The reason behind some electrical appliances in the United Kingdom (UK) having three pins is related to electrical safety and grounding. The three-pin plug and socket system used in the UK is known as the BS 1363 or "Type G" standard. It was introduced to improve electrical safety and prevent accidents caused by electric shocks and fires.
The three pins on the UK plug serve the following purposes:
Line (Live) Pin: This is the pin that carries the current from the power source to the appliance. It is typically connected to the brown-colored wire in the electrical cable.
Neutral Pin: The neutral pin completes the electrical circuit and carries the return current back to the power source. It is connected to the blue-colored wire.
Earth (Ground) Pin: The earth pin is a safety feature that provides a connection to the ground, which is a protective measure against electric shock. If there is a fault in the appliance that causes the metal parts to become live, the excess current will be diverted safely to the ground through the earth pin, preventing harm to the user. This pin is connected to the green and yellow striped wire, which is the ground wire.
The combination of the three pins, along with the design of the socket, ensures a secure and safe electrical connection between the appliance and the power supply. The system also includes shutters on the live and neutral sockets to prevent accidental contact with live parts.
The three-pin system is widely used in the UK and in countries that have adopted the British standard, offering a high level of safety for electrical appliances and users.