I just finished running network lines as part of a basement finishing product. I bought non-plenum cable, because I wasn't planning on running any cable inside the air ducts, but just realized that I actually did end up running cable across the bottom of my cold air return vent.
Basically, the cold air return is two studs wide, so there are two runs of 15" cable or so at the bottom of the cold air return, about two inches below the grate that lets air into the return.
I will be amazed if the inspector even asks about plenum vs. non-plenum cable, but is there anything I need to do for family safety? It's too late to run metal conduit, but I could wrap the cable in some kind of insulation and tape it. Thanks
If the inspection includes the duct work then they might notice it.
The point of plenum rated cable is it's resistance to outgassing during a fire. If regular wire catches fire the jacketing on it tends to put out rather toxic fumes, not to mention act somewhat like a lit fuse carrying the fire along. Suffice to say that putting such wire inside a well-fed air plenum is a way to spread the fire and harm anyone unlucky enough to still be around breathing it (like asleep in bed). For peace of mind, just re-run the cable properly or in the ducts with the correct stuff. Yeah, pain in the butt but a lot less trouble down the line should anything go wrong.
You and your family gonna live there? Replace it with proper plenum wiring.
The fumes when it burns are the problem. I think some of the more modern non-plenum stuff is better than in the olden days. But the gasses release are very bad.
Basically, when I framed, I set up a cold air return in two adjacent spans between the 2x4 framing studs - one side is drywall, with a 30" grate about 6" off the ground - the other side is tin, with a duct starting about 3 feet off the ground and running to the main cold air return, which leads to my furnace. Ideally, that way when the furnace draws in cold air, it will draw air from the floor level of my basement.
A couple inches below the grate, I have 3 non-plenum cables, running for a span of about 30". There's no way to replace them now, although I suppose I could cut the cable at both ends of the span, put an RJ-45 port at each end, and run plenum patch cables across the span. However, I think the easier solution is to install a fireblock between the area where the cables are and the cold air return. Assuming that I can do that, (I need to open the grate tonight and check), I think I'll be ok.
Please DO NOT run any cables inside air ducts except those which are required for the operation of the ducts themselves. An example of an acceptable cable would be one used to power a damper. No other cables, including plenum rated cables, are permitted in the air ducts.
Plenum cable is permitted in a plenum air return, but that is not a duct. Plenum spaces are sometimes found above the ceiling in commercial office buildings. Instead of running a complete system of return ducts, grates are installed in the ceiling and room air passes though them on its way back to the furnace or A/C unit. Because these spaces are the only place wires can be run in such structures, you are allowed to use plenum cable in them. The interior of an air duct is not considered a plenum for running cables. Significantly stricter rules apply.
Besides the fact that it's a code violation to run your alarm, automation or structured wiring system cables in air ducts, it is also a life safety hazard. Perhaps I should say that the other way around. Because it's a life safety hazard, it's against code. Either way, please don't do it.
In Canada, damper motors are wired with mineral jacketed cable or armoured BX. There are also restrictions with respect to how much cable can be exposed. Check with your local building codes and your AHJ to be on the safe side.
In addition to Robert's coments, building codes may allow you to run standard FT-4 as well (for communications and network). In Vancouver (for instance) you don't need to run plenum rated wire in a plenum if the total length of the wire run (from panel to device) doesn't exceed 9 meters. Some would interpret this part of the code to mean the total
*exposed* length of wire inside the plenum, but I've always believed it's better to err on the side of "safety". What's really interesting is that the wire wholesaler we use doesn't sell FT-4 jacketed CAT5 or CAT6. He only carries the plenum rated stuff.
It's always best to check with both your local codes and your AHJ before you start any project like this. Your family is worth the few minutes this is going to take.
On 29 Nov 2005 01:06:59 -0800, snipped-for-privacy@comcast.net wrote (with possible editing):
While you're right about those cables not being allowed in a duct, I am still not so sure it's a duct and not a plenum. I've read and re-read his post and it still isn't clear to me. It doesn't sound like everything is enclosed in tin and the wires may be below the tin part. That sounds like a plenum, not a duct.
Theron - do the wires go through a channel enclosed on all sides by sheet metal or is the only sheet metal on the top?
Sorry - this is much more complicated than I imagined, but I appreciate the help.
Here's what I have - I have an interior wall in my basement, running North-South and framed by 2x4 lumber separated 16" on center. Two adjacent gaps in the framed wall serve as a cold air return for the furnace, as follows.
On the West side of the wall is a living area, and the furnace is on the East side of the wall. On the relevant area, the west side of the wall is tin, the east side is drywall.
On the east side, I have a 30" wide grate about 6" off the ground to allow air into the wall. On the west side, I have two 8" ducts that run from the wall to the furnace's main cold air return to allow the furnace to draw air from the basement, through the wall. Those ducts are about 3-4' from the ground.
At about 3" off the baseplate, I have a set of holes drilled through the 2x4s on center running four cat 5e cables (3 phone, 1 ethernet). Therefore, the cables run for about 30" across the bottom of the gap in the wall I am using to feed cold air into the furnace.
Here's an ascii, which should come out right with a non-proportional font:
Top View Side View
D x D F F F D x D F 8 F 8 F G x T888 F F F G x T F F F G x T888 F F F D x D GGGGGGGGGGGGG D x D GGGGGGGGGGGGG FxxxxxFxxxxxF FFFFFFFFFFFFF
D = Drywall x = cat 5e cable, non-plenum rated T = Tin 8 = 8 inch duct to main cold air return G = grate F = Framing lumber
Looks to me like you've got a plenum and not a "duct". Now if you were to ask your local AHJ, he would tell you what you've done is a very big "no-no". In fact, in most instances (and jurisidictions), he may even make you remove it. I don't believe you're allowed to run *any* wire, combustible piping, etc. inside a cold air return although I have seen a couple of instances where vacuum piping was passed (go figure). If you absolutely *have* to have it there, see if you can enclose it in metal conduit or a short run of BX (yes, it may mean you're going to have at least one splice). The better way would be to find another route for your wire but that may not always be possible at this late stage.
My current plan is just to install a firestop between the cables and the plenum or duct or whatever it is. Since the cables are actually below the grate, I can toenail some 14 1/2" blocks across the gaps and block the area with the cables from the area where I want cold air to circulate. (That's what I would have done if I had realized what I was doing at the time).
Grate solution, then the wires are no longer in the duct, plenum, airspace or what ever else it could be called! If sheet metal is easier for you to work with you could use that to put a "floor" in the return.
That's the same solution that came to mind as I studied your diagram. Just put a piece of metal over the wires to isolate them from the air circulation area. You might it easiest to do using a couple of 14.5" lengths of light gauge metal stud material. You should just be able to drop them in with the legs pointing down between the drywall. (Upside down U).
| __ | ||X ||
The outer lines are the wall or grates. X is the wire. The lines on both sides and above the X is the piece of metal stud. The underline is the baseplate.
After reviewing the ASCII drawing it appears this is a plenum -- not a duct as the gentleman originally wrote. In that case, Plenum rated cable is acceptable. If it's a network cable, splicing is NOT the best idea. Also, unless the ends are properly protected, BX isn't a good idea either. It is possible to simply run conduit in the plenum space with J-boxes outside the plenum. EMT will do the job just fine.
is "a chamber at higher than atmospheric pressure."
The NEC defines a plenum as a "compartment or chamber to which one or more air ducts are connected and that forms part of the air distribution system."
Regarding wire and cable in ducts and plenum spaces, the code states: "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 covering shall be installed in ducts or plenums specifically fabricated to transport environmental air."
At first glance I didn't take exception to Mr. Olson's suggestion of using BX to jacket non-plenum rated cable. That advice is incorrect. For fire safety reasons, NEC prohibits this practice if the run exceeds
4 feet and its use is restricted to cables required to operate the duct system itself. It's not allowed as a means of avoiding using plenum cable.
NEC discusses the above as follows: "Flexible metal conduit and liquidtight flexible metal conduit shall be permitted, in lengths not to exceed 1.2 m (4 ft), to connect physically adjustable equipment and devices permitted to be in these ducts and plenum chambers."
Also, if you do choose to use BX in those limited applications where it is permitted you must use connectors which "effectively close any openings in the connection." IOW, you can't just slip a cut off piece of BX jacket over your regular cable and run it in a duct or plenum.
There is a great deal more in tne code about running cables, not just in plenum spaces but throughtout your home. Anyone wanting to make significant changes to house wiring would do well to order a copy of the code. It's available on CD-ROM, in bound book format and as a downloadable PDF file.
Thanks for your help, Robert (and everyone). If I can, I have one more code question. In Chapter 300, there's an exception to the rule for wires that travel through studs or joists perpendicular to the stud or joist. (I apologize for not having an exact citation - I don't have the code here).
I assume that I don't fall within that exception, because it wouldn't make sense, but I can't quite figure it out. Do you know what the code authors are trying to refer to with that section.
I stated: "In Canada, damper motors are wired with mineral jacketed cable or armoured BX. There are also restrictions with respect to how much cable can be exposed. Check with your local building codes and your AHJ to be on the safe side." What part of my "advice" was incorrect, Robert?? Perhaps it would be better if you didn't just "glance" at my posts, but *read* them before you responded.
And I stated: "There are also restrictions with respect to how much cable can be exposed. Check with your local building codes and your AHJ to be on the safe side."
You're wrong there, buddy. This part refers to the type of *connection* allowed inside a duct and doesn't refer to runs *through* a duct. From what I understand you're not even allowed to make runs *through* a duct at all, but only *to* equipment controlling devices that have to do with the duct (fan blowers, dampers, shutters). The sections of the NEC you just posted confirms this. And once again, I'd like you to point out
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