Updating Home Wiring

May 3, 2005 11:05 PM

Can wiring (Romex - 12/2) be run through (perpendicular to) a cold air return?

If not, what are my options? I'd prefer to not have to use conduit if at all possible, however I'd like to do it right, so whatever is necessary I'll do. Additional information that may be helpful: built in 1928, wiring is currently all knob-and-tube style (though already updated to 100-amp service with circuit breaker box), located in Rockford, IL.

posted by shawnmk to home & garden (5 comments total)

From the the electrical wiring FAQ, page 2:

Many electrical codes do not permit the routing of wire through furnace ducts, including cold air return plenums constructed by metal sheeting enclosing joist spaces. The reason for this is that if there's a fire, the ducting will spread toxic gasses from burning insulation very rapidly through the building. Teflon insulated wire is permitted in plenums in many areas.

More information about what you are trying to do would be helpful. Just add an outlet somewhere?
posted by Chuckles at 12:06 AM on May 4, 2005

Doh! I should have read the title... You will have to do quite a bit of research before you try a project like updating the whole house. The electrical wiring FAQ is a great place to start, but don't stop there.

Someone else must have direct experience at this...
posted by Chuckles at 12:33 AM on May 4, 2005

You should not ever run through the ductwork. You risk electrifying all of the ductwork (and registers) if the romex ever frays.
I am sure it is against code, I know it is in Chicago. You should go around it.
posted by lee at 5:42 PM on May 4, 2005

If you are set on wiring through the ductwork, some places may make exceptions if you run VERY EXPENSIVE plenum-rated cable. I know in the case of network cable the cost was usually 5 - 10 times the FT-1 rated (PVC, toxic at above 50 deg C or so) cable per foot. As it's electrical cable you'll probably have to ensure it is BX-armored for an application like this, at least tripling your cost again... You're probably up to $3 a foot already.

If it is BX-armored you can at feel safe that it won't chafe open the insulation and short out to the duct-work (the BX-armour is terminated to ground and will trip the breaker before that's a problem).

I recall we were required to do this when wiring up a local college -- the above-drop-ceiling area was used as an air-return.

But, I am NOT an electrician.
posted by shepd at 10:31 AM on May 5, 2005

Just to clarify, it is not metal ductwork, per se. As Chuckles mentioned, it is sheetmetal covering the space between two floor joists. I would be drilling through the wooden 2x12 joists which make up the sides of the return air duct.

I think it'll work to turn the area beneath the duct into a closet, so I'll just plan on running the wire through a small section of conduit where it needs to go below the joists.
posted by shawnmk at 11:13 PM on May 5, 2005