The standard US NEC electrical wire color code for 120/240V AC is Black or Red for hot, White or Gray for neutral, and Bare or Green for ground. The IEC standard (used in Europe and the UK post-2006) uses Brown for hot, Blue for neutral, and Green/Yellow stripe for ground. Because mixing these standards or misinterpreting legacy wiring can result in fatal shocks or equipment destruction, you must identify the governing regional standard before making any terminations.
The Master Electrical Wire Color Code Reference Table
Use this table as your primary bench and jobsite reference. It maps the core conductor functions across the three most common wiring standards you will encounter in residential and light commercial environments.
| Function | US/Canada (NEC) 120/240V | US/Canada (NEC) 277/480V | Europe/UK (IEC 60446) | Old UK (Pre-2006) |
|---|---|---|---|---|
| Line 1 (Hot/Live) | Black | Brown | Brown | Red |
| Line 2 (Hot/Live) | Red | Orange | Black (or Brown w/ marker) | Yellow |
| Line 3 (Hot/Live) | Blue | Yellow | Gray (or Brown w/ marker) | Blue |
| Neutral | White or Gray | Gray or White | Blue | Black |
| Ground (Earth) | Bare, Green, or Green/Yellow | Bare, Green, or Green/Yellow | Green with Yellow Stripe | Green (or Green/Yellow) |
Regional Variants and Standard Applications
Understanding which standard applies to your region is the first step in safe wiring. The rules governing these colors are not arbitrary; they are engineered to prevent cross-standard catastrophes.
North America (NEC / NFPA 70)
In the US and Canada, the National Electrical Code (NFPA 70) dictates color schemes. For standard residential NM-B (Romex) cable, the outer sheath color indicates the wire gauge (White for 14 AWG, Yellow for 12 AWG, Orange for 10 AWG), but the internal conductor colors follow the 120/240V column above. When pulling individual THHN/THWN-2 wires in conduit, you must manually select the correct insulation colors.
Europe and Modern UK (IEC 60446)
The International Electrotechnical Commission (IEC) standard is used across mainland Europe. The UK officially harmonized with the IEC color code in 2006. According to the UK Health and Safety Executive (HSE), the transition was implemented to align UK fixed wiring with European appliance flex colors, reducing fatal errors when working on imported machinery.
Legacy UK Wiring (Pre-2006)
If you are working in a UK home built before April 2006, you will likely encounter the old color code. The most dangerous trap here is the neutral wire: it was Black. In the modern IEC standard, Black is a live/hot phase conductor. Splicing a modern IEC appliance into legacy UK fixed wiring without verifying the conductors will result in a direct short or an energized chassis.
The 'Rows People Get Wrong' Field Notes
Even experienced DIYers trip over specific edge cases in the color code tables. Here are the most common field mistakes and how to avoid them.
- Using White as a Hot Wire (Switch Loops): The NEC allows a white wire to be used as a hot conductor in a 2-wire switch loop or a 3-way switch setup, but only if it is permanently re-identified at both ends with black or red tape/paint. People frequently forget the tape at the switch box, leading the next person to assume the white wire is a safe neutral. Always re-identify.
- The 208V High-Leg Delta Trap: In commercial 240V 3-phase high-leg delta systems, the B-phase (which measures 208V to neutral instead of 120V) must be Orange. If you mistakenly wire a 120V appliance to the high leg because someone used Black wire instead of Orange, you will instantly destroy the appliance and risk a fire. Always check for Orange in commercial panels.
- Solid Green vs. Green/Yellow in IEC: Under IEC rules, the protective earth must be Green with a Yellow stripe. Solid green is strictly forbidden for ground in IEC regions because it was historically used for telecom and data lines. Using solid green for earth in an EU installation will fail inspection and confuse telecom technicians.
- Gray vs. White in 277/480V Systems: While White is acceptable for neutral in 120/240V systems, Gray is the preferred and heavily enforced neutral color for 277/480V commercial systems. This prevents a 277V hot wire (Brown/Orange/Yellow) from being accidentally paired with a 120V White neutral.
Decision Path: Which Wire Color Do I Use?
Use this decision tree to select the exact cable type and conductor colors for your specific project. Do not deviate from these baseline configurations.
| If your project is... | Then select this cable/wire type | Terminate as follows |
|---|---|---|
| Standard US 120V receptacle or lighting circuit | 14/2 or 12/2 NM-B (Yellow or White jacket) | Black to Brass (Hot), White to Silver (Neutral), Bare to Green (Ground) |
| US 240V baseboard heater or water heater (no neutral required) | 12/2 or 10/2 NM-B | Black to L1, White wrapped in Red tape to L2, Bare to Ground |
| US 240V dryer or range (requires both 120V and 240V) | 10/3 or 8/3 NM-B | Black to L1, Red to L2, White to Neutral, Bare to Ground |
| UK/EU single-phase plug or appliance flex | 3-core PVC flexible cable | Brown to Live (L), Blue to Neutral (N), Green/Yellow to Earth (E) |
| Conduit pull for US 3-phase 208Y/120V commercial panel | Individual THHN/THWN-2 wires | Phase A: Black, Phase B: Red, Phase C: Blue, Neutral: White, Ground: Green |
Safe Interpretation When Markings Are Faded or Missing
Open a panel in a house built in the 1970s, and you will likely find white wires that have oxidized to a dirty gray, or black wires coated in drywall dust and paint. In older installations, UV exposure, heat, and chemical off-gassing from insulation can severely fade conductor colors. Furthermore, you may encounter 'bootleg' wiring where a handyman used whatever scrap wire was left in their van.
Never trust faded or unverified colors. Follow this strict verification protocol:
- De-energize and Lock Out: Turn off the main breaker. If you are testing a subpanel, turn off the feeder breaker and lock it out.
- Verify Dead: Use a non-contact voltage tester (NCVT) on all conductors, followed by a multimeter set to AC Voltage to confirm 0V between all hots and the panel chassis.
- Continuity Test the Ground: With the circuit dead, set your multimeter to continuity (the diode/beep setting). Place one probe on the suspected ground wire and the other on the known ground bus bar. A reading of less than 1.0 ohm confirms it is a ground.
- Continuity Test the Neutral: Place one probe on the suspected neutral and the other on the neutral bus bar. Again, you should read less than 1.0 ohm. Note: Ensure all loads on the circuit are unplugged, or you will read continuity through the appliance.
- Live Voltage Verification (If required for tracing): If you must energize the circuit to trace a hot wire at a distant outlet, use a solenoid voltage tester or a CAT III/IV digital multimeter. Measure Hot-to-Suspected Neutral (should read ~120V) and Hot-to-Suspected Ground (should read ~120V). Finally, measure Neutral-to-Ground; under load, this should read less than 2V. If Neutral-to-Ground reads 120V, the neutral is open or missing, and the 'white' wire you are looking at is likely a bootleg ground or an open hot.
When in doubt, abandon the existing wire and pull a new, properly color-coded circuit. The cost of a new spool of 12 AWG THHN is a fraction of the cost of a miswired circuit causing a fire or an electrical shock.
