Circuit breaker: It is  a safety device which is used in place of fuse (fig 16.26-a) due to any fault when the current exceeds the safety limit, then the button of the circuit breaker moves upward. Due to which the button of the circuit breaker moves upward.

Due to which the circuit breaks and the flow of the current stops in it. The button of the circuit breaker is pressed after the correction of the circuit. The circuit again gets completed and the current flows in it.

Circuit-Breaker-Fig. 16.26 (a)

Fig. 16.26 (a) circuit breaker

The principle of circuit breaker is explained in fig. 16.26 (b). When the current flows in the electric circuit, then it flows through the coil of the circuit breaker due to which the coil becomes electromagnet. When the current is within its limits, the contact points of the circuit are connected to each other and the circuit is completed. A soon as the current exceeds a certain limit, the magnetic force of the electromagnet is so much increased that it attracts the iron strip A towards it. Hence the contact points are separated and the circuit breaks.

principle of circuit breaker is explained

Earth wire

Most of our appliances such as electric iron, kettle, refrigerators and motors etc. are such that their outer part is of some metal. Usually the outer part is insulated from the live part of the appliance through which the current flows. Because of this insulation no current flows through the outer metal casing and one can safely touch it as we usually do. But sometime due to long use or due to carelessness the insulation is damaged and the outer casing also gets live. Now if some one touches it, he may receive a severe electric shock which may prove even fatal. In order to avoid such a situation, an additional wire is used along with the live and neutral wires. This wire is known as earth wire

 wire is known as earth wire

Because its one end is connected directly to earth by means of a water pipe leading to ground or by means of an earth terminal. Thus now the electric circuit consists of three wires live, neutral and earth wire. This circuit requires three pin sockets and three pin plugs for connection (fig. 16.27 a,b).

circuit requires three pin sockets

Now whenever the metal casing of the appliance, due to faulty insulation, gets connected with the live wire, the circuit shorts and a large current would immediately flow to ground through the earth wire. It causes the fuse wire to melt or the circuit breaker breaks the circuit. Therefore, the person which is using the appliance is being saved.