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Ground fault- Why doesn't anyone get shocked?

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    #31
    Originally posted by mbrooke View Post
    . 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.
    I know of one farm between line extensions , i mean literally the cows are all standing on 'earth', or in mud that could be any potential

    And yes, i've grounded everything, you name it , if you showed up in steel toed boots you'd be made into it all, etc, ad naseum....

    But i digress.....how can 'equo' exist in any plane with changing parameters?

    ~RJ~

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      #32
      Originally posted by mbrooke View Post
      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.
      I work with a lot of what you described. Mostly rural areas. Lines do fall onto other lines on occasion, nobody been shocked yet, don't know if it is just luck or if voltage just isn't as high as you are suggesting it can possibly be - meaning return path must be lower impedance than you are suggesting.

      Several years ago we did have a 38.5kV conductor drop onto a 4.16kV local distribution line, it caused damages to many things all over the small town. But was enough hit and miss that I think one can say if you weren't on the phase it dropped on you probably had no damages. I don't know how much risk of shock may have been with this event, but AFAIK it dropped on a phase conductor and not the MGN, which maybe changes things some.
      I live for today, I'm just a day behind.

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        #33
        Originally posted by kwired View Post
        I work with a lot of what you described. Mostly rural areas. Lines do fall onto other lines on occasion, nobody been shocked yet, don't know if it is just luck or if voltage just isn't as high as you are suggesting it can possibly be - meaning return path must be lower impedance than you are suggesting.

        Several years ago we did have a 38.5kV conductor drop onto a 4.16kV local distribution line, it caused damages to many things all over the small town. But was enough hit and miss that I think one can say if you weren't on the phase it dropped on you probably had no damages. I don't know how much risk of shock may have been with this event, but AFAIK it dropped on a phase conductor and not the MGN, which maybe changes things some.



        Did you blow out any lightning arrestors on the 4.16kv?


        Around here a few years back there was a really bad ice storm. On one home the 13.2kv conductor fell on the 120/240 secondary, several homes needed a complete and I mean complete re-wire. Everything that could arc did.

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          #34
          Originally posted by mbrooke View Post



          Did you blow out any lightning arrestors on the 4.16kv?


          Around here a few years back there was a really bad ice storm. On one home the 13.2kv conductor fell on the 120/240 secondary, several homes needed a complete and I mean complete re-wire. Everything that could arc did.
          Don't know about the lightning arrestors, that would have been POCO issue. I got several service calls, some electronic control boards in appliances were pretty common failure items, maybe some control transformer failures in HVAC units, I replaced many GFCI receptacles that failed, couple houses just about every GFCI in the house failed. Would get people all on same block fed by same phase or even same transformer that had problems, across the street (probably on another phase) no issues at all.
          I live for today, I'm just a day behind.

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            #35
            Originally posted by kwired View Post
            Don't know about the lightning arrestors, that would have been POCO issue. I got several service calls, some electronic control boards in appliances were pretty common failure items, maybe some control transformer failures in HVAC units, I replaced many GFCI receptacles that failed, couple houses just about every GFCI in the house failed. Would get people all on same block fed by same phase or even same transformer that had problems, across the street (probably on another phase) no issues at all.
            Was there any visible damage on control boards or GFCIs?

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              #36
              Originally posted by mbrooke View Post
              Was there any visible damage on control boards or GFCIs?
              Too long ago to be able to answer, but seems like in most GFCI instances no, never opened any of them up either though. I didn't get too involved with appliance control boards - let the appliance repair guys do that, but with easier availability today with internet suppliers, I may entertain the idea a little more if it were to happen now.
              I live for today, I'm just a day behind.

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                #37
                Originally posted by kwired View Post
                Too long ago to be able to answer, but seems like in most GFCI instances no, never opened any of them up either though. I didn't get too involved with appliance control boards - let the appliance repair guys do that, but with easier availability today with internet suppliers, I may entertain the idea a little more if it were to happen now.
                Always take pics, never regret it latter on. But I'm the same, back then I rarely thought to look at anything in depth. The internet has truly sparked curiosity in humanity.

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                  #38
                  Originally posted by mbrooke View Post
                  The internet has truly sparked curiosity in humanity.
                  Do you mean it has made it has made people curious in general, or made people curious about people?
                  Master Electrician
                  Electrical Contractor
                  Richmond, VA

                  Comment


                    #39
                    Originally posted by LarryFine View Post
                    Do you mean it has made it has made people curious in general, or made people curious about people?
                    To the last part.


                    But people are curious in general.

                    Comment


                      #40
                      Using 34.5 kV, 3ph OH primary wye MGN, large wire (556 ph, 336 neu), I_fault at sub = 9.47 kA LLL, 11.5 kA LN.

                      N-E voltage for L-N primary fault at service transformer:

                      1 SPAN (11.1 kA): 216 V
                      1/4 MILE (9.7 kA): 916 V
                      1/2 MILE (8.4 kA): 1.52 kV
                      1 MILE (6.7 kA): 2.2 kV
                      2 MILES (4.9 kA): 2.4 kV
                      3 MILES (4.0 kA): 2.2 kV
                      4 MILES (3.3 kA): 1.8 kV
                      BB+/BB=?

                      Comment


                        #41
                        Originally posted by mbrooke View Post
                        To the last part.
                        Originally posted by mbrooke View Post
                        The internet has truly sparked curiosity in humanity.
                        This could be taken to mean that the internet has sparked curiosity about humanity. Maybe?
                        Master Electrician
                        Electrical Contractor
                        Richmond, VA

                        Comment


                          #42
                          Originally posted by mivey View Post
                          Using 34.5 kV, 3ph OH primary wye MGN, large wire (556 ph, 336 neu), I_fault at sub = 9.47 kA LLL, 11.5 kA LN.

                          N-E voltage for L-N primary fault at service transformer:

                          1 SPAN (11.1 kA): 216 V
                          1/4 MILE (9.7 kA): 916 V
                          1/2 MILE (8.4 kA): 1.52 kV
                          1 MILE (6.7 kA): 2.2 kV
                          2 MILES (4.9 kA): 2.4 kV
                          3 MILES (4.0 kA): 2.2 kV
                          4 MILES (3.3 kA): 1.8 kV
                          HUGE thanks.

                          I somewhat anticipated these numbers.


                          So, how are those 2.4kv rendered safe? Does this mean I should stick to 12.47kv distribution? What do the numbers look like for that?


                          Does your model assume metal water mains or just take the 336 neut and its ground rods?

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                            #43
                            Originally posted by LarryFine View Post
                            This could be taken to mean that the internet has sparked curiosity about humanity. Maybe?


                            Humanity, the existence of reality and the universe.

                            Comment


                              #44
                              Originally posted by mbrooke View Post
                              So, how are those 2.4kv rendered safe?
                              Body resistance and breaker clearing time.

                              Originally posted by mbrooke View Post
                              Does this mean I should stick to 12.47kv distribution?
                              Nope

                              Originally posted by mbrooke View Post
                              What do the numbers look like for that?
                              Similar

                              Originally posted by mbrooke View Post
                              Does your model assume metal water mains or just take the 336 neut and its ground rods?
                              I modeled some low endpoint impedances to account for multiple earth attachments but not a particular parallel line. Most water lines are going to plastic nowadays.

                              I can model in a pipe but not much would change. N-E voltage might drop slightly but elsewhere on the system you would get similar results. This is not a specific model or a model to fit all cases, just an example to show the drill may have thousands of volts on it during the fault.
                              BB+/BB=?

                              Comment


                                #45
                                Originally posted by mbrooke View Post
                                Humanity, the existence of reality and the universe.
                                Larry is a philosopher. I'm a fill-osopher as my eating habits would prove.
                                BB+/BB=?

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