Meaning of wire color

Insulating sheath

Black, white, green, red, blue, orange, brown and gray. The color of the insulating sheath outside the wire usually has its own referential meaning. So when fiddling with a new light, in addition to turning off the circuit breaker, make sure what each colored wire you're going to touch next means.
There was no systematic color coding for residential electricity in the United States, and there was not even a set of standards used correctly. In 1879, shortly after Edison first introduced the electric light, the insurance industry began to issue some safety guidelines. The first set of formal guidelines appeared in 1881, including addressing capacity, insulation and installation. However, there is no classification of wire colors.
In 1882, the National Board of fire insurers (nbfu) also adopted early safety regulations. In 1893, the national insurance Power Association began to try to unify the different electrical installation codes and specifications of various states, and put forward the national coding standard of electric lamps and power supply devices for building wiring.
The first national electrical code (NEC) was proposed by nbfu in 1897. It also ignores the standardization of wire color. Later, in 1928, NEC was updated and revised. One of the requirements was to establish a specification for the color of grounding wire, which was later white or natural gray. These colors were also prohibited from being applied to live wire and neutral wire.
A further color coding is the new version launched by NEC in 1937, which uses the color coded line with "multi branch circuit", and stipulates that the lines of three branch circuits should use color, red and white. More branches can be added with other colors, such as yellow and blue.
In 1953, NEC changed the color of grounding wire to green or bare wire. Green is also prohibited for circuit wires (such as live wires and neutral wires).
The 1971 version of NEC encodes color multi branches to run. Although white, natural gray, green and yellow green stripes are still retained, these colors are also prohibited from being used for grounding wires. This specification has lost the rigid color coding requirements of access wires, because there are not enough colors to distinguish the system, voltage and circuit.
Recently in the United States, the grounding wire is green, yellow green stripe or bare wire, the neutral wire should be white or gray, and the circuit wire may be black, red, blue, yellow, orange or yellow. The specific color depends on the voltage.
These color standards are from the United States, and the codes of other countries are different (Canada is very similar to the United States). For example, the grounding wires of Australia, New Zealand and the United States are the same color, and their neutral wires are blue or black. Moreover, the live wire can be used in any color except the grounding wire and neutral wire. Red and Brown are the recommended colors for single-phase wires, and red, white and blue are the recommended colors for multiphase live wires.
The UK recently (2004) changed the system of compliance with the International Electrotechnical Commission (EC). Their grounding wire color (yellow and green stripes) remained unchanged, and the neutral wire color changed from the original color to blue. Similarly, single-phase wires used to be red, but they turned brown. In addition, the marking and coloring of multiphase lines in the UK have also changed: L1 from red to brown, L2 from yellow to black, and L3 from blue to gray.