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Consider a situation where you need to run two circuits through an emt conduit using a common ground wire. The THHNs will originate in an external breaker panel (using dual afgf breakers) and terminate in a junction box inside the house where they will be spliced with romex to make run to equipment.

Following colors appear to be commonly available: black, red, blue, green, white.

How do you choose five colors that are NEC compliant. Remember that all wires travel together in the conduit.

Let it flow...

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The available colors are considerably more than that through any decent supplier. Get out of the big box (heck even the big box near me carries more colors than that)

However, at the most basic...

You don't need a grounding wire since you have EMT which is a grounding conductor, but if you do choose to have a grounding wire it has to be green or bare, and green or bare can't be used for anything else. wIth properly assembled EMT you'd just have a grounding screw at the box where the connection to NM/B is made and connect the NM/B grounding wire to that screw.

Neutrals can be white or gray. White or gray (in conduit) can't be anything other than neutral.

All other colors (black brown red orange yellow blue purple) can be hots. There are even striped versions for yet more easily distinguished "colors".

An acceptable and compliant method is to group a pair of black and white wires for each circuit using colored tape, or different numbers of loops of black tape so that you can distinguish the groups.

Another acceptable and compliant method is to run blue and white and red and gray. Or black and white and red and white and tape group the white neutrals to their respective hots. Any of the hot colors for hots, I'm not going to list even all the options that are possible from what colors you list, you should get the idea.

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  • This is very helpful. I definitely screwed up. Four colors are okay, fifth is not. Must rewire! – cryptic0 Nov 27 '20 at 1:09
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    If you have a really good supplier, they'll even be able to get you white or grey wire that is itself striped various colors, which is handy if you have 3, 4, or more neutrals in a pipe[ – ThreePhaseEel Nov 27 '20 at 2:12
  • @ThreePhaseEel I have one each of black, white, red, green and blue. I need to pull them all out and replace blue with white. I should be good with the colors I already have. – cryptic0 Nov 27 '20 at 3:28
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99% of my work is in EMT conduit.

Neutrals MUST be white or gray. Ground wires are green, yellow-green-stripe or bare, but you don't need em in EMT conduit. Hots are everything else including yellow or pink.

Any competent electrical supply stocks all 11 colors in solid or stranded THHN. Stranded is much easier to work with if you can figure out the craft of attaching it to terminals (hint: use screw-and-clamp receps). And I do own 11 colors.

However, you can just use black-white, and wrap the pair with tape to indicate that it is paired. You can also use colored tape to mark both black and white wires, i.e. the yellow-tagged ones are circuit A and the green-tagged ones are circuit B.

You are not allowed to use tape to redefine wire purpose: a white wire can't be made a hot with black tape. Therefore any tape markings are not for that purpose.

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  • Both answers were equally helpful, so I chose the first one as the answer. – cryptic0 Nov 27 '20 at 1:08

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