Plenum cable for cold air return?

[rhughes]

I'm starting to run some low voltage wire for motion detectors, door/other sensors, network, cable TV, etc. throughout my 30 year old home. There's a very convenient cold air return from my family room on the first floor to the rather large furnace room in the basement where my servers are setup that I'd like to use for some of the cable. The rest of the basement is finished without easy access to the floor above. The cold air return is formed by the joists between the floor and ceiling with no actual metal duct work and is actually open at the end to the basement itself (as well as to the HVAC air return). Is plenum rated cable really necessary here? Would non-plenum cable likely be a code violation, dangerous or cause problems with insurance if there were a fire at some point?

Thanks for any advice.

 

[upstatemike]

I'm starting to run some low voltage wire for motion detectors, door/other sensors, network, cable TV, etc. throughout my 30 year old home. There's a very convenient cold air return from my family room on the first floor to the rather large furnace room in the basement where my servers are setup that I'd like to use for some of the cable. The rest of the basement is finished without easy access to the floor above. The cold air return is formed by the joists between the floor and ceiling with no actual metal duct work and is actually open at the end to the basement itself (as well as to the HVAC air return). Is plenum rated cable really necessary here? Would non-plenum cable likely be a code violation, dangerous or cause problems with insurance if there were a fire at some point?

Thanks for any advice.

Any cable through an air duct must be plenum rated. The rating relates to what kind of toxic fumes the insulation will give off in the event of a fire and not the temperature inside of the ductwork. You would certainly risk a code issue if you do not use plenum wire. Even if you do, it will probably cause unwelcome extra scrutiny by the inspector when he sees wires in your ductwork. IMO it would be better to find another route if at all possible.

 

[sic0048]

I'm starting to run some low voltage wire for motion detectors, door/other sensors, network, cable TV, etc. throughout my 30 year old home. There's a very convenient cold air return from my family room on the first floor to the rather large furnace room in the basement where my servers are setup that I'd like to use for some of the cable. The rest of the basement is finished without easy access to the floor above. The cold air return is formed by the joists between the floor and ceiling with no actual metal duct work and is actually open at the end to the basement itself (as well as to the HVAC air return). Is plenum rated cable really necessary here? Would non-plenum cable likely be a code violation, dangerous or cause problems with insurance if there were a fire at some point?

Thanks for any advice.

This is exactly what plenum wire is designed for. Putting non-plenum wire in that space would certainly be a code violation. If there was a fire and the insulation burned, a non-plenum rated cable may give off toxic gases which would be vented to other areas of the house by the HVAC. I personally don't think it is worth the risk. While plenum rated cable is more, there are just some things that are worth paying for.

 

[rhughes]

Thanks for the replies! I'll try and find another way or otherwise pay up for plenum.

 

[nightwalker]

Thanks for the replies! I'll try and find another way or otherwise pay up for plenum.

Even if you use plenum cable it may be against some local codes for residential wiring. The plenum wire was mostly designed for commercial where the entire ceiling was a big duct and there was no way around having some wire up there. For residential most inspectors do not like and some do not allow wire in ducts no matter what it's rating is.

 

[liftn]

If your house is on fire I don;t think your biggest concern would be your cables! Stop Drop and roll.......

 

[BraveSirRobbin]

If your house is on fire I don;t think your biggest concern would be your cables! Stop Drop and roll.......

Not the cables, but the toxic fumes emitted from the melting insulation Still I see your point, though I know of places so fire paranoid that they will not let you bring Styrofoam cups inside (because of their toxicity when melted).

 

[Rustytek]

If your house is on fire I don;t think your biggest concern would be your cables! Stop Drop and roll.......

Not the cables, but the toxic fumes emitted from the melting insulation Still I see your point, though I know of places so fire paranoid that they will not let you bring Styrofoam cups inside (because of their toxicity when melted).

Styrofoam cups - I remember the good old days (as a kid) when I painted the cup and watched it melt in the oven with the door open. Cough, cough. Plenum should be fine in the duct. Cough, cough.

 

[rhughes]

After checking things out, the cold air return really is the easiest access for what I need. How about running the cable through 1 inch metal conduit so none of the cable was exposed within the cold air return? Since the cold air return is a straight shot and open at one end, this would actually be easy to do and a lot cheaper than buying a bunch of plenum cable.

 

[sda]

There are specific NEC rules for running cables in duct.

800.154 says:
Types CMP, CMR, CMG, CM, and CMX and communications wire installed in compliance with 300.22 shall be permitted.

300.22.B says:
Ducts or Plenums Used for Environmental Air
Only wiring methods consisting of Type MI cable, Type MC cable
employing a smooth or corrugated impervious metal sheath
without an overall nonmetallic covering, electrical metallic
tubing, flexible metallic tubing, intermediate metal conduit,
or rigid metal conduit without an overall nonmetallic cov-
ering shall be installed in ducts or plenums specifically
fabricated to transport environmental air. Flexible metal con-
duit shall be permitted, in lengths not to exceed 1.2 m
(4 ft), to connect physically adjustable equipment and de
devices permitted to be in these ducts and plenum chambers.
The connectors used with flexible metal conduit shall effectively
close any openings in the connection. Equipment and
devices shall be permitted within such ducts or plenum
chambers only if necessary for their direct action upon, or
sensing of, the contained air. Where equipment or devices
are installed and illumination is necessary to facilitate maintenance
and repair, enclosed gasketed-type luminaires (fixtures)
shall be permitted.

Got all that? If you want to make "code", you'd have to run sealed metal conduit in the duct and run the CMP through that.

BSR - "Not the cables, but the toxic fumes emitted from the melting insulation"
That's the basis for the extreme rules for running cable in duct.

Then again ... My ducts are flex and use non-toxic when burned materials. And nothing else in my house when burned emits toxic fumes.

My air handler has a whole bunch wires in the air stream for fan power and various other controls. I guess some rules don't apply.

RHughes:
"The cold air return is formed by the joists between the floor and ceiling with no actual metal duct work and is actually open at the end to the basement itself (as well as to the HVAC air return). Is plenum rated cable really necessary here? Would non-plenum cable likely be a code violation, dangerous or cause problems with insurance if there were a fire at some point?"

I'm trying to figure out what you're describing. Is it a hole in the floor? Is the air return in the wall in the wall and "joists" are really "studs"? How big is it?Where's the HVAC air return?

I doubt if your wiring would cause a fire, whether its in a duct or somewhere else, but insurance companies are always looking for a reason to deny a claim. If a contractor does some work and your house burns down because of it, they'll pay you and go after the contractor. There's been "talk" that they can't deny a claim if the homeowner does the work.

Personally, I wouldn't run cables through the ducts. Aside from the fact that its a touchy issue, the cables could interfere with air flow. Find or make another route.

Then again, I've put temp sensors in my registers and returns using short stubs, 2inches to 8inches, of plenum cable.

 

[sda]

After checking things out, the cold air return really is the easiest access for what I need. How about running the cable through 1 inch metal conduit so none of the cable was exposed within the cold air return? Since the cold air return is a straight shot and open at one end, this would actually be easy to do and a lot cheaper than buying a bunch of plenum cable.

Make sure the cables enter and exit the conduit outside of the duct and you use sealed fittings inside the duct. Rigid or IMC with threaded connectors are OK. EMT with compression connectors "should" be OK. The idea is to keep the conduit airspace separate from the duct airspace.

You might want to bump up the conduit size to 1-1/2 or 2. The cost is negligible now and it'll be easier to pull more cables later.

None of this helps if something catches fire on the first floor near the return, the cables start to burn and emit toxic gases, the heater is on and the poison gas gets sucked into the return. Sleep well

 

[rhughes]

I'm trying to figure out what you're describing. Is it a hole in the floor? Is the air return in the wall in the wall and "joists" are really "studs"? How big is it?Where's the HVAC air return?

Imagine an unfinished basement with the joists running parallel to each other. One inner wall of my first floor family room runs parallel to these joists. Now imagine the large return vent from the HVAC runs perpendicular across the bottom of the joists in the ceiling of the basement. The cold air return in the family room was formed by openning up a large hole at the bottom of the inside of the family room wall leading into the space between the joists, framing higher up in the wall to seal the area around a large register in the wall, and closing the area at the bottom of the joists in the basement with plywood running the entire length to the HVAC return. Hope this makes sense.

I don't know if this is the way it should be, but the space between the joists is not sealed at the end of the run to the HVAC return vent. That is, the space between the joists runs the entire length of the house with no interruption. I would have thought it would be sealed after the HVAC return vent to form an enclosed space, but its not. This gives me extremely easy access to run cable from the family room to the furnace room in the basement. I can then hide wiring in the family room behind baseboards leading up to the wall register. I don't mind paying up for plenum if I need to, but running some metal conduit would cost 10's of dollars as opposed to the 100's of dollars premium for plenum cable.

Btw, thanks for all the comments!

 

[sda]

Imagine an unfinished basement with the joists running parallel to each other. One inner wall of my first floor family room runs parallel to these joists. Now imagine the large return vent from the HVAC runs perpendicular across the bottom of the joists in the ceiling of the basement. The cold air return in the family room was formed by openning up a large hole at the bottom of the inside of the family room wall leading into the space between the joists, framing higher up in the wall to seal the area around a large register in the wall, and closing the area at the bottom of the joists in the basement with plywood running the entire length to the HVAC return. Hope this makes sense.

I don't know if this is the way it should be, but the space between the joists is not sealed at the end of the run to the HVAC return vent. That is, the space between the joists runs the entire length of the house with no interruption. I would have thought it would be sealed after the HVAC return vent to form an enclosed space, but its not. This gives me extremely easy access to run cable from the family room to the furnace room in the basement. I can then hide wiring in the family room behind baseboards leading up to the wall register. I don't mind paying up for plenum if I need to, but running some metal conduit would cost 10's of dollars as opposed to the 100's of dollars premium for plenum cable.

Btw, thanks for all the comments!

"technically" you're supposed to run CMP (plenum) in metal conduit.

I think I understand. You have a hole in the wall and the wall base plate has been cut out so the hole enters the basement. The joist space in the basement is boxed in and opens near the HVAC return vent. Is the plywood sealed to the joists? Probably not. I hope your return air filter is at the unit otherwise you're drawing in dirty air.

An idea comes to mind, but don't know if it'd work with your layout. You'd have to close the unused portions of the "duct" where the family room return drops in. In the family room, come down into the basement from the next stud bay over from return.

A picture or sketch is worth 1K words.

 

[sic0048]

The bigger issue I think is from the sound of it, his whole basement is a plenum.

I also think that from the sound of it, you could pretty easily find another spot along the parallel wall to drill up from the basement and into the family room. Same wall, but different location, and therefore not in the air duct - although you might need to seal the space between the two joists somewhere after the air return so as to not put the wire in the duct again.

Although I could be completely misreading the description. A picture or two would certainly help everyone understand the exact construction method.

 

[rhughes]

The bigger issue I think is from the sound of it, his whole basement is a plenum.

Yeah, I'm a bit concerned about that. It seems the cold air return space should be sealed off after the furnace duct return. I'm hesitant to do that in case it was meant to be left open, but it doesn't seem as if there would be much of a draw from the family room with it open. Any ideas?

I also think that from the sound of it, you could pretty easily find another spot along the parallel wall to drill up from the basement and into the family room. Same wall, but different location, and therefore not in the air duct - although you might need to seal the space between the two joists somewhere after the air return so as to not put the wire in the duct again.

Okay, you guys aren't going to let me get away with running non-plenum cable through the cold air return no matter what I do. You're right that I can move over a couple of joists, but will have to open up the family room wall to get access to the space since the basement is finished under the family room with no easy access. But, I'm pretty handy with patching drywall, so I'll do it the right way and avoid that nagging feeling that I've put my family at additional risk. :unsure: And, no plenum premium.

Again, thanks for the input. Btw, we probably don't want to conduct a poll on how many people actually do run regular non-plenum cable through their ducts and cold air returns, do we? I bet it would be a significant number.