In the US and Canada (NEC standard), the standard home wiring color codes are black for hot, white for neutral, and bare or green for ground. In Europe and the UK (IEC 60446 harmonized standard), brown is hot, blue is neutral, and green-and-yellow is ground. Because misidentifying a conductor can be fatal, always verify with a meter before touching any wire.
The Master Home Wiring Color Codes Reference Table
Read this table by matching your region's column to the circuit function. This covers standard single-phase residential branch circuits (120V/230V nominal). For three-phase or high-voltage feeders, consult the specific NEC Article 210 or IEC 60446 phase-coloring matrices.
| Function | US / Canada (NEC) | Europe (IEC 60446) | UK (Post-2006 Harmonized) | UK (Pre-2006 Legacy) |
|---|---|---|---|---|
| Line / Hot (Single Phase) | Black (or Red) | Brown | Brown | Red |
| Line / Hot (Phase 2 / 240V) | Red (or Black) | Black (with brown sleeve) | Black (with brown sleeve) | Yellow |
| Neutral | White (or Gray) | Blue | Blue | Black |
| Earth / Ground | Bare, Green, or Green/Yellow | Green / Yellow | Green / Yellow | Green |
| Switched Hot (Travelers) | Red, Black, or Blue | Brown or Black (sleeved) | Brown or Black (sleeved) | Red or Yellow |
Regional Variants and the 'Rows People Get Wrong'
While the table above covers the baseline, real-world jobsites and retrofit projects are full of exceptions. Here is where DIYers and apprentices make dangerous assumptions.
1. The White Wire Used as a Hot Conductor (US/NEC)
In a standard 2-wire switch loop or a 240V-only appliance circuit (like a baseboard heater), a white wire is often used to carry ungrounded (hot) current. Under NEC 200.7(C)(2), this is legal only if the white wire is permanently re-identified with black tape, paint, or a marker at every point where the conductor is visible and accessible. If you see a white wire connected to a brass (hot) screw on a switch or a black wire nut in a ceiling box, treat it as live until proven otherwise.
2. The UK Legacy vs. Harmonized Shock Hazard
The UK changed its wiring colors in 2006 to harmonize with Europe. The most dangerous translation error occurs with the neutral wire. Pre-2006 UK neutral was black. Post-2006 UK hot (line) is brown, but the second phase (or switched hot) is black. If you are working in a UK home built between 1970 and 2004, that black wire is neutral. If you are working in a home wired after 2006, that black wire is a live phase. Always check the consumer unit for a warning label, and never trust the color without a voltage test.
When extending circuits in older UK or European homes, you will inevitably splice old colors to new colors. The IET Wiring Regulations (BS 7671) require clear labeling at the junction box and the consumer unit to warn future workers of the mixed color codes. Never just twist them together and hide them in the wall.
3. Solid Green vs. Green/Yellow Stripe (Grounding)
In the US, solid green and green-with-a-yellow-stripe are both acceptable equipment grounding conductors (EGC) under NEC 250.119. However, in IEC and UK jurisdictions, only green-and-yellow is permitted for earth. Solid green is strictly forbidden for grounding in Europe to prevent confusion with older telecom or low-voltage control wiring.
Safe Interpretation When Markings Are Faded or Missing
Old cloth-covered wiring, sun-faded THHN in attic junction boxes, or cheap imported NM-B cables where the jacket color bleeds into the insulation can make visual identification impossible. Never guess. Use this three-step verification protocol:
- De-energize and Expose: Turn off the breaker. Strip back 3/4 inch of insulation to expose fresh, unfaded copper and inner jacket colors if dealing with NM-B.
- Non-Contact Voltage Test (NCVT): Restore power. Use a properly rated CAT III or CAT IV NCVT pen. The hot conductor will trigger the pen. Neutral and ground should not. (Note: NCVTs can be fooled by phantom voltage in parallel runs; this is just step one).
- Multimeter Verification (The Definitive Test): Set your multimeter to AC Voltage (V~).
- Measure Suspected Hot to Suspected Ground: You should read nominal line voltage (114V–126V in the US, 216V–253V in the EU/UK).
- Measure Suspected Neutral to Suspected Ground: You should read less than 2V. If you read line voltage here, you have an open neutral or a miswired bootleg ground.
- Measure Hot to Neutral: Should read nominal line voltage.
If you are dealing with ungrounded legacy systems (like pre-1960s knob-and-tube or early metal-clad cable with no EGC), you will not have a reliable ground reference. In this case, measure Hot to a known, verified grounded metal water pipe or the grounding bus in the main panel to identify the live conductor.
Home Wiring Color Codes FAQ
Can I use a white wire as a hot wire in a 3-way switch loop?
Yes, but it must be re-identified. When running 14/3 or 12/3 NM-B cable between 3-way switches, the white wire is routinely used as a traveler (which carries hot potential depending on switch state). The NEC requires you to wrap the ends of this white wire with black or red electrical tape, or use a permanent marker, at both switch boxes to indicate it is an ungrounded conductor. Do not leave it white, or the next person to open the box may grab it assuming it is dead.
What color is the ground wire in older US homes?
In US homes built after the mid-1960s, the ground is typically a bare copper wire inside NM-B (Romex) cable, or a green-insulated THHN wire in conduit. In homes built before the 1960s, you may find no ground wire at all (ungrounded circuits), or occasionally a green cloth-covered wire in older armored cable (BX). If there is no ground, you cannot simply connect a modern 3-prong outlet without adding a GFCI breaker or receptacle to provide shock protection, per NEC 406.4(D).
Why does my 240V appliance cable have a white wire?
If you are wiring a pure 240V load (like an electric baseboard heater or an older air handler) using 2-wire cable with a ground, the cable will contain a black, a white, and a bare wire. The white wire is used as the second hot leg (L2). It must be marked with black tape at both ends. However, if you are wiring a 120/240V appliance like an electric dryer or range using 3-wire cable, the black and red are the hot legs, and the white is the neutral used to power the 120V control boards and timers. Always check the appliance manufacturer's wiring diagram.
Are home wiring color codes legally enforced in existing installations?
Electrical codes operate on a 'grandfather' principle. If your home was wired in 1975 using the color codes legal at that time, you are not legally required to tear open the walls and rewire it to 2026 standards just to sell the house or pass an inspection. However, if you are extending or altering that circuit, the new work must comply with the current NEC (or local equivalent), and you must safely transition between the old and new color schemes in an accessible junction box. Local Authority Having Jurisdiction (AHJ) rules always supersede general guidelines.
