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Thread: Exhaust Hood connection

  1. #1
    Join Date
    Sep 2010
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    131

    Exhaust Hood connection

    I am wiring up an exhaust hood and the 14x14 duct is covering the normal knockout to this location. Can liquidtite or any other raceway be installed in this duct to feed the hood? or do I have to come out of the roof and run liquidtite to the hood from the outside?

    The hood is round (i'm sure you have all seen them before) and are a pain to get into from the outside.

    Please help and Thank you.

  2. #2
    Join Date
    Sep 2010
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    131
    I apologize I meant to say the exhaust fan from the hood.

  3. #3
    Join Date
    Sep 2010
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    131
    I am having a horrible day explaining things. This is all in relation to feeding the exhaust fan that is located on the roof. The hood really has nothing to do with it. The exhaust fan connection is located within the 14x14 ductwork. So I think we make the connection to the exterior of the exhaust fan. Is there any code requirements stopping me from running it in the ductwork? This is exhausting the cooktop hood.

  4. #4
    Join Date
    Oct 2007
    Location
    AZ
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    2,707
    I wouldn't even consider doing it.

    As far as NEC? I have no idea. They allow you to do lots of bad/crazy stuff
    Disclaimer: The opinions expressed here are solely mine and do not necessarily reflect the views of other members of this community. Do not misunderstand them as an encouragement to violate the NEC. Also, don't forget that the NEC is not necessarily the AHJ.

  5. #5
    Join Date
    Dec 2008
    Location
    Raleigh NC
    Posts
    268
    The round exhaust hoods at restaurants where the top unlatches and is on a hinge? I've usually just penetrated the roof with emt through a witches hat, and then brought carlon over to the JB.

    On the make-up air units, there is sometimes room in the curb to come up right next to the duct, but usually not in the exhaust units.

  6. #6
    Join Date
    Oct 2006
    Posts
    3,254
    The NEC doesn't directly say you cant do it but installation instructions on the unit are going to send you to the mechanical code and there you will find it is not allowed.

  7. #7
    Join Date
    Feb 2003
    Location
    NE Arkansas
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    2,222
    A look at NFPA 96 -which covers such systems- ought to make clear that you can't do that - even though the fans are conveniently set up to allow you to do just that.

    The NEC specifically bans any wiring from inside the hood. I would consider that to include the ducting, right up to the fan blades.

    You have a few issues to consider. First off, sanitary requirements are harder to meet when there are additional places to trap grease. Secondly, the hood cleaner -if he's conscientous- will want to actually remove the fan and set it aside as he does his thing.

    (I know, the fans often are hinged for cleaning, but I've seen quite a few where the cleaner removed the hinges).

  8. #8
    Join Date
    May 2005
    Location
    Richmond, Virginia
    Posts
    21,838
    I've gotten roof fans power by hole-sawing through the side of the curb from the roof, lowering a pullstring or fishtape through the hole, and hoisting up the end of MC with an angle connector on it.

    Then, I screw a rectangular WP box with a threaded 1/2" KO on the back, and either put a disco switch there, or make joints with a blank plate, and run the wires in liquid-tight to the fan or a disco.

    Added: I also apply a ring of silicone to the back of the box for rain-tightness.
    Code references based on 2005 NEC
    Larry B. Fine
    Master Electrician
    Electrical Contractor
    Richmond, VA

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