An external socket is usually an electrical socket installed outdoors which needs to be protected from the elements. The term is widely used in England; the same device in the US is called an outdoor outlet or exterior outlet. The sockets themselves are no different from those installed inside houses and other structures. The difference between internal and external sockets is the nature of the connection to the power source.
An experienced do-it-yourselfer can generally install an external socket in an hour or so. All electrical work should be done in compliance with local and national electrical and building codes, which often require permits and inspection of competed work. Likewise, all supplies and equipment should be code-compliant.
The two most important elements of code compliance are the type of cable used and the type of outlet. Most electrical codes require that any cable run outdoors be rated for exterior use, such as underground feed (UF) cable. When conducting electricity to outlying buildings like garages or sheds, UF cable can be buried directly in the ground, at least 18” (45.72 cm) deep. Additionally, ground fault circuit interrupter (GFCI) outlets are usually required in outdoor work, unless the circuit is protected by a GFCI circuit breaker.
Conducting electricity from the inside to the outside of a structure is probably the greatest challenge faced by the householder installing an external socket. Some householders provide outside power by means of extension cords or electric cable through windows, doorways or other openings such as dryer exhaust outlets. This is a dangerous, illegal and impractical approach. A hole must be drilled in the exterior wall for an electric cable to pass through. An external junction box should be mounted to the exterior wall, with its back knockout right over the hole.
External junction boxes are specially built for outdoor use, with special attention paid to ensuring that water cannot penetrate. They have holes similar to the knockout holes in interior junction boxes, but they’re fitted with screw-in plastic plugs that provide a watertight seal to every unused hole. Cable enters the exterior junction box only through conduit which is attached with a watertight seal. The coverplates are fitted over diecut gaskets which also create a watertight seal, and spring-loaded caps with rubber gaskets automatically cover each external socket.
Cable carrying power from inside a structure to outside should be rated for exterior use. It’s secured to the junction box as with internal work, and the seams where the box touches the exterior wall should be sealed with silicon caulking to prevent moisture from entering. Outdoor wiring in some respects is easier than inside wiring, because there are no walls involved. Some jurisdictions permit UF cable to be run along exterior walls as long as it’s supported every 36 inches (91.5 cm). Many jurisdictions, though, require exterior cable to be run inside conduit or buried.