Abstract: A motor protector for three-phase electric motors includes two independent sensing transformers for simultaneously sensing the voltage across two phases of a three-phase power supply to detect failures in all of the power lines including either the primary or secondary side of a line transformer. A first relay is actuated by the electric power sensed across the one phase and a second relay is actuated by the electric power sensed across said other phase through a set of contacts of the first relay for disconnecting the second sensing transformer from the power supply when there is a failure that results in a reduction in voltage in the one phase to prevent production of feedback voltages through the phase windings of a line transformer. For a wye-delta line transformer configuration the one phase is a high leg and the other phase is the low leg.