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Re: wiring in return air [Re: lite bulb] #192569 02/17/10 09:56 PM
Joined: Jan 2004
Posts: 1,507
George Little Offline
Alan, when you read 300.22(C)(2) Exception it tells us that "This section (meaning Section 300.22(C)) does not apply to the stud spaces of dwelling units.
I've had this discussion with Jeff Sargent from NFPA and that's his understanding also. Job is approvable.

For the sake of the disbelievers, I've seen contractors take a piece of metal panning material 3 by 24" and nail it on above the box and band it around the box and nail it below the box. Now you've divorced the wiring from the air flow.

George Little
2017 / 2014 NEC & Related Books and Study Guides
Re: wiring in return air [Re: George Little] #192571 02/17/10 11:56 PM
Joined: Aug 2007
Posts: 853
leland Offline
Very interesting. I'm going back to 'most' of my jobs and do it the easy way!!!

Learned something new today. Tanx!

Re: wiring in return air [Re: leland] #192577 02/18/10 10:09 AM
Joined: Feb 2008
Posts: 165
Rewire Offline
The exception is for wires passing perpendicular you are still allowed to run horizontal.

Re: wiring in return air [Re: lite bulb] #192582 02/18/10 01:31 PM
Joined: Mar 2005
Posts: 399
Alan Nadon Offline
Rewire. I was looking at the same place you were, but I think we have different images of what the metal box is that was going to be used. You are thinking, solid box suitable for a dust enviroment I pictured a standard metal device box with screw holes, etc. Could be we are both right or both wrong.
I would have to see it to judge it. Guess that is why inspectors still make house calls.

If it was easy, anyone could do it.
Re: wiring in return air [Re: Alan Nadon] #192603 02/19/10 10:07 AM
Joined: Feb 2008
Posts: 165
Rewire Offline
I used a 1900 box with a 4x4 block of wood covering the back ran emt horizontaly from the adjoing stud void this was the fix I cleared prior with the local AHJ.

Re: wiring in return air [Re: Rewire] #192607 02/19/10 10:53 AM
Joined: Dec 2000
Posts: 4,287
electure Offline
I see what you're trying to do now... smile

The last time I did this, I used a putty pad to wrap the box.

Re: wiring in return air [Re: electure] #192608 02/19/10 02:06 PM
Joined: Jul 2004
Posts: 9,571
gfretwell Online Content
Caution, I have my HVAC hat on.
As a design issue I would want the box sealed to the plenum air, just so it does not become part of the return venting system and pack with dirt. George's idea of the metal deflector would work but you are also compromising the effectiveness of that plenum for returning air. If the HVAC guy computed that he needed a 14.5 x 3.5 duct, you have just choked that down to 11 or 12 inches and if it is not a smooth transition the turbulence effect makes it worse than that.
I doubt they really slice things that finely in residential systems but I also think they are likely to err on the small side most of the time and make ducts smaller than they should be. This will only make that worse.
I agree the electrical code may be somewhat ambiguous on this but you could have an HVAC issue.

Greg Fretwell
Re: wiring in return air [Re: gfretwell] #192612 02/19/10 04:07 PM
Joined: Apr 2002
Posts: 7,235
HotLine1 Offline
This sounds like a really good idea....

From the words of Rewire...

"this was the fix I cleared prior with the local AHJ."

Re: wiring in return air [Re: lite bulb] #192623 02/20/10 12:58 PM
Joined: Feb 2002
Posts: 2,233
harold endean Offline
You might also want to check with any fire marshal. Where I am from, the fire sub code people do not want any wire in any duct work.

Re: wiring in return air [Re: harold endean] #192626 02/20/10 01:29 PM
Joined: Jun 2004
Posts: 1,273
Tesla Offline
I like the fire putty pad solution a lot.

You've stopped dust intrusion and addressed fire transmission at one stroke.


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