The House Wiring is generally done with two systems: The Tree System or The Ring System. In the tree system, the L and N wires from the cable are connected to two bus bars in the distribution box.
The Tree System:
In the tree system, the L and N wires from the cable are connected to two bus bars in the distribution box.
A fuse is used for domestic lighting. The bulbs and the plug point for the fan or table lamp are connected in this circuit, each in parallel across L and N, and operated by a separate switch on the livewire side.
The fuse is connected to two or more three-pin power plug points which can be used for irons, toaster, hot plates, etc. The third wire is the earth wire connected to the metal body of the appliance which is earthed.
As branches to different sections of the house from the distribution box, the method is referred to as the tree system.
The tree system has some disadvantages. If a fuse blows off, two or more appliances have to be checked. Too many wires of different ratings crowd into the distribution box from different sections of the house. If extra points are required at a later stage there may not be place in the distribution box for extra wires. This system is rapidly being replaced by the ring system.
The Ring System:
The ring system consists of the three wires L, N and E, forming three separate rings round the house.
The main advantages of the ring system are that the supply can be tapped at any convenient point in the house; moreover each appliance is operated by a separate fuse. If the fuse blows off, only that appliance is to be checked. This system involves les wiring and is cheaper to set up.
It must be noted that bulb resistances are high and so the current is small. Fuses and connecting wires for lighting purposes are thinner than those used for heating appliances. The resistance of a heating appliance is low and so the current drawn is comparatively high.
