Black, white, green, red, blue, orange, brown, and gray-the colors of the insulation sheaths on electrical wires usually have their own symbolic meanings. Therefore, when setting up new light fixtures, in addition to turning off the circuit breaker, you should also determine the meaning of each colored wire you encounter.
Initially, residential electricity in the United States lacked a systematic color coding system, and there wasn't even a standard for its proper use. Shortly after Edison introduced the electric light in 1879, the insurance industry began issuing safety guidelines. The first formal set of guidelines appeared in 1881, covering addressing capacity, insulation, and installation. However, it did not classify wire colors.
In 1882, the National Fire Underwriters' Association (NBFU) also adopted early safety regulations. In 1893, the National Electric Insurance Association began attempting to unify the different electrical installation guidelines and regulations across states, proposing a national coding standard for building wiring of light and power supply installations.
The first National Electrical Code (NEC) was proposed by the NBFU in 1897, but it also neglected the standardization of wire color issues. Later, in 1928, NEC updated its standards, one requirement being the establishment of a color code for grounding wires, which became white or natural gray. These colors were also prohibited from being used on live and neutral wires.
A further color coding system was introduced by NEC in 1937, allowing color-coded wires to be used in "multi-branch circuits," specifying that three-branch circuits should use black, red, and white wires. More branches could have additional colors added, such as yellow and blue.
In 1953, NEC changed the grounding wire color to green or bare wire. Green was also prohibited for use on circuit wires (such as live and neutral wires).
NEC's 1971 version implemented color multi-branch coding, although white, natural gray, green, and yellow-green stripes were still retained, and these colors were also prohibited for grounding wires. This standard abandoned the rigid color coding requirements for circuit wires because there were not enough colors to distinguish between systems, voltages, and circuits.
Currently in the United States, grounding wires are green, yellow-green striped, or bare wire; neutral wires should be white or gray; and live wires may be black, red, blue, yellow, orange, or yellow, depending on the voltage.
These color standards are US-based; other countries have different codes (Canada's are very similar). For example, Australia and New Zealand use the same grounding wire color as the US, and their neutral wires are blue or black. Furthermore, live wires can be any color other than grounding and neutral. Red and brown are recommended colors for single-phase wires, while red, white, and blue are recommended colors for multi-phase live wires.
The UK recently (2004) changed its system to comply with the International Electrotechnical Commission (EC). Their grounding wire color (yellow-green stripes) remains unchanged, but the neutral wire color changed from black to blue. Similarly, single-phase wires, previously red, are now brown. In addition, the markings and colors for multi-phase lines in the UK have changed: L1 changed from red to brown, L2 from yellow to black, and L3 from blue to gray.
