What condition occurs if one phase of voltage to a three-phase motor opens?

When one phase of voltage to a three-phase motor opens, the condition that occurs is known as single phasing. In a three-phase motor, each phase is designed to contribute to the motor’s overall operation. If one phase becomes disconnected, the motor is left to operate on just the remaining two phases.

This condition leads to a significant imbalance in the voltage supply. The motor may still attempt to run, but it will experience reduced torque, increased current in the functioning phases, and may overheat due to the lack of balance. This can result in damage if the motor is not quickly shut down. Therefore, recognizing the signs of single phasing is crucial for troubleshooting and maintaining the integrity of three-phase motor systems.

The other conditions listed do not accurately describe the situation that occurs specifically as a result of one phase being opened. Phase shifting refers to the adjustment of phase angles in alternating current systems, motor stalling generally involves a failure to turn but can happen under various circumstances, and overvoltage implies an excessive voltage situation across the motor, which is not directly caused by a loss of one phase.