NCERT Class 10: Science Learning Concepts

Science: Chapter 13-Magnetic Effects of Electric Current-Concepts

13.7 Domestic Electric Circuits
Two separate circuits are formed in the domestic wiring, one for high power rating appliances called power circuit and other for low power rating called lightning circuit.
Power circuit: The circuit which draw heavy current (15A) from mains and used for high power rating devices such as microwave, oven, air conditioners, geysers, washing machine, etc. is known as power circuit.
Lightning circuit : The circuit which draw small amount of current from the mains and used for low power rating devices such as bulb, tube light, fans, T.V., Computer, etc. having a current rating of 5A is known as lightning circuit.
Domestic circuit wiring consists of a main fuse, meter, one light bulb and a socket.

A fuse in a circuit prevents damage to the appliances and the circuit due to overloading. Overloading can occur when the live wire and the neutral wire come into direct contact. (This occurs when the insulation of wires is damaged or there is a fault in the appliance.) In such a situation, the current in the circuit abruptly increases. This is called short-circuiting. The use of an electric fuse prevents the electric circuit and the appliance from a possible damage by stopping the flow of unduly high electric current.

When current in the circuit exceeds the value of the fuse rating, the fuse wire melts due to overloading. This creates a gap in the circuit. This is called breaking a circuit.

If a fuse with larger rating is used with an appliance, then the whole purpose of using fuse is destroyed as the fuse wire will not melt and it will allow more current due to which the appliance can catch fire. In case if we use a fuse of lower rating then it will go off even before the body receives enough current.
Thus, when fuse wire is burnt, the fuse plug is taken out of the socket and a new fuse wire of identical rating is connected to complete the circuit.