When a three-phase motor single-phases, it

When a three-phase motor single-phases, it

• A. Draws power from all three phases equally
• B. Draws power from only one phase
• C. Draws power from two phases
• D. It stops drawing power

Answer: (B)

The key idea is that three-phase motors rely on a balanced trio of currents to create a smooth rotating magnetic field. If one supply phase drops out (single phasing), only two phases remain energized, so the motor no longer has three equal windings. The two remaining phases still drive current through two windings, effectively feeding the motor from two phases. This produces a pulsating magnetic field and greatly reduced torque, while the current in the remaining windings rises and the motor runs hot and unbalanced. It may stall or trip protections if a heavy load is applied. So, when single-phased, a three-phase motor continues to draw power from two phases, not from just one, and not from three equally.

The key idea is that three-phase motors rely on a balanced trio of currents to create a smooth rotating magnetic field. If one supply phase drops out (single phasing), only two phases remain energized, so the motor no longer has three equal windings. The two remaining phases still drive current through two windings, effectively feeding the motor from two phases. This produces a pulsating magnetic field and greatly reduced torque, while the current in the remaining windings rises and the motor runs hot and unbalanced. It may stall or trip protections if a heavy load is applied. So, when single-phased, a three-phase motor continues to draw power from two phases, not from just one, and not from three equally.