The CBP is a changeover relay unit configured to allow a luminaire to be operated normally from the switched lighting supply and also when the local 240V un-switched supply fails. The changeover then draws power from the emergency supply. This can be 50V, 100V or 240V DC central battery systems or 240V AC static inverter systems. The associated control gear/lamp must be capable of being powered by both 240V AC and the voltage of the central battery being used. upon (un-switched) main failure, the main changeover relay de-energises, and the unit changes over to an intermediate state approximately 0.5s. after this period the emergency supply hold of relay also de-energises and connects emergency supply to the load. Upon restoration of the un-switched supply, the emergency supply hold off relay energises and breaks the emergency supply to the load. Again, after the 0.5s delay the main changeover. relay energises, and connects the switched lighting supply to load. The unit fitted with a dimming inhibit relay, which can be used with dimming control gear to reset dimming level to 100% during the emergency situation. The module is suitable for use with LED, fluorescent and conventional control gear.