Abstract: Control apparatus for three phase alternating current load protection wherein each of the phases of the load is connected to a corresponding current transformer. When the load is energized by a three phase power supply the transformers induce signals which are applied to a signal detection circuit. The detection circuit controls a relay means. If any of the three power phases is lost the detection circuit is interrupted causing the relay means to drop out, whereby the load, the power supply and auxilliary circuitry, as the case may be, are protected.