signals onto the wires under test this has the advantage in that the control circuitry for the disconnect device does not have to be designed to withstand the high test voltages which are used fig3 shows an embodiment of the present invention that comprises an arrangement similar to that shown in fig2 except that the disconnect device 8 is now connected to a control signal bus 16 u2032 which itself is interfaced to a building management system 18 which may receive an input from the control panel 10 or which may have the control panel 10 integrated therein the bus 16 u2032 may be a data bus of a recognised standard such as the digital addressable lighting interface dali or european information bus eib protocols thus individual disconnect devices 8 may be addressed on the bus to selectively connect and disconnect thus not only can the building management system 18 instruct the devices to disconnect but providing the disconnect devices 8 also support bi directional communication it may then poll each individual device to confirm that the disconnect has indeed occurred the test may then be performed only when all of the devices confirm that they have successfully disconnected fig4 illustrates an arrangement similar to that shown in fig3 but wherein each ballast unit 6 has a dali interface 20 associated therewith such that the lamp brightness can be controlled by suitable control of the high frequency ballast a multisensor 22 and a switch 24 are provided such that the control test panel 10 can be selectively connected to the dali bus.