Color of the center line in the distribution box

The center line in a distribution box, typically representing the neutral conductor, is usually colored white or gray in AC systems according to IEC and NEC standards.

Neutral (Center) Conductor Color

In most electrical distribution systems, the center line corresponds to the neutral or grounded conductor. Its primary function is to complete the circuit by returning current to the source and maintaining voltage balance across phases. The standard color coding is as follows:

• IEC (International Electrotechnical Commission) standard: Neutral wires are blue for AC systems, while protective earth is green/yellow striped .
• NEC (National Electrical Code, USA): Neutral wires are white or gray, while hot (live) wires are black, red, or other colors .
• DC systems: The neutral or grounded conductor is often white or gray, while positive and negative lines use other colors such as red and black .

Regional Variations

• Europe and UK: Blue is standard for neutral in AC distribution boxes, following IEC 60446 .
• North America: White or gray is used for neutral in both residential and commercial AC systems .
• Telecom/ICT DC distribution: ITU-T L.1203 recommends clear color coding to avoid confusion, often using white or gray for the neutral/center line .

Safety Considerations

Correct identification of the center line is crucial for:

• Preventing electric shock and fire hazards
• Ensuring proper connection of loads and breakers
• Simplifying maintenance and troubleshooting Always verify the wiring color codes in your region and follow local electrical codes, as some older installations may use non-standard colors. Using a voltage tester or multimeter can confirm the neutral line before performing any work.