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#95429 09/13/05 09:36 AM
Joined: Jan 2004
Posts: 1,507
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When installing NM cable in a dwelling unit, do the inspectors require metal wiring methods in CA returns?


George Little
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#95430 09/13/05 10:43 AM
Joined: Oct 2000
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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.


Joe Tedesco, NEC Consultant
#95431 09/13/05 01:00 PM
Joined: Jan 2004
Posts: 1,507
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Member
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.


George Little
#95432 09/13/05 01:20 PM
Joined: Aug 2003
Posts: 1,374
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Moderator
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. [Linked Image]


Ryan Jackson,
Salt Lake City
#95433 09/13/05 02:07 PM
Joined: Jul 2004
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Member
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. [Linked Image]


Greg Fretwell
#95434 09/13/05 07:57 PM
Joined: Mar 2001
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gfretwell,

What about the "hot" water heater?

#95435 09/13/05 08:52 PM
Joined: Jul 2004
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G
Member
We keep it outside.


Greg Fretwell
#95436 09/14/05 07:48 AM
Joined: Mar 2001
Posts: 2,056
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Why does hot water need to be heated, anyway?

#95437 09/14/05 09:09 AM
Joined: Jan 2004
Posts: 1,507
G
Member
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?


George Little
#95438 09/14/05 11:16 AM
Joined: Jan 2005
Posts: 5,445
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Cat Servant
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As luck would have it, there is a new pic in the Photo forum that illustrates this issue.

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