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Thread: 501.15(B)(2) - conduit Boundary Seals: Class I, Division 2 to Unclassified areas

  1. #11
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    Sorry, I was just yanking your chain. Attached is the Proposal that got this problem started in the 2005 NEC. Note Donnie Cook, the Chairman of CMP14 at the time, was concerned that there was no identification of a suitable sealing method.

    2005 ROP P14-34.pdf

    Explanation of Negative:
    COOK: I agree with the first sentence of the submitter's substantiation. I do not agree with the proposed text or the referenced text in
    504.70. The text provides no guidance for installers or inspectors as to what is an acceptable seal. Almost anything would have some
    affect on gas or vapor passing through a conduit; rags, caulk, silicone, wax, plumbers putty, a four bend saddle in the conduit with water
    collected like a plumbing trap, bubble gum, but which ones would "minimize" the passage of the gases? If paper towels are used, do you
    need one or two of them to minimize the passage of gas? If caulk or silicone is used, would the installer or inspector know the affect of
    the material on conductor insulation? Would conduits that depend on a single compression seal to prevent flammable liquids from
    entering the conduit system be safe with bubble gum as a boundary seal (see 501.5(B)(2), Exception No. 4)?
    I believe the proposed text will result in inconsistent installations, inconsistent inspections and certainly inconsistent interpretations
    of the requirement. Until clear text is proposed, that is enforceable; I will not support this change. I agree that a Division 2 to
    unclassified location, boundary seal does not need to be explosionproof, but I am not aware of a seal that is manufactured and listed to
    minimize the passage of gas or vapor that is not also explosionproof.
    To this day, his concerns have not been addressed directly by CMP14 or any NRTL.


    My concern is that, while I agree that most Division 2/Unclassified seals are unnecessary - some still are. Usually, for Division 2, there should be no gases to migrate in the first place.

    The problem is, if preventing the migration of gases is the actual purpose, then, unlike the Section 504.70 cited for intrinsically safe systems, those gases (if present) still could be ignited by Division 2 wiring methods. SO - if seal is needed at all, it should be explosionproof.

    It would have been better to have stated no boundary seals were needed except in a few cases. Two examples:

    1. Where grade is the boundary and the gases/vapors involved are heavier than air.
    2. Where there is a reasonable expectation that the Division 2 location has a positive pressure with respect to the Unclassified location AND there is reason to believe the gases would collect in the unclassified location.

    In either case the seal should be explosionproof.

    BTW the same problem actually exists in Section 504.70 since circulating ground currents could still ignite the subject gases. (Hence the emphasis of Sections 504.50 and 60)
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    "Bob"
    Robert B. Alexander, P.E.
    Answers based on 2014 NEC unless otherwise noted.

  2. #12
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    Quote Originally Posted by rbalex View Post
    Sorry, I was just yanking your chain. Attached is the Proposal that got this problem started in the 2005 NEC. Note Donnie Cook, the Chairman of CMP14 at the time, was concerned that there was no identification of a suitable sealing method.

    2005 ROP P14-34.pdf



    To this day, his concerns have not been addressed directly by CMP14 or any NRTL.


    My concern is that, while I agree that most Division 2/Unclassified seals are unnecessary - some still are. Usually, for Division 2, there should be no gases to migrate in the first place.

    The problem is, if preventing the migration of gases is the actual purpose, then, unlike the Section 504.70 cited for intrinsically safe systems, those gases (if present) still could be ignited by Division 2 wiring methods. SO - if seal is needed at all, it should be explosionproof.

    It would have been better to have stated no boundary seals were needed except in a few cases. Two examples:

    1. Where grade is the boundary and the gases/vapors involved are heavier than air.
    2. Where there is a reasonable expectation that the Division 2 location has a positive pressure with respect to the Unclassified location AND there is reason to believe the gases would collect in the unclassified location.

    In either case the seal should be explosionproof.

    BTW the same problem actually exists in Section 504.70 since circulating ground currents could still ignite the subject gases. (Hence the emphasis of Sections 504.50 and 60)
    Excellent Bob.
    This provides justification to simply install an explosion proof seal - when/where required.
    This may sound ridiculous, but what about drilling a small hole (say,.5" dia?) in the conduit, inject it with foam (i.e. Polywater), then pressurize the conduit to see if it meets the criteria of "minimizing the passage of gases permitted"...
    Of course you'd need to 'patch' the hole with some sort of field welded metallic plug.

  3. #13
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    Quote Originally Posted by Dale001289 View Post
    field welded metallic plug.
    With wire in it?
    The more they overthink the plumbing, the easier it is to stop up the drain

  4. #14
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    Quote Originally Posted by dkidd View Post
    With wire in it?

    Why couldn't you drill the hole prior to pulling cable - at the approximate boundary location?

  5. #15
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    See Section 300.18(B). It may not be directly applicable, but it more or less speaks to your suggestion.
    "Bob"
    Robert B. Alexander, P.E.
    Answers based on 2014 NEC unless otherwise noted.

  6. #16
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    Quote Originally Posted by rbalex View Post
    See Section 300.18(B). It may not be directly applicable, but it more or less speaks to your suggestion.

    I don't think this Article is necessarily a show-stopper to my idea, however, I don't believe the client would approve of welding conduit where cable was already installed, even if the surrounding foam protects the cable. What might be acceptable is a RGS plug - of course, this plug doesn't yet exist, plus you'd have to drill and tap a concave surface. Some R&D would be required.

    So basically, I'm right back where I started: using the EYS conduit seal at the boundary.

  7. #17
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    The problem is that welding will damage the internal galvanizing and any manner of repair is questionable.

    Getting back to the original question at hand, except in those cases where an explosionproof seal is actually necessary as I outlined earlier, you can use any fitting you want and shove duct seal it if you wanted to.

    Edit add: I guess technically you couldn't use an actual explosionproof seal fitting since they are listed to be used with a specific sealing compound.
    "Bob"
    Robert B. Alexander, P.E.
    Answers based on 2014 NEC unless otherwise noted.

  8. #18
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    Quote Originally Posted by rbalex View Post
    The problem is that welding will damage the internal galvanizing and any manner of repair is questionable.

    Getting back to the original question at hand, except in those cases where an explosionproof seal is actually necessary as I outlined earlier, you can use any fitting you want and shove duct seal it if you wanted to.

    Edit add: I guess technically you couldn't use an actual explosionproof seal fitting since they are listed to be used with a specific sealing compound.
    Suppose I were to install a C-H "C" condulet at the Div 2 boundary and fill it with Polywater foam - wouldn't that violate the following excerpt from 501.15(B)(2):
    "The conduit run between the conduit seal and the point at which the conduit leaves the Division 2 location, shall contain no union, coupling, box or other fitting...?"

  9. #19
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    Quote Originally Posted by Dale001289 View Post
    Suppose I were to install a C-H "C" condulet at the Div 2 boundary and fill it with Polywater foam - wouldn't that violate the following excerpt from 501.15(B)(2):
    "The conduit run between the conduit seal and the point at which the conduit leaves the Division 2 location, shall contain no union, coupling, box or other fitting...?"
    If you have established that the conduit body/foam is the seal, I don't see a problem - especially if you didn't need it in the first place.
    "Bob"
    Robert B. Alexander, P.E.
    Answers based on 2014 NEC unless otherwise noted.

  10. #20
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    Bob if you're ok with it then I am ok with it - thanks


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