The standard US house wire color code (per NEC NFPA 70) designates black or red for ungrounded (hot) conductors, white or gray for grounded (neutral) conductors, and bare copper or green for equipment grounding. In Europe and the UK (per IEC 60446 and BS 7671), the standard is brown for hot, blue for neutral, and green-and-yellow for earth. However, assuming a wire is safe based solely on its jacket color is a leading cause of residential electrical shocks, as older homes, switch loops, and multi-wire branch circuits frequently violate these conventions.
The Master House Wire Color Code Reference Table
The table below provides the definitive color codes for residential single-phase wiring across major global standards. This assumes standard copper conductors in either non-metallic sheathed cable (like NM-B/Romex) or individual THHN/THWN wires in conduit. Note: Aluminum wire uses the same color coding for insulation, but bare aluminum is rarely used for grounding in modern residential branch circuits.
| Conductor Function | US & Canada (NEC / CEC) | Europe & UK (IEC 60446 / BS 7671) | Australia & NZ (AS/NZS 3000) |
|---|---|---|---|
| Line 1 / Hot / Phase Carries current from source to load. |
Black (or Red) | Brown | Red (or Brown) |
| Line 2 / Hot / Phase 240V circuits, MWBCs, or 3-way travelers. |
Red (or Black) | Black (or Blue for Line 3) | White (or Black) |
| Neutral / Grounded Return path to source; carries current. |
White (or Gray) | Blue | Black (or Blue) |
| Earth / Equipment Ground Safety path for fault current; no normal current. |
Bare Copper, Green, or Green/Yellow | Green-and-Yellow stripe | Green-and-Yellow stripe |
| Switched Leg / Traveler Switch loops and multi-way switching. |
Any color except White, Gray, Green (often Red/Black) | Any color except Blue, Green/Yellow (often Brown/Black) | Any color except Green/Yellow, Black (often Red/White) |
Regional Variants and the "Rows People Get Wrong"
While the table above represents modern code, the reality of residential wiring is messy. Electricians frequently bend color rules for convenience, and older homes often predate current standards. Here is a breakdown of the regional variants and the specific table rows that cause the most dangerous misunderstandings on the jobsite.
The UK Pre-2004 Harmonization Trap
If you are working in a UK home built or wired before April 2004, the color codes were entirely different. The old UK standard used Red for Hot and Black for Neutral. In 2004, the UK harmonized with the European IEC standard (Brown/Blue) to align with the rest of the EU (UK Health and Safety Executive). If you open a junction box in a 1990s London flat and see a black wire, it is likely the neutral, not a hot phase. Mixing up old UK black (neutral) with new IEC black (Line 2 hot) will result in a dead short or a shocked homeowner.
Rows People Get Wrong: The White Wire Exception
In the US/Canada NEC system, the most dangerous assumption is that a white wire is always a neutral. Under NEC Article 200.7(C), a white wire can be used as an ungrounded (hot) conductor in specific scenarios, such as a 2-wire switch loop or a 240V baseboard heater circuit. The code requires the installer to re-identify the white wire with black tape, paint, or a permanent marker at every termination point. In practice, lazy installers skip the tape. If you see a white wire connected to the brass (hot) screw of a single-pole switch, it is carrying 120V live current, not returning it.
Rows People Get Wrong: The Red Wire in MWBCs
A Multi-Wire Branch Circuit (MWBC) uses a single 12/3 or 14/3 NM-B cable to feed two separate 120V circuits. The black wire is on Phase A, the red wire is on Phase B, and they share the white neutral. Because the two hot legs are 180 degrees out of phase, the neutral only carries the imbalance of the load, preventing it from overloading. The fatal mistake here occurs during panel work: if an DIYer disconnects the shared white neutral while both the black and red breakers are still ON, the two 120V circuits will series-link through whatever appliances are plugged in, sending 240V through 120V devices and instantly destroying electronics or starting a fire.
Safe Interpretation When Markings Are Faded or Missing
In homes built between the 1930s and 1960s, you will frequently encounter cloth-braided wire or early PVC insulation. Over decades of attic heat and load-cycling, white insulation yellows and eventually turns dark brown, becoming visually indistinguishable from the hot wire. Black insulation can fade to a dull gray. When visual identification fails, you must rely on systematic electrical testing.
The "Proving Unit" Testing Method
Never trust a non-contact voltage tester (NCVT or "tick tracer") to prove a circuit is dead. NCVTs are highly susceptible to phantom voltage and capacitive coupling, often failing to beep on a live wire hidden behind thick insulation, or beeping on a dead wire running parallel to a live one. Instead, use a CAT III 600V (minimum) digital multimeter (DMM) and follow the live-dead-live testing protocol required by OSHA lockout/tagout guidelines:
- Test the Meter: Measure a known live source (like a nearby live outlet) to verify your DMM and leads are functioning correctly.
- Test the Target: Measure the suspect wire against a known good ground (like the bare copper in the box or the panel ground bar). Then measure it against the suspected neutral.
- Test the Meter Again: Re-test the known live source to ensure your meter didn't blow an internal fuse or fail during step 2.
Identifying Unknown Conductors Under Load
If you are troubleshooting a live circuit and need to identify which faded wire is the neutral and which is the hot, measure the voltage between the unknown wires and the bare equipment ground. The hot wire will read nominal voltage (114V–126V in the US; 220V–240V in the EU/UK). The neutral wire should read less than 2V to ground under normal load. If you measure 120V between a suspected neutral and the ground, you have an "open neutral" fault upstream, and that neutral wire is currently energized at line potential. Treat it as a hot conductor, shut off the breaker, and trace the break in the return path.
