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    Grounding Myths

    I am still watching and learning from the May 2016 Electrical Safety Month grounding videos. Thanks for all you do!

    My question, the grounding myth video demonstrates the damaging lightning current flow from the axillary electrode through the electrical system to the electrical service grounding electrode, i.e. the slide addressing the auxiliary electrode on the CNC machine or solar panels.

    Would the damage still occur if the bonding required by NFPA 70-250.58, 250.106, NFPA 780-4.14 and any required intersystem bonding were properly installed?

    Thanks
    Carl Johnson

    #2
    Hi Carl:

    Welcome to the forums.

    Can you post a link to the video you're referring to?
    You make the lights come on and we make them go off.

    Comment


      #3
      Originally posted by mgookin View Post
      Hi Carl:

      Welcome to the forums.

      Can you post a link to the video you're referring to?
      Subject matter starts at 7:37.

      Mike gets into dangers around 11:37.

      [COLOR=RoyalBlue]I will have achieved my life's goal if I die with a smile on my face.[/COLOR]

      Comment


        #4
        Originally posted by Smart $ View Post
        Subject matter starts at 7:37.

        Mike gets into dangers around 11:37.

        Thanks Smart $.

        Originally posted by Carl Johnson View Post
        I am still watching and learning from the May 2016 Electrical Safety Month grounding videos. Thanks for all you do!

        ...

        Thanks
        Carl Johnson
        FYI: Mr. Holt does not participate on this forum. He just owns it!

        Originally posted by Carl Johnson View Post
        ...

        My question, the grounding myth video demonstrates the damaging lightning current flow from the axillary electrode through the electrical system to the electrical service grounding electrode, i.e. the slide addressing the auxiliary electrode on the CNC machine or solar panels.

        Would the damage still occur if the bonding required by NFPA 70-250.58, 250.106, NFPA 780-4.14 and any required intersystem bonding were properly installed?

        Thanks
        Carl Johnson
        Good question.

        There are some 780 guys who come on here from time to time who can provide a much better answer than I can. Since today's a holiday, maybe one will be along later in the week.

        You can also try to reach out to Mr. Holt. He's right up there in your neck of the woods (if you call palm trees the woods).
        You make the lights come on and we make them go off.

        Comment


          #5
          Originally posted by Carl Johnson View Post
          ...
          Would the damage still occur if the bonding required by NFPA 70-250.58, 250.106, NFPA 780-4.14 and any required intersystem bonding were properly installed?
          ...
          You'd have to define what you mean by properly installed in order to answer that question. If you define it as Code-compliant, yes the damage may still occur... and that is the problem.
          [COLOR=RoyalBlue]I will have achieved my life's goal if I die with a smile on my face.[/COLOR]

          Comment


            #6
            I'm far from an expert, but as a PV installer I've taken a pretty keen interest in Mike's comments on this issue, and here is what I've gathered, for what my opinion's worth:

            - In a close lightning strike, none of the NEC requirements will likely do you any good. My understanding is that only a proper lightning protection system (NFPA 780) has a chance to help you here.
            - In a farther away lightning strike, bonding with 250.66 size conductors may avoid side flash you might have with bonding conductors that are too small. But the arrangement is at least as important. Your best bet to prevent lightning induced currents from traveling where you don't want is to have all grounding electrodes tied together below the spot where all the above ground systems are bonded to it. Avoid putting other metal parts with equipment bonding in contact with the earth. This way, voltage gradients in the ground are more likely to only travel through the grounding electrode system and back to the earth, and not through other wiring.
            - Auxiliary electrodes are BS and can only do harm. They are permitted by the code because some manufacturers of equipment do not properly understand the issues and demand electrodes, and the NEC allows you to follow the instructions for that equipment. That way, when the equipment is destroyed by a lightning induced voltage gradient, you can still make a warranty claim because you followed instructions.
            - In the case of solar panels, God help you navigate the 2008 or 2014 codes if you live or work on projects in a high lightning area. 690.47(D) in these code cycles is a huge mistake. The size of a bonding conductor to a solar array (or another other electrical equipment on a roof), as far as I know, has little to no effect whatsoever on the likelihood of a lightning strike occurring. If you want real lightning protection for solar arrays, then back to NFPA 780.

            Comment


              #7
              Grounded Path for Return Current - Ground Rods

              If electricity takes all conductive paths, wouldn't it be considered unsafe in theory to ever touch a ground rod under normal working conditions?

              If the ground rod is bonded to your electric panel's neutral bar, wouldn't there always be at least 2 paths for return current 24/7 for a service to a house, since electricity doesn't take the path of least resistance, but all paths depending on how much resistance per path? Or is the ground rod path so high in earth resistance getting back to the source that it does have current on it but is so low that a human cannot even sense it?

              Comment


                #8
                Originally posted by Lmeagles36 View Post
                If electricity takes all conductive paths, wouldn't it be considered unsafe in theory to ever touch a ground rod under normal working conditions?

                If the ground rod is bonded to your electric panel's neutral bar, wouldn't there always be at least 2 paths for return current 24/7 for a service to a house, since electricity doesn't take the path of least resistance, but all paths depending on how much resistance per path? Or is the ground rod path so high in earth resistance getting back to the source that it does have current on it but is so low that a human cannot even sense it?
                Yes, the ground rod is a higher resistance path than bonded pathways. An example of a higher current pathway is residential services supplied from same transformer and one or more of their neutrals bonded to all-metal common water mains.

                However, even with substantial current flowing through the grounding system, what matters is the touch voltage... another name for a specific type of voltage drop.
                [COLOR=RoyalBlue]I will have achieved my life's goal if I die with a smile on my face.[/COLOR]

                Comment


                  #9
                  Originally posted by Smart $ View Post
                  ...supplied from same transformer and [COLOR=#ff0000]two[/COLOR] or more of their neutrals bonded to all-metal common water mains.
                  ...
                  [COLOR=#ff0000]Correction[/COLOR]...
                  [COLOR=RoyalBlue]I will have achieved my life's goal if I die with a smile on my face.[/COLOR]

                  Comment


                    #10
                    Originally posted by Lmeagles36 View Post
                    If electricity takes all conductive paths, wouldn't it be considered unsafe in theory to ever touch a ground rod under normal working conditions?

                    If the ground rod is bonded to your electric panel's neutral bar, wouldn't there always be at least 2 paths for return current 24/7 for a service to a house, since electricity doesn't take the path of least resistance, but all paths depending on how much resistance per path? Or is the ground rod path so high in earth resistance getting back to the source that it does have current on it but is so low that a human cannot even sense it?
                    First of all, the original question was mainly about lightning. The dangers presented by lightning are different from and in some ways opposite to those presented by man-made electricity and potential faults. If not for lightning, a lot of the danger from excessive or improper grounding would go away.

                    As far as your questions, the ground rod path is likely so much higher in resistance that hardly any current takes it. (An exception would be if the grounding electrode is a metal water pipe that connects over to the grounded conductor in another building. But that is not so relevant to whether it's safe to touch). The point of the electrode is to have less resistance than a human body, such that any amount of current flowing through that body would be harmless. A human does not sense current unless that human becomes a path for enough current to feel. There could be millions of amps flowing through a bare wire touched by a human, but unless that human serves as a good enough path compared to the wire to draw some current, the human will feel nothing. (Think about birds sitting on high voltage wires; they do not become a path because they are not touching another object that turns themselves into a path. It's similar if you touch a ground rod but not something else that has at a potential difference from the ground rod.) Remember that current is proportional to voltage for a given resistance, so touching a higher voltage wire is more likely to make you feel something. Lightning has a very, very high voltage.

                    Comment


                      #11
                      touching a high voltage line even if you are standing on a huge glass insulator can be deadly. you and the line will not conduct amps to/from the source, but you and the line are already at different charge potentials. the mere fact that to balance that charge you need amps, can kill you.

                      you dont want to be the item touching it, right at 1:09 into the video.


                      Comment


                        #12
                        Originally posted by FionaZuppa View Post
                        touching a high voltage line even if you are standing on a huge glass insulator can be deadly. you and the line will not conduct amps to/from the source, but you and the line are already at different charge potentials. the mere fact that to balance that charge you need amps, can kill you.
                        Just as important, you are a capacitor to ground. The total current through that capacitance may be small, but the high voltage arc, even at low current, can cause thermal injury.
                        You want the capacitive current to flow through your equipotential suit (in the case of transmission line voltages), not your body.

                        Comment


                          #13
                          Thanks for the clarity jaggedben.
                          Another question I have about electricity taking all conductive paths relates to someone being in a body of water (swimming pool, lake, etc).
                          I hear and read stories of people being shocked in pools where they claim they feel something tingle their skin, but still maintain muscle control.

                          If 120 volts comes into contact with the water and people are swimming near by (but not touching ground of any sort), would the current seek ground by merely going around their bodies, or would it also go thru their bodies since the human body is conductive and the current will take any and all conductive paths to ground it is given?

                          Comment


                            #14
                            Originally posted by Lmeagles36 View Post
                            ...
                            If 120 volts comes into contact with the water and people are swimming near by (but not touching ground of any sort), would the current seek ground by merely going around their bodies, or would it also go thru their bodies since the human body is conductive and the current will take any and all conductive paths to ground it is given?
                            It'd go around AND through, proportional to conductivity.
                            [COLOR=RoyalBlue]I will have achieved my life's goal if I die with a smile on my face.[/COLOR]

                            Comment


                              #15
                              Originally posted by Lmeagles36 View Post
                              Thanks for the clarity jaggedben.
                              Another question I have about electricity taking all conductive paths relates to someone being in a body of water (swimming pool, lake, etc).
                              I hear and read stories of people being shocked in pools where they claim they feel something tingle their skin, but still maintain muscle control.

                              If 120 volts comes into contact with the water and people are swimming near by (but not touching ground of any sort), would the current seek ground by merely going around their bodies, or would it also go thru their bodies since the human body is conductive and the current will take any and all conductive paths to ground it is given?
                              There is a voltage gradient in the water as a result of the current flow. The human becomes part of the current path.

                              The wet human body is a parallel path within the water and the resistance of the wet human is less than the resistance of the water, so the parallel resistances, the water and the human, act as a current divider with the most current flowing on the human.
                              Don, Illinois
                              (All code citations are 2017 unless otherwise noted)

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