Wires in ducts

Reply

  #1  
Old 08-05-12, 02:46 PM
Member
Thread Starter
Join Date: Dec 2010
Location: US
Posts: 32
Received 0 Votes on 0 Posts
Wires in ducts

I live in an old house. It had the electrical service signed off in 1985, but I think the previous owner/builder continued to build and add to it after that. It has a semi-finished basement - the walls are covered, but the ceiling still open. He has run wires both along and cross-wise in the floor joists above. He then later added a heating system and used a couple of between-joist spaces for ducting. He just covered that section of "duct" with plywood and ran the conditioned air in one end and out the other. This has actually worked very well and having opened up the ducts they are very clean and free of mold, etc.

But there are wires inside one of the ducts and quite a few running cross-wise!

I intend to remove the wires that run inside of the ducts, just moving them to the other side of the joist. My question is about the ones running cross-wise. There are quite a number of them and most of them there is no easy way to re-route.

Can I pull those cross-wise wires out, drill the hole larger, put in a section of conduit, caulk it, and then run the wires through the conduit? That is very do-able. Anything else is very tough.

Thanks.
 
Sponsored Links
  #2  
Old 08-05-12, 03:11 PM
Tolyn Ironhand's Avatar
Group Moderator
Join Date: Nov 2007
Location: Twin Cities, MN
Posts: 12,965
Received 59 Votes on 52 Posts
Wiring in a dwelling that runs perpendicular to the long dimension of a joist or stud space is OK. 300.22(C) exception 2008.

Your cables are fine. If you want to put them in conduit, that is OK too. If it were me, I would just foam the holes in the joists.
 
  #3  
Old 08-05-12, 05:28 PM
Member
Thread Starter
Join Date: Dec 2010
Location: US
Posts: 32
Received 0 Votes on 0 Posts
I like that answer.

Thanks.
 
  #4  
Old 08-05-12, 05:49 PM
chandler's Avatar
Banned. Rule And/Or Policy Violation
Join Date: Dec 2005
Location: USA
Posts: 39,967
Received 2 Votes on 2 Posts
Scott, Fatbear,am I reading there are line voltage wires running across joist bays THROUGH supply ducts?? I know you can do it in returns, but I question supply. I also stand to be educated.
 
  #5  
Old 08-05-12, 06:32 PM
Member
Thread Starter
Join Date: Dec 2010
Location: US
Posts: 32
Received 0 Votes on 0 Posts
Yes, they are supply ducts. Hot or cold forced air passes through them. The hot air doesn't seem to get all that hot, but it is still pretty warm. The cables are standard Romex. It has been this way for about 26 years, the place hasn't burned down, and the cables appear OK, but it really does make me nervous.

If it really, truly is safe, then I'll leave them and just remove the cables that run along the inside of the ducts. If there is any doubt, then will my plan to pull them out, put 1-1/4" conduit cross-wise through the ducts and seal around it, then pass the wires through the conduit remove that doubt?

Thanks again.
 
  #6  
Old 08-06-12, 03:37 PM
Tolyn Ironhand's Avatar
Group Moderator
Join Date: Nov 2007
Location: Twin Cities, MN
Posts: 12,965
Received 59 Votes on 52 Posts
Code does not differentiate between supply and return air, it only states "environmental air".

Heat from a furnace will never get hot enough to damage Romex.

Around here the supplies are always run in ductwork and only the returns use joist/stud spaces. I have never seen a joist/stud space used for a supply. Ductwork is never penetrated here.

The concern here is not damage to the cables, but of the toxic smoke they give off when they burn if there was a fire and the furnace was running. Installing a conduit chase is a fine option.
 
  #7  
Old 08-07-12, 06:12 AM
Member
Join Date: Jan 2012
Location: Canada
Posts: 2,739
Received 15 Votes on 15 Posts
Tolyn Ironhand nailed my concerns.
I would also be a bit concerned with there being any damage to the cables as they where pulled through the duct work.
When I use to wire homes with communication cables, I would generally follow the outside of ducts, but avoid running inside them. Crossing them was fine provided there was no sharp edges to damage the cable casing.

Going back a few years when I was installing computer networks, we would run plenum cable for all walls and ceilings because they had lower fume rate then standard cable. This was when CAT5e was starting to be common cabling. I hear some of the newer CAT6 cable is firewall rated.
 
  #8  
Old 08-07-12, 10:18 AM
Member
Thread Starter
Join Date: Dec 2010
Location: US
Posts: 32
Received 0 Votes on 0 Posts
The ducts are just wooden joists spanned by 1/4" plywood. No sheet metal is involved.

I'm not really too worried about fumes in case of a fire. The fact is, this house is all wood framed and finished. No dry wall exists to slow down a fire. We either get out immediately or we are doomed. I doubt that fumes will form and disperse through the ducts that fast. (Am I wrong?)
 
  #9  
Old 08-07-12, 10:38 AM
ray2047's Avatar
Group Moderator
Join Date: Mar 2006
Location: USA
Posts: 33,597
Received 13 Votes on 11 Posts
From what I have read burning plastics can create anesthetic like gases that. If your asleep they can put you in an even deeper state of unconsciousness so you aren't awakened by the fire in time to get out before the toxic fumes kill you. (But I can't cite a source. Just something I read in a fire alarm pitch long ago.)
 
  #10  
Old 08-07-12, 10:48 AM
Member
Thread Starter
Join Date: Dec 2010
Location: US
Posts: 32
Received 0 Votes on 0 Posts
Hmmm. My original idea was to use PVC conduit. So if I pull the cross-wise cables out, put in conduit chases across the ducts and put my wires through those, will the plastic conduit burn and generate the same anesthetic gasses? Does that mean I need to use steel conduit? I really don't want to do that because then you have to tend to the ends to make sure sharp edges don't cut the wires. I don't even know how to do that. I suppose there is some sort of end attachment for steel conduit to protect the cables where they enter/exit. But that sounds like a lot of hassle and expense.
 
  #11  
Old 08-07-12, 11:52 AM
ray2047's Avatar
Group Moderator
Join Date: Mar 2006
Location: USA
Posts: 33,597
Received 13 Votes on 11 Posts
Read the last sentence of my post and keep that in mind. What I said could be wrong. You might though want to research it.
 
  #12  
Old 08-07-12, 01:03 PM
Member
Thread Starter
Join Date: Dec 2010
Location: US
Posts: 32
Received 0 Votes on 0 Posts
Late breaking news: I just got an email from an application engineer at the company that makes ROMEX cable. In reference to my question about the cross-wise cables, he said ROMEX is not rated to be inside a duct with conditioned air. So that is that. I also asked him about my conduit across the duct idea. He hasn't answered that, but my suspicion is that he won't for legal nervousness reasons or something.
 
  #13  
Old 08-07-12, 06:35 PM
CasualJoe's Avatar
Member
Join Date: Jan 2010
Location: USA
Posts: 10,042
Received 26 Votes on 20 Posts
My original idea was to use PVC conduit. So if I pull the cross-wise cables out, put in conduit chases across the ducts and put my wires through those, will the plastic conduit burn and generate the same anesthetic gasses?
In my opinion, using PVC conduit defeats the purpose of installing the conduit at all. IIRC, NM cable sheathing is PVC or nylon and the conductor insulation is PVC so what have you gained by putting NM cables in PVC conduit?
 
  #14  
Old 08-07-12, 07:10 PM
Member
Thread Starter
Join Date: Dec 2010
Location: US
Posts: 32
Received 0 Votes on 0 Posts
What I have gained is any heated air around the cables is limited and can get out through the ends of the conduit.

Latest word from the ROMEX guy: putting the cross-wise cables in conduit will work fine. No word on material, it's probably out of his perview, but maybe I should play it safe and use metal. So how do I finish the ends where the cable enters/exits so it won't cut into the cable? Filing seems like a PIB. Do they make some sort of plastic insert that will protect the cable? I don't think I want a clamp or anything like that which will restrict air flow. I would like the warm air to be able to exit from the ends of the conduit without restriction.
 
  #15  
Old 08-07-12, 07:44 PM
Tolyn Ironhand's Avatar
Group Moderator
Join Date: Nov 2007
Location: Twin Cities, MN
Posts: 12,965
Received 59 Votes on 52 Posts
I recommend using steel (EMT) but I think if the conduit is longer then 24" it is required to be bonded to ground.
For the ends, use a connector on each end and install a plastic bushing to protect the cable.

he said ROMEX is not rated to be inside a duct with conditioned air
That explains why we do not penetrate supply ducts.
 
  #16  
Old 08-07-12, 08:33 PM
Nashkat1's Avatar
Member
Join Date: Mar 2012
Location: USA
Posts: 8,470
Received 1 Vote on 1 Post
how do I finish the ends where the cable enters/exits so it won't cut into the cable? Filing seems like a PIB. Do they make some sort of plastic insert that will protect the cable?
If you can use 1" or smaller EMT, you can ream each end with a conduit reamer, and protect that edge with a knock-on bushing.

You can probably buy a conduit-reaming screwdriver, or screwdriver attachment, at your local big box HI center. You might have to go to a supply house for the knock-on bushings.
 
  #17  
Old 08-07-12, 08:55 PM
Member
Thread Starter
Join Date: Dec 2010
Location: US
Posts: 32
Received 0 Votes on 0 Posts
OK, I guess I've got a plan. Knock-on bushings. Sounds like just the thing I need. There is no "local" big box. It's Ace hardware or a long drive. If I have to make the long drive, I'll just go to an electrical supplier for everything. I was originally going to use 1-1/4" PVC because I have a piece and because I thought having lots of air space around the conductors would be a good thing. If I have to buy 1" EMT, that is fine.
 
  #18  
Old 08-07-12, 09:30 PM
Member
Thread Starter
Join Date: Dec 2010
Location: US
Posts: 32
Received 0 Votes on 0 Posts
I forgot to add: THANK YOU ALL FOR THE HELP.
 
  #19  
Old 08-08-12, 10:26 AM
Member
Join Date: Sep 2011
Location: USA
Posts: 71
Received 0 Votes on 0 Posts
how are you going to get a length of conduit to span between the 2 joists if its longer than the span of the 2 joists (so each end sits in the joist, say 16 inches on center and your conduit is 16 inches long) how do you manuver the conduit into the hole or are you going to use 2 8" pieces of conduit and couple them together. Just something that popped in my head.
 
  #20  
Old 08-08-12, 11:49 AM
Member
Thread Starter
Join Date: Dec 2010
Location: US
Posts: 32
Received 0 Votes on 0 Posts
I actually did think about that. Putting the coupling in the middle is one way and is easy to do as the ducts will be completely open. I'm also considering another way:

I want to seal around the conduit so the air stays in the duct. (I will also be sealing the ducts better everywhere else.) To do that, my intention was to drill the holes oversize and fill the gap with foam or caulking. I would just drill the hole on one side at a small angle. The angle plus the oversize hole will give me enough slop to get the 18" piece of conduit into the duct through a 14.5" joist space.

Oh boy, I guess that means I need fire retardant foam!
 
  #21  
Old 08-08-12, 10:14 PM
Nashkat1's Avatar
Member
Join Date: Mar 2012
Location: USA
Posts: 8,470
Received 1 Vote on 1 Post
Oh boy, I guess that means I need fire retardant foam!
I would use fire retardant caulk rather than foam - less messy and may be more effective.
 
  #22  
Old 08-10-12, 01:19 PM
Member
Thread Starter
Join Date: Dec 2010
Location: US
Posts: 32
Received 0 Votes on 0 Posts
OK, I will look into fire retardant caulk. I hope they sell it at Ace. That's where I normally go, since almost anyplace else becomes a half-day journey.
 
  #23  
Old 08-12-12, 03:42 PM
Member
Thread Starter
Join Date: Dec 2010
Location: US
Posts: 32
Received 0 Votes on 0 Posts
Just a quick note, not a question: I just pulled out the first cross-wise cable. The sheathing was noticeably drier than on the rest of the cable. It was still supple enough that it would certainly have been safe for some years yet, but it clearly does not belong in those ducts.
 
  #24  
Old 08-12-12, 04:42 PM
Nashkat1's Avatar
Member
Join Date: Mar 2012
Location: USA
Posts: 8,470
Received 1 Vote on 1 Post
Good point, and thanks for the update!
 
Reply

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Thread Tools
Search this Thread
Display Modes
 
Ask a Question
Question Title:
Description:
Your question will be posted in: