Vertical electrical wiring question.

When we purchased our present house there was already a run of 3' diameter gray PVC conduit run in a chase from the unfinished basement to the attic above the second story. There are about 6 runs of 12-2/gnd Romex run from through this (as well as a few telephone, cable TV and home network cables).
I am bothered by several things about this arrangement, and would like to clean it up if practical. In part this is driven by a requirement to run several new circuits to the attic to feed some new remodel work. Also, quality / code wise the present Romex exits at the top of the PVC conduit, is folded over the edge, and is banded to the conduit with electrical tape. This bothers me, as I'd rather not use this approach for new runs.
My concept involves: 1. Cutting the existing Romex where it exits the conduit in the attic and pulling it back down to the basement. 2. Adding two large junction boxes, perhaps 12" x 12" x 8", one connected to both the basement and attic ends of the 3" conduit. 3. Replacing the vertical runs with #12 THHN. This would use less volume, and simplify adding additional circuits.
My questions are. Is this OK? Better that existing / Worse? Other suggested approaches?
A big part of what bothers me about the existing arrangement is the "hanging weight" of the Romex vertically unsupported through 2+ stories. Just doesn't seem wise. So several separate questions: 1. What is the allowed unsupported vertical run length for #12 THHN?. 2. Would I be aby better off, to keep the wires from 'swinging' (can't think of a better word) inside of the 3" conduit, to run several 1" EMT lengths up inside of the 3" and put the THHN inside of thise?
Thanks for your thoughts. Bruce
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pbs wrote:

Don't think of it as conduit, think of it as a chase which is what it really is at present and why power and phone / CATV circuits are sharing it. If you convert to using it as "real" conduit plan on finding a way to run a separate conduit up for the phone / data since they can't share a conduit.
NEC article 300.19 covers supporting conductors in a vertical raceway and indicates one cable support to be provided at the top of the vertical raceway or as close to it as practical. Intermediate supports to be provided as necessary to limit the supported conductor length to the valise in table 300.19(a) which indicate a 100' maximum for #18-#8 copper conductors. I presume your run is about 20'.
You will be able to get a much higher fill if you were to install a run of smaller conduit through the chase and pull THHN through it. NEC annex C lists a fill of 26 #12 THHN conductors in 1" EMT conduit, 23 in 1" ENT.
The only real problem I see is the way the cable is fastened at the top. You should install a vertical stud next to the chase so that the romex can come straight out of the chase and be secured to the stud with proper clamps/straps/staples. I would be a bit concerned about fire stopping the chase so it can't act as a chimney. You should be able to get a bag of intumescent material from an electrical supply house that can be stuffed in the end of the chase to stop fires. Easily removable when you need to access the chase, but when exposed to fire will expand to seal fully.
Pete C.
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wrote:

Or you could run one fat cable, and put a sub-panel at the top.
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Goedjn wrote:

What a great idea, when you trip a breaker you get to climb up into the attic in the dark to reset it.
Pete C.
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wrote:

You could run another small cable, so there would be light up there.

:-)
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wrote:

Hmmm. I didn't do mine right, I think, but I'm not sure how bad you all would find it.
In the shaft with the heating duct, there was between 1 and 2 square feet of empty space, and between the 1st and 2nd floor, was a piece of plywood as a firestop I guess. I don't know how thick, I can't see it, but I drilled a half inch hole through it with a 6 foot drill bit and a 1 foot extension, and reaching down as far as I could.
I ran one 12-2 Romex cable and one phone line, though the half inch hole.
I didn't even think of plugging up the rest of the hole, (which is 8 feet from me when I lie on a piece of plywood in the attic). Is this bad? How bad?
I think I stapled the Romex to the side of the bottom piece of an attic truss, what functions as a floor joist, then continued vertically another 5 feet to the top piece of the same truss and stapled it again, then up the truss almost to the peak, with a couple more staples, and from one truss to the next to the center of the attic, where I mounted a ceiling fixture. Is this OK?
(I also connected ceiling lights in 2 bedrooms but I'd have to go look where the wires go, exactly. I forget where I connected them, but I know I used a box.)

Don't think this will work for me since the hole is 8 feet from the closes place I can get.

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mm wrote:

Dunno, I'm not an inspector, I'm just a guy who does all his own electrical work and keeps a copy of the NEC on hand.

Plywood is likely just the continuous sub floor of the 2nd floor. It would function as a fire stop.

A pretty full 1/2" hole.

Considering the fill of the 1/2" hole, probably not that bad. If you were really concerned you could take a couple of the intumescent fire stop material packets that are available and sandwich them around the cables up top, fasten them together with a couple cable ties and drop the doughnut down the cables so it rests over the hole. I doubt that would buy you much for such a small hole though.

Attic truss should be ceiling joist (for the 2nd floor presumably). The bottom chord of a roof truss is not rated for floor loading. As for the fastening it sounds like that bottom chord would qualify as the top of the raceway / chase which would be fine.

If the cable is hanging loose in space between the bottom and top chords of the truss that's ok for suspended cable length, but not for cable protection. The cable should either travel up one of the truss webs to the ceiling, or should be fastened to a vertical stud to cover the distance. If you install a vertical stud, be sure to only rigidly fasten it at one end, the other end must be able to slide up and down or you can compromise the truss.

That sounds ok.

Not sure, boxes need to have covers and be accessible i.e. not buried behind sheetrock. Wires need to be fastened to studs or joists as appropriate when they are running parallel and protected from damage i.e. not exposed on the front of a stud, but on the side where it is sheltered.

I wouldn't worry too much about a fairly full 1/2" hole in plywood between two open spaces, it's a lot less of a threat than a 20' straight run of 3" dia conduit which could get quite a draft going in a fire.
Pete C.

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pbs wrote:

You need to pull all the communication cables out and run them separately. Running them in the same conduit, or chase as somebody said, is asking for interference problems. If they are run in the same chase they should be shielded from the power cables by a metal shield.
Bill Gill
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Bill Gill wrote:

If it's not giving you any problems currently I wouldn't worry too much about it. RF lines like CATV aren't very sensitive to power line interference and newer phone lines and cat 5 network cables have more twist which also helps reject interference. If you want to do something about it the easiest thing to do would be to sleeve the com cables in grounded EMT conduit in the chase.
Pete C.
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wrote:

Coax is already shielded. Some other cables (such as Cat5) aren't shielded, but protected by other means (twisted pair).

--
Mark Lloyd
http://notstupid.laughingsquid.com
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Mark Lloyd wrote:

But I don't believe the NEC allows it.
Bill
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Bill Gill wrote:

The NEC doesn't allow low voltage com lines to share conduit with power lines, this does not apply to a chase.
Pete C.
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wrote:

I think you're right about that. I was just saying that interference is unlikely.

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