How to reverse a 3-phase motor

Written by eric w. thompson
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How to reverse a 3-phase motor
Three-phase motors run in reverse when two of the phases are exchanged. (Big electric motor in a marble quarry. Alentejo, Portugal image by mrfotos_fotolia from Fotolia.com)

Three-phase motors rely on a polyphase system for delivering continuous alternating current. Instead of the single power lead used in single-phase electrical systems, three-phase systems use three power leads. Each power lead is a phased 120 degrees apart from the other two leads, making them perfectly balanced. When each phase of the three-phase system is connected to its proper terminal in the three-phase motor, the motor runs forward, as it was designed. However, if so desired, the motor can be reversed by switching the order of the phases.

Skill level:
Moderate

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Things you need

  • Padlock
  • Flathead screwdriver

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Instructions

  1. 1

    Shut the breaker off that supplies power to the three-phase motor, then lock the breaker with a padlock to prevent the breaker from being turned on while you are working on the motor.

  2. 2

    Unscrew and remove the cover of the motor using a flathead screwdriver, and determinate two of the three phases using a flathead screwdriver. It doesn't matter which two phases are removed: T1, T2 or T3.

  3. 3

    Swap the two phases and refasten them using a flathead screwdriver. Reinstall the cover.

  4. 4

    Restore the power. The motor now runs in reverse because two of the phases have been swapped.

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