In electrical wiring, color dictates function, not just phase. In the US (NEC), black and red are hot, white and gray are neutral, and bare or green are ground. In the EU and UK (IEC), brown is hot, blue is neutral, and green/yellow is ground. Misinterpreting these standards is a leading cause of shock hazards and dead shorts.
The Master Color Code Wiring Reference Table
Use this table as your primary bench and jobsite reference. Always verify the regional standard before trusting the insulation color, especially in older buildings or imported machinery.
| Function | US / Canada (NEC) 120/240V | US / Canada (NEC) 277/480V | EU / UK / AUS (IEC 60446) | Old UK (Pre-2004 BS 7671) |
|---|---|---|---|---|
| Line / Hot (Phase 1) | Black | Brown | Brown | Red |
| Line / Hot (Phase 2) | Red | Orange | Black | Yellow |
| Line / Hot (Phase 3) | Blue | Yellow | Grey | Blue |
| Neutral | White or Grey | Grey | Blue | Black |
| Ground / Earth | Bare, Green, or Green/Yellow | Bare, Green, or Green/Yellow | Green/Yellow | Green |
Regional Variants and Standard Crossovers
Knowing which standard applies to your region prevents catastrophic cross-wiring, particularly when working on imported appliances or older homes.
North America (NEC / NFPA 70)
In the US and Canada, the National Electrical Code (NEC) governs wire colors under Article 310.12. For standard 120/240V residential split-phase systems, black is your primary hot, red is your secondary hot (used in 240V appliances or multi-wire branch circuits), and white is strictly neutral. If you step into commercial 277/480V three-phase systems, the colors shift entirely to Brown, Orange, and Yellow for the hots, with Grey as the neutral. Mixing up a 120V black hot with a 480V yellow hot in a shared conduit pull is a common commercial error.
Europe, UK, and Australia (IEC 60446)
The International Electrotechnical Commission (IEC) standardizes colors across most of the globe. Brown is single-phase hot, blue is neutral, and green/yellow is earth. For three-phase, the hots are Brown, Black, and Grey.
The UK Harmonization Shift: If you are working in a UK home built before 2004, you will encounter the old BS 7671 colors: Red (hot), Black (neutral), and Green (earth). In 2004, the UK harmonized with the IEC. A red wire in a pre-2004 UK ceiling rose is a hot; a black wire in that same ceiling rose is a neutral. However, in a post-2004 IEC cable, that exact same black wire is a Phase 2 hot. Always check the building year and look for modern brown/blue cables mixed with legacy red/black cables in junction boxes.
The 'Rows People Get Wrong' Field Notes
Charts assume perfect factory conditions. In the field, wires get repurposed, faded, or misused. Here is how to handle the edge cases that cause the most blown breakers and shocks.
In standard 14/2 or 12/2 NM-B cable used for switch loops (power going down to a switch and back to a light), the white wire is often used as the returning hot leg. Under NEC 310.12(A), this white wire must be permanently re-identified at every termination point using black electrical tape, paint, or a permanent marker. If you see a white wire connected to a brass (hot) screw on a switch, treat it as hot until proven otherwise.
Faded, Painted, or Missing Markings
Never guess a wire's function based on faded insulation or a wire that has been painted over by a previous homeowner. If the color code wiring is illegible, follow this safe interpretation protocol:
- De-energize the circuit at the breaker and verify it is dead using a non-contact voltage tester (NCVT) and a multimeter.
- Map continuity: Use your multimeter in continuity mode. Test the mystery wire against a known bare copper ground. If it beeps, it is a ground. Test it against a known neutral bundle in the panel; if it beeps, it is a neutral.
- Voltage test: If continuity tests are inconclusive, cap all bare ends, re-energize the circuit, and carefully measure AC voltage from the mystery wire to a known ground. ~120V (or ~230V in IEC regions) indicates a hot. ~0V indicates a neutral or an open traveler.
- Re-identify: Once mapped, wrap the wire with correctly colored phase tape at both ends.
Travelers in 3-Way and 4-Way Switches
When running 14/3 or 12/3 NM-B cable for 3-way stairway switches, you will have a black, red, white, and bare wire. The black and red are typically used as the 'travelers' between the two switches. However, the NEC does not strictly mandate traveler colors. An electrician might use the white wire as a traveler and the black as the common. Always trace the common screw (usually a darker brass or black screw) rather than trusting the color code in multi-way switch legs.
Frequently Asked Questions About Color Code Wiring
What does a blue wire mean in US residential wiring?
In standard US residential 120/240V wiring, a blue wire usually appears in 14/3 or 12/3 NM-B cable as a second traveler for 4-way switch setups, or as a dedicated hot leg for a ceiling fan's light kit (allowing separate wall switches for the fan and light). However, if you are looking at THHN wire in conduit, blue is the designated Phase 3 hot for 120/208V commercial three-phase systems. Context and cable type dictate the function.
Can I use white wire for hot if I run out of black?
Yes, but with strict conditions. NEC 310.12(A) allows a white or grey wire to be used as an ungrounded (hot) conductor only if it is permanently re-identified. You must wrap it with black or red electrical tape, or use indelible marker or paint, at every single point where the conductor is accessible or terminated. You cannot just tape it at the panel and leave it white at the receptacle. If you are pulling individual THHN wires in conduit, simply buy a spool of black THHN instead—it is safer and saves time.
How do I safely test wire colors when the insulation is faded or painted over?
Never rely on visual inspection for painted wires. Turn off the breaker, verify zero voltage with a multimeter, and use the continuity method. Disconnect the wire from the device, set your multimeter to the ohms/continuity setting, and touch one probe to the wire and the other to the panel's neutral bus bar. A reading near 0 ohms means it is a neutral. A reading of infinite resistance (OL) means it is likely a hot or a disconnected traveler. Once identified, apply fresh phase tape.
Is the ground wire always bare copper?
No. While bare copper is standard in residential NM-B (Romex) cable to save manufacturing costs and reduce cable diameter, insulated ground wires are required in many commercial and industrial applications. In conduit systems (EMT/PVC), individual THHN ground wires must be insulated and colored green or green with a yellow stripe. Appliance power cords also frequently use insulated green or green/yellow ground wires. Treat bare copper, green, and green/yellow as identical in function, but never use a bare wire in a wet location or where it might short against an exposed metal junction box.
