The BS 1363 plug, commonly known as a "13-amp plug", is a large plug that has three rectangular prongs forming a triangle. Live and neutral are 4 × 6 × 18 mm spaced 22 mm apart. 9 mm of insulation over the base of the pins prevents people from touching a bare connector while the plug is partly inserted. Earth is 4 × 8 × 23 mm.

The plug is unusual in that it has a fuse inside, for protection, in addition to a circuit breaker in the distribution panel. The fuse is required to protect the cord, as British wiring standards allow very high-current circuits to the socket. Accepted practice is to choose the smallest standard fuse (3 A, 5 A, or 13 A) that will allow the appliance to function. Using a 13 A fuse on an appliance with thin cord is considered bad practice. The fuse is 1 inch long, conforming to standard BS 1362.

UK wiring regulations (BS 7671) require sockets in homes to have shutters over the live and neutral connections for safety reasons (e.g. to prevent children from inserting metal objects into them). These are incorporated into all BS 1363 sockets and are opened by the insertion of the (longer) earth pin. The shutters also help prevent the use of plugs made to other standards. On plugs for Class II appliances that do not require an earth, the pin is often plastic and serves only to open the shutters and to enforce the correct orientation of live and neutral. It is sometimes possible to open the shutters with a screwdriver to insert other plug types but this should be avoided as such plugs will not have a fuse.

*Data extracted from website: http://en.wikipedia.org/wiki/Domestic_AC_power_plugs_and_sockets