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How does a GEC limit overvoltage from lightning and grid surges?

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    How does a GEC limit overvoltage from lightning and grid surges?

    I'm trying to get a deeper and accurate understanding of how a Grounding Electrode Conductor works.

    What is most confusing to me is that I know a GEC doesn't help with ground faults from hot to the safety ground path--so if it doesn't help in that case, how does it lower the voltage from lightning strikes, unintentional contact with high-voltage lines, grid surges from switching feeders, etc.?

    #2
    I don't think it's effective for much at all other than giving a warm feeling to the dirt worshippers.
    If Billy Idol is on your playlist go reevaluate your life.

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      #3
      Originally posted by PetesGuide View Post
      I'm trying to get a deeper and accurate understanding of how a Grounding Electrode Conductor works.

      What is most confusing to me is that I know a GEC doesn't help with ground faults from hot to the safety ground path--so if it doesn't help in that case, how does it lower the voltage from lightning strikes, unintentional contact with high-voltage lines, grid surges from switching feeders, etc.?
      The answer is that it doesn't, nor is it supposed to.

      What it is supposed to do is limit the voltage from earth to the grounded conductor of the electrical system when those events happen. Since there is a dead short between earth and the grounded conductor (the GEC) it probabl does indeed limit that voltage difference.
      Bob

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        #4
        Originally posted by PetesGuide View Post
        I'm trying to get a deeper and accurate understanding of how a Grounding Electrode Conductor works.

        What is most confusing to me is that I know a GEC doesn't help with ground faults from hot to the safety ground path--so if it doesn't help in that case, how does it lower the voltage from lightning strikes, unintentional contact with high-voltage lines, grid surges from switching feeders, etc.?
        The contact resistance between the electrode and earth is too high to trip OCPD at household voltage, but it may still reduce the applied voltage when the source is distribution voltage. Or lightning, when compared to other, more destructive alternate paths.

        Sent from my XT1585 using Tapatalk

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          #5
          NFPA 780 covers lightning arrester systems. Only a whole house surge protector would protect against an overhead primary falling onto a secondary, or a power company surge.
          Electricians do it until it Hertz!

          Comment


            #6
            Originally posted by petersonra View Post
            The answer is that it doesn't, nor is it supposed to.

            What it is supposed to do is limit the voltage from earth to the grounded conductor of the electrical system when those events happen. Since there is a dead short between earth and the grounded conductor (the GEC) it probabl does indeed limit that voltage difference.
            Still not clear enough for me. Is this a question of semantics, where my use of lower means something different than limit? NEC 2011 250.4(A)(1) states: "Electrical systems that are grounded shall be connected to earth in a manner that will limit the voltage imposed by lightning, line surges, or unintentional contact with higher-voltage lines..."

            And in https://www.mikeholt.com/PopGraphic.php?id=4380 Mike Holt states, "Metal parts of the electrical installation are grounded to the earth to reduce voltage on the metal parts from lightning..."

            Is this not what actually happens? I'm trying to understand what the electrons are doing in these events and why.

            P.S. I'm interested in what happens in systems grounded as per NEC, but without NFPA 780 lightning protection systems installed.

            Comment


              #7
              Basically the idea is that if you have a sizable wire connection to the earth then if any potential difference that develops, for any reason, between the earth and the electrical system, current will take the wire route instead of a human or some other more easily damaged wire or other thing. I believe it's far more helpful in tripping ground detection ( if a high voltage source faults to a low voltage source ) than for helping with a lightning strike. Also protects somewhat against shock in certain fault situations. The lightning thing I think is less about what happens in a strike and more about limiting the static potential that can develop around thunderstorms.

              Comment


                #8
                Originally posted by PetesGuide View Post
                Still not clear enough for me. Is this a question of semantics, where my use of lower means something different than limit? NEC 2011 250.4(A)(1) states: "Electrical systems that are grounded shall be connected to earth in a manner that will limit the voltage imposed by lightning, line surges, or unintentional contact with higher-voltage lines..."

                And in https://www.mikeholt.com/PopGraphic.php?id=4380 Mike Holt states, "Metal parts of the electrical installation are grounded to the earth to reduce voltage on the metal parts from lightning..."

                Is this not what actually happens? I'm trying to understand what the electrons are doing in these events and why.

                P.S. I'm interested in what happens in systems grounded as per NEC, but without NFPA 780 lightning protection systems installed.
                Hello,


                I recommend you watch this video by Mike Holt:


                https://www.youtube.com/watch?v=qNZC782SzAQ


                The EGC provides a low impedance conducting path to the power supply to eliminate the fault, if it has a grounding electrode, but it is not connected to the same ground in the system, there is a great possibility of having different gradients of potential during an event.


                The electrode and the EGC are not a protective mesh for the "step voltage".


                The grounding system, as stated in the section, limits the high voltage due to external events at the same reference potential. (Land)

                Regards
                Minor R.

                Comment


                  #9
                  Originally posted by PetesGuide View Post
                  I'm trying to get a deeper and accurate understanding of how a Grounding Electrode Conductor works.

                  What is most confusing to me is that I know a GEC doesn't help with ground faults from hot to the safety ground path--so if it doesn't help in that case, how does it lower the voltage from lightning strikes, unintentional contact with high-voltage lines, grid surges from switching feeders, etc.?
                  As you noted, it doesn't help with a "source" fault as source faults, by design (and code) take the low impedance neutral back to source. Well, technically, they also take the ground path...but for OCPD purposes, the neutral path is required.

                  We live in an electrically charged world. The electricity we create in our generating plants and distribute on wires to our homes is but our taming of the charges. There are many "untamed" charges around us...and the positive charges like to hook up with negative charges. Charges being imposed on things in and around our house may be different than the charges on the ground. They want to get together.

                  If we make it easy for them to get together, then it becomes an orderly everyday hook up. We make it easy by bonding all the electrical things together in the house, to include the dedicated EGC. This completes the easy path to the panel, and the GEC gets it to the electrode and to the earth. This orderly every day hookup ensures charges don't build up to the point where the potential difference gets to an unsafe level...and violently comes together.

                  As for lightning, the GEC really doesn't help much on a direct strike...you need LPS for that. But lightning doesn't just affect what the bolt touches. There are all sorts of charges associated with lightning...some get imposed on the structure...some ride the wires...both inside the house as well as on utility poles. As these charges flow through the house and the wires, they are trying to equalize...headed to (our from) the earth. A house "grounded" to ground (the GEC playing an important role in the connection) makes it easy to complete the connection.

                  As for man made sources along the distribution lines....surges...and power line faults...these desire to go back to source. If these faults are imposed on the house in some way, the low impedance path within the house to ground helps ensure dangerous buildup does not occur in the house itself.
                  Last edited by JPinVA; 11-07-18, 02:04 PM.

                  Comment


                    #10
                    Originally posted by jaggedben View Post
                    Basically the idea is that if you have a sizable wire connection to the earth then if any potential difference that develops, for any reason, between the earth and the electrical system, current will take the wire route instead of a human or some other more easily damaged wire or other thing. .
                    But current takes all paths, it doesn't matter if one is better or not. The only ways I can see bonding to dirt helping is:

                    1. It causes enough fault current to trip an OCPD (unlikely at less than 600v of course)

                    2. There is some sort of ground detector which opens the circuit.

                    3. Ita a low energy source such as Capacitive coupling or a high impedance fault, in which case the voltage difference can be "shunted"
                    Ethan Brush - East West Electric. NY, WA. MA

                    "You can't generalize"

                    Comment


                      #11
                      you ever see a picture of lightning, it travels through the sky and to the earth, the earth is obviously a good enough conductor for it.

                      https://www.youtube.com/watch?v=hG2p9N1MHlk&t=108s

                      skip to 5:36,
                      to see that distribution voltage will also move pretty good through earth. also consider the fact that in substations we use a ground grid to reduce step potential. earth is usually considered a high resistance relative to 120V yes most people would agree with that, at a higher voltage many people might say it's conductive. it will definitely conduct electricity.

                      or go ask a dairy farmer (cattle are very sensitive and are good ground fault indicators(actual ground(earth and currents from electrical system)))
                      Last edited by Wire-Smith; 11-07-18, 07:07 PM.

                      Comment


                        #12
                        Originally posted by PetesGuide View Post
                        ... I know a GEC doesn't help with ground faults from hot to the safety ground path--so if it doesn't help in that case, how does it lower the voltage from lightning strikes, unintentional contact with high-voltage lines, grid surges from switching feeders, etc.?
                        250.4 General Requirements for Grounding and Bonding.
                        The following general requirements identify what grounding and bonding of electrical systems are required to accomplish. The prescriptive methods contained in Article 250 shall be followed to comply with the performance requirements of this section.

                        (A) Grounded Systems.
                        (1) Electrical System Grounding.
                        Electrical systems that are grounded shall be connected to earth in a manner that will limit the voltage imposed by lightning, line surges, or unintentional contact with higher-voltage lines and that will stabilize the voltage to earth during normal operation.


                        So, 250.4 says it identifies what grounding and bonding are required to accomplish. And it is "prescriptive". It is going to tell us what to do and how to do it. No selection or choices on our part.

                        250.4.A.1 tells you what the grounding and bonding is going to do.
                        "will limit the voltage imposed by lightning, line surges, or unintentional contact with higher-voltage lines and that will stabilize the voltage to earth during normal operation"

                        So, follow the rules and all good things will happen - or not.
                        1. "and that will stabilize the voltage to earth during normal operation" So, is a lightning strike "normal operation. No. Wait a minute, it's normal operation, what is to stabilize.

                        2. So, is there any expectation that grounding/bonding "will limit the voltage imposed by lightning"? No. Lightning strike hits close and raises the distribution MGN to 50KV. And the house? The house neutral/ground is tied right to the MGN. It goes right up with it.

                        3. "unintentional contact with higher-voltage" Ok consider dropping a substation 69KV line across a 7200V feeder to suburban housing transformers. 69KV is 40KV to ground, the 7200V line jumps to 40KV, the service to the house jumps to 1300V and it is going to stay there until the substation protective relays open the feeder CBs - Or until the house CB opens or the meter disintegrates. And the ground rod is .................
                        ......................................
                        .......................................
                        ......................................
                        doing nothing until - Ahhh something flashed over.

                        4. "line surges" So, what is that? It is not a switching transient, nor contact with a higher voltage line, nor lightning strike induce. "Surge" is not defined in the NEC. It is not defined in IEEE 100.

                        I have this picture in my mind of a Gary Larsen cartoon. House covered is arcing slime. Guy standing next to the house looking at the distribution line. There is a bulge traveling down the distribution line looking like a snake that swallowed a pig. "Oh, oh, here comes another surge."

                        Not to be confused with Art 280, 285 Surge Arrestors, Surge Protective Devices.

                        So 250.4, 250.4.A.1, No clue what they are talking about.

                        ActionDave in post 2 nailed it.


                        the worm (is being driven out of the ground by the "surges")
                        Without data you’re just another person with an opinion – Edwards Deming

                        Comment


                          #13
                          Originally posted by electrofelon View Post
                          But current takes all paths, it doesn't matter if one is better or not.
                          Current takes paths proportionally to their resistance/impedance, so it certainly may matter which path is 'better.'

                          Additionally, there's the effect on potential difference. If some touch potential develops between earth and some metal part, that potential is there until a path -maybe you - comes along to carry current. Of there is already a low resistance path, then that potential is somewhere between significantly reduced or effectively gone.


                          The only ways I can see bonding to dirt helping is:

                          1. It causes enough fault current to trip an OCPD (unlikely at less than 600v of course)

                          2. There is some sort of ground detector which opens the circuit.

                          3. Ita a low energy source such as Capacitive coupling or a high impedance fault, in which case the voltage difference can be "shunted"
                          I think you're overlooking the mitigation of a variety of possible touch and step potentials from situations other than a ungrounded conductor faulted to ground.

                          Comment


                            #14
                            Originally posted by JPinVA View Post
                            As you noted, it doesn't help with a "source" fault as source faults, by design (and code) take the low impedance neutral back to source. Well, technically, they also take the ground path...but for OCPD purposes, the neutral path is required.

                            We live in an electrically charged world. The electricity we create in our generating plants and distribute on wires to our homes is but our taming of the charges. There are many "untamed" charges around us...and the positive charges like to hook up with negative charges. Charges being imposed on things in and around our house may be different than the charges on the ground. They want to get together.

                            If we make it easy for them to get together, then it becomes an orderly everyday hook up. We make it easy by bonding all the electrical things together in the house, to include the dedicated EGC. This completes the easy path to the panel, and the GEC gets it to the electrode and to the earth. This orderly every day hookup ensures charges don't build up to the point where the potential difference gets to an unsafe level...and violently comes together.

                            As for lightning, the GEC really doesn't help much on a direct strike...you need LPS for that. But lightning doesn't just affect what the bolt touches. There are all sorts of charges associated with lightning...some get imposed on the structure...some ride the wires...both inside the house as well as on utility poles. As these charges flow through the house and the wires, they are trying to equalize...headed to (our from) the earth. A house "grounded" to ground (the GEC playing an important role in the connection) makes it easy to complete the connection.

                            As for man made sources along the distribution lines....surges...and power line faults...these desire to go back to source. If these faults are imposed on the house in some way, the low impedance path within the house to ground helps ensure dangerous buildup does not occur in the house itself.
                            I like a lot of what you said here. Lightning can be many thousands of volts, and even high frequency involved, that means impedance is a factor and not just resistance. Also keep in mind it is seeking path to earth and not to the source like we have with a fault from an ungrounded system conductor. A reason we must use many items if present as grounding electrodes is because those items generally have a low impedance to earth. Now you may still have some stray currents finding other paths because current does take all available paths, but the lower impedance paths will carry more current than the higher impedance paths.

                            Originally posted by electrofelon View Post
                            But current takes all paths, it doesn't matter if one is better or not.
                            Correct it takes all paths, but divides in different levels dependent on impedance of each path.

                            A ground rod at a building service with resistance to earth of 25 ohms, may just be low enough to let the thousands of volts imposed on it through the rod instead of arcing across an air gap someplace on the EGC elsewhere in the building.

                            Somewhat of a crapshoot what may happen, especially the more direct the lightning hit is.
                            I live for today, I'm just a day behind.

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                              #15
                              Originally posted by jaggedben View Post
                              Current takes paths proportionally to their resistance/impedance, so it certainly may matter which path is 'better.'
                              How? Please explain.

                              Additionally, there's the effect on potential difference. If some touch potential develops between earth and some metal part, that potential is there until a path -maybe you - comes along to carry current. if there is already a low resistance path, then that potential is somewhere between significantly reduced or effectively gone.
                              Yes but you have to pretty much be standing right on the electrode for it to make any difference.




                              I think you're overlooking the mitigation of a variety of possible touch and step potentials from situations other than a ungrounded conductor faulted to ground.
                              Im open, please explain!
                              Ethan Brush - East West Electric. NY, WA. MA

                              "You can't generalize"

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