" pole and the "T3" wire to the "T1" pole.

Tips and warnings

  • Make sure the motor has absolutely no power going to it for at least twenty-four hours. Many AC motors run on 220-current which can be fatal.
  • Follow all safety guidelines and precautions.

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