Wire Color Codes: What the Colors Mean (and When They Lie)
Black is hot, white is neutral, green is ground — until a switch loop, a 240V circuit, or a previous owner's creativity says otherwise. The color conventions, the legal re-markings, and the rule that colors are clues, not proof.
⚠️ Before you start
- Colors are convention, not verification — every conductor is live until your tester says otherwise, whatever its color.
- Re-marking has rules: white used as a hot must be re-identified (tape/marker) at every visible point; grounds are never anything but grounds.
- The scariest wire in any house is the one a previous hand mis-colored. Test like everyone before you was colorblind and in a hurry.
🧰 Tools you'll need
- Non-contact tester and multimeter — the actual arbiters
- Phase tape (red, blue, white, green) for proper re-marking
The two rules the code actually writes
Here's the secret that reorganizes everything: the NEC reserves colors for safety conductors only:
- White or gray = grounded conductor (neutral) — Article 200.6. Its job: carrying current back, at (nominally) zero volts to ground, every hour of its life.
- Green, green-with-yellow, or bare = equipment ground — 250.119. Its job: carrying current only during a fault, and being trustworthy enough to bet a life on.
Those identities are protected. A green wire is never anything else, period. A white can moonlight as a hot only in specific cases and only re-identified (wrapped with colored tape/paint at every point of visibility). Everything else — black, red, blue, and the whole rainbow — is unregulated hot conductor territory, governed by convention and the installer's discipline rather than statute.
The residential conventions
- Black — hot. The default ungrounded conductor everywhere.
- Red — the second hot: the other leg on 240V circuits, the second switched conductor in three-ways/travelers, the interconnect on smoke detectors, the "switched" wire generally. Red in a box is a question worth answering before touching.
- White — neutral… with the two great exceptions below.
- Bare/green — ground, always, no exceptions, including the day someone before you used it otherwise (that's not an exception; that's a violation you now get to fix).
- Blue, yellow — conventionally travelers and switch legs pulled in conduit; in cable-wired homes you'll rarely see them except in smart-switch pigtails.
Where white lies (legally)
The switch loop. Old two-conductor cable to a switch: power comes down on one conductor, returns switched on the other — both are hots in function, one is white in costume. Code requires that white be re-identified (black tape at both ends) — requirement honored unevenly across seventy years of work, which is why the switch box is where testers earn their keep. (Since the 2011 cycle, 404.2(C) generally requires an actual neutral at switch locations in new work — the smart-switch era's quiet enabler.)
240V circuits in cable. Two-conductor cable feeding a water heater or straight-240 load: both conductors are hots, so the white gets re-marked and works as the second leg. Black-plus-taped-white on a double-pole breaker is correct old work; black-plus-untaped-white is correct function with incorrect paperwork — fix the tape while you're there.
The commercial color world
Where conduit lets installers choose colors, convention crystallized (and many specs and 210.5(C) identification rules formalize it per building):
- 120/208V three-phase: black, red, blue phases; white neutral.
- 277/480V three-phase: brown, orange, yellow phases; gray neutral. (Mixing up the two neutral colors in a dual-voltage building is a genuinely dangerous sloppiness — 277 bites hard.)
- High-leg delta: the B-phase running ~208V to neutral must be orange (110.15) — one of the code's few mandated hot colors, and a system that hurts people who don't know it exists.
- Isolated grounds run green/yellow stripe; travelers and switch legs take the pinks/purples/whatever-the-spec-says — the point is the building's convention, documented and followed.
The rule above the rules
Colors are the map; the tester is the territory. Every seasoned electrician carries the same two scars-turned-habits: the white that was hot, and the black that was (surprise) a neutral someone borrowed. So: identify by color, verify by meter, re-mark what you correct, and leave every box more honest than you found it. The color code's real function isn't telling you what a wire is — it's telling the next person what you did. Write clearly.
📞 When to call a professional
This is reference material for the trade and serious students. Homeowners finding creative colors in their boxes — whites taped black, reds doing mystery jobs, grounds carrying current — have found exactly the archaeology a licensed electrician should excavate.
Frequently asked questions
What are the only colors the code actually reserves?
Just the safety ones: white or gray for the grounded conductor (neutral) — 200.6; green, green/yellow, or bare for equipment grounds — 250.119. Everything else (black, red, blue, orange, yellow, brown, purple...) is ungrounded-conductor territory by convention, not statute. The reserved colors may never be used as hots without proper re-identification (whites, in limited cases) or ever (greens — no exceptions).
Why is the white wire hot in my switch box?
The switch loop: cable runs from the light down to the switch, and both conductors are part of the switched hot path. Modern code (404.2, 200.7) requires the white in that use to be re-marked (tape/paint) — and post-2011 code requires a neutral at most switch locations, changing new work. In old work, the un-re-marked white-that's-hot is one of the most common surprises in residential boxes.
What do the colors mean on 240V and three-phase work?
Residential 240V: both hots — typically black and red (or black + re-marked white in old two-conductor cable). Commercial three-phase convention: 120/208V systems run black-red-blue with white neutral; 277/480V systems run brown-orange-yellow with gray neutral. The 'high-leg' delta's wild B-phase must be orange (110.15) — one of the few colors the code does mandate in context.