Wiring through joists w/ Hot Air Ducts

[Tara Lynn]

I'm in the process of buying a house and the lower level is an unfinished basement. There is NM cable drooping unsupported under the joists to single bulb light fixtures. Naturally I want to get this fixed as soon as possible. I've been told to just staple the wire to the bottom of the joists, but I believe this violates NEC 334.15(C). Even if it didn't, it would look awful and possibly cause problems someday when I finish the basement.

So the solution is to drill holes in the joists and rewire. However, there is a hot air duct (uninsulated) that runs parallel to and between the joists that the wiring has to cross.

How should this be handled? Does NM cable have to protected from the potentially hot duct? Should it be run in a conduit? How should I route the cable around the duct?

Thanks

-T

[SQLit]

Stapling the wire up with the proper staples is done every day and is the accepted method of straping NM. As to the bottom of the joists, I would not. Every time I put something on the bottom of a joist I had to move it. Drill a 3/4 inch hole in the center of the joist and run the cable there. NM should never touch something hot. A couple of inches clearance is fine.

[Doug Miller]

Not when it *crosses* the joists, it's not. The NEC _specifically_prohibits_ that practice. Stapling NM that runs parallel to a joist, to the face of that joist, is fine.

And how does he get around the duct?

[rck]

_specifically_prohibits_

I had a house like that. The "duct" was the space between the joists with sheet metal nailed to the bottom of the joists. I hired an electrician to wire from one side to the other. He went all the way around the cellar, said there was no other way to cross the duct.

Bob

[Clark W. Griswold, Jr.]

Must be a recent code change in your area or overkill. Those types of ducts are usually return air so temp is not a concern. There wouldn't have been any problem drilling a hole on each side and running the romex straight through. Caulk the holes when done.

[Doug Miller]

Yes, there was: nail a 1x4 across the joists below the duct, and staple the NM cable to the 1x4. This *does* comply with the NEC.

[Doug Miller]

Correct, that *is* a code violation. However, the code does explicitly permit NM cable to be stapled to running boards that cross the joists. So wherever you need to cross joists, nail a 1x4 to the joists and staple the cable to the

1x4. When the cable runs parallel to a joist, code permits (requires, in fact) that it be fastened to the face of the joist.

A 1x4 across the joists solves *all* of those issues.

[volts500]

While the NEC does allow one to pass a Romex type cable straight through a cold air return as described, a safer method, and also permited by code, would be to install a 1/2" EMT with a connector attached at each end (to serve as bushings) and pass the Romex through the conduit.

[Shake-Hull]

[HA HA Budys Here]

So use PVC

[Chris Lewis]

According to volts500 :

In Canada, the CEC does not permit you to do that. Hint: if the wire ever overheats, it's injecting noxious fumes _directly_ into your air handling. I'm surprised the NEC permits it.

[That said, I _have_ seen it in older homes at least.]

There's an exception for teflon coated wire (certain types of CAT-5 for example). And conduit of course. If you use EMT, you could probably get away with strapping it to the ducting for ground.

[phil-news-nospam]

In sci.engr.electrical.compliance Doug Miller wrote: | In article , "rck" wrote: |>

|>I had a house like that. The "duct" was the space between the joists with |>sheet metal nailed to the bottom of the joists. I hired an electrician to |>wire from one side to the other. He went all the way around the cellar, said |>there was no other way to cross the duct. | | Yes, there was: nail a 1x4 across the joists below the duct, and staple the | NM cable to the 1x4. This *does* comply with the NEC.

On the side of the 1x4, right?

[phil-news-nospam]

In sci.engr.electrical.compliance Chris Lewis wrote: | According to volts500 : |> While the NEC does allow one to pass a Romex type cable straight through a |> cold air return as described, a safer method, and also permited by code, |> would be to install a 1/2" EMT with a connector attached at each end (to |> serve as bushings) and pass the Romex through the conduit. | | In Canada, the CEC does not permit you to do that. Hint: if the wire | ever overheats, it's injecting noxious fumes _directly_ into your air | handling. I'm surprised the NEC permits it. | | [That said, I _have_ seen it in older homes at least.] | | There's an exception for teflon coated wire (certain types of CAT-5 for | example). And conduit of course. If you use EMT, you could probably | get away with strapping it to the ducting for ground.

I wouldn't trust ducting for ground. How about a PVC conduit throught the duct?

[Chris Lewis]

According to :

If the wire overheated or in case of a fire, you'd get toxic fumes in the plenum from the PVC and shortly thereafter, from the romex too. That's why (we) ban bare romex in air plenums in the first place - toxic fumes from plastic sheathing...

Given it's only a short sleeve buried _inside_ the ducting, as long as it had the proper bushings at either end, I doubt that an inspector would care if it was grounded or not.

Better still, use a PVC conduit sleeve to route the wire _under_ the plenum. Just don't go _through_ the plenum. The PVC conduit is sufficient physical protection for bridging the joists, even without the sheet metal on the bottom of the plenum.

[v]

But that should be for reasons of physical protection as from puncture & abrasion, not heat? (Same reason as not to run it under the joists.) Because a "hot" air duct is just "warm", its not hot enought to melt the cable. I'd think a "hot" thing would be like smoke pipe from a conventional furnace.

But it still doesn't get him under the duct. Can he furr and go between the furring strips? Does he really need flush clear to bottom of joist, or could the future (speculative if ever) finish go on the furring or on tracks anyway? What's more important to him, or will he insist on a combo that can't be done?

-v.

[phil-news-nospam]

In sci.engr.electrical.compliance Chris Lewis wrote: | According to : |> | There's an exception for teflon coated wire (certain types of CAT-5 for |> | example). And conduit of course. If you use EMT, you could probably |> | get away with strapping it to the ducting for ground. | |> I wouldn't trust ducting for ground. How about a PVC conduit throught |> the duct? | | If the wire overheated or in case of a fire, you'd get toxic fumes in | the plenum from the PVC and shortly thereafter, from the romex too. | That's why (we) ban bare romex in air plenums in the first place - toxic | fumes from plastic sheathing...

So what non-metallic can be used?

| Given it's only a short sleeve buried _inside_ the ducting, as long as | it had the proper bushings at either end, I doubt that an inspector | would care if it was grounded or not.

But if the code requires it be grounded, then this is not the course I would take.

| Better still, use a PVC conduit sleeve to route the wire _under_ the plenum. | Just don't go _through_ the plenum. The PVC conduit is sufficient physical | protection for bridging the joists, even without the sheet metal on the | bottom of the plenum.

Then you're committing space between any future ceiling finish and the joists, in which case the crossmember could do the job, too.

[Chris Lewis]

Essentially none. Consumer-available non-metallic conduit is pretty well all PVC. Almost all plastics have a noxious fumes issue anyway.

For the most part you'd be at least strapping the bottoms of the joists for a ceiling finish, no matter how you routed the wire, so, you're losing that

3/4" of headroom anyway.

True enough.

[Clark W. Griswold, Jr.]

A little bit of reality goes a long ways in this situation. While I wouldn't run romex for any length inside a plenum, crossing 18" of floor joist is not a major threat to the occupants of the building. If there is enough flame to burn through the plenum and vaporize 18 inches of plastic, the occupants have far worse problems to deal with.

[phil-news-nospam]

In sci.engr.electrical.compliance Chris Lewis wrote: | According to : |> So what non-metallic can be used? | | Essentially none. Consumer-available non-metallic conduit is pretty well | all PVC. Almost all plastics have a noxious fumes issue anyway.

What about wood?

What I mean is a tube made of wood, with a hole drilled down the middle of sufficient size to hold the cable with sufficient heat dissipation. Maybe it would be the same wood as the joists.

[Chris Lewis]

Of course, the incremental risk of 18" worth of PVC isn't very high.

It's not hard to see that hot air entering the return vent could melt the PVC and produce fumes that are 100% captured and ejected into other rooms, adding quite a bit of toxic fume load to prevent occupants from waking up - toxic fumes directly generated from the fire tend to rise away from the flame point, and not go into a return duct (which is on or near the floor).

I'm sure the rule is primarily focused at using the duct for a raceway, but they decided to simplify it as much as possible - it generally doesn't cause that much of a hardship anyway.

It's more of a hardship in buildings which use dropped ceilings as a air plenum. Here, _any_ wire in a dropped ceiling used as a plenum _must_ be in conduit, tho, I believe they now accept teflon (despite the fact that at higher temperatures teflon produces _really_ nasty fumes).