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Ground fault- Why doesn't anyone get shocked?

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    #16
    Originally posted by LarryFine View Post
    Let's say that does happen.

    Your system neutral, your water piping, your grounding electrodes, the earth around your house, everything around you, all energized to 3600v relative to the grounded neutral back at the sub-station.

    You'd never know it because all of those things are at the same potential. You'd be like a bird on a primary wire or a lineman in a metallic suit tied to the line he's working on; no potential difference.

    That's what equipotential bonding is all about. Preventing voltage gradients means preventing current flow. The absolute voltage is not as important as relative voltages between conductive surfaces.
    Ditto.
    BB+/BB=?

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      #17
      Originally posted by mivey View Post
      Ditto.
      But what if the home has plastic water pipes and just a single ground rod? Your outside using a corded drill with a metal frame and barefoot.
      Our comedian shamelessly joked about a blackout. Talk about dark humor.

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        #18
        Originally posted by romex jockey View Post
        how would... say...TN−C−S vs. TN−C fator in? ~RJ~
        Good question- though I'd say TT has an advantage if the MV and LV noodles are tied together. Uo as is can withstand something like 8kv short time (I think).
        Our comedian shamelessly joked about a blackout. Talk about dark humor.

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          #19
          Originally posted by mbrooke View Post
          But what if the home has plastic water pipes and just a single ground rod? Your outside using a corded drill with a metal frame and barefoot.
          You could experience a shock. Transferred voltage.
          BB+/BB=?

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            #20
            Originally posted by mivey View Post
            You could experience a shock. Transferred voltage.
            How much is typical though?
            Our comedian shamelessly joked about a blackout. Talk about dark humor.

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              #21
              Originally posted by mbrooke View Post
              How much is typical though?
              It varies. Time to clear also matters. Go through the substation design steps.
              BB+/BB=?

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                #22
                Originally posted by mivey View Post
                It varies. Time to clear also matters. Go through the substation design steps.
                It can get to 1.2 seconds coordinating reclosers in series vs a 15T that will blow in a few cycles. So the voltage must be below 300 volts I'd assume.


                Our comedian shamelessly joked about a blackout. Talk about dark humor.

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                  #23
                  Originally posted by mbrooke View Post
                  It can get to 1.2 seconds coordinating reclosers in series vs a 15T that will blow in a few cycles. So the voltage must be below 300 volts I'd assume.


                  The design deals with how many amps you can withstand for how long without electrocution.

                  Transferred voltage is what you are asking about I believe.
                  BB+/BB=?

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                    #24
                    Originally posted by mivey View Post
                    The design deals with how many amps you can withstand for how long without electrocution.

                    Transferred voltage is what you are asking about I believe.


                    Neutral to remote earth voltage.


                    Guy using a metal drill or an electric barbecue in his backyard, feet are bare on grass.


                    The graph applies to all cases where voltage is high enough to push enough current across the body between two points like the hand and legs.
                    Our comedian shamelessly joked about a blackout. Talk about dark humor.

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                      #25
                      Originally posted by mbrooke View Post
                      Neutral to remote earth voltage.


                      Guy using a metal drill or an electric barbecue in his backyard, feet are bare on grass.


                      The graph applies to all cases where voltage is high enough to push enough current across the body between two points like the hand and legs.
                      I'll make a model.
                      BB+/BB=?

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                        #26
                        Originally posted by mivey View Post
                        I'll make a model.
                        I owe you now
                        Our comedian shamelessly joked about a blackout. Talk about dark humor.

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                          #27
                          Originally posted by mbrooke View Post
                          But what if the home has plastic water pipes and just a single ground rod? Your outside using a corded drill with a metal frame and barefoot.
                          I would think risk increases, and would if lightning struck the MGN instead of having ungrounded conductor fall on it as well. I don't know how much that risk increases though. Isn't part of reason we have such grounding to lower potential for these kinds of events? MGN conductor, and the fact it is extended to EGC's is probably low enough impedance that voltage divide in the fault case is not 50-50 at the fault point, the MGN is probably lower impedance than the ungrounded conductor during this event, that would place higher voltage across the segment from supply to fault point. There would still be a rise on the grounded conductor above earth, but actual impedance of different portions of the circuit will determine how much, and it probably will vary from one location to another even though you still have a ungrounded to grounded conductor fault to start this thing.
                          I live for today, I'm just a day behind.

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                            #28
                            Originally posted by kwired View Post
                            I would think risk increases, and would if lightning struck the MGN instead of having ungrounded conductor fall on it as well. I don't know how much that risk increases though. Isn't part of reason we have such grounding to lower potential for these kinds of events? MGN conductor, and the fact it is extended to EGC's is probably low enough impedance that voltage divide in the fault case is not 50-50 at the fault point, the MGN is probably lower impedance than the ungrounded conductor during this event, that would place higher voltage across the segment from supply to fault point. There would still be a rise on the grounded conductor above earth, but actual impedance of different portions of the circuit will determine how much, and it probably will vary from one location to another even though you still have a ungrounded to grounded conductor fault to start this thing.
                            Under typical conditions I would agree. But picture a scenario where the NESC allows the MGN to be smaller then the phase conductors and there are a limited number of parallel paths. 4 ground rods per mile and at every transformer is IMO substantially more impedance then copper water mains, gas mains and TELCO shields. The scenario I have in mind is predominately farms out in the boonies- no gas, well water and only a single thin phone line strung underneath the single phase line going for miles.
                            Our comedian shamelessly joked about a blackout. Talk about dark humor.

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                              #29
                              Originally posted by mbrooke View Post
                              Your outside using a corded drill with a metal frame and barefoot.
                              Who uses corded drills anymore?
                              Ethan Brush - East West Electric. NY, WA. MA

                              "You can't generalize"

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                                #30
                                Originally posted by electrofelon View Post
                                Who uses corded drills anymore?
                                Good point, but picture any grounded power tool. Or an electric grill.
                                Our comedian shamelessly joked about a blackout. Talk about dark humor.

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