How to reverse a 3-phase motor

Written by eric w. thompson | 13/05/2017
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

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.

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.

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.

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

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

Things you need

  • Padlock
  • Flathead screwdriver

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