an interrupter / isolator assembly having a conducting member connected to one contact of a vacuum switch and movable to engage either an earth contact or an isolator contact incorporates a cam member for operating the conducting member and actuating the switch contacts , there being a degree of lost motion between the cam member and conducting member such that making or breaking of a current path between the second contact and either the isolator or earth contact occurs within the vacuum switch and not at the isolator or earth contact .