In the United States, the National Electrical Code (NEC) strictly governs conductor identification to prevent lethal cross-wiring and equipment damage. Whether you are pulling 12/2 NM-B for a standard receptacle or terminating THHN in a commercial panel, relying on memory is dangerous. Below is the definitive reference for standard US wiring colors, followed by the edge cases that trip up even experienced DIYers.
Standard USA Wire Color Code Chart (NEC AC Power)
This table applies to standard 120V/240V single-phase residential systems and 120V/208V or 277V/480V three-phase commercial systems. The NEC outlines these requirements primarily in NFPA 70 (NEC) Articles 200, 210, and 250.
| Function | USA Color (NEC) | Practical Application | Re-identification Rule |
|---|---|---|---|
| Ungrounded (Hot) Phase 1 | Black | Standard 120V branch circuits, switch legs | Can be re-identified with colored tape at terminations |
| Ungrounded (Hot) Phase 2 | Red | 240V appliance hots, 3-way switch travelers | Can be re-identified with colored tape |
| Ungrounded (Hot) Phase 3 | Blue | 3-phase commercial panels, multi-wire branch circuits (MWBC) | Can be re-identified with colored tape |
| Grounded (Neutral) | White or Gray | Return path for 120V circuits, 240V/120V appliance neutrals | NEVER use as a hot wire without permanent re-identification (black/red tape) |
| Equipment Ground | Green, Green/Yellow, or Bare | Fault current path back to the main panel | NEVER use as a current-carrying conductor (hot or neutral) |
| High-Leg (Wild Leg) | Orange | 120/240V 3-phase Delta systems (B-Phase measures 208V to ground) | Mandated by NEC 110.15; must be orange at all terminations |
Rows People Get Wrong (and How to Fix Them)
The chart above looks simple until you open a junction box and see a white wire connected to a black wire. Here are the specific scenarios where standard colors are legally modified or commonly misapplied.
The White Wire Switch Loop
In older homes (and even some new ones using 2-wire cable), the power goes to the light fixture first, and a 2-wire cable drops down to the switch. In this 'switch loop,' the white wire carries 120V hot down to the switch, and the black wire carries the switched hot back up. The NEC requires the white wire to be permanently re-identified with black or red tape at both ends to warn future workers that it is a hot conductor, not a neutral.
240V Baseboard Heaters and Water Heaters
Pure 240V loads (like baseboard heaters) do not require a neutral. Installers often run 12/2 NM-B (Black, White, Bare). Because there is no neutral, the white wire is used as the second hot leg. Just like the switch loop, the white wire must be wrapped in black or red tape at the breaker and the device terminal. If you see a white wire on a 2-pole breaker, assume it is hot until proven otherwise.
3-Way and 4-Way Switch Travelers
Traveler wires run between multi-way switches. The NEC does not mandate a specific color for travelers, except that they cannot be white, gray, green, or bare. In practice, electricians use the black and red wires from a 3-conductor cable (12/3 or 14/3). However, if you are pulling individual THHN wires in conduit, you might see blue, yellow, or brown travelers. Never assume a traveler is neutral just because you are confused by the color.
DC vs. AC Color Confusion
Do not mix up automotive/solar DC wiring with AC mains. In standard US DC systems (like solar battery banks), Red is Positive and Black is Negative. However, the NEC (Article 690) now specifies that for grounded DC systems, the grounded conductor (often the negative in modern setups) should be White or Gray, while the ungrounded positive is Red. Always verify if a system is AC or DC before applying the color chart.
Regional Variants: NEC vs. IEC vs. Old UK
If you are working on imported machinery, RVs with European wiring, or older international properties, the US color code will not apply. The International Electrotechnical Commission (IEC) harmonized colors for Europe and the UK in 2004. For a deep dive into international standards, refer to the IEC international standards catalog.
| Function | USA / Canada (NEC) | Europe / UK (IEC Post-2004) | Old UK (Pre-2004) |
|---|---|---|---|
| Phase 1 (Hot) | Black | Brown | Red |
| Phase 2 (Hot) | Red | Black | Yellow |
| Phase 3 (Hot) | Blue | Gray | Blue |
| Neutral | White or Gray | Blue | Black |
| Earth / Ground | Green, Green/Yellow, Bare | Green/Yellow | Green (or Bare) |
Painters frequently spray over exposed wires in panels, turning black, red, and white wires into a uniform coat of latex white. Dirt and heat can also fade THHN insulation over decades. Never trust wire color alone. Always treat every conductor as energized until you have physically tested it. Turn off the breaker, verify your multimeter is functioning on a known live source, and test Line-to-Neutral and Line-to-Ground. If you measure 0V on both, the circuit is dead. If you are unsure, hire a licensed electrician.
FAQ: USA Wire Color Codes
What color is the ground wire in the USA?
In the US, the equipment grounding conductor must be Green, Green with a Yellow stripe, or Bare (uninsulated) copper. In NM-B (Romex) cable, it is almost always bare copper. In conduit systems using THHN wire, electricians typically pull a green insulated wire. You will never see a bare wire used for anything other than a ground in standard AC wiring.
Can I use a white wire as a hot wire?
Yes, but only under specific NEC conditions, such as a switch loop or a pure 240V load where no neutral is required. When you do this, you are legally required to 're-identify' the white wire by wrapping it with black or red electrical tape (or using a permanent marker approved for the purpose) at every point where the insulation is visible (terminations and splices). This warns anyone opening the box that the white wire is carrying live voltage.
What is the color code for 240V outlets (like a dryer or range)?
Modern 240V/120V appliances (which require both 240V for heating elements and 120V for control boards) use a 4-wire setup. The colors are: Black (Hot 1), Red (Hot 2), White (Neutral for the 120V components), and Green or Bare (Equipment Ground). Older 3-prong dryer outlets lacked the separate ground wire, using the neutral as a combined ground/neutral, but this was banned for new installations in the 1996 NEC.
How do I test wire colors if they are faded or painted over?
Use a two-step verification process. First, use a Non-Contact Voltage Tester (NCVT) to check for the presence of an electromagnetic field around the wire. Second, use a digital multimeter. With the circuit live (exercise extreme caution), measure the suspect wire against a known bare ground. If it reads ~120V, it is a hot wire. If it reads ~0V against ground, but ~120V when measured against a known hot wire, it is a neutral. Always wear safety glasses and insulated gloves when testing live, unidentified circuits.
