Supply to a House
The electric power line enters our house through three wires. One is called the earth wire or ground wire. This carries no electricity. The earth wire is connected to a large metal plate buried deep in the ground. The remaining two wires carry electricity. One of these is maintained at zero potential by connecting it to the earth at the power station itself and this wire provides the return path for the current. This wire is called the neutral wire. The other wire is at a high potential. This wire is called the live wire. In fact potential of this wire changes from positive to and negative again negative to positive, 60 times per second. This is called 60 Hz AC The current in any appliance accordingly changes its direction 60 times in a second. The effective average magnitude of the potential difference is 110 V. That is why it is called 110 V, 60 Hz AC supply.All electrical appliances are connected across the neutral and live wires. The same potential difference is therefore applied to all of them and hence these are connected in parallel to the power source.
There is a color convention for wiring. According to this convention, the live line is carried by a wire with black insulation, the neutral by a wire with white insulation and the earth by a wire with green insulation. It is important that a live wire is not allowed to come in contact with the neutral or the earth wire. In this case, the circuit is completed with a negligible resistance and hence a large current flows through the wires. A lot of heating occurs in the wire and this may lead to accidents. So it is advisable to use correct color codes so that the chances of wrong connections are reduced.The appliances used in our house need 110 V of potential difference between their live and neutral terminals. But the current drawn is different for different appliance. The current requirement of heaters is around 10 A, and that of the bulb is order of 1 ampere. So two types of switches and sockets are available in the market, one meant for a minimum current of 5A and other for a maximum of 15A. The appliances drawing heavy currents are connected to the 15A - boards and other to the 5A - boards.
