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Household wiring does not usually use three-phase supplies and the clash only occurs in three-phase systems. Wiring to the old standard can be detected by use of a red wire. The new standard colour code does not use red. Where new wiring is mixed with old, cables must be clearly marked to prevent interchange of phase and neutral.
British electric clock connector, three-pin, made by MK. Showing the rear of the plug with its 2 A fuse. Fused plugs and sockets of various proprietary and non-interchangeable types are found in older public buildings in the UK, where they are used to feed AC electric wall clocks.
During the first 50 years of commercial use of electric power, standards developed rapidly based on growing experience. Technical, safety, and economic factors influenced the development of all wiring devices and numerous varieties were invented. After the two-prong electric plug was introduced in the 1920s, the three-pin outlet was developed.
Compared to modern electrical wiring standards, these are the main technical shortcomings of knob-and-tube wiring methods: never included a safety grounding conductor did not confine switching to the hot conductor (the so-called Carter system prohibited as of 1923 places electrical loads across the common terminals of a three-way switch pair)
Note that the wires in the 6-wire cable are coloured with two colours in a ratio of four to one in length, with the first colour mentioned being the predominant one, e.g. if the indicated colour of the wire is W-B then the wire will be coloured white for 12 mm, then blue for 3 mm and so on.
The single-phase colours of red phase and black neutral are replaced by brown phase and blue neutral. These colours have been used in appliance flexible cables since 1969. The cable core colours are described in IEC 60304 (1982-01), Standard colours for insulation for low- frequency cables and wires.
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The first rubber-insulated cables for US building wiring were introduced in 1922 with US patent 1458803, Burley, Harry & Rooney, Henry, "Insulated electric wire", issued 1923-06-12, assigned to Boston Insulated Wire and Cable . These were two or more solid copper electrical wires with rubber insulation, plus woven cotton cloth over each ...