Why does a plug have three pins?

You know that each electrical plug has three pins. These three pins are connected to three wires, which in turn are connected to an electrical appliance. Two of these three pins are of the same size while the third pin is thicker than the other two. The third pin is usually connected to a green wire. This is known as the ‘earth wire’. Do you know what is the function of the third pin? The third pin and the third wire (green) in an electrical lead carry no current, when everything is normal. One end of this lead is connected to the body of the electrical appliance, and the other end is connected to a metal plate buried in the ground. In fact, the third pin connects the body of the electrical appliance to the Earth. This is known as electrical grounding. It is a precaution in case, a live wire accidentally comes into contact with the metal frame of the appliance. Sometimes, the electrical appliance may develop a fault which makes the electricity flow to the metal casing. In such a situation, anyone touching the appliance receives an electric shock. The electricity flows from the casing, through the person, into the ground. The shock felt by the person depends on the intensity of current. If, for example, the person has wet hands, the shock experienced would be of a greater intensity, because wet skin conducts electricity better than dry skin. Third pin or earthing is a method used to prevent faulty appliances from giving shocks. It is very important to ensure that all electrical equipments are properly grounded. This is done with the help of the third pin of a plug. In case, a properly grounded appliance develops a fault, the electricity would flow into the ground from the metal work through the earth wire and a person touching the appliance would not receive a shock. Since, the resistance of the wire is lower than that of a person, it is easier for the current to flow through the wire. Therefore, very little current flows through a person if he or she touches the faulty appliance. Since the resistance of the wire is very low, a very large amount of current flows through it. This causes the fuse wire to melt and cut off the electrical supply. Hence, the third pin of the plug serves as a safety device against electrical shocks.

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