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In the 2020 Edition of the National Electric Code, in Section 110.15, titled High-Leg Marking, it states,

...only the conductor or busbar having the higher phase voltage to ground shall be durably and permanently marked by an outer finish that in orange in color or by other effective means. An other effective means may be marking engraving with "high" or the voltage.

Obviously, only the highest-voltage leg shall be marked with an orange outer finish or with "high". However, does it mean that only that leg should be marked at all, or does it mean that orange or "high" is allowed on only that leg, meaning that other legs may be marked with other colors or words less strong than "high" such as "medium" and "low"?

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  • Interesting question. I thought most residential systems used equal(or almost equal) voltages on each leg except for neutral/ground. Industrial/commercial might have it set up as one high voltage and one or more lower.
    – crip659
    Sep 21 at 12:23
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    @crip659 - The first bit of 110.15 says "On a 4-wire, delta-connected system where the midpoint of one phase winding is grounded..." putting this completely out of residential systems. Certainly marking other legs as "hot" seems reasonable. The point is to identify the highest present voltage (if a grounded conductor is present as noted in 110.15).
    – Jon Custer
    Sep 21 at 14:56

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The excerpt is referring to marking inside a 3-phase panel. Unlikely that you'd see that in residential in the US/Canada, but they do exist here and there, especially in mixed-commercial space that has been converted to lofts/apartments. The reason is electrical safety: for single-phase loads, the "high" leg has a higher voltage than the other two legs.

The term High-leg refers to a specific type of 3-phase electrical service (called a high-leg or "wild-leg" delta) in which one of the phases is tapped at the center to provide a split-phase supply like what you'd traditionally get in a US dwelling.

enter image description here For example, a 240V 3-phase "high-leg" delta gives you:

  • 240V phase to phase (L1-L2, L2-L3, L3-L1)
  • 120V phase to neutral on 2 legs (L1-N and L2-N)
  • 208V phase to neutral on 1 leg (L3-N: the high leg)

The busbar connected to L3 in this instance is the one that needs to be specially marked so that 120V equipment is not connected to any single-pole circuits on that bus, which will have 208V in this example.

It's not very common to find in residential settings in North America, although I won't say it's unheard-of. You can usually identify a high-leg delta service if you see a pole with 3 transformers but one is a lot larger than the other two.

This is what they are talking about when marking with orange:

enter image description here

The second leg in that example is your high leg.

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  • Great description. Note that wild leg service could be done even with just two transformers: the one center-tapped plus one more to provide the wild leg.
    – Greg Hill
    Sep 21 at 16:19
  • Thank you so much! This also clearly shows in practice that other legs (as shown by the first leg) are allowed to be marked, though only in other colours. Sep 22 at 3:54
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First, carefully read NEC 90.1(A) and (B). "This Code is not intended as an instruction manual for untrained persons". One should not read NEC as a novice and pop up with "What's this? What's this?" questions. It's also off-topic here; questions here must have a basis in a real world problem related to residential.

One should obtain proper training materials. For starters, DIY how-to books found at your local library. Once you have exracted everything from them, perhaps Mike Holt (the paid-for materials, not the forum) - but for 99% of DIYers there's no reason to go beyond the DIY books + forums like this one for what they don't cover.

90.B also says "Compliance results in an installation that is not necessarily efficient, convenient or adequate for good service". In other words, NEC is slumlord bare minimum for safety, it is NOT a design guide or best practice. Creating real usability is up to you.

Conductors must be marked

ALL conductors most be natively colored, or marked, to distinguish 3 classes of wire from one another:

  • Grounds: Green, yellow/green, or bare.
  • Neutral: White or gray
  • Hot: all other colors

Really? There are no other color requirements???

Really. You are set to establish your own color standards. In household/residential, there is almost never a need to distinguish the 2 hot wires from each other, so black-black is fine. In fact it is helpful if you have 3-4 circuits in a conduit, then the other 3 circuits can be red-red, blue-blue and orange-orange, or what have you on the truck.

Wiring Prince's house with 120/208V? Purple, pink, black, white. The only requirement is that colors be consistent within your installation.

Likewise in 3-phase it is often not important to distinguish one phase from another. So again black-black-black is fine. Your second circuit could be orange-orange-orange or even orange-red-brown if you're feeling autumnal. After all, they're all the same voltage just differently phased.

However, if you are trying to synchronize 3-phase motors to all run in the same direction (or the correct direction), you may regret a choice like black-black-black LOL. Like I said up top, NEC doesn't cover usability.

Popular color schemes are black-blue-red and orange-yellow-brown. But these are "conventions" not requirements. Note orange mentioned several times here.

... Except for "wild-leg delta"

However, there is one special type of 3-phase. It contains standard split-phase 120/240V with neutral in the middle, and adds a 3rd phase in a "delta" arrangement positioned 240V from the existing two "phases". Thus, it is 208V from neutral - higher voltage than the other two phases. Suddenly we care.

So NEC has a rule that in wild-leg delta installations, the wild-leg must be orange. (implying the other 2 phases cannot be orange).

That rounds out our coverage of NEC color codes. Really. That's it.

NEC is silent on the use of orange in other installations. So it's absolutely legit to have a 3-phase that is orange-orange-orange, so long as it's not a wild-leg. Or orange-yellow-brown is actually a popular color coding for equal-leg-voltage 3-phase installations. And of course a split-phase circuit can be orange-black-white if you prefer.

However again, due to the "consistent within your installation" rule, an installation that does have wild-leg 3-phase and other equal-leg services too should abstain from using orange anywhere but the wild-leg. Thus their 277/480V should be something like yellow-brown-not orange.

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  • Thank you so much for this clarification! It confirmed my interpretation that even the usage of orange is allowed to be used on other legs, because it only required the high leg to be marked in orange, given that other effective means aren't used. It didn't limit the use of range to only the high leg. This means that the wording of this NEC section is stupid because the high leg wouldn't be distinguished. Sep 22 at 4:01
  • @CoastCity Do you actually have a wild-leg installation? How do you know you do? You are correct that orange is free to be used in a facility where a wild-leg service is not present. Sep 22 at 7:03

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