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Domestic Electric Circuit

Domestic Electric Circuit

Electric power is usually generated at places which are far from the places where it is consumed.

The power is transmitted over long distances at high voltage to minimize the loss of energy during transmission. For a given electric power, the current becomes low at a high voltage and therefore the loss of energy due to heating H a I2)becomes less. So the alternating voltage is stepped up at the generating station. It is then transmitted to the main sub-station. This voltage is stepped down and is transmitted to the switching transformer station or the city sub station. At the city sub-station it is further stepped down to 110 V and supplied to the consumer.

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.

House Wiring

The figure shows the ring system of electric wiring. Wiring starts from the main fuse - box, run around all the main rooms of the house and then come back to the fuse box again.
The fuse box contains a fuse of rating about 30A. A separate connection is taken from the live wire of the ring for each appliance. The terminal of the appliance is connected to the live wire through a separate fuse and a switch. If the fuse of one appliance burns out, it does not affect the other appliances.

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