Cold air return dilemma

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aelectricalman

aelectricalman

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KY
I have a problem where I am forced to run a wire through a cold air return. I know that I am not allowed to place an electrical box in this return but what does the electrical bible say about just sending a wire through the cold air return. I usually just ignore the whole situation and stay away from c a r's and have never really known the formal definition of what is and what is not allowed. Could someone please clear this up for me. Thank you.


Chris Hill
Alpha Electrical Contractors
 
Re: Cold air return dilemma

My understanding is that in the event of a fire, the toxic fumes from the wire burning will be carried through the air return spreading the fumes. So if you create a "Chase pipe" for the wire to pass through that area, the wire isn't really in the return, it's in the chase. If the wire were to start emitting toxic fumes they wouldn't go into the return air just the air in the "Chase" and eventually out the end of the "Chase" which is Not in the air return.
I've always used a piece of 1/2" metal flex about 12" longer then the width of the Return, 6" inches out both sides, used male adaptors and plastic bushings on both ends. Insulators would spray the small gaps around the holes I drilled for the flex to make it air tight. 3/4" EMT works good too if you have a nice clean, straight shot....don't forget the bushings!!!

I've never read article 300.22. until about 1 minute ago, but it's looks like I've been doing it right!
:D

Dave
 
Re: Cold air return dilemma

So, if it is the fumes that are the problem, how can the plumbers run their pipe thru one. Isn't PVC burning pretty nasty. Weird. Thanks for help guys.
 
Re: Cold air return dilemma

"how can the plumbers run their pipe thru one."

I can't believe they ARE allowed to. Copper, or rigid is fine but PVC? :D

Dave
 
Re: Cold air return dilemma

By Dave: Ok, ok, I tried pvc once back in High School, BUT I didn't Inhale!
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Wasen't that THC or PCP?

Oh no I open my big mouth :eek: :D

But to more on track with the question:
300.22(C) exception does allow wiring to pass through perpendicular to the long dimension without being in any conduit or other raceway.

300.22 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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But for communication wiring 800.51 require that they be listed for use in ducts and plenum's. (CMP rated)

See 725.71(A) for door bell wire and thermostat wire It has to be CL2P rated

[ March 06, 2005, 04:36 AM: Message edited by: hurk27 ]
 
Re: Cold air return dilemma

Originally posted by davedottcom:
I've never read article 300.22. until about 1 minute ago, but it's looks like I've been doing it right!
:D

Dave
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Dave your way is fine but unnecessary, if you are just passing NM across the width of a plenum made of a stud bay you do not need a sleeve.

300.22 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.
Click to expand...
As far as the plumbers, different people write those codes. ;)
 
Re: Cold air return dilemma

a word of caution concerning raceways in return air ducts. we worked in a twelve story building that had bus duct (high and low voltage)running verticaly through their building. at the top of the (480 volt) bus duct there was a cable tap box that fed a motor control center in the roof mechanical room. from this tap box they ran four two and a half inch emt through a large chase into the bottom of the motor control center. the bus duct blew up twice ---the first time they blamed it on moisture from a roof leak they couldn't find??? the second time they realized that the moisture was caused by condensation of the air in the feeder raceways that ran through an area that was a common air return back into the mechanical room. the high negative pressure in the mechanical room drew the warm air from the electrical room thru these raceways and into the cold raceway where it condensed water and ran back down the raceway into the tap box!!!
 
Re: Cold air return dilemma

To make sure I am code compliant, my wire is running Horizontal through a stud space, from left to right. This is Legal? Thank you.
 
Re: Cold air return dilemma

Chris also said in the opening post that it is not allowed to place an electrical box in the cold air return. This is only true of non-metallic boxes, correct? I believe a metal box can be placed in a cold air return for a switch or receptacle, with wiring in metal conduit specified by 300.22(C).
 
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