The electric plug made its appearance in the US in the 1920s. It was then two pronged. Some electricity companies had a split tariff-the cost of electricity for lighting was lower than for heating and other appliances. So people began connecting their low-wattage appliances, such as toasters and hair dryers, to light fittings. Thus a need for safer plugs lead to the development of three-pin plugs-the third, the earth pin, would blow the fuse in case of a short circuit and disconnect the supply. Subsequently, different countries started improving on them to find more efficient plugs to meet their own requirements.