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2018-12-09
Chen Jihong: The country should have its own numerical control brain, which is our mission.
Residential electricity use in the United States began without systematic color coding, or even a set of standards for proper use. In 1879, shortly after Edison introduced electric lights, the insurance industry began issuing safety guidelines. Formal guidelines appeared in 1881 and included addressing capacity, insulation, and installation. But there is no classification of the wire color.
In 1882, the National Fire Underwriters Board (NBFU) also adopted early safety regulations. In 1893, the National Insurance Electricity Association began to try to unify the different electrical installation guidelines and specifications in various states, and proposed a national coding standard for electric lights and power installations for building wiring.
The National Electrical Code (NEC) was proposed by the NBFU in 1897, which also ignored the normalization of the color problem of wires. Later in 1928, NEC updated and revised its version. One of the requirements was to establish a specification for the color of ground wires, which was later white or natural gray, and also prohibited the application of these colors to live wires and neutral wires.
Further color coding is a new version introduced by NEC in 1937, which uses color-coded lines with "multi-branch circuits" and stipulates that the lines of three-branch circuits should be black, red and white. More branches can be added to other colors, such as yellow and blue.
In 1953, NEC changed the color of the ground wire to green or bare wire. Green is also prohibited for circuit lines (such as live and neutral lines).
NEC's 1971 version put the color multi-branch code to run, although the white, natural gray, green and yellow-green stripes remained, and these colors were also banned for ground lines. This time the specification dropped the rigid color coding requirements for the path wires because there were not enough colors to distinguish the system, voltage and circuit.
In the United States today, the ground wire is green, yellow-green striped or bare, the neutral wire should be white or gray, and the circuit line may be black, red, blue, yellow, orange or yellow, depending on the voltage.
These color standards are for the United States, and other country codes are different (Canada is very similar to the United States). For example, Australia and New Zealand and the United States have the same ground wire color, and their neutral wire is blue or black. Also, the live wire may be any color other than the ground wire and the neutral wire. Red and brown are the recommend colors of single-phase wires, and red, white and blue are the recommend colors of wires charged with multiphase flow.
The UK has recently (2004) changed its system to comply with the International Electrotechnical Commission (EC). Their ground wire color (yellow-green stripes) remained the same, and the neutral wire color changed from black to blue. Similarly, the single-phase wire used to be red and now it's brown. In addition, the British multiphase line marking and coloring has also changed: L1 from red to brown, L2 from yellow to black, L3 from blue to gray.
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