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Thread: Sealing Around Hole Going from Class 1 Div 2 into Unclassified, Pressurized Cabin

  1. #11
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    Quote Originally Posted by rbalex View Post
    HVAC can be an integral part of an NFPA 496 system. A Type Z system isn’t very difficult to achieve with HVAC. It still needs to be an NFPA 496 system though.
    I would think that a critical part of that 496 system,*which might be hard to achieve in the area of the cab, is a source of clean air.
    If the cab is completely surrounded by a Division 1 or 2 area, is Division 2 air an acceptable pressurization source? I would hope not, but I do not have a copy of the standard to refer to.

  2. #12
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    Quote Originally Posted by MAC702 View Post
    A/C is usually a recirculating system that doesn't "pressurize" the conditioned space. Could you clarify this?
    Yes, so it is a "somewhat pressurized" cabin, in that it's only 2/10'' water column pressure, which comes from the air intake system of the AC (so it's not just recirculating inside air). (There is a higher pressure inside the cabin than there is outside of it.)

    Quote Originally Posted by rbalex View Post
    Basically, threaded conduit connections permit the transmission of gasses through the bulkhead.
    That kinda puts us back at square 1 then with the unclassified grommet & caulking then?

    I do remember reading that in the 2017 NEC 501.15(A)(1) - Class I Div. I
    - Revision to no longer allow conduit bodies (only cabbed elbows) between seal fitting and explosionproof enclosure.
    - Increased volume in raceway system created by use of conduit bodies was hazard cited.

    Quote Originally Posted by GoldDigger View Post
    If the cab is completely surrounded by a Division 1 or 2 area, is Division 2 air an acceptable pressurization source? I would hope not, but I do not have a copy of the standard to refer to.
    The air intake is on the back side of the cabin, and the edge of the C1D2 zone only extends into the front face of the cabin (right where we're trying to mount this intercom unit).

  3. #13
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    Quote Originally Posted by GoldDigger View Post
    I would think that a critical part of that 496 system,*which might be hard to achieve in the area of the cab, is a source of clean air.
    If the cab is completely surrounded by a Division 1 or 2 area, is Division 2 air an acceptable pressurization source? I would hope not, but I do not have a copy of the standard to refer to.
    A clean air source is usually only a matter of ducting.
    "Bob"
    Robert B. Alexander, P.E.
    Answers based on 2014 NEC unless otherwise noted.

  4. #14
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    Quote Originally Posted by GoldDigger View Post
    I would think that a critical part of that 496 system,*which might be hard to achieve in the area of the cab, is a source of clean air.
    If the cab is completely surrounded by a Division 1 or 2 area, is Division 2 air an acceptable pressurization source? I would hope not, but I do not have a copy of the standard to refer to.
    I think usually they just move the intake high enough that it is above the classified area. it is not like the classified area extends indefinitely above ground level.
    Bob

  5. #15
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    Quote Originally Posted by DangerZoneNick View Post
    ...

    That kinda puts us back at square 1 then with the unclassified grommet & caulking then?

    ...
    This may blow your mind but, if you had adequate pressurization, you could make the opening large enough that vibrations wouldn't cause contact with the conduit and nothing is needed to fill the void.


    Quote Originally Posted by DangerZoneNick View Post
    ...

    I do remember reading that in the 2017 NEC 501.15(A)(1) - Class I Div. I
    - Revision to no longer allow conduit bodies (only cabbed elbows) between seal fitting and explosionproof enclosure.
    - Increased volume in raceway system created by use of conduit bodies was hazard cited.

    ...
    That applies only to the enclosure seal - not the boundary seal. No threads have been allowed between the seal and the boundary longer than I've been in the business (nearly 50 years).
    "Bob"
    Robert B. Alexander, P.E.
    Answers based on 2014 NEC unless otherwise noted.

  6. #16
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    Quote Originally Posted by DangerZoneNick View Post
    Good afternoon guys,

    I have this intercom unit that has 2 lines coming out the bottom (or possibly just one if we can fit the audio and power cables through the one hole) that is positioned in a Class 1 Division 2 hazardous zone on the outside of the cabin of a drilling rig.

    We have ordered some conduit sealing fittings, but the problem arises with the actual process of passing the conduit line through the wall. It's a 3/4''NPT threaded pipe, so we will have to cut a hole in the wall large enough to pass the conduit through, but in order to prevent the gasses from also entering through the wall, we're not sure exactly what to use. My initial thought was to just use a rubber grommet, but others are saying that we also need additional caulking around the ingress hole. However, I can't seem to find any sort of caulking or sealant that's rated for Class 1 Div 2 (besides the stuff that goes inside of the conduit sealing itself).

    What are your thoughts?

    Attachment 18685Attachment 18686Attachment 18687Attachment 18688
    Also sorry my pictures aren't the greatest, and I can't figure out how to rotate them vertically)

    Thanks!
    https://www.roxtec.com/us/products/s...xtec-spm-seal/

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