When pulling NM-B cable, terminating a 3-phase motor, or troubleshooting an old fuse box, guessing a conductor's function is a fatal mistake. The colour codes for electrical wiring dictate exactly which wire carries the load, which returns it, and which saves your life during a fault. Below are the definitive reference tables, followed by regional breakdowns and field protocols for unmarked wires.
Global Electrical Wiring Colour Code Reference Tables
The tables below map the standard colour codes for electrical wiring across the world's dominant standards. Read the AC table first for mains voltage (120V-480V), then the DC table for low-voltage control circuits, solar arrays, and battery banks.
AC Mains Power Wiring (Single & Three-Phase)
| Function | US / Canada (NEC) | EU / IEC 60445 | UK (Post-2004 BS 7671) | Old UK (Pre-2004) |
|---|---|---|---|---|
| Line / Phase 1 (L1) | Black | Brown | Brown | Red |
| Line / Phase 2 (L2) | Red (or Blue) | Black | Black | Yellow |
| Line / Phase 3 (L3) | Blue | Grey | Grey | Blue |
| Neutral (N) | White or Grey | Blue | Blue | Black |
| Earth / Ground (PE) | Green, Green/Yellow, or Bare | Green/Yellow | Green/Yellow | Solid Green |
DC Power & Control Wiring
| Function | US / Canada (NEC) | EU / IEC 60445 |
|---|---|---|
| Positive (Grounded) | White with Red stripe / Red | Brown |
| Positive (Ungrounded) | Red | Brown |
| Negative (Grounded) | White with Black stripe / Black | Blue |
| Negative (Ungrounded) | Black | Blue |
| DC Ground / Bond | Green, Green/Yellow, or Bare | Green/Yellow |
Regional Variants: NEC vs. IEC vs. Old UK Standards
Knowing which standard applies to your region—and more importantly, which standard the original electrician used when the building was wired—is critical for safe interpretation.
North America: The NEC (NFPA 70)
In the US and Canada, the National Electrical Code (NEC) governs wire colours. The NEC strictly mandates that the grounded conductor (Neutral) must be White or Grey (Article 200.6), and the equipment grounding conductor must be Green, Green with Yellow stripes, or Bare (Article 250.119). Unclassified "hot" or "line" conductors can be any colour except white, grey, or green. In practice, US residential wiring relies heavily on Black (hot), White (neutral), and Bare (ground) inside standard 12/2 or 14/2 NM-B Romex cables. For 240V appliances, you will often see 10/3 NM-B containing Black, Red, White, and Bare.
Europe & Modern UK: IEC 60445 & BS 7671
The International Electrotechnical Commission (IEC) standardized European colours to ensure cross-border safety. The UK officially harmonized with the IEC colours in 2004 via Amendment 2 to BS 7671 (The IET Wiring Regulations). If you are working in a UK home built after April 2006, you will see Brown (Live), Blue (Neutral), and Green/Yellow (Earth).
Homes wired before 2004 use the old UK colours: Red (Live), Black (Neutral), and solid Green (Earth). The danger arises when old and new cables are mixed in the same junction box. A modern Blue wire (Neutral) could be incorrectly wired to an old Black wire (which was also Neutral, but old Black was sometimes used as a switched live without proper sleeving). Always treat old UK Black wires as potentially live until tested.
Which Standard Applies to You?
- US/Canada: Always default to NEC. If you see Brown/Blue/Green-Yellow in a US home, it is likely an imported appliance cord or a 3-phase industrial machine wired to IEC standards.
- UK/Aus/NZ: Post-2004/2006 builds use IEC (Brown/Blue). Pre-2004 builds use the old regional colours (Red/Black).
- EU Mainland: IEC 60445 has been standard since the 1970s. Brown/Blue/Green-Yellow is virtually universal.
The "Rows People Get Wrong" & Faded Wire Protocols
Reference tables assume perfect conditions. On the jobsite, wires fade, electricians cut corners, and switch loops break the rules. Here is how to handle the most common colour code failures.
The Rows People Get Wrong
1. The "White is Always Neutral" Fallacy (NEC Regions)
In a standard cable, white is neutral. However, in a switch loop (where power goes to the light fixture first, then down to the switch), the white wire in the 2-wire cable is used to carry the hot feed down to the switch. NEC Article 200.7(C) requires this white wire to be re-identified with black tape or paint at both ends to indicate it is a hot conductor. If you see a white wire connected to a brass (hot) screw on a switch, it is carrying 120V. Do not touch it.
2. The 240V Appliance "White Hot" (NEC Regions)
For pure 240V loads (like older baseboard heaters or well pumps) that do not require a neutral, electricians often use 12/2 NM-B (Black, White, Bare). The white wire is used as the second hot leg. By code, it must be wrapped in black or red phase tape. If the tape is missing, you have two 120V hot legs on opposite phases, not a hot and a neutral.
3. Solid Green vs. Green/Yellow Earth (UK/IEC)
Old UK wiring used solid green for the earth wire. Modern IEC uses green/yellow. If you are replacing an old UK consumer unit or light fixture, you must sleeve the old solid green earth wire with modern green/yellow PVC sleeving to prevent future electricians from mistaking it for an old black neutral or a control wire.
Safe Interpretation When Markings are Faded or Missing
THHN insulation in commercial conduit, or old rubber-insulated wires in pre-1960s homes, often fade to a uniform dirty grey or brown. Never rely on visual guessing. Use this field protocol to identify unmarked conductors safely:
- De-energize and Expose: Turn off the main breaker. Strip back 1/2 inch of insulation to expose clean copper if the wire ends are heavily oxidized or painted over.
- Initial NCVT Sweep: Turn the power back on at the breaker. Use a high-sensitivity Non-Contact Voltage Tester (like the Klein NCVT-4 or Fluke 1AC-II) to identify which wires are emitting an electromagnetic field (the "hot" wires). Mark them immediately with red phase tape.
- The Multimeter Ground-Reference Test: Set your multimeter to AC Voltage (V~). Measure between the suspected Hot and a known, verified ground (like a metal water pipe or the grounding busbar in the panel). A reading of ~120V (US) or ~230V (UK/EU) confirms the hot leg.
- Neutral vs. Ground Differentiation: This is where amateurs get shocked. Both neutral and ground should read 0V to ground. To tell them apart, measure the voltage between the suspected Neutral and Ground while the circuit is under load (e.g., plug in a hair dryer or heavy lamp on the same circuit). The Neutral will show a slight voltage drop (typically 0.5V to 2.0V) due to the resistance of the wire carrying return current. The Ground wire carries no current under normal operation and will read a true 0.00V.
- Permanent Re-identification: Once identified, de-energize the circuit again and wrap the wire ends with OSHA-compliant phase tape (e.g., 3M Scotch 35 series). Do not use cheap masking tape or standard black electrical tape, as the adhesive degrades and falls off inside hot junction boxes within a year.
By treating colour codes as a strong hint rather than an absolute guarantee, and by verifying every conductor with a meter, you bridge the gap between textbook theory and jobsite reality.
