What action reverses a three-phase AC motor's rotation?

Swapping two of the line conductors is the method used to reverse the rotation of a three-phase AC motor. In three-phase systems, the motor's rotation direction is determined by the sequence in which the individual phases are supplied to the motor windings. Each phase carries an alternating current that creates a rotating magnetic field, and changing the order of two of the phases alters the direction of this field.

When two line conductors are swapped, the phase sequence changes, which directly impacts the motor's magnetic field direction. This results in the motor reversing its rotation. It’s a straightforward procedure and is commonly employed in practice to control the direction of motor operation without needing to modify the motor itself.

Other actions, such as reversing the voltage or adjusting the frequency, do not directly affect the motor's rotation direction. Instead, reversing the voltage would simply change the polarity without altering the phase sequence that dictates rotation. Similarly, adjusting the frequency influences the motor's speed but does not impact the direction. Therefore, swapping the conductors is the correct and most effective means of reversing the motor's rotation.