Abstract: An electrical control system for controlling a plurality of electrical loads comprises an electrical drive unit capable of providing a plurality of separate electrical signals each at a different reference level and a fixed frequency coded electrical interrogator signal, and for each electrical load there is provided a switching unit arranged to receive the signals from the drive unit and arranged to be connected via a control link for a different part of the interrogator signal to a contactor control unit and during that part of the interrogator signal a control signal representative of the condition of the switching unit is supplied to the contactor control unit. The contactor control units are connected to respective contactors in the supply circuits of separate electrical loads and the contactor control units serve to control the operation of the contactors in response to the signals received from the associated switching units.