If you lose a phase on a three-phase motor, what could happen to the motor?

When a three-phase motor loses one of its phases, it can continue to operate in a condition known as "single-phasing." However, this operation is not viable for the long term and leads to significant risks. The loss of one phase causes an imbalance in the voltages supplied to the motor. As a result, the motor will attempt to run with only two of the three phases, which can significantly increase the current in the remaining phases, leading to two primary issues.

First, operating under single-phase conditions generates excessive heat, due to the motor working harder to compensate for the lost phase, which can ultimately lead to overheating and thermal damage. The increase in current may also cause the motor to draw more power than it's designed for, leading to further strain on windings and insulation, which can result in electrical failure.

If the motor is not equipped with protective devices such as overload relays, it could suffer from catastrophic failure over time, including winding burnout. Therefore, the failure to shut down or the risk of damage from operating under this condition is why "it would single phase and could be damaged" is the most accurate answer.