If an electric motor designed for a grounded 3 phase circuit loses one phase while fully loaded, what can happen?

When a grounded 3-phase electric motor loses one phase while under full load, it continues to operate but may not function efficiently. The motor relies on all three phases to balance the load and provide smooth operation. If one phase is lost, the remaining two phases will attempt to carry the load, leading to an uneven distribution of current. As a result, the motor can experience excessive current draw in the two remaining phases.

This situation, often referred to as "single phasing," can cause the motor to overheat because the reduced current-carrying capacity leads to increased heating within the windings. The motor is designed to function optimally with all three phases; without one, it can cause an overload condition that may ultimately damage the motor's insulation or windings. Therefore, monitoring for loss of a phase is essential to prevent long-term damage to the motor.

The other possibilities such as operating normally or cooling down do not accurately reflect the stress placed on the motor in this scenario. Stopping instantly is not typically the behavior of a motor when a phase is lost; instead, it continues to run until it is damaged or the overload condition causes it to trip a protective device.