In our homes electricity is brought from electric power station by two insulated wires of aluminium or copper. Out of these two wires, one wire is in red insulation and is called live wire and the other wire is in black insulation and is called neutral wire. The electricity coming in our house is actually alternating current having 220 V potential. Both the live wire and neutral wire enters in a box where a main fuse is put on the live wire.
These wires then pass through electricity meter present in the house. After the electricity meter, these wires enter into main switch which is used to switch off the electricity supply whenever required. After the main switch, these wires are connected to live wires of two separate circuits present in the house to supply electricity. Out of these two circuits, one circuit is of 5A rating which is used to run electric appliances with low power ( such as tube lights, bulbs and fans) and the other circuit is of 15A rating which is used to run electric appliances with high power ( such as air conditioners, refrigerators, electric iron and heaters). It should be noted that all the circuits in house are connected in parallel so that switching off one circuit does not affect the other circuit. One more advantage of parallel connection of circuits is that each electric appliance gets equal voltage.
In house, a third wire called earth wire having green insulation is usually connected to the body of metallic electric appliances. The earth wire sends the current from the body of the appliance to the earth whenever a live wire incidentally touches the body of metallic electric appliances. Thus, the earth wire is a protective measure, which saves us from severe electric shocks. Each electric appliance has a separate switch to ‘on/off’ the flow of current to it. The diagram to show the general scheme of domestic electric circuit is shown below in Figure.
Overloading and Shortcircuiting
The amount of current passing through a wire depends on the power rating of the wire. When the amount of current passing through the wire exceeds the maximum permissible limit, the wires get heated to such an extent that fire may be caused. This is known as overloading.
Shortcircuiting means coming in contact of live wire with neutral wire. This happens when the insulation of wires get damaged. Due to shortcircuiting the resistance of wires become very small which leads to flow of large amount of current through the wires. It results in heating of wires to such an extent that fire may be caused in the building.
Test Your Understanding and Answer These Questions:
- Explain the domestic electric circuit with the help of a diagram.
- Why different electrical appliances in a domestic circuit are connected in parallel?
- What is the function of earth wire? Why is it necessary to earth the metallic appliances?
- Explain what is short circuiting and overloading in an electric supply.