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Thread: Motor fuel dispensing facilities

  1. #1
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    Motor fuel dispensing facilities

    Article 514.9/A A listed seal shall be provided in each conduit run entering or leaving a dispenser or any cavities or enclosures in direct communications therewith. The sealing fitting shall be the first fitting after the conduit emerges from the earth or concrete.
    Then theres 505.16/A-2 Explosionproof Equipment.
    Conduit seals shall be provided for each conduit entering explosionproof equipment where there are splices etc.
    ? Are we trying to keep the vapor out of the dispenser J box where the splices are ( 505.16 )or we trying to keep the vapor from leaving the containment below the dispenser ( 514.9 ).
    BND

  2. #2
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    Re: Motor fuel dispensing facilities

    Seals must be provided at the classification boundaries to minimize the passage of flammable gasses through the conduit system. Seals are provided at explosionproof enclosures to contain the explosion within the enclosure.
    Don

    [ May 25, 2004, 11:48 AM: Message edited by: don_resqcapt19 ]
    Don, Illinois
    "It is the first responsibility of every citizen to question authority." B Franklin

  3. #3
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    Re: Motor fuel dispensing facilities

    Don
    I understand this, my ? is in a dispenser containment do we seal the gas's leaving the containment with the seal at the point of the conduit entering the containment or do we seal at the point of the entry into the dispenser.
    I feel the latter is better because if an ignition is going to occur this is the *most likely spot.
    If you have a seal on the first fitting leaving the ground on the power end and a seal as the last fitting entering the dispenser J box, I do not see the need for the seal stated in 514.9 .
    If you place the seal as to 514.9 and you have one-two & sometimes three capped elbows before you get to the dispenser J box. This leaves 3 chances for a mistake - a cross threaded cap or a forgotten cap ( witch I have came across more then once ) letting the gas's into the J box.
    Why are we trying to keep the gas's out of a couduit that is sealed at the power end ??
    BND

  4. #4
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    Re: Motor fuel dispensing facilities

    BND,

    I must admit what threw me was that you did a verbatim quote for 514.9(A) but you “free-styled” 505.16(A)(2). I realize the correct reference was 505.16(B)(2) and you may want to re-read it. BTW are you really installing to a Zone rather than Division classification system?

    In any case, using 505.16(B) (2) indicates the enclosures under consideration are Division “explosion-proof” rather than Zone protection type “d” or “e.” In this case only arcing, sparking, or heat producing (ASH) devices are considered unless the conduit is 2” or largerand the enclosure contains terminals, splices, or taps. Even if the seal is required because of one of these conditions and not otherwise exempted through an exception it still can be as much as 18” from the enclosure. The required boundary seal may be as much as 10’ from the boundary. In other words, the enclosure seal and the boundary seal may, in fact, be the same seal.

    BTW in this application gases will get into the conduit – period. (They will get into the explosion-proof enclosures too.) However, if everything is sealed properly there will be no ready source of ignition (no ASH) in the raceway. Conductors properly sized will not generate enough heat to ignite the gases in this application, which are typically Group D (or IIA if you’re using Zones).

    [ May 26, 2004, 03:26 PM: Message edited by: rbalex ]
    "Bob"
    Robert B. Alexander, P.E.
    "I know that you believe you understand what you think the NEC says, but I am not sure you realize that what you read is not what it means." (Corollary to Charlie's Rule)

  5. #5
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    Re: Motor fuel dispensing facilities

    Bob
    Nice name, Same as mine.
    I agree that there is no ready source of ignition in the conduit raceway, but the chance of a hot wire slipping out of a wire nut and arking is a real posibleity.
    I there for beleve the seal would better protect the system if placed at the entry of the dispenser splice box with any unions or caped elbows on the suppy side of the seal.
    I do not understand the code reasoning on this.
    Bob/BND

  6. #6
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    Re: Motor fuel dispensing facilities

    Extracted from 505.16 FPN No.1:
    Seals are provided in conduit and cable systems to minimize the passage of gases and vapors and prevent the passage of flames from one portion of the electrical installation to another through the conduit. …. Unless specifically designed and tested for the purpose, conduit and cable seals are not intended to prevent the passage of liquids, gases, or vapors at a continuous pressure differential across the seal…
    The first part is what Don pointed out in his response. It is important to note that, depending on its location and use, a given seal may only provide for one of the functions.

    The second part of the quote is important for “explosion-proof” equipment – most poured seals are NOT “ … specifically designed and tested … to prevent the passage of liquids, gases, or vapors…”

    As I said in my first response gases WILL get into both the conduit and enclosures. You are correct that a loose connection at a terminal could cause an arc inside the enclosure. That is exactly what an explosion-proof enclosure is designed for - to contain a possible internal explosion – not prevent it. What it was designed to prevent is the propagation of the explosion to the outside. This covers the second function; i.e., “… prevent the passage of flames…”

    Note the first function is to only “… minimize the passage of gases and vapors…” Placing the boundary seal such that no other fitting is between it and the boundary minimizes but does not prevent the migration of ignitable materials.

    Oh yeah, you still didn't say whether you were really using Zones or not

    [ May 27, 2004, 03:35 PM: Message edited by: rbalex ]
    "Bob"
    Robert B. Alexander, P.E.
    "I know that you believe you understand what you think the NEC says, but I am not sure you realize that what you read is not what it means." (Corollary to Charlie's Rule)

  7. #7
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    Re: Motor fuel dispensing facilities

    BND,
    Conduit seals shall be installed within 450 mm (18 in.) from the enclosure. Only explosionproof unions, couplings, reducers, elbows, capped elbows, and conduit bodies similar to L, T, and Cross types that are not larger than the trade size of the conduit shall be permitted between the sealing fitting and the explosionproof enclosure.
    The explosionproof fittings that are used in the 18" or less of conduit between the enclosure and the seal will contain the hot gasses within the conduit system. If the dispenser is more than 18" from the point where the conduit emerges from the ground, 2 seals will be required. If the conduit length will be 18' or less, it is possible to use a single seal.
    Don
    Don, Illinois
    "It is the first responsibility of every citizen to question authority." B Franklin

  8. #8
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    Re: Motor fuel dispensing facilities

    Don,

    You are actually allowed up to 10' from the boundary 505.16(B)(4)

    Bob
    "Bob"
    Robert B. Alexander, P.E.
    "I know that you believe you understand what you think the NEC says, but I am not sure you realize that what you read is not what it means." (Corollary to Charlie's Rule)

  9. #9
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    Re: Motor fuel dispensing facilities

    Bob,
    You are correct as long as there are no threaded fittings between the boundry and the seal. I guess the point that I was trying to make is that the enclosure seal must be within 18" of the enclosure and that in some cases, this may require the use of two seals and in other cases, you can make a code compliant installion with a single seal.
    Don
    Don, Illinois
    "It is the first responsibility of every citizen to question authority." B Franklin

  10. #10
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    Re: Motor fuel dispensing facilities

    I must be somewhat confused. I have always installed a boundary seal and a seal at the 18 inch point as well. I was under the impression that a boundary seal was always required.No?

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