Why have yellow/green color become the internationally recognized grounding wire identifier?

The International Electrotechnical Commission (IEC), the world's most authoritative electrical standards organization, specifies that safety grounding conductors must use alternating green and yellow conductors. This special color scheme requires alternating stripes of the two colors every 25 mm, creating a unique visual identifier. The choice of the yellow-green combination was based on rigorous human factors research. The two colors provide a sharp contrast in most lighting conditions, making them easily identifiable even for those with color blindness and difficult to confuse with other functional conductors.

In electrical equipment, the grounding conductor fulfills the crucial function of conducting fault current to the earth. When insulation failure causes the equipment casing to become live, a good grounding system can trigger protective devices to disconnect power within milliseconds, preventing electric shock accidents. Standardized colors enable operators to instantly identify grounding conductors, significantly reducing the risk of misoperation during emergency repairs or routine maintenance. Studies have shown that standardized color coding can increase electrical maintenance efficiency by 40% and reduce accident rates by over 60%.

While the IEC standard has been adopted by most countries, the United States maintains its unique grounding conductor specifications. According to the US National Electrical Code (NEC), grounding wires can be either bare copper wire or solid green insulated conductors. This difference stems from the history of electrical engineering. Early US electrical systems used green as a grounding color, a color that remains in place today to maintain system continuity. In contrast, the UK and EU countries strictly enforce the yellow-green stripe standard, with regulations such as BS 7671 clearly stipulating legal liability for non-compliance.

Special circumstances often require workarounds. High-voltage substations may use orange grounding wires, while offshore platforms may use blue. These exceptions require special approval from regulators, prominent warning signs on the equipment, and specialized training for personnel.