On Fri, 09 Jun 2006 18:22:46 GMT, "Pete C."
wrote:

pbs wrote:

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

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.


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