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#95429 - 09/13/05 06:36 AM Cold Air Returns
George Little Offline
Member

Registered: 01/18/04
Posts: 1492
Loc: Michigan USA
When installing NM cable in a dwelling unit, do the inspectors require metal wiring methods in CA returns?
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George Little

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#95430 - 09/13/05 07:43 AM Re: Cold Air Returns
Joe Tedesco Offline
Member

Registered: 10/07/00
Posts: 3325
Loc: Boston, Massachusetts USA
 Quote:
See 300.21(C)

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.
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#95431 - 09/13/05 10:00 AM Re: Cold Air Returns
George Little Offline
Member

Registered: 01/18/04
Posts: 1492
Loc: Michigan USA
Joe- the issue that seems to have come up is the wording "passing through" versus "terminating in" the CA. If it passes through the CA perpendicular to the long dimension I don't see a problem but when you start installing boxes it's debatable. I'm curious how this forum feels about it.
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#95432 - 09/13/05 10:20 AM Re: Cold Air Returns
Ryan_J Offline
Moderator

Registered: 08/19/03
Posts: 1355
Loc: West Jordan, Utah, USA
I think the code prohibits it. I also think that it is a silly prohibition. The IRC allows anything, other than gas piping, to be installed in a plenum. For example, I could run a 4" ABS lengthwise through a plenum, and that wouldn't matter. I can't do this with 14-2 NM cable, however.
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Ryan Jackson,
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#95433 - 09/13/05 11:07 AM Re: Cold Air Returns
gfretwell Offline

Member

Registered: 07/20/04
Posts: 9045
Loc: Estero,Fl,usa
The "passing through" language is meaningful.
When you install a box in a return plenum, the box becomes a return air register. It is just like the dumb idea of PCs "breathing" through the diskette drive.
They end up packed with dirt.
In a dwelling that dirt could be combustible.

BTW a Florida guy would ask why you are "returning" cold air? That is the supply side.
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Greg Fretwell

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#95434 - 09/13/05 04:57 PM Re: Cold Air Returns
Redsy Offline
Member

Registered: 03/28/01
Posts: 2138
Loc: Bucks County PA
gfretwell,

What about the "hot" water heater?

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#95435 - 09/13/05 05:52 PM Re: Cold Air Returns
gfretwell Offline

Member

Registered: 07/20/04
Posts: 9045
Loc: Estero,Fl,usa
We keep it outside.
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Greg Fretwell

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#95436 - 09/14/05 04:48 AM Re: Cold Air Returns
Redsy Offline
Member

Registered: 03/28/01
Posts: 2138
Loc: Bucks County PA
Why does hot water need to be heated, anyway?

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#95437 - 09/14/05 06:09 AM Re: Cold Air Returns
George Little Offline
Member

Registered: 01/18/04
Posts: 1492
Loc: Michigan USA
Hot water needs to be heated for cleaning dishes as in a restaurant. They are called booster heaters and are used to increase the temperature to a higher level to meet health department requirements,

How did we migrate to this from derating NM cable?
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George Little

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#95438 - 09/14/05 08:16 AM Re: Cold Air Returns
renosteinke Offline
Cat Servant
Member

Registered: 01/22/05
Posts: 5305
Loc: Blue Collar Country
As luck would have it, there is a new pic in the Photo forum that illustrates this issue.

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