Electrical appliances are earthed for safety purposes. Many electrical appliances, such as ovens, cooking ranges and refrigerators have metal casings. If a live wire inside the unit touches the metal case, it may induce a serious electrical shock. Proper grounding reduces such dangers.
Most appliances have three electrode conductors: the live wire; the neutral wire that carries current and voltage to the motor; and the earth wire that is connected to the part of the appliance that does not carry current like the metal case. In case of a wiring system defect inside the unit, the current flows into the ground wire and back to the fuse. Depending on the amount of current, the circuit breaker may or may not trip.
In the United States, the three-prong plug is connected to the standard receptacle, providing protective earth connection. The wiring system, which runs around residential and commercial buildings, is permanently grounded to the metal pipes connected to the underground water system or a metal rod driven several feet in the ground.
Grounding appliances is not common in other countries. In the United Kingdom, the appliances have two-prong plugs and do not have an earth terminal. In order to provide protection from electrical shocks, the appliance is insulated twice and is designed in a way that the electrical wires cannot touch the metal case.