AC color code wiring dictates the specific function of each conductor in an alternating current circuit. In the US and Canada (NEC), standard 120V/240V single-phase uses Black (Line 1), Red (Line 2), White (Neutral), and Bare/Green (Ground). In Europe and most international regions (IEC), the standard is Brown (Line), Blue (Neutral), and Green/Yellow (Ground). Because mixing these standards or misinterpreting faded wires can result in lethal shocks or destroyed equipment, you must verify the standard applicable to your region before terminating any connections.
The Master AC Color Code Wiring Reference Table
The table below maps the exact conductor colors for single-phase, three-phase, and international systems. Bookmark this for quick bench or jobsite reference.
| Function | US/Canada (NEC) Single-Phase | US/Canada (NEC) 3-Phase | Europe / Int'l (IEC 60446) | Old UK (Pre-2004) |
|---|---|---|---|---|
| Line 1 (Hot/Phase) | Black | Black | Brown | Red |
| Line 2 (Hot/Phase) | Red | Red | Black | Yellow |
| Line 3 (Hot/Phase) | N/A (or Blue for 480V) | Blue | Grey | Blue |
| Neutral | White or Grey | White or Grey | Blue | Black |
| Ground / Earth | Bare, Green, or Green/Yellow | Bare, Green, or Green/Yellow | Green with Yellow Stripe | Green |
Sources: NFPA 70 National Electrical Code (NEC) and Electrical Technology IEC/UK Wiring Color Codes.
Rows People Get Wrong (and How to Fix Them)
Even experienced DIYers and junior electricians trip over specific edge cases in AC color code wiring. Here are the most common failure points and how to handle them.
The 'White Wire as a Hot' Switch Loop
In older homes (pre-2011 NEC), it was common practice to run a 2-wire NM-B cable (Black, White, Bare) from a ceiling fixture down to a wall switch. The black wire carried constant hot down, and the white wire carried the switched hot back up. The white wire in this scenario is acting as a Line conductor, not a neutral. NEC 200.7(C) requires this white wire to be permanently re-identified with black electrical tape or paint at both ends. If you see a white wire connected to a switch terminal (not a receptacle screw), assume it is hot until proven otherwise.
The High-Leg Delta 'Orange' Wire
If you are working on a commercial 3-phase panel in the US (specifically a 240V High-Leg Delta system), you will encounter an Orange wire. This is the 'wild leg' or 'high leg' (Phase B). It measures 208V to ground/neutral, while the other two phases (Black and Red) measure 120V to ground. Never connect a standard 120V load to the orange high-leg; it will instantly destroy the appliance and trip the breaker.
Old UK Black vs. US Black
If you are repairing an imported UK appliance or working in a pre-2004 British home, a Black wire is the Neutral. In the US, Black is always Line (Hot). Connecting a US black (hot) to a UK black (neutral) terminal will short the circuit or electrify the appliance chassis. Always check the manufacturing sticker on imported gear to confirm the wiring standard it was built to.
Safe Interpretation When Markings Are Faded or Missing
Never trust wire color alone, especially in older homes where previous owners may have used whatever scrap THHN was left in their truck. If you open a junction box and the colors are faded, painted over, or non-standard, follow this verification sequence:
- Visual Inspection: Look for re-identification tape. Check if a white wire has black tape wrapped around the insulation near the wire nut.
- NCVT Sweep: With the breaker ON, use a Non-Contact Voltage Tester to identify which wires are energized. Keep in mind that NCVTs can give 'phantom' readings on neutral wires running parallel to hot wires in the same conduit.
- Multimeter Verification (The Gold Standard):
- Set your meter to AC Voltage (V~).
- Measure Line-to-Ground (Hot to Bare/Green). You should read nominal voltage (~120V in US, ~230V in EU).
- Measure Line-to-Neutral (Hot to White/Blue). You should read the same nominal voltage.
- Measure Neutral-to-Ground. This should read very close to 0V (typically < 2V). If you read 120V between Neutral and Ground, you have an open neutral or a bootleg ground—a severe shock hazard.
AC Color Code Wiring FAQ
What is the AC color code wiring for a 240V outlet?
For a standard US 240V-only circuit (like a NEMA 6-50 welder outlet), you use two hot wires: Black (Line 1) and White (Line 2, which must be re-identified with black or red tape at both ends), plus a Bare/Green ground. However, for a 120V/240V appliance (like a dryer or range using a NEMA 14-50), you use four wires: Black (Line 1), Red (Line 2), White (Neutral), and Bare/Green (Ground). Never use the ground wire as a neutral return path.
Can I use a white wire as a hot in AC color code wiring?
Yes, but only under specific conditions outlined in NEC Article 200.7. You can use a white wire as a hot conductor in a cable assembly (like NM-B) for a switch loop or a 240V pure load, provided you permanently re-identify the white insulation with black tape, paint, or another effective means at every location where the wire is visible and accessible. You cannot use a white wire as a hot if you are pulling individual THHN conductors through a conduit; in conduit, you must pull a black, red, or blue wire for hot.
How do I wire a 3-way switch using standard AC color codes?
In modern NEC-compliant 3-way switch wiring (requiring a neutral at the switch box), you will typically use a 3-wire NM-B cable (Black, Red, White, Bare) between the two switches. The White wire is the neutral (spliced through, not connected to the switch). The Black and Red wires act as the 'travelers' between the brass terminals on the two switches. The incoming Line (Hot) connects to the black common screw on switch #1, and the Load (going to the light) connects to the black common screw on switch #2. Always use the Bare/Green wire to bond the green ground screws on both switches and the metal box.
