Standard Color Codes for Wiring Electrical: NEC, IEC & UK Reference

Wire insulation colors are the first line of defense against shock and short circuits. Before opening a panel, junction box, or fixture, consult this master reference to identify the function of every conductor and verify it against your local standard.

Master Reference Table for Electrical Wire Colors

The table below maps conductor functions to the three most common global standards. Always identify which standard your building was wired under before making assumptions based on insulation color.

Regional Variants and the "Rows People Get Wrong"

While the table above provides the baseline, real-world jobsites are full of exceptions, legacy wiring, and code allowances that trip up even experienced DIYers. The National Fire Protection Association (NFPA 70 / NEC) and the Institution of Engineering and Technology (IET) both permit specific re-identifications that change how you must read a circuit.

The "Rows People Get Wrong" Notes

• White Used as a Hot Wire (Switch Legs): In US residential wiring, a 2-wire cable (black and white) is often run from a ceiling fixture down to a wall switch. The black wire carries constant hot down to the switch, and the white wire carries the switched hot back up to the fixture. NEC 200.7(C)(2) requires the white wire to be re-identified with black or red tape at both ends, but in older homes, this tape is frequently missing. If you measure 120V on a white wire with the switch ON, it is a switch leg, not a neutral.
• Black Used as a Neutral (Old UK / 240V Appliances): If you are working on pre-2004 British wiring, black is the neutral, not a hot leg. Conversely, in North American 240V-only appliances (like older baseboard heaters or water heaters), a 2-wire cable with black and red is used. There is no neutral; both are 120V hot legs combining for 240V. Assuming the white wire is always neutral will get you killed in a 240V baseboard heater junction box where someone used a black/red cable.
• Grey vs. White Neutrals: Both are valid neutrals under the NEC. However, in Multi-Wire Branch Circuits (MWBC) or 3-phase commercial panels, white and grey are sometimes used to distinguish between different neutral buses or voltage systems (e.g., 120V vs. 277V). Never assume a grey wire is just a "dirty white" wire in a commercial panel; it may belong to a completely different phase system.

Safe Interpretation When Markings Are Faded or Missing

THHN insulation fades under UV exposure or heat, and older rubber-insulated wires in pre-1960s homes often turn entirely black or crumble to dust. When you cannot rely on color, follow this bench-tested verification sequence:

1. Non-Contact Voltage Test (NCVT): Use a reliable NCVT (like a Klein or Fluke) to identify which wires are energized. Note that NCVTs can pick up "phantom voltage" from adjacent live wires in the same Romex bundle, so a beep does not guarantee a wire is a dedicated hot leg.
2. Multimeter Line-to-Ground Test: Set your multimeter to AC Volts (600V range). Measure between the suspected hot wire and a known, verified ground (like a bare copper wire or the metal box if properly bonded). A reading of 114V–126V confirms a hot leg. A reading near 0V indicates a neutral or ground.
3. Multimeter Line-to-Neutral Test: Measure between the confirmed hot wire and the suspected neutral. You should read nominal line voltage (120V in North America, 230V in Europe).
4. Re-Identification: Once you have definitively identified a wire's function that violates standard color codes, you must re-identify it. Under NEC 200.7(A), you can use colored electrical tape or heat shrink tubing to mark a white wire being used as a hot leg (use black, red, or blue tape). You cannot use white or grey tape to re-identify a colored wire as a neutral in a standard branch circuit.