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Thread: Hazardous Lacation Seal Off

  1. #1
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    Hazardous Lacation Seal Off

    I will describe as best as I can . Imagine a trench about 100 ft long. I ran one 4" and two 1" inch PVC conduits on this trench. I stubbed up on both ends where I needed with rigid pipe. I used rigid elbows then made some nipples to get up to where I needed . This is a class one division one location. I had it all ready for inspection. Then got corrected. Inspector said that there should be no couplings (rigid coupling from nipple I made) going up before seal off. That it should be one whole piece . Then sent me this in a email.....

    VIOLATION TYPE: VIOLATION CODE SECTION: CODE Seal off fittings Location 93.501.14 (A) (4) NECIn hazardous locations where seal off fittings are required to be installed, there shall be no other fittings between the seal off fitting and the boundary of the hazardous area.

    We have done that type of install many times and passed . Inspector may be right but I'm a little confused . My 90 manufactured elbow had a 9" nipple on to reach above grade then that's where seal off would go. Anyway I didn't argue at all and changed them all to one complete sweeping elbow to seal off . What am I not understanding. Thank you guys .

  2. #2
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    I'm assuming they were citing Section 501.15(A)(4) rather than 501.14(A)(4).

    Unless it is an Article 514 (Fuel Dispensing) application, below grade is usually Unclassified and grade would be the Division I/Unclassified boundary. If that be the case, and the 9" nipple crosses rather than terminates in a coupling at the boundary, the description of your common practice should be acceptable.
    "Bob"
    Robert B. Alexander, P.E.
    Answers based on 2014 NEC unless otherwise noted.

  3. #3
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    Furthermore you should be able to make this seal within 10' of the boundary (grade).

    I don't understand how the screwed fitting of a conduit nipple introduces additional risk, maybe someone can help clarify?

  4. #4
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    Quote Originally Posted by MRKN View Post
    Furthermore you should be able to make this seal within 10' of the boundary (grade).
    ...
    Quite right.

    Quote Originally Posted by MRKN View Post
    I don't understand how the screwed fitting of a conduit nipple introduces additional risk, maybe someone can help clarify?
    Remember, for the "typical" case, below grade is unclassified. Where threaded interfaces are at the boundary, they provide a pathway for the Division 1 (and possibly 2 if that were the case) volatiles to be introduced into the unclassified location.
    "Bob"
    Robert B. Alexander, P.E.
    Answers based on 2014 NEC unless otherwise noted.

  5. #5
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    I'm confused (of course). If he's in a classified area and below grade is unclassified, would a seal off not be needed as the 1st fitting ?

    Apparently, like is inspector, I am misreading 501.15(A)(4)
    At my age, I'm accustomed to restaurants asking me to pay in advance, but now my bank has started sending me their calendar one month at a time.

  6. #6
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    Quote Originally Posted by augie47 View Post
    I'm confused (of course). If he's in a classified area and below grade is unclassified, would a seal off not be needed as the 1st fitting ?

    Apparently, like is inspector, I am misreading 501.15(A)(4)
    It often happens that the Code doesn't tell the whole story in a single Section. A "boundary" may be created by by various conditions: grade, an impenetrable barrier, often the surface of an imaginary "envelope", etc.

    In the OP case, grade is the boundary. Section 501.15(C)(1) requires the seal to be accessible so it can't be underground (without dancing around all the speculative ways it could be made accessible). Section 501.15(A)(4) permits the seal to be on either side and within 10' of the boundary but prohibits a laundry list of essentially threaded equipment between the boundary and the seal. As I mentioned above, a coupling between the seal the boundary provides a pathway between the various classifications.
    "Bob"
    Robert B. Alexander, P.E.
    Answers based on 2014 NEC unless otherwise noted.

  7. #7
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    Quote Originally Posted by rbalex View Post
    Remember, for the "typical" case, below grade is unclassified. Where threaded interfaces are at the boundary, they provide a pathway for the Division 1 (and possibly 2 if that were the case) volatiles to be introduced into the unclassified location.


    I see now, screwed fitting/threaded interface would fall under the definition of union/fitting/coupling in 501.15(A)(4). Thanks.

    Could you argue the orientation in which the seal is installed would still introduce a threaded interface for gases to be introduced into an unclassified area if the liberty was taken to install the seal on the 10' inside of the boundary?


  8. #8
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    Quote Originally Posted by MRKN View Post


    I see now, screwed fitting/threaded interface would fall under the definition of union/fitting/coupling in 501.15(A)(4). Thanks.

    Could you argue the orientation in which the seal is installed would still introduce a threaded interface for gases to be introduced into an unclassified area if the liberty was taken to install the seal on the 10' inside of the boundary?


    Send me an envelope with $250 cash in it and I will make you a 10ft length of conduit with a 90 in the middle of the run so you can put your seal off before the next coupling or other fitting.
    85deg. an Sunny today.

  9. #9
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    From what I can tell as long as the threaded fitting is below grade and therefore in an unclassified zone it's acceptable. The problem is when it's above grade and therefore in a hazardous area. So while I appreciate the humor in your comment I don't think it's quite accurate.

  10. #10
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    Quote Originally Posted by rbalex View Post
    It often happens that the Code doesn't tell the whole story in a single Section. A "boundary" may be created by by various conditions: grade, an impenetrable barrier, often the surface of an imaginary "envelope", etc.

    In the OP case, grade is the boundary. Section 501.15(C)(1) requires the seal to be accessible so it can't be underground (without dancing around all the speculative ways it could be made accessible). Section 501.15(A)(4) permits the seal to be on either side and within 10' of the boundary but prohibits a laundry list of essentially threaded equipment between the boundary and the seal. As I mentioned above, a coupling between the seal the boundary provides a pathway between the various classifications.
    seals are threaded. if you have one on the D1 side how come no hazardous gases can get into the conduit leading to the non-hazardous side?
    Bob

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