Why does swapping two leads reverse the motor?

Why does swapping two leads reverse the motor?

• A. Original phase sequence A-B-C produces rotation in one direction; swapping creates A-C-B, reversing rotation.
• B. It changes the magnitude of the stator field.
• C. It changes the rotor speed independently of field.
• D. It changes the rotor polarity.

Answer: (A)

The direction of rotation is set by the order in which the stator windings are energized. In a three‑phase system, the currents are 120 degrees apart, creating a magnetic field that appears to rotate around the stator. The sense of that rotating field depends on which phase leads the others. If the original phase order produces rotation in one direction, swapping two leads changes the phase sequence to the opposite order, so the rotating field now moves the other way. The rotor then tends to follow this rotating field, causing the motor to spin in the opposite direction. The magnitude of the stator field and the rotor’s response in speed are governed by the supply frequency and slip, not by just swapping leads. The rotor’s polarity isn’t a controlling factor in an induction motor.

The direction of rotation is set by the order in which the stator windings are energized. In a three‑phase system, the currents are 120 degrees apart, creating a magnetic field that appears to rotate around the stator. The sense of that rotating field depends on which phase leads the others. If the original phase order produces rotation in one direction, swapping two leads changes the phase sequence to the opposite order, so the rotating field now moves the other way. The rotor then tends to follow this rotating field, causing the motor to spin in the opposite direction. The magnitude of the stator field and the rotor’s response in speed are governed by the supply frequency and slip, not by just swapping leads. The rotor’s polarity isn’t a controlling factor in an induction motor.