As part of a moveable carriage assembly, a plurality of trolley wheels are capable of being driven, in worm-gear fashion, along a coil which is rotatable about its axis. One end of the coil is conductive and the other end of the coil is preferably non-conductive. A further part of the traveling carriage assembly electrically interconnects a conductive trolley wheel with an electrical contact situated remote from one end of the coil. Multiple conductive wheels are electrically interconnected.