What happens when a 3-phase motor loses one phase?

What happens when a 3-phase motor loses one phase?

• A. It will stall and stop immediately
• B. Single phasing will cause the motor to trip the overload heaters
• C. It will run with no change in performance
• D. It will automatically switch to a safe mode

Answer: (B)

Losing one phase in a three-phase motor creates an unbalanced, single-phased condition. The three-phase field that normally produces steady torque becomes distorted, so the motor loses most of its available torque and can’t deliver the required output under load. The two remaining windings carry more current than normal, causing extra heating in the windings. That overheating is what often triggers the motor’s thermal overload protection, which trips to stop the motor and prevent damage. So, when a phase is lost, the motor won’t run normally and the protective overload will typically trip.

Losing one phase in a three-phase motor creates an unbalanced, single-phased condition. The three-phase field that normally produces steady torque becomes distorted, so the motor loses most of its available torque and can’t deliver the required output under load. The two remaining windings carry more current than normal, causing extra heating in the windings. That overheating is what often triggers the motor’s thermal overload protection, which trips to stop the motor and prevent damage. So, when a phase is lost, the motor won’t run normally and the protective overload will typically trip.