In North America (NEC), standard AC wire color codes are Black or Red for hot, White or Gray for neutral, and Green or Bare Copper for ground. In Europe and the UK (IEC/BS 7671), the standard is Brown for line (hot), Blue for neutral, and Green/Yellow for earth (ground). However, regional variations, older installations, and specific circuit types introduce critical exceptions that can cause severe shock hazards or equipment damage if misinterpreted.

SAFETY WARNING: Always de-energize the circuit at the breaker panel and verify it is dead with a known-working digital multimeter or non-contact voltage tester before touching any conductors. Never assume a wire is safe based solely on its insulation color.

The Master AC Wire Color Code Reference Table

The table below maps the primary AC conductor functions across the four major global standards. Use this as your bench and jobsite quick-reference.

Conductor Function US & Canada (NEC / CEC) Europe & Modern UK (IEC 60446 / BS 7671) Old UK (Pre-2004) Australia & NZ (AS/NZS 3000)
Line / Hot 1 Black Brown Red Red (or Brown)
Line / Hot 2 (or Traveler) Red Black (with brown sleeve) Yellow White (or Black)
Line / Hot 3 Blue Grey Blue Blue
Neutral White or Grey Blue Black Black (or Blue)
Earth / Ground Green, Green/Yellow, or Bare Green/Yellow Green/Yellow (or Bare) Green/Yellow
Switched Leg (Hot return) Any color except White/Grey/Green (often Black or Red) Brown (with sleeve) or Black Red (with sleeve) Any color except Earth/Neutral

Rows People Get Wrong (And How to Fix Them)

Color codes are strictly enforced for neutrals and grounds, but the 'hot' conductors have exceptions that frequently trap DIYers and junior apprentices.

1. The White Wire Used as a Hot (Switch Loops)

In standard US switch loops (power to the light fixture first, then down to the switch), the 2-conductor cable sends hot down to the switch and switched-hot back up. NEC 200.7(C) allows the white wire to be used as a hot conductor in this scenario, but only if it is permanently re-identified with black or red tape, paint, or heat shrink at both ends. If you open a junction box and see a white wire connected to a black wire with no tape, assume it is hot until proven otherwise.

2. The High-Leg Delta (Orange Wire)

In commercial 240V 3-phase delta systems, the 'B' phase (high leg or wild leg) measures roughly 208V to ground, while phases A and C measure 120V to ground. Per NEC 110.15, this high leg must be identified by an orange outer finish. Mistaking an orange wire for a standard 120V line and wiring it to a standard receptacle will instantly destroy 120V appliances and create an arc flash hazard.

3. 3-Way Switch Travelers

When wiring 3-way switches, the two 'traveler' wires carry the hot current between switches. The NEC does not mandate a specific color for travelers, but explicitly forbids using white/gray (reserved for neutral) or green/bare (reserved for ground). Standard practice is to use the black and red wires in a 3-conductor NM-B cable. Do not assume a red wire is always a secondary hot phase; in residential 3-way circuits, it is almost always a traveler.

Regional Standards: Which Code Applies to You?

Wire colors are dictated by the electrical code governing your specific region. Applying the wrong regional standard can lead to catastrophic miswiring, especially when working on imported machinery or older homes.

  • North America (US & Canada): Governed by NFPA 70 (NEC) and the Canadian Electrical Code (CEC). Nominal voltages are 120V/240V split-phase for residential, and 208V/480V 3-phase for commercial.
  • Europe & Modern UK: Governed by IEC 60446 and regional adoptions like the UK's BS 7671 (IET Wiring Regulations). The UK harmonized with European colors in 2004, shifting from Red/Black to Brown/Blue. Nominal voltage is 230V single-phase and 400V 3-phase.
  • Australia & New Zealand: Governed by AS/NZS 3000. While they have largely aligned with IEC colors (Brown/Blue/Green-Yellow) in modern flexible cords, older fixed wiring often used Red (hot), Black (neutral), and Green (earth).
Pro Tip for UK/EU Retrofits: If you are adding a new circuit to a pre-2004 UK installation, you will have a mix of old (Red/Black) and new (Brown/Blue) colors in the same consumer unit. Use permanent warning labels at the distribution board indicating that both old and new color codes are present, as required by BS 7671.

Faded, Unmarked, or Mystery Wires: Safe Interpretation

Insulation fades, painters tape over wires, and previous owners ignore code. When you encounter a wire with missing, faded, or untrustworthy color markings, follow this strict verification sequence:

  1. De-energize and Isolate: Turn off the breaker and lock it out if possible.
  2. Continuity Check (Ground): With power off, set your multimeter to continuity/resistance. Measure from the mystery wire to a known ground (like the metal box or bare copper). A reading near 0 Ω means it is likely a ground wire.
  3. Energize and Test (Voltage): Turn the power back on. Set your multimeter to AC Voltage (V~).
    • Measure Mystery Wire to Known Ground. If you read nominal line voltage (e.g., ~120V in US, ~230V in EU), it is a Hot/Line wire.
    • Measure Mystery Wire to Known Hot. If you read ~0V, it is likely a Neutral (or another wire on the same phase).
    • Measure Known Neutral to Known Ground. You should read < 2V. If you read line voltage, the neutral is floating or broken upstream.
  4. Re-identify or Replace: Once identified, immediately wrap the exposed insulation with high-quality vinyl electrical tape (e.g., 3M Scotch Super 33+) or slide on heat-shrink tubing to mark its true function. If the insulation is crumbling or heavily degraded, pull new wire.

Decision Path: Picking the Right Wire for Your Next Run

Stop guessing which cable to buy at the hardware store. Use this decision tree to select the exact wire type and color configuration for your specific project.

Your Project Scenario Decision / Condition Concrete Pick (Buy This)
Standard US 120V Receptacle Circuit (20A) Needs Hot, Neutral, Ground. Max 20A load. 12/2 NM-B Cable.
Black (Hot), White (Neutral), Bare (Ground). Terminate on a 20A breaker.
US 3-Way Switch Wiring Needs Common, two Travelers, and Ground between switches. 12/3 or 14/3 NM-B Cable.
Black (Common), Red & White (Travelers - wrap white in black tape at both ends), Bare (Ground).
US 240V Baseboard Heater or EV Charger Needs two Hots and Ground. No neutral required for pure 240V loads. 10/2 or 8/2 NM-B Cable.
Black (Hot 1), White (Hot 2 - must be taped black or red at both ends), Bare (Ground).
UK/EU Standard 230V Socket Radial Needs Line, Neutral, Earth for a 20A/32A radial circuit. 2.5mm² or 4mm² Twin & Earth.
Brown (Line), Blue (Neutral), Green/Yellow (Earth).

When in doubt, always size your wire for the breaker protecting it, not just the load. A 20A breaker requires a minimum of 12 AWG copper (US) or 2.5mm² copper (EU/UK). Never downsize the wire to save money; the breaker will not trip before the wire melts.