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Thread: Bonding screw in the distribution (sub) Panel

  1. #51
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    Quote Originally Posted by FionaZuppa View Post
    yikes.
    am i not asking correctly.

    surely any ~6+mA that loops from any CCC (from gfi) to the egc will trip the gfi, yes? the egc creates a path around the gfi.

    so what i am asking is, if thats the case then whats the hazard in connecting the egc to the N bar in sub panel ??

    the gfi is the tiny box, the small squigly is the gfi ocpd pigtail, etc. light blue box is the sub panel with a 3 wire (L-N-L) feeder.


    and just for clarity, doesnt gfi kinda monitor the egc, because any wrongful leakage between CCC's the gfi could care less about, its only that fault current that goes outside of those CCC's, which is either earth (technically egc) or the egc wire itself.
    "Kinda" is the key. Any GFCI protected conductor that contacts something that gives you an alternate path will trip the GFCI when current leaking the intended circuit is over 4-6 mA. Does not change the voltage drop on the neutral - which equates to voltage rise on the EGC to true ground if you use the feeder neutral for connecting to your EGC's, and such neutral to EGC bonding does not change the balance of load side of any GFCI's connected to that feeder, they work just like GFCI breakers installed in a service panel do neutral and EGC are bonded together at service panels. This all going back to my comment that any hazards are the same as a result of using the neutral for EGC beyond the service equipment/first disconnect of separately derived system whether you install GFCI's or not. Is also the same reason a rise in voltage on EGC results in shocks/electrocutions at docks and marinas even though GFCI's were on the circuits involved. The rise is not because of a fault in the branch circuit - it is simply voltage drop on a normally current carrying grounded conductor that gets bonded to EGC's.

  2. #52
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    Quote Originally Posted by kwired View Post
    The rise is not because of a fault in the branch circuit - it is simply voltage drop on a normally current carrying grounded conductor that gets bonded to EGC's.
    good point. so then gfi ocpd on both sides??

    if the load only uses L-L how much voltage would there be on the egc ?

  3. #53
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    Quote Originally Posted by HI9869 View Post
    I am a home inspector . . . I have asked building inspector locally and electricians locally and I can not seem to get a clear understanding. So, hopefully someone can lay this out in laymen terms so I can be a better inspector. Thank you in advance.
    Just a reminder from the OP.

    Quote Originally Posted by FionaZuppa View Post
    so then gfi ocpd on both sides??
    Your returning again and again to ground fault detection is way out in the weeds from the OP asked question.
    Another Al in Minnesota

  4. #54
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    Quote Originally Posted by al hildenbrand View Post
    Your returning again and again to ground fault detection is way out in the weeds from the OP asked question.
    My thought as well, has nothing to do with OP's question and GFCI at the load end of a feeder won't care if you use the grounded feeder conductor for equipment grounding, but any voltage drop on that feeder grounded conductor will result in elevated voltage to true ground on any EGC's you connect to it. It may only be a volt or two but in the right circumstances, like around a swimming pool, that is a lot.

    Quote Originally Posted by FionaZuppa View Post
    good point. so then gfi ocpd on both sides??

    if the load only uses L-L how much voltage would there be on the egc ?
    Depends on how much voltage drop there is on the grounded conductor from the point in question to the point where the source is grounded.

  5. #55
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    Quote Originally Posted by kwired View Post
    Depends on how much voltage drop there is on the grounded conductor from the point in question to the point where the source is grounded.
    what grounded conductor if all the loads are pole-to-pole 240v?

    perhaps post #2 was a tad confusing, throwing in egc bonded to N ? not really sure why that came up.

    for OP, egc (gnd) bar bonded to the panel itself makes sense to me, as long as all other CCC's are isolated from the panel metal.

  6. #56
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    Quote Originally Posted by FionaZuppa View Post
    what grounded conductor if all the loads are pole-to-pole 240v?

    perhaps post #2 was a tad confusing, throwing in egc bonded to N ? not really sure why that came up.

    for OP, egc (gnd) bar bonded to the panel itself makes sense to me, as long as all other CCC's are isolated from the panel metal.
    From the OP: "I am a home inspector trying to understand what is correct and why in the distribution (sub) panel. My understanding is that beyond the service disconnect point (main panel) (in what I call the sub panel, I believe is called a distribution panel by NEC) ground (bare copper wire) and neutral (white wire) is separated and not bonded.


    IMO the main topic of the thread is why do we separate the two beyond the service equipment?
    If you have a panel with no neutral load - then it is acceptable to use the neutral bus as a grounding bus - you would seldom find such a panel in a dwelling though that didn't also supply loads that operate line to neutral though, and this is the situation where OP usually sees this.

    Even though it isn't code compliant, IMO you are still better off using the feeder neutral for equipment grounding path beyond that subpanel then to not have any equipment grounding at all, and if you do it doesn't change how a GFCI in that panel or even downstream of that panel will function. It does increase the possibility of a rise in voltage on that EGC to true ground though, and a GFCI won't detect that either.

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