1 feed, 2 conduits

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bcm

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Hi folks!

I have a strange situation, and while there seems to be reasonable info in the NEC about multiple circuits in a conduit/raceway, I am not finding anything about ONE circuit in multiple conduits/raceways.

Here's the situation. I need to route 3#1 + 1#6 ground from the 6th floor electrical room of a hotel into the attic directly above (about 12" between floors). There are (3) unused, existing 1" rgs conduits between the 6th floor electrical room and the attic. Can I route 2#1s in one of the 1" conduits and then 1#1 + 1#6 gnd in the other and then use a junction box to bring them all back together into a 1-1/4" conduit in the attic?

Is there a limit to the # of conduits you can break a feed into?

I can't just core from 6th to the attic because the building is post-tensioned, so this seems to be the only solution.

Thanks!!
 
No, what you are suggesting would be a violation of 300.3(B). All conductors of the same circuit must be installed in the same raceway.

Chris
 
david luchini said:
Just out of curiosity, how would this violate 310.4? There doesn't appear to be any paralleling proposed.
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I agree its not allowed but it has nothing to do with 310.4.

300.3 (B) would appear to be the main issue.

If you can't install a larger conduit there are a couple things that you might be able to do.

One would be to break the load up into multiple feeds, if that is possible.

Another might be to use transformers to change the voltage enough that you can use smaller wire and fit all three wires in a 1" conduit and use the conduit as the ground.

Is this three phase delta? Might be some options if it is 240 3 wire.
 
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david luchini said:
Just out of curiosity, how would this violate 310.4? There doesn't appear to be any paralleling proposed.
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'Cause I had a
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This really needs to be engineered, JMO

Can you look at the original construction drawings? Since it's PT your existing conduit run was probably designed and accounted for in the drawings.

If the drawings are short on those details then one will have to X-ray, if you can get the owner to spring for it

You might find that depending on how the conduits were held in place there might be more room than you think. I'd scope down conduits and see if you can pick up welding marks implying fins welded to the sides of the conduits, or if there were steel saddles for the conduit raceway. They had to hold the conduits in place some how, rebar lashing is common here.

Short on any of the above, the last time I heard of about the same situation the conduits went outside the building.

Good Luck!
 
Dennis Alwon said:
How will you do this and still not violate 300.3(B) as well as 310.4(A). You cannot run #6 in parallel. 1/0 or larger except under certain conditions.
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I agree with Dennis. The OP would violate 300.3(B) and the #6 parallel would violate 310.4(A).

I think your only solution would be one of the 1"rgs conduits as a nipple between two jboxes, assuming you can limit the length to 24" or less.
Run your conductors in 1-1/4" from the panel to j-box, through the 1" nipple to the attic box, and back to 1-1/4" to continue your run in the attic.
 
"I can't just core from 6th to the attic because the building is post-tensioned"

what is post-tensioned?
 
What is the actual load being served? Could you use high temperature splices in junction boxes, and 90C conductors and get down to #2 conductors, or could you use a 100% rated breaker, and get down to a #2 conductor? With #2 compacted conductors, you might just make the area limits, though you might have to deal with jamming issues.

Does anyone know of low voltage cables made with the 'compact sector' conductors sometimes used in medium voltage cables (see, for example, the picture on this page, which doesn't really help because it is an Indian supplier, but the picture carries the idea http://www.tradeindia.com/fp310334/LT-XLPE-POWER-CABLES.html )?

-Jon
 
david luchini said:
I agree with Dennis. The OP would violate 300.3(B) and the #6 parallel would violate 310.4(A).

I think your only solution would be one of the 1"rgs conduits as a nipple
between two jboxes, assuming you can limit the length to 24" or less.
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I don't think you made the exception of using a RMC nipple in this case.
Put it this way I don't think the code intended for multiply nipples. While it may be a nipple, in thought, but it's still a raceway.

Run your conductors in 1-1/4" from the panel to j-box, through the 1" nipple to the attic box, and back to 1-1/4" to continue your run in the attic.
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If they cut the conduits at floor level they would not make the exception of 250.86 Exc #2 cause they don't know how it's attached.

If they they leave some conduit can one put a hogs head on it, or a thread-less coupling, your box and a bonding bushen, and do as you imply?
 
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Whoops. I misread the OP. I thought that there were 6 floors to go, not just penetrating one floor from electrical room to attic. If this is less than a 24" nipple, as opposed to a complete run, then you get to use 60% fill.

If you can get 'compact stranded' conductors, then your #1 THHN conductors will have a cross section of 87mm^2, and your #6 will be 29mm^2. Total fill will be about 290mm^2, which is allowed in a 1" rigid nipple.

-Jon
 
thanks 480, so if you core drill you have to xray to assure you miss the 'cables', or there is just no core drilling?
 
jusme123 said:
thanks 480, so if you core drill you have to xray to assure you miss the 'cables', or there is just no core drilling?
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If you know (and you actually know, you're not guessing or assuming) where the cables are, you can go ahead and drill them. I've done this in the past, where I've seen the slabs prior to installation so I know where I can and can't drill.

If you're not 110% sure, then you need to find out where they are. Xraying is one option.
 
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