Today there are about 20 types in common use around the world, and many obsolete socket types are found in older buildings. A proliferation of types developed for both convenience and protection from electrical injury. Plugs and sockets for portable appliances became available in the 1880s, to replace connections to light sockets with wall-mounted outlets. Different standard systems of plugs and sockets are used around the world.
Electrical plugs and sockets differ from one another in voltage and current rating, shape, size, and connector type. AC power plugs and sockets connect electric equipment to the alternating current (AC) mains electricity power supply in buildings and at other sites.
