Running NM

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  #1  
Old 04-15-05, 08:23 AM
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Running NM

My cold air returns to the furnace are in the floor joist bays. When running NM through joists, can I go through a cold air return?
 
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Old 04-15-05, 08:24 AM
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Yes, if you are talking about the short way through, perpendicular to the air flow. Caulk around the holes.
 
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Old 04-15-05, 08:41 AM
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Does the cable need to be protected or be plenum rated??
 
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Old 04-15-05, 09:37 AM
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John,

Can you point me to the code on that one. I have heard of people doing it but I never have as I usually don't see the need..anyway it would have to maintain the fire rating of the item breached....BUT with that said....

Check out Art 300-22(b) in regards to ducts used for Environmental Air.
 
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Old 04-15-05, 11:54 AM
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Originally Posted by ElectricalMan
Can you point me to the code on that one. I have heard of people doing it but I never have as I usually don't see the need..anyway it would have to maintain the fire rating of the item breached...
My wire run will be perpendicular to the joists and the cold air return. How do you make the run from one side to the other without going through the cold air return?
 
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Old 04-15-05, 12:00 PM
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Question. Is this enclosed metal ducting installed within the joists or is the space between the joists being used as an air handling purpose?
 
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Old 04-15-05, 12:47 PM
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To form the cold air return the HVAC guys fasten sheet metal to the bottom of two adjacent joists to close off a joist bay...so you have the subfloor above, a joist on each side and sheet metal across the bottom to create the plenum. This has been very typical construction here for years.

I notice 300-22(b) has an exception that allows running through a plenum for dwellings if the run is perpendicular to the plenum...that is if I understand the exception correctly. Can someone confirm this?
 
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Old 04-15-05, 12:52 PM
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I think that's the exception John was refering to. It still is in 300.22 (C). in the 2005 code and looks kosher to me.
 
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