In the USA, the standard AC wire color code for 120V/240V residential split-phase systems uses black for the first ungrounded (hot) conductor, red for the second hot, white (or gray) for the grounded (neutral) conductor, and bare copper or green for the equipment grounding conductor. These rules are governed by the National Electrical Code (NEC) Articles 200, 210, and 250. However, commercial 3-phase systems and international imports use entirely different palettes. Below is the definitive reference for identifying, testing, and interpreting AC wire colors on the bench and in the panel.
The Complete USA AC Wire Color Code Reference (NEC)
The following table outlines the mandated conductor colors based on system voltage and phase configuration. Always assume these apply to standard THHN/THWN-2 in conduit or NM-B (Romex) cable sheaths.
| System Type | Phase A (Hot 1) | Phase B (Hot 2) | Phase C (Hot 3) | Neutral (Grounded) | Ground (EGC) |
|---|---|---|---|---|---|
| 120V/240V 1-Phase (Residential) | Black | Red | N/A | White or Gray | Bare or Green |
| 208V/120V 3-Phase (Wye) | Black | Red | Blue | White or Gray | Bare or Green |
| 480V/277V 3-Phase (Wye) | Brown | Orange | Yellow | White or Gray | Bare or Green |
| 240V 3-Phase High-Leg Delta | Black | Orange (High Leg) | Blue or Red | White or Gray | Bare or Green |
Rows People Get Wrong & Faded Wire Protocols
Even experienced journeyman electricians can get tripped up by specific edge cases in the color code matrix. Here are the most common pitfalls and how to handle degraded insulation.
The High-Leg Delta 'Stinger' (Orange Wire)
In older commercial buildings with a 240V 3-phase high-leg delta service, Phase B (the high leg) measures 208V to ground, while Phases A and C measure 120V to ground. NEC Article 215.8 mandates this high leg must be identified by an outer finish of orange. The most common bench and jobsite mistake is assuming an orange wire in a 240V panel is just a standard hot leg and wiring a 120V control circuit to it. This instantly fries 120V appliance control boards and creates a severe shock hazard. If you see orange in a 3-phase panel, always meter it to ground before assuming its voltage class.
Switch Loops and Re-identified Neutrals
In standard residential switch loops (pre-NEC 2011), a 2-wire cable runs from the ceiling fixture to the wall switch. The white wire is used as the ungrounded (hot) feed down to the switch, and the black wire returns the switched hot to the fixture. NEC 200.7(C) requires that when a white wire is used as a hot, it must be permanently re-identified with black tape, paint, or a marker at both terminations. If you open a switch box and see a white wire connected to the brass screw, do not assume it is a neutral.
Protocol for Faded, Missing, or Sun-Baked Markings
When working with pre-1970s cloth-covered wiring, or THHN that has been baked in outdoor PVC conduit by UV and heat, black and white insulation often fades to an identical grayish-brown. Never trust visual color on old work. Follow this protocol:
- De-energize the circuit at the breaker and verify the meter is functional on a known live source (OSHA standard practice).
- Isolate the suspect conductors so they are not touching ground or each other.
- Re-energize and use a True-RMS multimeter (e.g., Fluke 117) to measure from the suspect wire to a known, verified equipment ground.
- A reading in the 114V–126V nominal range identifies the ungrounded (hot) conductor. A reading of 0V indicates a neutral or ground.
- De-energize again, apply fresh colored heat-shrink tubing or electrical tape to re-identify the wires, and document it on the panel schedule.
Regional Variants: USA (NEC) vs. IEC vs. Old UK
If you are repairing imported appliances, working on international marine/RV systems, or bench-testing European power supplies, the USA color codes do not apply. The International Electrotechnical Commission (IEC 60446) standardizes colors for most of the world, which differs drastically from the NEC. Furthermore, the UK transitioned from its own legacy colors to IEC harmonized colors in 2004, meaning older UK equipment still uses the legacy palette.
| Standard / Region | Unrounded (Hot / Line) | Grounded (Neutral) | Protective Earth (Ground) |
|---|---|---|---|
| USA & Canada (NEC / CEC) | Black, Red, Blue (120/208V) | White or Gray | Bare Copper or Green |
| Europe & UK (IEC 60446 / Post-2004) | Brown (Single Phase) | Blue | Green with Yellow Stripe |
| Old UK (Pre-2004 Legacy) | Red | Black | Green |
| Australia & NZ (AS/NZS 3000) | Brown (Active) | Blue or Black | Green/Yellow Stripe |
Practical Translation: If you are wiring a UK-imported 240V kettle or bench power supply, the blue wire is the neutral (not a hot leg like in US 3-phase), and the brown wire is the hot. The most dangerous mistake is treating an IEC black wire as a neutral; in the old UK standard and in IEC 3-phase systems, black is an active hot conductor. Always check the manufacturer's schematic on the nameplate rather than relying on regional assumptions.
Frequently Asked Questions
Can I use a white wire as a hot wire in the USA?
Yes, but only under specific conditions outlined in NEC Article 200.7. The most common application is a switch loop, where a 2-wire cable runs to a switch and the white wire carries the ungrounded (hot) feed. However, the code strictly requires you to permanently re-identify the white wire with black or red tape, paint, or heat-shrink at every point where the insulation is visible. You cannot use a white wire as a hot feed in a standard branch circuit run from the panel.
What is the AC wire color code for a 480V 3-phase system in the USA?
For 480V/277V 3-phase Wye systems, which are standard in large commercial and industrial facilities in the USA, the ungrounded conductors must be Brown (Phase A), Orange (Phase B), and Yellow (Phase C). The grounded neutral is white or gray, and the equipment ground is bare or green. Do not use black, red, and blue in a 480V panel; those colors are reserved for the lower 208V/120V systems to prevent catastrophic overvoltage connections.
How do I safely test wire colors if the insulation is faded or missing?
Never guess based on faded cloth or sun-baked THHN. Use a non-contact voltage tester (NCVT) to confirm the presence of voltage, then use a True-RMS multimeter to measure the suspect conductor against a verified equipment grounding conductor (like a bare copper wire bonded to the metal box). A reading of 114V–126V confirms it is the hot leg. A reading of 0V to ground, but 120V to the confirmed hot leg, identifies it as the neutral. Always follow OSHA electrical safety guidelines for testing and lockout/tagout procedures.
Where can I find the official legal code for these wire colors?
The official mandate for conductor identification in the USA is published in NFPA 70: National Electrical Code (NEC), specifically in Articles 200 (Use and Identification of Grounded Conductors), 210 (Branch Circuits), and 250 (Grounding and Bonding). Remember that while the NEC is the national baseline, your local state or municipal building code may have amendments that supersede it.
