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Thread: Gas station grounding?

  1. #1
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    Gas station grounding?

    Ok, so at a gas station/c-store, when running underground conduits to dispensers, sumps, tanks, etc, I recall somewhere in chapter 5 of the nec, it states that bonding of these rigid conduits cannot depend on a double locknut. Basically where my pipes come up beside the building into the gutter. So my questions are:

    1.Am I required to use a bonding bushing or bonding locknut?
    2.Does this rule change if the conduit run only has stub ups of rigid, and the rest being pvc?
    3.If a ground bar is set in the exterior gutter, does my egc from the ground bar to the panel inside need to be larger than what is required for the largest load, no matter the number of points out in the feild?
    4.It states that bonding needs to be retained on the circuits back to the service. Does a pvc chase from the exterior gutter to the interior gutter eliminate this since bonding cannot be done on pvc?

    Thank you
    Duke

  2. #2
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    The rule is Section 501.30(A).

    PVC raceways will require bonding jumper's across them. They may be either internal or external as appropriate.
    "Bob"
    Robert B. Alexander, P.E.
    Answers based on 2014 NEC unless otherwise noted.

  3. #3
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    Bob, would you mind elaborating ? This has always been a bit perplexing to me.
    In reading 501.30 and 514.16 it would appear if I have a metallic conduit system from my pumps back to my service equipment I would need bonding means other than double-locknut.
    Would this be regardless of a wire type equipment ground being installed ?\
    If I take advantage of 514.8 Exception 2 and use PVC in my underground run and obviously have an equipment grounding conductor, what purpose does the 501.30 bonding serve going back to the service point ?
    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.

  4. #4
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    How long has 501.30(A) or at least it's present wording/requirement existed?

    Back in the early 90's we redone a lot of gas stations as laws required the owners to replace their old tanks and piping systems. We always ran RMC/IMC all the way but never put any bonding jumpers between all the raceways. We had at least one inspector that was pretty likely to catch that detail as well if it was there back then.

    I don't see a good reason to bond them if it transitions to PVC underground though??

  5. #5
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    Where to begin?

    I guess Article 510 (one of the most overlooked) is as good as any. It notes in Section 510.2:

    510.2 General. The general rules of this Code and the provisions of Articles 500 through 504 shall apply to electrical wiring and equipment in occupancies within the scope of Articles 511 through 517, except as such rules are modified in Articles 511 through 517. Where unusual conditions exist in a specific occupancy, the authority having jurisdiction shall judge with respect to the application of specific rules.
    [rbalex note: underlines‚Äč mine]
    In other words, you won't find all you need to know about electrical installations in gas stations in Article 514 alone.

    Section 501.30 and it's direct predecessors have been around longer than I've been in the business; i.e., the prohibition against double-locknut and locknut/bushing bonding solely has also been around longer than I've been in the business. The primary perceived problem with double-locknut and locknut/bushing bonding in Section 501.30 is you can't achieve the number of wrenchtight thread contacts required by various parts of Section 500.8 for each device component of the bond.

    In my early days of hazardous location design, I realized that bonding, not grounding, was the major wiring method safety issue. In fact, in the 2002 cycle, one of my (rejected) Proposals was to rename Article 250 Bonding and Grounding. At the time, 2002 and earlier, it was only titled "Grounding." In 2005 cycle, CMP 5 recognized I was right, I just got the order wrong (Grounding and Bonding).

    The current state of affairs is the CMP 5's reluctance to correctly call most electrical grounding conductors (EGC) what they actually are; i.e., electrical bonding conductors (EBC). Properly connected metal raceways are quite effective as EGCs (or EBCs).

    CMP 14 has always had a paranoia about potential arcing across threads in a classified location where circulating currents may be present on the EGCs. However, they seem to be happy where threaded (tapered or not) metal raceway are effectively the EGCs. [Sections 501.10(A)(1)(a) and (B)(1)(1)] I'm not sure how they are now comfortable with threadless fittings for metal raceways in Class I, Division 2 [2017 NEC, Section 501.10(B)(1)(1)]. It does appear a couple of the hyper-bonding members have disappeared.
    Last edited by rbalex; 01-26-17 at 04:56 PM. Reason: Corrected ECS <ashamed> and EGG <VERY ashamed> to EGC
    "Bob"
    Robert B. Alexander, P.E.
    Answers based on 2014 NEC unless otherwise noted.

  6. #6
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    Due to my thick head, I'm afraid the answer might still elude me. If I read your answer correctly, I would still need to address the double locknut situation all the way back to the service (or point of neutral bond) regardless of the introduction of the PVC conduit ?
    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.

  7. #7
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    Quote Originally Posted by augie47 View Post
    Due to my thick head, I'm afraid the answer might still elude me. If I read your answer correctly, I would still need to address the double locknut situation all the way back to the service (or point of neutral bond) regardless of the introduction of the PVC conduit ?
    Yes. Although I'm not quite sure what the prohibition's purpose is if the bonding connection is outside the classified location. To be honest I don't believe any other of the CMP 14 members did either at the time I could actually discuss it with them at a personal level. My best understanding is they were also attempting to get the absolute lowest impedance of the effective ground-fault current path. Of course, depending on the actual installation, a locknut may not actually be in the effective ground fault current path but CMP14 didn't want to confuse the issue with an extraneous exception.
    "Bob"
    Robert B. Alexander, P.E.
    Answers based on 2014 NEC unless otherwise noted.

  8. #8
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    Perhaps that's why it is so often overlooked.
    In this area I'd say it is addressed on 10% of the installs.
    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.

  9. #9
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    I do agree with the bonding bushing in a way, on a full rigid job out to the dispensers and tub/tanks. It would be two ways for a ground fault path in a classified location. Not a terrible idea. What I don't understand fully understand is how bonding a 10' stub out from the building is doing anything. I certainly could be missing something though.

    The bonding back to the service with pvc introduced in any of the raceways seems a bit extreme to me, but on the other hand, they most likely aren't speaking of gas station exactly. It still pertains to it though.

    I haven't checked in a while, but I remember Wayne and/or Gilbaro requiring a rmc raceway for warranty claims. Seems odd they could do that though.

    And the ground sizing question would be in the instance of bringing all of your dispenser grounds back to the gutter, then to the panel in fewer conduits than out in the field. Instead of bringing multiple grounds through the same raceway.

  10. #10
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    Quote Originally Posted by Dr Duke View Post
    I do agree with the bonding bushing in a way, on a full rigid job out to the dispensers and tub/tanks. It would be two ways for a ground fault path in a classified location. Not a terrible idea. What I don't understand fully understand is how bonding a 10' stub out from the building is doing anything. I certainly could be missing something though.

    The bonding back to the service with pvc introduced in any of the raceways seems a bit extreme to me, but on the other hand, they most likely aren't speaking of gas station exactly. It still pertains to it though.

    I haven't checked in a while, but I remember Wayne and/or Gilbaro requiring a rmc raceway for warranty claims. Seems odd they could do that though.

    And the ground sizing question would be in the instance of bringing all of your dispenser grounds back to the gutter, then to the panel in fewer conduits than out in the field. Instead of bringing multiple grounds through the same raceway.
    Start by reading Section 250.4 and understanding the implications of Subsections 250.4(A)(3),(4) and (5) and 250.4(B)(2),(3) and (4). Even small, usually inconsequential, "(n)ormally non-current-carrying electrically conductive materials ..." can become energized and need an effective ground-fault current path or, in the case of ungrounded systems, simply a fault path. Whether those small, usually inconsequential, normally non-current-carrying electrically conductive materials are "likely to become energized" may be a subject of some debate but Subsections 250.4(A)(3) and 250.4(B)(2) would strongly suggest that simply enclosing electrical conductors is a sufficient concern and it doesn't even matter whether it's in a classified location or not; it's simply a general rule.

    When not using the raceway system as the EGC, EGC's are sized just as they would otherwise be in Section 250.122.

    NOTE: I don't generally make a big deal about this because I usually understand what is intended; but, when we are trying to be a bit more technically accurate, there is no such thing as a "ground" conductor. There are only "grounded" or "grounding" conductors.
    "Bob"
    Robert B. Alexander, P.E.
    Answers based on 2014 NEC unless otherwise noted.

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