Swipe the diagram to see the switch loop
- On a switch loop: white feeds the switch, black comes back to the light. Never the other way round (§200.7(C)(1)).
- That white has to be re-identified with tape or paint at both ends, and it is not allowed at all in a raceway.
What the NEC actually mandates
Two conductors. That is the whole list. Everything else is convention, manufacturer habit, or a local amendment your AHJ added.
Grounded conductor (neutral) WhiteGray §200.6 — 6 AWG and smaller: continuous white or gray outer finish, or three continuous white/gray stripes. 4 AWG and larger may instead be re-identified at terminations. |
Equipment grounding conductor GreenGreen + yellow stripeBare copper §250.119 — 6 AWG and smaller must be continuously identified. 4 AWG and larger may be re-identified at every accessible point. |
Ungrounded conductors (hot) BlackRedBlueBrownOrangeYellow The code does not pick a color for hots. It reserves the two above so a hot can never be mistaken for a neutral or a ground, and leaves the rest to you. |
Convention is not code
Black, red and blue on 120/208 is common practice, not a code requirement. It is worth following for consistency, but the NEC does not specify it. What 210.5(C) does require, where a building has more than one voltage system, is that the identification is consistent and that the method is documented or posted at the panelboard.
Common conventions by system voltage
None of these are code. They are what the trade settled on, and they are worth following for the same reason you drive on the right. Everyone else is.
120/240 V single phase BlackRed |
120/208 V three phase BlackRedBlue |
277/480 V three phase BrownOrangeYellow |
High leg (delta) Orange This one is code. §110.15: the high leg of a 4-wire delta gets marked orange, or durably identified some other way, at each point of connection where the grounded conductor is also present. |
Gray: the argument you will eventually have
On new work gray is a grounded conductor, same as white. 200.6 lists both. If someone on site insists gray is not a neutral, they are not making it up, and the history is worth knowing before you argue.
Before the 2002 NEC the wording was "white or natural gray". Natural gray was never really a color. It was what white rubber insulation looked like as it aged. Because the wording was unclear, actual gray insulation got installed as an ungrounded conductor in some jobs. The 2002 edition deleted the word "natural" and settled it: white or gray, both grounded.
Old panels: do not trust gray on sight
The NEC carries a note about exactly this. Gray may have been used as an ungrounded conductor in the past, so take care working on existing systems. On anything pre-2002, test it before you touch it. On new work, gray is a neutral.
Switch loops: which wire goes where
In a cable assembly you may re-identify a white or gray conductor and use it as an ungrounded conductor. There is a direction rule attached to it.
The re-identified conductor may only carry power TO the switch. The conductor returning from the switch to the light must be a different color. Running it the other way round is not permitted, and it leaves a switched hot wearing the insulation color the code reserves for a neutral.
Supply to the switch White, taped black Re-identify by marking, tape or paint at its termination and at every point the conductor is visible and accessible. |
Return from switch to the outlet BlackRed §200.7(C)(1) permits the re-identified conductor for the supply to the switch, not as the return conductor from the switch to the outlet. |
Not in a raceway
This allowance is for cable assemblies and flexible cords. A white or gray conductor in a raceway may not be re-identified and used as an ungrounded conductor at all.
Where more than one system shares a building
This is the one that gets enforced. 210.5(C): if a building is fed by more than one voltage system, every hot has to be identified by system and by phase.
Tape, tags, color, whatever your AHJ takes. The half people miss is the second half. The method itself has to be documented and available, or posted at each panel. A perfect color scheme that only lives in your head is still a violation.
In practice that is a card in the panel directory pocket or a laminated tag zip-tied inside the door, listing which color means which system. It costs a few minutes and it is the difference between a pass and a correction notice.
This is the NEC as published. Your state or city may have amended it, and plenty of them are a cycle or two behind. Check what your AHJ actually enforces before you bet a job on any summary, including this one.
Common questions
Does the NEC require hot wires to be black?
No. The code reserves white and gray for the neutral and green for the ground, so a hot can be anything else. Black is habit, not law. The one hot the code does name is orange, for the high leg of a 4-wire delta.
Can I use a white wire as a hot wire?
Only where the code allows it, and only if you permanently re-identify it everywhere you can reach, to something other than white, gray or green. Never in a raceway. On a switch loop there is a direction rule people miss: 200.7(C)(1) lets you use that white as the supply TO the switch, but not as the return from the switch back to the light. Feed in white, come back in black.
Is gray a neutral or a hot?
On new work it is a neutral. 200.6 lists white and gray together as grounded conductors. The confusion is real though: before the 2002 NEC the wording was "white or natural gray", and because that was unclear some older installations used actual gray for an ungrounded conductor. The code warns about it. Test before you trust the color on an old system.
What color is the ground wire in US wiring?
Green, green with a yellow stripe, or bare. At 6 AWG and smaller that identification runs the length of the conductor. At 4 AWG and larger you can mark it green at each accessible point when you install it.
Which NEC edition applies to my work?
Whichever one your AHJ has adopted, which is often a cycle or two behind. The NEC lands every three years and every state adopts on its own schedule. Check locally before you bet a job on any summary.