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I am about to install a vent to the outside for the range hood exhaust in the kitchen. In the same bulkhead that will have this vent, there is some electrical wire (some 12/2 NM and some low voltage speaker wire).

Do I have to do anything special to keep the wire away from the vent? I can't imagine it is an issue (it never occurred to me), but my Father-in-law wondered if there was anything in the "code" about this situation.

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Will the conductor be running through a plenum ceiling (e.g, do air returns share the same air as cabling?) Is the vent directly from the range and not dependent on the bulkhead's air space to get it outside? –  Tim Post May 15 '12 at 15:25
    
@Tim Post-The vent is inside a metal duct, it does not use the bulkhead's air space. The bulkhead will have a metal tube running through it and the remox is in the same bulkead but not in the metal duct itself. –  auujay May 15 '12 at 15:30
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2 Answers 2

up vote 8 down vote accepted

There are a few things I can find in the NEC that may apply here. NEC Article 300.8 states that no raceway or cable tray can have elements of any other system besides electrical in it; no plumbing, no fuel gas, no ductwork. This implies that using the vent line itself, or any of its mounting hardware, to support the cable is a no-no; if the wire and the duct go in the same direction for a while, each system needs its own supports connected to the structural members, independent of any other support for any other subsystem in the building.

NEC 300.22 specifically covers wiring within spaces that handle exhaust or environmental air. Basically, a vent line cannot have any electrical wiring installed within it. Not nonmetallic, not MC, not rigid conduit, nothing. So, you can't drill a hole and fish the cable through your range hood vent. This is because the vent line carries exhaust gases and particulate matter that may be flammable (in the case of a range hood, that would mainly be grease particles suspended in the hot air from frying, and also uncombusted natural gas), and having a wire that could, in some imaginable case, cause a spark would be an extremely bad thing to have in a line with flammable gases or particulates.

As an aside, for environmental air (as in your HVAC system), the NEC just states that the cable must be plenum-rated in order to be legal in an open space used for air handling, and must be armored in some way when installed inside a metal air-handling duct.

Additionally, NEC 300.4 covers basic protection of nonmetallic wire against damage. These include things like minimum depth of installation in a wall, properly anchoring electrical wire to structural members etc etc, but also covers protecting the wire from sharp metal edges. Ductwork can have quite a lot of sharp metal edges; extra protection, such as bushings and rigid conduit, are recommended and/or required for any run of cable that passes close enough to ductwork etc for contact to be a concern.

Given that you follow those three articles' guidelines, I cannot find anything saying that Romex can't be in close proximity to ductwork. I would just avoid having the conduit actually contact the ductwork by securing it to the nearest structural member, and I would protect it with plastic or metal rigid conduit if contact with the metal duct is unavoidable at any point.

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IEE wiring regulations BS 7671 section 522.2.1 (i) (ii) (iii) &( iv) to shield from heat, place sufficiently from heat source and select a system with regard to the additional temperature. This would therefore require you to place a protective shield around the cables to protect them from any possible heat emmitted.

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Since the original poster is referring to 12/2NM it is clear that he is in North America. A British Standard does not apply. –  Speedy Petey May 2 at 0:35
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