Colour Code for Wires: NEC, IEC, and UK Wiring Color Charts

When you open a junction box, the insulation colour tells you the wire's job. Here is the exact colour code for wires across major global standards, followed by how to handle unmarked or legacy cables.

The Master Wire Colour Code Reference Table

The table below maps the function of a conductor to its required insulation colour across the four most common wiring standards. Use this as your primary bench reference before stripping any cable.

Rows People Get Wrong (and Why It Matters)

Misinterpreting a single row in the chart above doesn't just trip a breaker; it creates lethal shock hazards or fire risks. Here are the most common field mistakes.

1. The Old UK Black Neutral vs. IEC Black Hot

This is the deadliest mix-up in European wiring. In pre-2004 UK installations, black is the neutral. In modern harmonized IEC wiring, black is Phase 2 (a live hot conductor). If you are extending an old UK circuit and splice into a modern IEC-colored cable without verifying, you will connect a live 230V phase directly to a neutral bus, causing an immediate dead short and arc flash.

2. White as a Hot Conductor (Switch Loops)

Under NEC Article 200.7(C)(1), a white wire can be used as an ungrounded (hot) conductor in a switch loop, but only if it is permanently re-identified with black tape or paint at both ends. Many DIYers and even careless contractors skip the tape. When you open a light fixture and see a white wire, never assume it is neutral—test it first.

3. The High-Leg Delta Orange Trap

In US 240V 3-phase high-leg delta systems, Phase B (the high leg) measures 208V to ground instead of the standard 120V. The NEC strictly mandates this leg be colored Orange. Plugging a standard 120V single-phase load into an orange high-leg will instantly destroy the appliance and risk a fire.

Regional Standards: Which Code Applies to You?

Wire colours are not universal; they are dictated by the Authority Having Jurisdiction (AHJ) in your region. Here is how to determine which standard governs your workbench or jobsite.

• North America (US & Canada): Governed by the NFPA 70 (National Electrical Code) and the Canadian Electrical Code (CEC). If you are in the US or Canada, use the NEC column. Note that Canada sometimes differs slightly on 3-phase colors, but single-phase residential (Black/Red/White/Green) is identical.
• Europe & Modern UK: Governed by IEC 60446 and the harmonized HD 308 S2 standard. The UK officially adopted these colors in 2004 (with a transition period ending in 2006). The UK Health and Safety Executive (HSE) provides strict guidance on mixing old and new colors in the same installation.
• Australia & New Zealand: Governed by AS/NZS 3000 (Wiring Rules). While they have largely harmonized with IEC for earth (Green/Yellow), their single-phase active and neutral colors (Red and Black) remain distinct from Europe.

Faded, Missing, or Unmarked Wires: The Safe Interpretation Protocol

THHN insulation degrades under UV exposure and high ambient heat. A white neutral wire in a hot attic can turn pale grey or even yellowish over a decade. A green ground wire can fade to look bare or white. Never trust faded insulation.

If you encounter unmarked, faded, or suspicious wiring, follow this exact protocol:

1. De-energize and Lock Out: Turn off the main breaker for the panel feeding the circuit. Use a non-contact voltage tester (NCVT) on the wires to confirm they are dead.
2. Trace the Ground: Set your digital multimeter to continuity mode (the diode/beep setting). Place one probe on the bare/green wire and the other on the panel's ground bus bar. A reading of < 1 ohm confirms it is the equipment grounding conductor.
3. Trace the Neutral: Place one probe on the white/grey wire and the other on the panel's neutral bus bar. Again, you need a < 1 ohm reading. (Note: Ensure the neutral is disconnected from the hot bus during this test to avoid parallel path false positives).
4. Identify the Hot: Once ground and neutral are proven via continuity, the remaining conductor(s) are your ungrounded hot legs.
5. Re-identify: Apply colored heat-shrink tubing or high-quality 3M Super 33+ electrical tape at both ends of the wire to restore the correct colour code for wires before energizing.

Decision Tree: Picking the Right Wire Color for Your Next Run

Stop guessing at the hardware store. Use this decision path to select the exact cable type and colour code for wires for your specific project.