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Thread: GFCI on ungrounded system (system grounding, not equipment grounding)

  1. #31
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    Sounds like a toaster! IIRC, they are required to be ungrounded for that reason.

  2. #32
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    Quote Originally Posted by gadfly56 View Post
    Not necessarily. Say we have our ungrounded system. You open the Romex at point A and the hot touches a piece of completely UNgrounded steel. You open the Romex at point B and touch the hot to the same steel at a different point; a second fault. Nothing happens, because both points are at the same potential.
    The wire is still faulted to the steel, that is an unintended connection, there just is no current flow to other points of potential from the source at that point all, you have done is join (maybe not a solid connection but is a connection) that conductor to that piece of steel but never developed any place for current to flow. Could be minor amount of current in parallel between both fault point, but as I said probably not that solid of a connection and resistance of those connections probably means the copper wire is still carrying the bulk of what parallel current is present. Still not tripping a GFCi as it won't see this any different then running a parallel set of conductors between two points in a circuit.

  3. #33
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    Quote Originally Posted by kwired View Post
    The wire is still faulted to the steel, that is an unintended connection, there just is no current flow to other points of potential from the source at that point all, you have done is join (maybe not a solid connection but is a connection) that conductor to that piece of steel but never developed any place for current to flow. Could be minor amount of current in parallel between both fault point, but as I said probably not that solid of a connection and resistance of those connections probably means the copper wire is still carrying the bulk of what parallel current is present. Still not tripping a GFCi as it won't see this any different then running a parallel set of conductors between two points in a circuit.
    Yes, exactly so, but I've created two faults without tripping the GFCI. If you argue that they are really the same fault, then lifting either connection should clear the fault. It won't, so I submit there are two faults, not one.

  4. #34
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    This might be a great space shuttle experiment .......~RJ~

  5. #35
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    Quote Originally Posted by kwired View Post
    That is what I have been trying to get across this whole thread. It don't care what is grounded or not, it only wants to see that whatever goes out comes back, if not it went somewhere besides the intended path, that makes it trip.
    And with no deliberate ground in the system there is nowhere for any imbalanced current to flow in the circuit at the GFCI until after the second fault occurs.
    If you had an Equipment (Not) Grounding Conductor, E(N)GC, connecting to the center point of the transformer secondary and to the exposed metal of a load, then you could have imbalance at the GFCI when the first fault between hot and the ungrounded exposed metal occurs.

  6. #36
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    Well, up until reading this thread ,i thought planting a Grod for portable gennys was overkill.....~RJ~

  7. #37
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    Quote Originally Posted by gadfly56 View Post
    Yes, exactly so, but I've created two faults without tripping the GFCI. If you argue that they are really the same fault, then lifting either connection should clear the fault. It won't, so I submit there are two faults, not one.
    Yes you created two faults, you did not create an alternate current path that a GFCI will be able to detect.

    Ungrounded system - that alternate path is not a shock hazard to grounded objects until a ground reference is established in the system.

  8. #38
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    Quote Originally Posted by romex jockey View Post
    Well, up until reading this thread ,i thought planting a Grod for portable gennys was overkill.....~RJ~
    That's an interesting point... Do you mean that in the sense that it can provide a return path to the source and actually create a path for the unbalanced current to flow? Seems though to a certain degree this would provide a more "reliable" path for the unbalanced current than the current that would otherwise flow from capacitive charging.

    This is all interesting to me. Bonding is critical to have a low-resistance path to the source to clear ground-faults on grounded systems. We want high levels of current to flow to trip breakers. But now it seems grounding, though it does nothing to trip a breaker on a fault, could be beneficial to trip a GFCI considering the little bit of current it requires... Granted choosing a grounded system solely for this reason is unlikely.

    Quote Originally Posted by texie View Post
    GFCIs are only recognized for use on solidly grounded systems. I would think if one was applied on an ungrounded system you would have a number of unpredictable issues. Also, since most GFCIs are used in systems of less than 150 volts to ground the systems could not be an an ungrounded system anyway.
    Which leads me to this...

    By what standard? NEC? Or are you saying only recognized as such by the manufacturer?

  9. #39
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    Quote Originally Posted by MechEdetour View Post
    That's an interesting point... Do you mean that in the sense that it can provide a return path to the source and actually create a path for the unbalanced current to flow? Seems though to a certain degree this would provide a more "reliable" path for the unbalanced current than the current that would otherwise flow from capacitive charging.

    This is all interesting to me. Bonding is critical to have a low-resistance path to the source to clear ground-faults on grounded systems. We want high levels of current to flow to trip breakers. But now it seems grounding, though it does nothing to trip a breaker on a fault, could be beneficial to trip a GFCI considering the little bit of current it requires... Granted choosing a grounded system solely for this reason is unlikely.



    Which leads me to this...

    By what standard? NEC? Or are you saying only recognized as such by the manufacturer?
    UL 943, the very first sentence. Overview here: https://standardscatalog.ul.com/stan...n/standard_943

  10. #40
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    Quote Originally Posted by texie View Post
    UL 943, the very first sentence. Overview here: https://standardscatalog.ul.com/stan...n/standard_943
    Ahh ok. I wonder if the motive by that was to limit the scope of the standard or because of this very topic...

    Thanks for pointing that out.

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