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    #31
    Originally posted by K8MHZ View Post
    Are we maybe confusing an ungrounded system with a 2 wire receptacle? Or is it just me?
    It's just you. So far, I've only been discussing the former.

    Still, the same holds true for the latter: supply must have a grounded conductor.
    Master Electrician
    Electrical Contractor
    Richmond, VA

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      #32
      Originally posted by LarryFine View Post

      It's just you. So far, I've only been discussing the former.

      Still, the same holds true for the latter: supply must have a grounded conductor.
      Why wouldn't the latter have a grounded conductor?
      Cheers and Stay Safe,

      Marky the Sparky

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        #33
        Originally posted by K8MHZ View Post
        Are we maybe confusing an ungrounded system with a 2 wire receptacle? Or is it just me?
        Yep, it's just you.

        Roger
        Moderator

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          #34
          Originally posted by K8MHZ View Post

          Why wouldn't the latter have a grounded conductor?
          It would. I took the "2-wire receptacle" to mean no EGC.
          Master Electrician
          Electrical Contractor
          Richmond, VA

          Comment


            #35
            Originally posted by LarryFine View Post
            However, for a GFCI device to trip, there would need to be a sufficient difference of current between the lines involved and the earth created by the accidental contact, requiring one line to be better coupled to earth than the others.

            If all phases have the same coupling to earth, which is necessary to avoid nuisance tripping, no shock current would flow outside the current sensor. Any current to earth through a person would travel through all lines equally.
            Thinking about it, a shock current from an ungrounded system as a whole could trip a GFCI as long as the supply (line side) conductors is well-coupled to earth.

            However, wouldn't any difference between capacitive coupling on the line and load sides of the GFCI be seen as leakage current and cause nuisance tripping?


            Thinking about it even more, wouldn't any capacitive current be seen as leakage current?
            Master Electrician
            Electrical Contractor
            Richmond, VA

            Comment


              #36
              Originally posted by LarryFine View Post
              Thinking about it even more, wouldn't any capacitive current be seen as leakage current?
              Yes it is.
              That is partly why you see main feeder GF protection set in Amps, while mA levels are typically only used for 'people' protection or for small branches.

              Just because you can, doesn't mean you should.

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                #37
                Originally posted by LarryFine View Post
                There's almost always a specific exception to a generalization, but you're making my point in your example: a GFCI device requires that one circuit conductor be intentionally grounded to function.
                This is not _quite_ true, but close enough for 120V systems. For a GFCI to function current needs to flow in an imbalanced fashion on the sensed conductors. I've seen residual current detection trip because of capacitive coupled currents, using impedance grounding. I presume that if you had a large enough 120V ungrounded system, the capacitive charging current could be large enough to present a shock hazard and a GFCI would detect the residual current from contact.

                Back to the original 'bucket' scenario. If a hair dryer drops into an insulated bucket of normal tap water, some current will flow through the water from one AC terminal to the other. If a person were to somehow interpose themselves in this current path, they would feel a shock and the GFCI would not detect it. In the case of the hairdryer these terminals are very close together, and it would be difficult to get a finger close enough to intercept appreciable current. A grounded drain would actually _increase_ the hazard, because now there is a path for current to flow through a larger volume of water...though it would increase the chance of the GFCI tripping.

                Because tap water is not a very good conductor, the current might be limited to the point that the GFCI doesn't trip.

                -Jon


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                  #38
                  Originally posted by GoldDigger View Post
                  And if for some reason there is a voltage gradient in the water (more likely with a pool or tub than a sink) putting two hands in the water can cause a serious shock, but not a GFCI trip.

                  Sent from my XT1585 using Tapatalk
                  keeping in mind swimming pool water is required to have a ground reference by the required bond to a branch circuit equipment ground
                  not that i think every plastic sink should have the same

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