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

  1. #11
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    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.
    What about my generator, and probably thousands that are like it?

    Connect the 14-30 receptacle on mine to my premises wiring (with proper transfer equip. of course) and now the generator becomes a part of a grounded system - the 5-15 receptacles mounted on it still are usable and do have GFCI protection.

  2. #12
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    fix quote

    Quote Originally Posted by romex jockey View Post

    Missed that, my bad Al

    Ok, my $.02.....a toroidal coil senses an imbalance , it's not dependent on anything other than that

    ~RJ~
    Exactly, if you have an ungrounded system supplying a receptacle for example, the first ground will cause the GFCI to trip whether or not there is a load connected at the time. This assumes that the grounding connection is of low enough impedance to allow the trip current to flow.
    Last edited by jumper; 01-13-18 at 01:46 AM.

  3. #13
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    Quote Originally Posted by gadfly56 View Post

    Exactly, if you have an ungrounded system supplying a receptacle for example, the first ground will cause the GFCI to trip whether or not there is a load connected at the time. This assumes that the grounding connection is of low enough impedance to allow the trip current to flow.


    If you have an ungrounded system how do you get any current flow to trip the GFCI until there is a second ground fault? What goes out on one conductor has to come back on the other and there is no other path even with a ground fault for "leakage current" to flow until there is a second ground fault. This is disregarding current due to capacitive coupling - but even current involved in that situation is extremely low and takes a lot of capacitance before it is a problem.
    Last edited by jumper; 01-13-18 at 01:47 AM.

  4. #14
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    Quote Originally Posted by kwired View Post


    If you have an ungrounded system how do you get any current flow to trip the GFCI until there is a second ground fault? What goes out on one conductor has to come back on the other and there is no other path even with a ground fault for "leakage current" to flow until there is a second ground fault. This is disregarding current due to capacitive coupling - but even current involved in that situation is extremely low and takes a lot of capacitance before it is a problem.
    Are we talking about a system that is completely isolated from ground (floating), even accidental, or a system that could find earth (ground) on the first fault?
    Last edited by jumper; 01-13-18 at 01:47 AM.

  5. #15
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    Quote Originally Posted by gadfly56 View Post

    Are we talking about a system that is completely isolated from ground (floating), even accidental, or a system that could find earth (ground) on the first fault?
    TTBOMK grounded means it is intentionally connected at one point (often a neutral conductor) to some reference point that is called "ground" for whatever reason (even if that "ground" is just the frame of a generator), and ungrounded means there is no reference point to other objects of any kind (so floating I guess).
    Last edited by jumper; 01-13-18 at 01:48 AM.

  6. #16
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    Quote Originally Posted by gadfly56 View Post

    Are we talking about a system that is completely isolated from ground (floating), even accidental, or a system that could find earth (ground) on the first fault?
    An ungrounded system is completely isolated.
    If you don't think too good, don't think too much.

  7. #17
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    Quote Originally Posted by ActionDave View Post
    An ungrounded system is completely isolated.
    OK, I withdraw my previous comment in that case.

  8. #18
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    Quote Originally Posted by romex jockey View Post
    I've hooked up a world of hot tubs on a two pole gfci w/o a neutral

    I'm fairly sure i was sane at the time......

    ~RJ~
    Ok so this actually answers one of my questions. Don't really need to have a neutral per say... two hots of a grounded system will still allow a GFCI to provide protection. That "path to the source" I am pestering about will allow the leakage imbalance to occur.

    Quote Originally Posted by kwired View Post


    If you have an ungrounded system how do you get any current flow to trip the GFCI until there is a second ground fault? What goes out on one conductor has to come back on the other and there is no other path even with a ground fault for "leakage current" to flow until there is a second ground fault. This is disregarding current due to capacitive coupling - but even current involved in that situation is extremely low and takes a lot of capacitance before it is a problem.
    I'm still not convinced leakage current will "exist" on an ungrounded system because it will not have a return path (through earth) to the source.

    To hopefully add some clarity: If an ungrounded system has no faults - meaning there are no unintentional connections between ungrounded conductors and dead metal parts/equipment - and everything is hunky dory... Will a GFCI function if I have wet hands?

    To push it a bit further, in the case where a single ground-fault does exist, and now the system is unintentionally grounded, will a GFCI function as intended?

    It almost seems like a GFCI will only function on a grounded system, or an ungrounded system with a single ground-fault present. Amiright?
    Last edited by jumper; 01-13-18 at 01:49 AM.

  9. #19
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    No system is ever completely isolated from 'ground'. 'Capacitive charging current' has already been mentioned. Even an 'ungrounded' system will have capacitive coupling to ground, and this current can be large enough to cause a significant shock. If you touch a 'hot' conductor then one phase will be grounded through you, and your body will try to carry the capacitive charging current of the other two phases.

    Operating Room isolated ground systems are intentionally small (eg. a single room) to minimize capacitive current.

    In principal a GFCI could protect from shock in these situations, but as others have mentioned the GFCI might not be 'listed' for such use.

    -Jon

  10. #20
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    But this is an interesting bit of electrical theory we've going here.....

    It would appear the contention is that gfci's can't work w/o a path for current to travel

    So if we've an isolation Xformer (floating in space?) , H&N or H&H going through a toroidal to a load , said load side would need a source to loose current to?


    Is that the jist?

    ~RJ~

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