3 pin electric plugs and 3 wire electrical cables have become part and parcel of our daily life. They are designed to ensure safe supply of electricity to electrical appliances. They safeguard our lives, but we take them for granted.
Normally, three wires are there in an electrical cable used in our home and they have three different colors.
The Brown color wire is used by electric current for transmission of current. This wire is connected to a fuse on the live pin.
The Blue wire is the neutral wire. This wire is the exit route for the current from the appliance. The neutral wire has a voltage close to zero.
The third wire is Green or Yellow in color and is known as earth wire. This is used to protect the electrical apparatus and the person handling the equipment.
There are three pins in a common electric plug. Two of these are of the same size and the third one is bigger than the other two. The third pin is connected to the neutral (earth) wire. To know the importance of this pin, it is important to know electrical grounding.
Electrical Grounding (Earthing)
The third pin and third wire carry no current when the functioning of the appliance and passage of electricity are normal. One end of this lead is connected to the body of the electrical appliance and the other end to a metal plate buried in the ground. Thus the third pin connects the body of the electrical appliance to the earth. This is called electrical grounding (earthing).
The casing of electrical appliances are made of metal frames or at least will have some metal components like screws, nails etc. In case, the live wire happens to come in contact with these metal pieces, it will be dangerous to the person handling the appliance as the person may receive an electrical shock. The electricity will flow from the casing to the ground through the person. The intensity of shock will depend on the intensity of current. If the hands are wet, the intensity of shock will be severe as wet skin conducts electricity better compared to dry skin. The purpose of the earth wire is to take away such currents.
When a properly grounded appliance develops a fault, current flows through the wire to the ground. The wire is a good conductor compared to human body and hence electricity travels to ground through the wire. Hence only very low current passes through the body of the person even if he touches the faulty appliance. As very large current flows through the electrical wire, the fuse gets melted and cuts off electricity. Thus the third pin functions as a safety device.