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Old 05-10-2008, 02:09 PM   #1
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Running wire through a cold air return?


Hi,

I'm planning to run a new 15 amp circuit to a new ceiling fan in my living room while minimizing destruction of my walls and ceilings. I just realized I have a cold air return that runs half the length of my house and could serve as a good, obstruction-free conduit for running wiring where I need it to go. This cold air return isn't a traditional metal vent. It's merely an un-insultated joist bay in my finished basement. I'm assuming there's no unusual temperature variation - there's just room temp air being pulled through this joist bay towards the furnace.

Anybody have any idea if it's kosher to run electrical wiring through something like this?

thanks.

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Old 05-10-2008, 02:37 PM   #2
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Running wire through a cold air return?


oh oh pick me pick me i know the answer. you cannot run the wire like you propose. in an air handling space you may only run wires perpendicular to the duct. not sure what code off hand but it is code.

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Old 05-10-2008, 03:25 PM   #3
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Running wire through a cold air return?


i ran across an article from Carlon ent flex and rigid conduit that had something of that, its 82 pages i believe
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Old 05-10-2008, 03:36 PM   #4
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Running wire through a cold air return?


According to the 2005 NEC, 300.22 (B), MC cable, EMT, IMC, and rigid can be run in "ducts or plenums specifically fabricated to transport environmental air." Type NM cable (Romex) is not allowed inside of a duct.

The trick here is that all of these conduits need to be fastened at certain intervals, that can be difficult inside of a duct that's too small to crawl through.

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Old 05-10-2008, 03:49 PM   #5
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Running wire through a cold air return?


No, it is not Kosher to run a circuit through the duct.

the biggest reason is:

anything is a duct or plenum space must be plenum rated. That means it is specifically designed to not emit above a determined level of toxic fumes when exposed to fire.

typical NM is not plenum rated.
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Old 05-10-2008, 07:51 PM   #6
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Running wire through a cold air return?


Quote:
Originally Posted by nap View Post
the biggest reason is:

anything is a duct or plenum space must be plenum rated. That means it is specifically designed to not emit above a determined level of toxic fumes when exposed to fire.

typical NM is not plenum rated.
This is 100% correct. Nothing to do with securing the wire. You can run appropriate wires through a plenum, but what you're talking about is a DUCT, and you just can't use a duct as a conduit.

Very bad idea. Hypothetically, if you were to do this, how would they clean the ducts? It would wreck the wire. Find another way to route the wire.
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Old 05-10-2008, 11:29 PM   #7
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Running wire through a cold air return?


Great points guys but I think and I may be wrong but the OP is considering using a cold air return for the wiring path.... here in the north we see this on a regular basis for new home construction..... This is not a duct.... typically a void.... Interesting that this is against code in the US.

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Old 05-11-2008, 09:31 AM   #8
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Running wire through a cold air return?


Quote:
Originally Posted by Tattoo View Post
Great points guys but I think and I may be wrong but the OP is considering using a cold air return for the wiring path.... here in the north we see this on a regular basis for new home construction..... This is not a duct.... typically a void.... Interesting that this is against code in the US.

Cheers
yes, that is a duct. A cold air return duct. Just because is uses the floor and 2 floor joists and a sheet of metal for the walls of the duct, it is still a duct.

The problem is if for some reason there would be a fire, the non-rated plastic in the duct, plenum, void, whatever you want to call the space used to confine a column of air and directs it to another area, would transport the smoke deveopled from the heated/burned plastic to other area of the building.
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Old 05-11-2008, 11:04 AM   #9
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Running wire through a cold air return?


Quote:
Originally Posted by nap View Post
yes, that is a duct. A cold air return duct. Just because is uses the floor and 2 floor joists and a sheet of metal for the walls of the duct, it is still a duct.

It is not a duct, it is "Other Space Used for Environmental Air" which falls under Article 300.22(C). The exception to 300.22(C) permits NM cable to be run perpendicularly through the cold air return space.

So the OP can cross through the cold air return space between the joists, but he cannot use it as a raceway.

Here is the NEC text:
(C) Other Space Used for Environmental Air This section applies to space used for environmental air-handling purposes other than ducts and plenums as specified in 300.22(A) and (B). It does not include habitable rooms or areas of buildings, the prime purpose of which is not air handling.
FPN: The space over a hung ceiling used for environmental air-handling purposes is an example of the type of other space to which this section applies.

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.
Section 300.22(B) specifically states that ducts or plenums are specifically fabricated to transport environmental air.
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Old 05-11-2008, 01:14 PM   #10
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Running wire through a cold air return?


Ok
How does one run a romex to the other side of the basement with out passing through the cold air return?

My cold air return runs through the center of my basement which is two joist with sheet metal between them.

Can I use 1/2 " reg. metal conduit? to contain the romex from damage?

I have been looking at this for quite a while, wanting to add an outlet on the other side of the basement.
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Old 05-11-2008, 01:50 PM   #11
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Running wire through a cold air return?


You can run straight through the return air space between your joists, you can't run along the return air space. Perpendicular, not parallel.
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Old 05-11-2008, 03:43 PM   #12
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Running wire through a cold air return?


Quote:
Originally Posted by Silk View Post
It is not a duct, it is "Other Space Used for Environmental Air"
I didn't think I was losing my mind.... although it has been a long week
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Old 05-11-2008, 09:53 PM   #13
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Running wire through a cold air return?


Quote:
Originally Posted by Silk View Post
It is not a duct, it is "Other Space Used for Environmental Air" which falls under Article 300.22(C). The exception to 300.22(C) permits NM cable to be run perpendicularly through the cold air return space.

So the OP can cross through the cold air return space between the joists, but he cannot use it as a raceway.

Here is the NEC text:
(C) Other Space Used for Environmental Air This section applies to space used for environmental air-handling purposes other than ducts and plenums as specified in 300.22(A) and (B). It does not include habitable rooms or areas of buildings, the prime purpose of which is not air handling.
FPN: The space over a hung ceiling used for environmental air-handling purposes is an example of the type of other space to which this section applies.
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.
Section 300.22(B) specifically states that ducts or plenums are specifically fabricated to transport environmental air.
The exception above, as I see it, is in reference to 300.22(C) which means the area we are speaking of is not included within (C). I do not see where the type of build we are speaking of is not considered a plenum or duct. By adding a cover over the open areas of the cavities, would that not be specifically make it a duct specifically designed to carry environmental air?

. Here is an excerpt from a poster on Mike Holts forums concerning this:

Quote:
the stud bays or joist bays are not considered plenum spaces unless the space itself is used as a 'duct' or plenum. If a duct is installed in the space, it usually means that the duct is doing the job of a plenum, not the wall cavity.
Doesn't make him right but it does make him on my side.

Regardless of the outcome of that argument, OP wants to run lengthwise through the space, which still is not allowed in any of the sections. OP can still not do what he asked if he can do.
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Old 05-11-2008, 09:58 PM   #14
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Running wire through a cold air return?


It is either a plenum or a duct. And it isn't a plenum. Sorry, it is a duct.
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Old 05-11-2008, 10:51 PM   #15
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Running wire through a cold air return?


Quote:
Originally Posted by thekctermite View Post
It is either a plenum or a duct. And it isn't a plenum. Sorry, it is a duct.

Sorry it is "Other Space Used for Environmental Air". It does not have to be either a duct or a plenum.

The code states that a duct or a plenum is "specifically fabricated to transport environmental air"

A stud or joist cavity is not fabricated to transport environmental air, it is something that is "altered to be able to transport environmental air.

If it is either a duct or a plenum, then there would be no need for Section 300.22(C) because what it covers wouldn't exist.

Section 300.22(C) exception specifically addresses this type of situation
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.
It says that Section 300.22 does not apply to this situation. The section is titled "Wiring in Ducts, Plenums, and Other Air-Handling Spaces".

The exception says this section does not apply to this situation, therefore we cannot call it a duct or a plenum, by the NEC rules.

P.S. -- I was wrong about calling it an "other air-handling space", because if it doesn't apply to this section, it cannot even be referred to as that, because that is part of the section.


Last edited by Silk; 05-11-2008 at 11:05 PM.
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