I am running a new wire from the electrical panel to my flat panel tv. problem is there is a cold air return in the way. I am a bit worried running it across the bottom, in the basement, of the cold air return, seems like it would be a fire hazard. should I run it through conduit? if so what kind? flexible? metal? rubber? thanks.
The return air duct is always gonna be the same temp as the house within a few deg. I don't see a problem being against the outside of it. Additional I would just run the romex then (White or yellow rubber sleeve) If you ever want to put up a ceiling down there you just put up ferring strips (1x2s) to allow space.
I have a cold air return in my basement that is bordered by two floor joists (on the sides), the wooden subfloor on the top, and sheet metal on the bottom. Numerous romex electrical lines run through it (the wood floor joists have been drilled and the wires run through it). This is very common and safe. No conduit is required.
I agree with the above two answers with one exception: If the return duct is metal I would make sure it is grounded. EDIT: you ground the duct by attaching a bare copper wire to it with a screw and run the bare copper wie to a ground such as a metal water pipe or the service panel. If you use a water pipe buy a clamp designed for this purpose. When you run the romex across the duct make sure to use an insulated staple on the joist on each side and every 4 feet from the service panel and within a foot or so from the outlet box.
If possible run the new wire above the duct. There's always a possibility that the duct may need be removed for repair or replacement. As previously stated you may want to put a light or outlet in; therefore leave enough slack or form a loop so you'll have enough wire to do it later.
