The standard US NEC color code AC wiring uses Black, Red, and Blue for hot (line) conductors, White or Gray for neutral, and Green or Bare copper for equipment ground. In IEC regions (Europe, UK post-2004, and most international markets), Brown, Black, and Gray are hot, Blue is neutral, and Green/Yellow stripe is ground. Because guessing wire functions based on faded insulation or non-standard previous work can be lethal, always verify with a meter before making contact.
Global AC Wiring Color Code Reference Chart
The table below maps the exact conductor colors across the three most common standards you will encounter on the bench or in the field. This data aligns with NFPA 70 (NEC) Article 200/210 and IEC 60446 specifications.
| Function | US NEC (120/208/240V) | US NEC (277/480V 3-Phase) | IEC (230/400V) | Old UK (Pre-2004) |
|---|---|---|---|---|
| Line 1 (Hot) | Black | Brown | Brown | Red |
| Line 2 (Hot) | Red | Orange | Black | Yellow |
| Line 3 (Hot) | Blue | Yellow | Gray | Blue |
| Neutral | White or Gray | Gray (or White w/ trace) | Blue | Black |
| Equipment Ground | Green, Green/Yellow, or Bare | Green, Green/Yellow, or Bare | Green/Yellow Stripe | Green/Yellow Stripe (or Bare) |
The "Rows People Get Wrong" Field Notes
Reference charts look clean on paper, but real-world junction boxes are messy. Here are the specific color code scenarios that cause the most shocks and fried equipment in the field.
1. The White Wire Used as a Hot (Switch Loops)
In older US residential wiring, a 2-wire cable (black and white) was often run from a switch to a light fixture. The white wire was used to carry the switched hot back to the light. Under NEC 200.7(C)(1), this white wire must be permanently re-identified with black tape, paint, or a marker at both ends to indicate it is a hot conductor. The mistake: Electricians often tape the switch end but forget the fixture end, leaving a live white wire in the canopy that the next person assumes is a neutral.
2. The 277/480V High-Leg Delta (Orange Wire)
In commercial US panels fed by a 240V 3-phase delta transformer with a center-tapped neutral, you get 120V from Line 1 and Line 3 to neutral, but 208V from Line 2 to neutral. NEC 110.15 strictly mandates that this Line 2 (the "high leg" or "wild leg") must be colored Orange. The mistake: An apprentice sees an orange wire, assumes it's just a standard hot, and lands it on a 120V single-pole breaker. When they turn it on, 208V hits a 120V appliance, instantly destroying the electronics and creating a fire hazard.
3. Old UK Red/Black vs. IEC Brown/Blue Transition
If you are working in the UK or on imported European machinery, you will encounter the 2004 harmonization shift. Old UK fixed wiring used Red (Hot) and Black (Neutral). The new IEC standard uses Brown (Hot) and Blue (Neutral). The mistake: In homes wired between 2004 and 2006, extensions were often done using new IEC cables spliced into old UK cables. If you see a Black wire and assume it's the IEC Line 2 (Hot), you will grab a live Old UK Neutral. Always treat old UK Black as a current-carrying Neutral, and old UK Red as Hot.
Safe Interpretation When Insulation Fades or Goes Missing
When working on 40-year-old panels, THHN insulation becomes brittle, fades, or gets painted over. If you cannot rely on the color code AC wiring chart, you must electrically identify the conductors. Do not rely on a non-contact voltage tester (NCVT) to distinguish between neutral and ground; phantom voltages from adjacent wires will cause false positives on both.
The Pro DMM Testing Method:
- Identify the Hot: With the circuit energized and a load applied (e.g., a lamp plugged in and turned on), measure from the unknown wires to a known ground bus. The wire reading ~120V (or ~230V in IEC regions) is your Hot.
- Distinguish Neutral from Ground: Both the true Neutral and the true Ground will read ~120V when measured against the Hot wire. To tell them apart, measure the voltage between the suspected Neutral and the known Ground bus while the load is running.
- Read the Drop: A true neutral carries return current. On a 15A circuit with 50 feet of 14 AWG copper wire (resistance ~0.125 ohms), a 10A load will create a voltage drop of roughly 1.25V. Your DMM will read 0.5V to 2.0V between Neutral and Ground. A true equipment ground carries zero current under normal operation, so the DMM will read 0.0V between Ground and the Ground bus.
AC Wiring Color Code FAQ
What color is the hot wire in a standard US outlet?
In a standard US 120V receptacle, the hot wire (connected to the brass screw) is Black. If you are wiring a 240V appliance (like a dryer or baseboard heater) or a multi-wire branch circuit (MWBC), the second hot wire is Red. The neutral (silver screw) is White, and the ground (green screw) is Bare or Green.
Can I use a white wire for a hot line in a switch loop?
Yes, but only if you permanently re-identify it at both termination points. According to NEC 200.7(C)(1), you must wrap the white insulation with black or red electrical tape, or use a permanent marker, to visibly mark it as an ungrounded (hot) conductor. If you are pulling new wire for a switch loop today, NEC 2011 and later requires you to run a 3-wire cable (Black, Red, White) so the white is strictly reserved for neutral, eliminating the need for re-identification.
Why is my ground wire green and yellow striped?
The Green/Yellow striped insulation is the globally recognized IEC 60446 standard for protective earth (ground). It was adopted to provide a highly distinct, universally recognizable color that could never be confused with active current-carrying conductors (like solid green, which was historically used as a hot phase in some older 3-phase systems). The US NEC accepts Green/Yellow as a valid equipment grounding conductor alongside solid Green and Bare copper.
What happens if I swap neutral and ground at an outlet?
If you connect the white neutral wire to the green ground screw and the bare ground to the silver neutral screw, the outlet will still power a device, and a standard breaker will not trip. However, this creates a severe shock hazard. The equipment ground is now carrying normal return current, meaning the metal chassis of any plugged-in appliance becomes energized relative to true earth. Furthermore, if this outlet is downstream of a GFCI, the GFCI will detect the imbalance and trip immediately. Never bond neutral and ground anywhere except at the main service disconnect panel.
