ELECTRICITY IN THE HOME

Parallel Connections of Domestic Appliances Electricity boards distribute power to separate households using a pair of thick, insulated power cables. Each building is connected in parallel with these cables, one of which is live, the other is neutral. Each user needs to operate lighting and power circuits independently.

FUSES Fuses use the effect of heating of an electric current to break or open a circuit when excessive current flows. They reduce the danger of overheating by limiting the size of currents which can flow through wires and whole circuits. The fuse is placed in the live wire, often in the form of cartridge inside the plug. It breaks before the circuit before the cable can overheat and catch fire.

Pictures of fuses

Current Rating for a Given Appliance A microwave is connected in parallel to a 240V supply. The current used by the microwave is 7.5A. Calculate the power used by the device and the fuse required. Power=IV =7.5*1800 =1800W A 9A fuse can be used for a circuit to prevent damage to the microwave.

The Earth Wire The earth wire is a safety wire which connects the metal body of the appliance to the earth and prevents it from becoming live if a fault develops. It has a yellow-green insulation. Example: if the live wire were to work loose and touch the body of a kettle, a current would immediately flow to the earth and blow the fuse. If there were no earth wire the body of the kettle would remain live and lethal current would flow through anyone who touches it.

The Live Wire The potential of the wire goes alternately negative and positive, making current flow backwards and forward through the circuit. The live wire has a brown insulation.

The Neutral Wire The Electricity board earths the neutral wire by connecting it to a metal plate buried in the ground. Although current passes through the wire it remains at zero potential. The neutral wire usually has a blue insulation.