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

  1. #1
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    GFCI on ungrounded system (system grounding, not equipment grounding)

    A GFCI receptacle will work on a 2 wire circuit (grounded system) without an equipment ground. It senses current imbalances between the hot and neutral, which when present, it will trip. This makes sense to me and there is no less than a thousand articles on this topic. However, my questions is, will a GFCI receptacle work on an ungrounded system?

    On a grounded system, to my understanding the leakage would go through the body and into the ground to return to the source, and the resulting imbalance would cause it to trip. Technically there wouldn't be a return path through the ground to the source on an ungrounded system. You would be brought to the same potential, and there wouldn't be shock hazard. Am I right here?

    Seems like I answered my question writing this through... To me it seems like GFCIs are useless on ungrounded systems. Actually, can GFCIs even be used on ungrounded systems? There would be no grounded/neutral conductor. Am I going mad?
    Last edited by MechEdetour; 01-12-18 at 09:48 AM. Reason: typo in title

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    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~

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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~
    There's a difference between a circuit that does not use the grounded conductor and an ungrounded system.
    If you go and decide to dance with a gorilla the dance ain't over till the gorilla decides it's over.

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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~
    RJ, Your source, the PoCo transformer secondary, is solidly connected to Earth. The OP is asking about a source, and the attached wiring system, that is NOT connected to Earth.

    It's an interesting question.

    I'll take a stab at the theory. With an ungrounded system there is some form of ground fault detection attached to some form of an alarm. The first connection of one leg of the system to ground isn't the one that causes damage. . . the connection of the NEXT system leg is the one that completes a short circuit.

    A person normally would not come in contact with the ungrounded system conductors, but, in the case of a piece of equipment supplied from an ungrounded system through a GFCI receptacle (or breaker), if the piece of equipment is faulted in a manner that connects one ungrounded system leg to the person, that is the FIRST connection of the ungrounded system to ground. No current would flow except for what is necessary for the system ground fault detector. THAT current, passing through the person, if in excess of the 5 milliamp threshold, will trip the GFCI receptacle (breaker).
    Another Al in Minnesota

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    Quote Originally Posted by MechEdetour View Post

    Seems like I answered my question writing this through... To me it seems like GFCIs are useless on ungrounded systems. Actually, can GFCIs even be used on ungrounded systems? There would be no grounded/neutral conductor. Am I going mad?
    You wouldn't have any current flow to trip the GFCI on the first fault, so the GFCI wouldn't have any imbalance to cause a trip till after the second fault.

    In a perfect world your ungrounded system would have a ground fault indicator which would light up on the first ground fault and the problem would be corrected before the second ground fault.
    If you go and decide to dance with a gorilla the dance ain't over till the gorilla decides it's over.

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    Quote Originally Posted by al hildenbrand View Post
    RJ, Your source, the PoCo transformer secondary, is solidly connected to Earth. The OP is asking about a source, and the attached wiring system, that is NOT connected to Earth.

    It's an interesting question.
    Missed that, my bad Al

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

    ~RJ~
    Last edited by jumper; 01-13-18 at 01:45 AM. Reason: fix quote

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    Quote Originally Posted by ActionDave View Post
    You wouldn't have any current flow to trip the GFCI on the first fault, so the GFCI wouldn't have any imbalance to cause a trip till after the second fault.

    In a perfect world your ungrounded system would have a ground fault indicator which would light up on the first ground fault and the problem would be corrected before the second ground fault.
    And if user(s) ignores the ground fault indicator on first fault GFCI will still protect him if there is a second fault.

    I have a portable generator - 8000 W 120/240 neutral is not bonded to frame - so it is an ungrounded system. It has 14-30 receptacle and two GFCI protected 5-15 receptacles (factory mounted) on the unit.

    Fact it is ungrounded reduces shock hazard some, GFCI still would work if there were a second ground fault.

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    I think it comes down to whether the capacitive charging current is high enough to trip the gfci when the fault is made yes?
    Ethan Brush - East West Electric. NY, WA. MA

    "You can't generalize"

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    Quote Originally Posted by electrofelon View Post
    I think it comes down to whether the capacitive charging current is high enough to trip the gfci when the fault is made yes?
    I wouldn't say it comes down to only that, but yes capacitive charging current can trip a GFCI - even when part of a grounded system.

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    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.

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