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The Carter system, also known as the Chicago system, was a method of wiring three-way switches in the era of early knob-and-tube wiring. This now-obsolete wiring method has been prohibited by the USA National Electrical Code since 1923, [2] even in new knob-and-tube installations which are still permitted under certain circumstances. This ...
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)
Two-way: Three-way: A simple break-before-make changeover switch: C (COM, Common) is connected either to L1 or to L2. SPCO SPTT, c.o. Single pole changeover or single pole, centre off or single pole, triple throw Similar to SPDT. Some suppliers use SPCO/SPTT for switches with a stable off position in the centre and SPDT for those without.
A 3-way lamp, also known as a tri-light, is a lamp that uses a 3-way light bulb to produce three levels of light in a low-medium-high configuration. A 3-way lamp requires a 3-way bulb and socket, and a 3-way switch. In 3-way incandescent light bulbs, each of the filaments operates at full voltage. Lamp bulbs with dual carbon filaments were ...
The earliest standardized method of wiring in buildings, in common use in North America from about 1880 to the 1930s, was knob and tube (K&T) wiring: single conductors were run through cavities between the structural members in walls and ceilings, with ceramic tubes forming protective channels through joists and ceramic knobs attached to the ...
Those wiring methods acceptable by the NEC are found in chapter 3, thus all approved wiring method code articles are in the 300s. Efforts have been underway for some time to make the code easier to use. Some of those efforts include using the same extension for both code articles and for the support of wiring methods.
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English: "California" 3-way switch. Alternative to the conventional connection for a three-way switch. The lamp shell is never connected to the live terminal. A second lamp can be connected at A to light the end of a long corridor or as a pilot lamp to indicate the light in an outbuilding is left on.