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Thread: Conduit Seals

  1. #1
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    Conduit Seals

    I am currently doing a new gas station and dispensers. I have the conduit seals in place and the wires pulled. There is one spare conduit into each dispenser. The station will be testing and doing a final to open. In the past, I have, as other contractors have, not poured the conduit seals until all operations were tested and passed. This allowed the electrical contractor to make changes or corrections prior to the final action of pouring the seals. Was there ever an informational note or wording that allowed for this time between operation and testing? I have 2 answers from 2 AHJs. The first is that the seals must be poured prior to any operation. The second answer is, not to pour the seal until all operations have been tested. I fully understand the importance of the conduit seals, many of which have never been poured!

    A second question would be how to seal the spare conduit with no wires pulled?

    Thank you for your time for those who answer these questions.

    BigWyo

  2. #2
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    I'm going to answer your second question first. Cap both ends of the spare conduit with a coupling and a plug. Since there's no wiring inside there's not much chance of igniting anything, even with possible ignitable material inside.

    The first question is a bit more complicated. If fuel has already been introduced to the dispenser system, the first AHJ is correct - you already have your classified locations and must seal accordingly. If no fuel is present, the second AHJ's answer is OK. However in both cases you must have the area classification documented. [Section 500.4(A)]
    "Bob"
    Robert B. Alexander, P.E.
    Answers based on 2014 NEC unless otherwise noted.

  3. #3
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    Thank you, answers both questions.

  4. #4
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    Quote Originally Posted by rbalex View Post
    I'm going to answer your second question first. Cap both ends of the spare conduit with a coupling and a plug. Since there's no wiring inside there's not much chance of igniting anything, even with possible ignitable material inside.

    The first question is a bit more complicated. If fuel has already been introduced to the dispenser system, the first AHJ is correct - you already have your classified locations and must seal accordingly. If no fuel is present, the second AHJ's answer is OK. However in both cases you must have the area classification documented. [Section 500.4(A)]
    Bob,
    The question of sealing empty conduits seems to come up fairly often for me. Certainly they have to be capped to prevent the passage of gases but the question always seems to center around how. We see typically 2 scenarios. The first is there is a seal off in place. Should we pack and pour the empty seal off? Or can one simply put plug in the open end of the seal off? The issue I see with not pouring the seal off is that you then have 3 threaded joints (each end of the seal plus the side plug) which seems to violate the intent of the code requiring the seal to be the first fitting/joint.
    The second scenario is no seal off but simply use a coupling and plug as you indicated. Again there seems to be an issue of violating the first fitting joint rules.
    Your thoughts would be appreciated.

  5. #5
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    Quote Originally Posted by texie View Post
    Bob,
    The question of sealing empty conduits seems to come up fairly often for me. Certainly they have to be capped to prevent the passage of gases but the question always seems to center around how. We see typically 2 scenarios. The first is there is a seal off in place. Should we pack and pour the empty seal off? Or can one simply put plug in the open end of the seal off? The issue I see with not pouring the seal off is that you then have 3 threaded joints (each end of the seal plus the side plug) which seems to violate the intent of the code requiring the seal to be the first fitting/joint.
    The second scenario is no seal off but simply use a coupling and plug as you indicated. Again there seems to be an issue of violating the first fitting joint rules.
    Your thoughts would be appreciated.
    This is a very reasonable question; I'm surprised it hasn't been raised before.

    Section 501.15 IN No.2 outlines the main purposes of sealing: (in reverse order) prevent the passage of flames and minimize (not necessarily prevent) the passage of gases and vapors. A careful review of the rest of Section 501.15 reveals there are two primary types of seals: enclosure and boundary.

    With respect to the OPs question, I submit the "seal" in question can only be a boundary seal.

    Enclosure seals are critically important; they prevent the passage of flames AND there is a clear (and likely) source of ignition.

    Boundary seals are considerably less so. There is a modest potential that syphoning or differential pressure could cause gases or vapors to migrate. However, in the OP's scenario, both are nearly impossible whether the source is Division 1 or 2.
    "Bob"
    Robert B. Alexander, P.E.
    Answers based on 2014 NEC unless otherwise noted.

  6. #6
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    Install couplings and plugs with teflon tape on empty capped conduits if your afraid of transmission through it.

  7. #7
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    There is a modest potential that syphoning or differential pressure could cause gases or vapors to migrate. However, in the OP's scenario, both are nearly impossible whether the source is Division 1 or 2.

    I have noticed several installations where the seal off devices are inside the building. With warmer temps inside, and colder temps outside, do you believe the siphoning effect would be greater?

  8. #8
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    Quote Originally Posted by AKElectrician View Post
    Install couplings and plugs with teflon tape on empty capped conduits if your afraid of transmission through it.
    Teflon tape or other pipe joint compounds do little to improve the seal on our straight thread couplings. I typically use a plumbers pipe cap for this purpose.
    Don, Illinois
    (All code citations are 2017 unless otherwise noted)

  9. #9
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    Quote Originally Posted by don_resqcapt19 View Post
    Teflon tape or other pipe joint compounds do little to improve the seal on our straight thread couplings. I typically use a plumbers pipe cap for this purpose.
    Yep, in my view a plumbing cap would certainly achieve the desired result for spare raceways. You also get to satisfy the first fitting requirement at the boundary. Effective, cheap and swift. This is what is so frustrating with prescriptive codes as common sense and the code collide.
    I would not have an issue in approving a plumbing cap used for this purpose if it was my call. One would think that somebody like Appleton would have submitted a capping product for approval long ago. It just seems so simple but I guess I'm just a simple guy.

  10. #10
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    Quote Originally Posted by don_resqcapt19 View Post
    Teflon tape or other pipe joint compounds do little to improve the seal on our straight thread couplings. I typically use a plumbers pipe cap for this purpose.
    Your not using enough Teflon.

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