is evenly split across the two directions, the current in each direction is half of the total, allowing the use of wire with half the current-carrying capacity. In practice, it is impossible to ensure the load does split evenly, so regulations require a thicker wire, of at least 2/3 the current capacity of the fuse or circuit breaker. The innovation that made ring circuits feasible in the UK was the introduction of plugs that contained their own fuse. There were three competing designs but only one ultimately survived and became the version specified in British Standard 1363. BS1363 plugs, could historically be fitted with a range of fuses up to 13A though only the 3A and 13A are the official choices, though 5A are available and often fitted to small appliances that take a large inrush current. This means that every load plugged in is covered by an appropriate protective device in its plug, so that the whole ring may then be protected by (usually) a 32A breaker at the distribution panel. In contrast, circuits feeding any other kind of socket outlet need to be protected by a breaker that will not allow the socket's rating to be exceeded, and so the radial circuits generally used with outlets such as the European Schuko style outlets generally have to be protected by a 16A breaker at the distribution panel; this limits the total load on the circuit and hence such circuits tend to have fewer socket outlets. Cables are most commonly a single outer sheath containing separately-insulated and neutral wires, and a non-insulated protective earth to which sleeving is added when exposed. Such cable is commonly referred to as twin and earth or simply T & E. Standard sizes have a conductor cross sectional area of 1, 1.5, 2.5, 4, 6 and 10 mm2. With most domestic wiring using: The earthing conductor is uninsulated since it is not intended to have any voltage difference from surrounding earthed articles. Additionally, if the insulation of a or neutral wire becomes damaged, then the wire is more likely to earth itself on the bare earth conductor and in doing so either trip the circuit breaker, RCD, or rupture the fuse by drawing too much current. Earthing and bonding Earthing and bonding are used together to provide shock protection by avoiding a dangerous combination of magnitude and duration of the voltage to which people may