My house is over 100 years old and the cold air returns are simply sheet
metal nailed between two joists.
I know that when running romex though holes bored in the joists
according to the National Electrical Code I'd need to run type "MI" if
wiring through the cold air return joists.
I was wondering it it would be OK to run conduit across the /outside/ of
the return? I know that romex can only be run through holes in the joists.
On Friday, July 11, 2014 11:06:36 AM UTC-4, philo wrote:
I believe standard Romex is permitted to be used through bored holes,
just as it would if it were not a return duct. See section 300.22C of
NEC where they specifically exempt such spaces between joists. No need
to make it more complicated.
On Fri, 11 Jul 2014 08:49:30 -0700 (PDT), trader_4
This is the exception Trader is talking about
Exception: This section shall not apply to the joist or stud spaces
of dwelling units where the wiring passes through such spaces
perpendicular to the long dimension of such spaces.
Even if you do not want to exploit this exception, 300.22 allows these
other wiring methods (besides MI)
Type MC cable employing a smooth or corrugated impervious metal sheath
without an overall nonmetallic covering, electrical metallic tubing,
flexible metallic tubing, intermediate metal conduit, or rigid metal
conduit without an overall nonmetallic covering.
An easy fix is a short sleeve of EMT between the studs with bushings
on the ends and shove your Romex through the sleeve.
Or run a large enough conduit through the plenum to be able to call
it a "raceway" instead of a conduit - which allows you to run Romex
through it. I believe code also allows romex to be run through
conduit for "protection"
Well, I went down there the plan my work and saw that one of the cold
air returns is double-wide ...so I'd have to remove the sheet metal...
plus it's a long run and would require many holes.
I'm just going to run conduit, it's going to be a lot easier.
On Fri, 11 Jul 2014 13:21:48 -0400, firstname.lastname@example.org wrote:
Conduit IS a raceway. (Article 100 Definition)
"Raceway. An enclosed channel of metal or nonmetallic materials
designed expressly for holding wires, cables, or busbars, with
additional functions as permitted in this Code. Raceways include, but
are not limited to, rigid metal conduit, rigid nonmetallic conduit,
intermediate metal conduit, liquidtight flexible conduit, flexible
metallic tubing, flexible metal conduit, electrical nonmetallic
tubing, electrical metallic tubing, underfloor raceways, cellular
concrete floor raceways, cellular metal floor raceways, surface
raceways, wireways, and busways."
... and this is not a plenum.
"Plenum. A compartment or chamber to which one or more air ducts are
connected and that forms part of the air distribution system."
As for the original question,
Trader correctly cited the 300.22(C) exception.
Nobody's talking about a plenum here, just the space between
joists which is often enclosed as a cold air return -- and is
specifically excepted from those requirements by the section of
the Code cited in the paragraph below. (You *did* read that before
replying, didn't you?)
It doesn't matter at all how large the conduit is, as long as it's large enough for the
conductors being run through it. He's perfectly compliant with the NEC running Romex
through an air handling space inside 1/2" EMT.
1. Just ignore clare; as usual when attempting to give electrical advice, he's well wide of the
mark. There simply is no reason at all to think that anything larger than 1/2" EMT is needed.
2. The OP was asking about wiring through a cold air return between *joists*, not studs, so
presumably he has at least 7 1/4" to work with (assuming 2x8s).
yep, three joists.
Anyway, I ended up talking to a friend of mine who is a retired building
inspector and he gave me an easy work-around for Romex.
Though I cannot attach it directly to the joists, he said all I have to
do is use a "running board" . Basically I just need to run a board
across the joists then attach to Romex to that.
On Fri, 11 Jul 2014 14:39:00 -0400, email@example.com wrote:
A cold air return comprized of sheet metal nailed to 2 adjacent
joists is considered to be a plenum. Air duct #1 connects it to the
cold air intake of the furnace. Duct#2 opens to the conditioned living
space - it is part of the air distribution system on the return side.
Any communication cable installed through such an air return MUST be
plenum rated cable by code, so I'm sure power cables would also need
to be treeted as "in plenum"
On Friday, July 11, 2014 11:20:56 PM UTC-4, firstname.lastname@example.org wrote:
There are none so blind as those that will not see. I gave you the NEC cod
section. Others have discussed it here too. The code says Romex can
pass through joists that are part of a cold air return plenum, it's
specifically exempted. Plus you see it done all the time. Stop with the
On Fri, 11 Jul 2014 18:45:28 +0000 (UTC), Doug Miller
You are right. I thought there was some reference to using romex in
conduit where the fill ratio had to be a lot lower than with separate
conductors but I've been wrong before. I know there is a fairly broad
restriction on running romex in conduit - yet I know there are quite a
few situations where it is allowed, and even a few where it is
"required" for protection. OK - you don't NEED to use Romex - but if
you use romex you DO need to protect it, and conduit is the simlest.
cheapest, most effective solution.
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