The rotation of a three-phase motor can be reversed by interchanging which of the following?

• A. The collector ring
• B. Any two leads
• C. The starting winding
• D. The running winding

Answer: (B)

The direction of a three-phase motor is set by the order of the three-phase supply feeding the stator windings. When the phases are energized in a particular sequence, the magnetic field rotates in one direction. If you swap two of the supply lines, you invert that phase sequence, which flips the rotating magnetic field and makes the motor run in the opposite direction.

The collector ring is part of the rotor circuit in wound-rotor configurations and does not change the stator’s phase sequence. Likewise, the arrangement of starting versus running windings is not what determines rotation in a standard three-phase motor. Therefore, interchanging two of the supply lines is the correct way to reverse rotation.