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    #16
    Originally posted by kwired View Post

    Few years ago a local rural POCO had an underground 34.5 kVA that had a failure. They repaired it, for whatever reason their splice method failed when they energized it. It sent a surge down a nearby wire fence, arced across to telephone pedestal(s) near fence. There was damages in many buildings within a couple miles or so - all coming into facilities via telephone lines. Ground rod wasn't going to stop that, AFAIK most the telephone pedestals do ordinarily have a ground rod connected to them. I believe there was a couple grass fires associated with that incident as well.
    The ground resistance might be too high to prevent operation of upstream fuses to have caused such damages. I do not think any other reason..........

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      #17
      kwired: I also bet it happened in rural area; not in densely populated urban area where multigrounded neutral ground resistance is very low.

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        #18
        Originally posted by Sahib View Post
        Answer: Suppose ground resistance is zero. Consider 120V, Singe phase line with neutral grounded. Since ground resistance is zero, no matter how large a current flows through neutral to ground, the ground potential does not rise. Now Suppose a MV line contacts the 120V single phase line. A large short circuit current flows via phase, neutral and ground. But since ground resistance is zero, there is no rise in ground potential and the single phase line remains at 120V. In real situation also, there will be only a little rise above 120V if the ground resistance is close to zero.
        I don't think what you are saying is possible.
        If Billy Idol is on your playlist go reevaluate your life.

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          #19
          Originally posted by mbrooke View Post
          Bonding is more important than grounding. In fact article 250 is mostly around bonding, not grounding. Grounding has little if anything to do with people and property protection at 600 volts and under.
          Exactly the jist of the article's reference to GPR

          >>>>

          So it is perfectly possible for an AC or signal wire to have 5 kV or more between its two ends, for the short time that the lightning current lasts.
          That nanosecond of GPR is far less damaging if the entire residence assumes 1,000,000 volts

          VS. 1,000,000 volts on one end, 500,000 volts on the other, which is FAR more damaging.

          One can even read this theory into past code cycles. Remember when we didn't bond gas lines? The gas guys would have conniptions....then it evolved to 'within 6' , along with a flashover rationale. , these days we either bond the gas lines or fail inspections.


          ~RJ~

          Comment


            #20
            Originally posted by Sahib View Post
            The ground resistance might be too high to prevent operation of upstream fuses to have caused such damages. I do not think any other reason..........
            Don't know all details of what happened, would guess overcurrent protection did function maybe just not fast enough.

            Originally posted by Sahib View Post
            kwired: I also bet it happened in rural area; not in densely populated urban area where multigrounded neutral ground resistance is very low.
            It was in rural area, was also within 1 mile of the substation it was supplied from. After about a mile the line transitions to overhead conductors. This substation is a major hub for the region so to speak. Everyone within 30-50 miles of it is likely being powered through it in one way or another most of the time. The faulted line I mentioned just happened to be just one of the more localized lines leaving the substation.
            I live for today, I'm just a day behind.

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              #21
              Originally posted by romex jockey View Post
              Exactly the jist of the article's reference to GPR

              >>>>



              That nanosecond of GPR is far less damaging if the entire residence assumes 1,000,000 volts

              VS. 1,000,000 volts on one end, 500,000 volts on the other, which is FAR more damaging.

              One can even read this theory into past code cycles. Remember when we didn't bond gas lines? The gas guys would have conniptions....then it evolved to 'within 6' , along with a flashover rationale. , these days we either bond the gas lines or fail inspections.


              ~RJ~
              Yup- electronics are no different than people in a pool or hot tub. Basically the people/electronics are the high resistance and bonding is the ultra low resistance. The goal is to have most of the voltage drop across the bonding due to that ultra low resistance.


              In regards to gas lines- RJ- do you personally have any experience with csst? I know that was a major game changer.


              http://www.npihome.com/tag/american-gas-association/

              Comment


                #22
                In regards to gas lines- RJ- do you personally have any experience with csst? I know that was a major game changer.

                No more than any garden variety spark MBrooke , these days we're told to find some part of it that's solid & bond it






                ...ouch!


                ~RJ~

                Comment


                  #23
                  Originally posted by mbrooke View Post
                  Yup- electronics are no different than people in a pool or hot tub. Basically the people/electronics are the high resistance and bonding is the ultra low resistance. The goal is to have most of the voltage drop across the bonding due to that ultra low resistance.
                  ...
                  ...
                  More properly, the goal is to have most of the fault current flowing through the bonding, so that the identical voltage drop across person and bonding is low enough not to cause harm to the person.

                  Comment


                    #24
                    Originally posted by GoldDigger View Post
                    More properly, the goal is to have most of the fault current flowing through the bonding, so that the identical voltage drop across person and bonding is low enough not to cause harm to the person.
                    Oopps, voltage drop as in pulling down the voltage between two points... horrible choice of words.

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