A two wire system is usual to provide a supply and return to each item connection of equipment An earth lead would be the only electrical between any item of equipment and the ship's structure. With compound wound generators a third bus-bar would be introduced as the equalising connection between machines. A fuse is a type of switch which isolates a circuit if an excessive current flows To reconnect the circuit, after discovering the cause of the overload, the fuse must be rewired or re placed. The fuse is in effect a weak link in the circuit designed to break and protect equipment from semi-enclosed or rewirable fuse will have damaging high currents. provision for a wire to be replaced after it has burnt out. The correc rating of fuse wire should be replaced within the holder to reinstate the circuit. A cartridge fuse has the wire en closed within a ceramic body and not rewirable blown cartridge fuse must be replaced by one The cartridge fuse is to be preferred since the fusing current value is more reliable than for a rewirable type A circuit breaker is an isolating switch which also functions as a fuse. It has two designed ratin one of the normal safe working current other the overload current. The breaker is closed against the action of a spring to make the circuit and supply the section board or auxiliary. A trip mechanism ping when opens the breaker, a fast opening being ensured by the the breaker is tripped or opened also open if the overload current rating is exceeded for a period of time manually. It will