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Thread: sealing for IS conduits

  1. #1
    Join Date
    Feb 2003
    Location
    Illinois
    Posts
    23,807

    sealing for IS conduits

    We have EMT conduits containing intrinsically safe circuits leaving a Class I, Division 1 area and entering a sealed control room with no openings between the room and the classified area other than the raceways. The personnel door opens to an unclassified area. 504.70 kind of says we do not need an explosion proof seals, and it appears that we don't need a "sealing fitting" but can use seal the conduit itself with a product that is identified for the purpose of minimizing the passage of gasses and vapors.

    The language in 504.70 is not completed clear as it references 501.15 and the boundary between a Division 1 location and a non-classifed location requires a seal and sealing compound. That seems to conflict with the last part of 504.70 that says an explosion proof seal is not required.

    Just looking for other opinions. I am leaning towards the idea that as long as we use a product to that is identified for the purposes of minimizing the passage of vapors and gasses in the conduit at the boundary we will be complying with the intent of the code.

    We are looking as using PolyWater FST Duct Sealant for this. The manufacturer's information says the product meets the following code requirement:
    NEC 501.15(B)(2) Conduit Seals, Class 1 Division 2: A conduit seal shall be required in each conduit run leaving a Class 1, Division 2 location... and it shall be designed and installed tominimize the amount of gas or vapor within the portion of the conduit installed in the Division 2 location... Such seals shall not be required to be explosion proof...
    Don, Illinois
    (All code citations are 2017 unless otherwise noted)

  2. #2
    Join Date
    Apr 2004
    Location
    Mission Viejo, CA
    Posts
    5,246
    I have lots of opinions.

    Oddly enough, where only gas-minimizing seals for boundaries are under consideration, I agree with non-explosionproof seals for Division 1/unclassified applications in 504.70 applications but I'm a bit less enthusiastic about 501.15(B)(2) applications. Again, oddly enough, I believe most Division 2/unlcassified boundary seals are unnecessary in the first place; however, where they are necessary, they should be explosionproof. The reason is that IS circuits have no inherent ignition source and gas minimizing is all that is necessary, but IF there is a concern that there is sufficient amounts of gas to "minimize" from a Division 2 location THEN the wiring could still ignite it on the Division 2 side and a non-explosionproof seal is inadequate.

    That said, to my knowledge, there is still no recognized standard for gas minimizing, non-explosionpoof seals. In that case, I would rely on Section 500.8(A)(3).

    BTW 501.15(C)(1), Exception specifically exempts 504.70 seals from general compliance with the overall Section.
    Last edited by rbalex; 09-20-18 at 09:24 PM.
    "Bob"
    Robert B. Alexander, P.E.
    Answers based on 2014 NEC unless otherwise noted.

  3. #3
    Join Date
    Feb 2003
    Location
    Illinois
    Posts
    23,807
    Thanks Bob. This is a retro fit for an existing non-compliant installation.
    Don, Illinois
    (All code citations are 2017 unless otherwise noted)

  4. #4
    Join Date
    Dec 2011
    Location
    Ocala, Florida, USA
    Posts
    2,789
    Quote Originally Posted by don_resqcapt19 View Post
    We have EMT conduits containing intrinsically safe circuits leaving a Class I, Division 1 area and entering a sealed control room with no openings between the room and the classified area other than the raceways. The personnel door opens to an unclassified area. 504.70 kind of says we do not need an explosion proof seals, and it appears that we don't need a "sealing fitting" but can use seal the conduit itself with a product that is identified for the purpose of minimizing the passage of gasses and vapors.

    The language in 504.70 is not completed clear as it references 501.15 and the boundary between a Division 1 location and a non-classifed location requires a seal and sealing compound. That seems to conflict with the last part of 504.70 that says an explosion proof seal is not required.

    Just looking for other opinions. I am leaning towards the idea that as long as we use a product to that is identified for the purposes of minimizing the passage of vapors and gasses in the conduit at the boundary we will be complying with the intent of the code.

    We are looking as using PolyWater FST Duct Sealant for this. The manufacturer's information says the product meets the following code requirement:
    If you are referring to the exception, that is for the seal that is normally required entering enclosures. Not in reference to the seal required when a conduit penetrates the Class 1 div 1 boundary.


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