In the US and Canada (NEC standards), standard 120V/240V AC wire color codes are Black (Line/Hot), White (Neutral), and Bare or Green (Ground). In Europe and the UK (IEC standards), the standard single-phase colors are Brown (Line), Blue (Neutral), and Green/Yellow (Ground). Below is the complete master reference chart for AC and DC systems.
| Function | US / Canada (NEC) AC | Europe / UK (IEC) AC | DC Power (US / General) |
|---|---|---|---|
| Line 1 (Hot) | Black | Brown | N/A |
| Line 2 (Hot - 240V) | Red | Black (or Brown for 3-ph) | N/A |
| Neutral | White or Gray | Blue | White (or Black in auto) |
| Earth Ground | Bare, Green, or Green/Yellow | Green/Yellow | Green or Bare |
| Positive (+) | N/A | N/A | Red |
| Negative (-) | N/A | N/A | Black |
Regional Variants: 3-Phase and Old UK Color Codes
Wire color codes are not universal, and assuming a single standard applies globally is a fast track to a dead short or a lethal shock. The standard that applies to you depends entirely on your region's adopted electrical code. In North America, the National Electrical Code (NEC) dictates conductor identification under Articles 200, 210, and 215. In Europe, the UK, and most of the world, IEC 60446 (harmonized in the UK via BS 7671) is the governing standard.
The most significant regional clash occurs in the United Kingdom. Prior to April 2004, the UK used its own distinct color code (Red for Line, Black for Neutral). To harmonize with mainland Europe and the IEC, the UK transitioned to the Brown/Blue/Green-Yellow scheme. If you are working in a pre-2004 UK home, you will encounter the old colors in existing circuits, while new extensions will use IEC colors. Mixing these in the same junction box without clear labeling is a major safety violation.
Three-phase power introduces another layer of complexity. In the US, 3-phase colors change depending on the voltage class (208V/120V vs. 480V/277V). The IEC, however, maintains Brown, Black, and Gray for all 3-phase lines regardless of voltage.
| Phase / Function | US (NEC) 208V 3-Phase | US (NEC) 480V 3-Phase | Old UK (Pre-2004) | New UK / IEC (Post-2004) |
|---|---|---|---|---|
| Phase A / L1 | Black | Brown | Red | Brown |
| Phase B / L2 | Red | Orange | Yellow | Black |
| Phase C / L3 | Blue | Yellow | Blue | Gray |
| Neutral | White | Gray | Black | Blue |
| Earth Ground | Green / Bare | Green / Bare | Green | Green / Yellow |
The 'Rows People Get Wrong' Notes Section
Reference tables are clean, but real-world junction boxes are messy. Here are the specific rows and scenarios where DIYers and even junior tradespeople consistently misinterpret wire color codes.
1. The 'White is Always Neutral' Trap (Switch Loops)
In the US NEC table, White is listed as Neutral. However, in older switch loops (the cable running from a ceiling light down to a wall switch), the white wire is frequently used as the return hot from the switch to the fixture. Under NEC 200.7(C)(2), if a white wire is used as a hot conductor, it must be permanently re-identified with black tape or paint at both ends. If you see a white wire connected to a brass (hot) screw on a single-pole switch, do not assume it is safe to touch. It is carrying line voltage.
2. The High-Leg Delta Orange Wire
Look at the US 240V 3-Phase row. In a standard 240V Delta system, Phase B is often a 'high leg' or 'wild leg' that measures 208V to ground, rather than the standard 120V. The NEC (Article 110.15) strictly mandates that this high leg must be colored Orange. If you are wiring a subpanel in a commercial building and assume all three hots are 120V to neutral, plugging a 120V appliance into the orange leg will instantly destroy the appliance and create a fire hazard.
3. DC Black vs. AC Black
In DC systems (like automotive, telecom, or solar battery banks), Black is universally the Negative (-) return path. In US AC mains, Black is the Line (Hot) supply. When wiring an inverter in a solar setup, the transition point where DC Black (negative) meets AC Black (hot) inside the inverter chassis is a common point for catastrophic wiring errors. Always label DC wires with white heat-shrink tubing marked 'DC NEG' before they enter the AC enclosure.
4. Green vs. Bare Ground in Conduit
Both Green and Bare copper serve as Earth Ground in the US. However, if you are pulling THHN wire through metal conduit, you must use an insulated Green wire (or Green with a Yellow stripe) for the ground. You cannot use a bare wire inside a conduit with multiple circuits, as a stray strand of bare copper could short against a hot wire in a different circuit if the insulation gets nicked during the pull.
Safe Interpretation When Markings Are Faded or Missing
Never trust the jacket color on old wiring. In homes built before the 1960s, cloth-insulated wiring often featured black and white wires that have both faded to the same dusty gray over decades. Furthermore, UV exposure in attic spaces can bleach modern THHN wire jackets, turning black wire gray and red wire pink.
When wire colors are faded, painted over, or missing, you must electrically identify the conductors using a digital multimeter (DMM) before making any connections. Follow this exact verification sequence:
- De-energize and Expose: Turn off the breaker. Remove the device (outlet/switch) and pull the wires out of the box. Ensure no bare copper is touching the metal box or other wires.
- Energize and Test Hot-to-Ground: Turn the breaker back on. Set your DMM to AC Voltage (V~). Place one probe on a known, verified ground (like the metal box or a bare copper wire) and touch the other probe to each unknown wire. The wire that reads between 114V and 126V (in a 120V nominal system) is your Line (Hot).
- Test Hot-to-Neutral: Keep the red probe on the identified Hot wire. Touch the black probe to the remaining unknown wires. The wire that reads 114V-126V is your Neutral. (If you measure 0V between Hot and a wire, that wire is either a dead neutral, a ground, or a disconnected hot).
- Verify Neutral-to-Ground: To confirm the neutral, measure between the suspected Neutral and the known Ground. You should read less than 2V (ideally under 0.5V). If you read line voltage (120V) between Neutral and Ground, you have an open neutral upstream, and the circuit is unsafe.
- Re-identify: Once verified, de-energize the circuit again. Wrap the identified wires with colored electrical tape (Black for hot, White for neutral) at the termination point to restore the visual color code for the next person who opens the box.
By treating every unverified wire as energized and relying on DMM voltage thresholds rather than faded insulation, you eliminate the guesswork that leads to OSHA-documented electrical injuries. Always defer to your local Authority Having Jurisdiction (AHJ) if you encounter non-standard wiring that does not match these baseline NEC or IEC profiles.
