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Thread: NM cable inside of cold air return ?

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    NM cable inside of cold air return ?

    2017 NEC 300.22 C Exception, allows nm cable in cold air return perpendicular to the return ?

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    Yes if the return is formed with a stud space.
    Rob

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    All responses based on the 2014 NEC unless otherwise noted

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    Quote Originally Posted by infinity View Post
    Yes if the return is formed with a stud space.
    what about a manufactured floor truss, made of 2 x 4 s ? The HVAC man will close off a section of this space. Thanks

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    Foiled...

    I am no expert in plenum and such. However, I would say it is extremely reckless to allow a conductor to be in potential contact with any material that is conductive without an easy route to ground. I understand the ducts inner space is simply fiberglass, yet the outside is almost always tin, aluminum, or even a foil type of material. It would be impossible to properly bond any foil (w/o the chance of sepertion) thus creating a potential for an unsuspecting worker to become a ground source in the event of a short. Furthermore, the perpensity of condenstion buildup (due to age, improper install, enviroment, etc) acting as a conductor is just to much for a professional to sleep at night.

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    Quote Originally Posted by Stevenfyeager View Post
    what about a manufactured floor truss, made of 2 x 4 s ? The HVAC man will close off a section of this space. Thanks
    Is this in a dwelling? Even if so, the exception does not mention trusses. You cannot form a single closed ceiling cavity where trusses are involved without extra work. If the HVAC guy is closing off the section with metal ductwork, then your cabling is not in an air handling space. Your cabling could not go straight through his ductwork, or through another method of enclosing a single truss run, like it being sheetrocked from the inside.
    Electricians do it until it Hertz!

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    Quote Originally Posted by Ian S. View Post
    I am no expert in plenum and such. However, I would say it is extremely reckless to allow a conductor to be in potential contact with any material that is conductive without an easy route to ground. I understand the ducts inner space is simply fiberglass, yet the outside is almost always tin, aluminum, or even a foil type of material. It would be impossible to properly bond any foil (w/o the chance of sepertion) thus creating a potential for an unsuspecting worker to become a ground source in the event of a short. Furthermore, the perpensity of condenstion buildup (due to age, improper install, enviroment, etc) acting as a conductor is just to much for a professional to sleep at night.
    I believe that the code section that Steven has in the OP is for a plenum made from the void in a stud or ceiling space not in a piece of duct work.
    Rob

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    All responses based on the 2014 NEC unless otherwise noted

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    Quote Originally Posted by Ian S. View Post
    I am no expert in plenum and such. However, I would say it is extremely reckless to allow a conductor to be in potential contact with any material that is conductive without an easy route to ground. I understand the ducts inner space is simply fiberglass, yet the outside is almost always tin, aluminum, or even a foil type of material. It would be impossible to properly bond any foil (w/o the chance of sepertion) thus creating a potential for an unsuspecting worker to become a ground source in the event of a short. Furthermore, the perpensity of condenstion buildup (due to age, improper install, enviroment, etc) acting as a conductor is just to much for a professional to sleep at night.
    Conductor and cable are not the same thing here. NEC approved cables, including NM cable, are a wiring method and can contact non bonded conductive objects. Bonding of said objects is more a design choice than a requirement. Conductors are what is inside the cable assembly.

    Quote Originally Posted by infinity View Post
    I believe that the code section that Steven has in the OP is for a plenum made from the void in a stud or ceiling space not in a piece of duct work.
    But a framing member that is a truss made component would need additional closing to make it a useful duct/plenum. I don't know if that is still acceptable to run cables perpendicular through said plenum or not, as the HVAC guy is typically building all but one side of his duct in that case, where the most commonly seen application here is they have a natural occurring space other than they may have to pan off one side of it, and maybe the smaller "ends".
    I live for today, I'm just a day behind.

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