What term refers to the loss of one phase in a three-phase motor?

• A. VFD
• B. Bearing
• C. PLC
• D. Single Phasing

Answer: (D)

When three-phase power is applied to a motor, the three windings create a balanced rotating magnetic field that provides full torque. If one phase is lost, the motor is fed by only two phases, which makes the magnetic field unbalanced and pulsating. This drastic imbalance causes a large drop in starting and running torque, and the current in the remaining phases often rises, leading to overheating and potential winding damage. The term for this condition is single phasing, and it describes the electrical fault itself rather than a device or a mechanical component. VFD, bearing, and PLC refer to a drive, a mechanical part, and a control system, respectively, and do not name this fault. If single phasing occurs, restoring the missing phase or safely removing power to the motor are the immediate steps to prevent damage.