Abstract: Signals for controlling any of a wide variety of field devices such as circuit breakers, generators, transformer connections and the like are produced from a common function module. The particular device or devices to be operated are selected on an exclusive basis by a control module dedicated for that purpose. The control module cooperates with the common function module to produce the desired control and/or monitoring of the associated field devices and prevents any other control module from operating when it is selected. Exclusive operation is effected by an interruptible serial connection of a power line between control modules. A multiplexing arrangement switches the pertinent measurement data associated with a selected operation into a display panel. The combined modules provide direct control of all field devices at a remote location but can also be controlled by a distant supervisory equipment.