Phase unbalance in a three-phase system causes ___.

Phase unbalance in a three-phase system occurs when the currents in the three phases are not equal in magnitude or when the phase angles are not spaced evenly. This imbalance can lead to significant issues, particularly overheating in motors that are designed to operate under balanced conditions.

When one phase carries less current than the others, the motor may draw excessive current from the other phases to compensate for the imbalance. This can cause the motor to operate inefficiently, leading to increased heat generation, which can potentially damage the windings and other components of the motor. Therefore, overheating motors is a direct consequence of phase unbalance.

Additionally, phase shifting refers to the angle difference of the electrical currents in different phases. In the case of unbalanced phases, the ability of the system to maintain the proper phase angle relationships necessary for efficient operation is compromised. This shifting can lead to further complications in performance and reliability of equipment connected to the system.

Thus, the correct answer reflects that phase unbalance causes both overheating of motors and phase shifting, demonstrating its detrimental effects on the entire electrical system.