Run phases in separate conduit

[That Man]

I'm designing a lighting system. The power is 3 phase 480, but all the lights are 277V single phase. To allow for switching half of the lights off, I'm running two separate 3 phase circuits and alternating the wiring in the luminaires. with 6 phase conductors, 2 neutrals, and a ground, I was concerned about wire mis-identification and came up with a color coding scheme, but ultimately it proved impractical, so back to traditional brn x2 org x2 yel x2 gry x2 grn.

But I got to thinkin. Can I separate the phases? So for one set of lights:

run phase A from circuit 1, phase B from circuit 2, two neutrals and a ground.

Another set of lights:

run phase B from circuit 1, phase C from circuit 2, two neutrals and a ground.

The final set of lights:

run phase C from circuit 1, phase A from circuit 2, two neutrals and a ground.

This way I'll be running 5 conductors (4 current carrying) instead of 9 conductors (8 current carrying). Is there a prohibition against separating the phases like this?

 

[rambojoe]

My advice is dont do electrical engineering.
Stick to lighting design.

 

[That Man]

My advice is dont do electrical engineering.
Stick to lighting design.

Gee thanks

 

[hillbilly1]

It’s a little harder to do 50% than 33% because of that. WalMart for years set theirs up for thirds real easy to wire abc, abc. Home Depot wanted to change from fifty percent to thirds, but was difficult due to the panel setup. What I had to do was move the full boat over to another panel, then split them out with contactors……Look! A squirrel! That wasn’t the question you were asking. Back to your question, use colors with a stripe for the second set of three phase, that way it is easily identified.

 

[LarryFine]

As long as they're from the same feeder group, you could use a single neutral per two phases.

 

[That Man]

It’s a little harder to do 50% than 33% because of that. WalMart for years set theirs up for thirds real easy to wire abc, abc. Home Depot wanted to change from fifty percent to thirds, but was difficult due to the panel setup. What I had to do was move the full boat over to another panel, then split them out with contactors……Look! A squirrel! That wasn’t the question you were asking. Back to your question, use colors with a stripe for the second set of three phase, that way it is easily identified.

Are you saying Walmart was running single pole breakers? I'm just wondering because that would require a neutral for each phase right? one for each branch circuit?

 

[That Man]

As long as they're from the same feeder group, you could use a single neutral per two phases.

Maybe I'm going off track here... It was pointed out to me yesterday that for multiwire branch circuits, each circuit would require its own neutral per 200.4(A). However, maybe that isn't true for single wire branch circuits? I can have a shared neutral?

 

[David Castor]

What's the raceway? Has to be completely non-metallic to run individual phases in separate conduits.

 

[That Man]

What's the raceway? Has to be completely non-metallic to run individual phases in separate conduits.

OK, so this is THAT situation is it? For some reason I thought that was for doubling up phase conductors, like, three A phase in one conduit, for like a transformer where there's no room. If it applies to splitting the phases up in general, then that kills that idea.

I have to think about single phase breakers now though, and see if there's an advantage to doing that instead...

 

[That Man]

OK, so this is THAT situation is it? For some reason I thought that was for doubling up phase conductors, like, three A phase in one conduit, for like a transformer where there's no room. If it applies to splitting the phases up in general, then that kills that idea.

I have to think about single phase breakers now though, and see if there's an advantage to doing that instead...

Yeah, that totally works doesn't it? Using single pole breakers? Simply running two single phase circuits in one conduit isn't illegal right? It will result in the same, ideal amount of wiring (2H, 2N, 1G), which is way better than 9 wires. I'm tired, so maybe I'm missing something, but that sounds like it would work ya?

 

[LarryFine]

Maybe I'm going off track here... It was pointed out to me yesterday that for multiwire branch circuits, each circuit would require its own neutral per 200.4(A). However, maybe that isn't true for single wire branch circuits? I can have a shared neutral?

We wanted to make it clear that two wires of the same phase (or two groups of wires) can not share a single neutral, even if you expect the loads to be balanced. Thus, six circuits must be made up of two groups of phases, each group having an accompanying neutral.

I'm saying that, if the A and B phase you want to run are supplied from the same group as defined above, a single neutral may be shared. However, if the A phase comes from group #1, and the B phase comes from group #2, then each one requires a neutral from its group.

 

[LarryFine]

Yeah, that totally works doesn't it? Using single pole breakers? Simply running two single phase circuits in one conduit isn't illegal right? It will result in the same, ideal amount of wiring (2H, 2N, 1G), which is way better than 9 wires. I'm tired, so maybe I'm missing something, but that sounds like it would work ya?

As well as I'm picturing what you're asking, yes.

 

[That Man]

As well as I'm picturing what you're asking, yes.

See, where I think I went astray was starting off with two 3 pole breakers. In a 480/277 panel, if all I'm feeding is single phase loads, just use single pole breakers and all my hazards I keep running into are solved (I think). I'll have to have a bunch of neutrals at the origin panel instead of just two, but in my overhead conduits, where space is tight, I'll only have two neutrals to contend with, and that's the place I was worried about. I didn't want the electricians to have to wirenut 9 wires in the head of a luminaire. 5 wires sounds much more reasonable though.

 

[winnie]

The issue about non metallic raceways is only an issue when you don't have a complete circuit in a conduit. Say phase A in one conduit supplies a load, and phase B in a separate conduit completing a circuit.

If you have phase A and it's associated neutral in the same conduit, supplying a L-N load, then you don't have to worry about phases B or C.

Jonathan

 

[augie47]

I don't recall ever being so lost following a thread
A couple of rules you need to keep in mind in whatever plan you come up with
. 300.3(B) (B) Conductors of the Same Circuit. All conductors of the same circuit and, where used, the grounded conductor and all equipment grounding conductors and bonding conductors shall be contained within the same raceway, auxiliary gutter, cable tray, cablebus assembly, trench, cable, or cord, unless otherwise permitted in accordance with 300.3(B)(1)through (B)(4).

and, if you are sharing a neutral

210.4(B)(B) Disconnecting Means. Each multiwire branch circuit shall be provided with a means that will simultaneously disconnect all ungrounded conductors at the point where the branch circuit originates.

Unsure of the impact those sections have on your plans but you need to keep them in mind.

 

[That Man]

I don't recall ever being so lost following a thread
A couple of rules you need to keep in mind in whatever plan you come up with
. 300.3(B) (B) Conductors of the Same Circuit. All conductors of the same circuit and, where used, the grounded conductor and all equipment grounding conductors and bonding conductors shall be contained within the same raceway, auxiliary gutter, cable tray, cablebus assembly, trench, cable, or cord, unless otherwise permitted in accordance with 300.3(B)(1)through (B)(4).

and, if you are sharing a neutral

210.4(B)(B) Disconnecting Means. Each multiwire branch circuit shall be provided with a means that will simultaneously disconnect all ungrounded conductors at the point where the branch circuit originates.

Unsure of the impact those sections have on your plans but you need to keep them in mind.

No that 300.3 is a good overall “covers everything” rule to remember. I’m pretty sure all my problems are solved by using single phase circuits. I have a follow up question, but it’s different enough I’m going to open a new thread for it. Thank you all for your help.

 

[hillbilly1]

Are you saying Walmart was running single pole breakers? I'm just wondering because that would require a neutral for each phase right? one for each branch circuit?

That was back before the rule change. At that time single poles were allowed, so one neutral per three phases. Two people and one lift could pull and terminate an entire WalMart in one day.

 

[don_resqcapt19]

That was back before the rule change. At that time single poles were allowed, so one neutral per three phases. Two people and one lift could pull and terminate an entire WalMart in one day.

You can still do that using handle ties on the three single pole breakers. However project specifications often prohibit multiwire circuits because of the common disconnect (handle tie) rule.

 

[That Man]

That was back before the rule change. At that time single poles were allowed, so one neutral per three phases. Two people and one lift could pull and terminate an entire WalMart in one day.

Your comment caused me to think differently about the design, which resulted in a better design overall, so even if this isn't directly relevant to the issue I was having, it still ended up solving my problem, so thanks.

 

[robertd]

If you are using only two of the three phases with a shared neutral, the neutral conductor counts as a current carrying conductor for derating.