Can't bond ham shack ground to service entry ground

Discussion in 'General Technical Questions and Answers' started by AE0AQ, Mar 6, 2018.

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  1. AF7TS

    AF7TS Ham Member QRZ Page

    The issue with _separate_ ground rods is the danger from currents flowing through the earth.

    Current can enter via one ground rod, travel through equipment, and then return to earth via another ground rod. Much better that this current flow through an intentional heavy gauge bonding conductor.

    If you can run a wire in the soil around your house between the two ground rods, then this will both bond the rods together and act as part of your grounding electrode system.

    See https://forums.qrz.com/index.php?threads/grounding-dos-donts-why-part-3.338689/page-29#post-4394784 for some good comments on the size of the bonding wire.

    73
    Jon
    AF7TS
     
    N4UP, N0TZU and W6KCS like this.
  2. W6KCS

    W6KCS Ham Member QRZ Page

    OP: Do you have your coax entries grounded? Where? NEC 820 covers that and there are some simplified explanations on the web. You mentioned your tower was grounded at the service ground, but is the coax entry grounded there too?
     
  3. AE0AQ

    AE0AQ Ham Member QRZ Page

    Hey guys, thanks so much for all the information! I do get it. Some way or other I have to get the two ground rods connected. Presently I just have an OFC dipole on a Rohn pushup mast on top of my house so RF grounding shouldn't be a big issue, but I sure like my house and would like to keep it from burning to the ground from a lightning strike. But part of my routing is going to have to be following several offsets of the building on top of concrete slab. Not sure how I will be able to do this without sharp bends around corners, and because of foot traffic I have to keep it close to bldg. I don't know if I will be defeating my purpose with relatively sharp bends in the wire.
     
  4. W6KCS

    W6KCS Ham Member QRZ Page

    Did you see my question about the coax entries?
     
  5. WA7ARK

    WA7ARK Ham Member QRZ Page

    No, the issue is that if lightning strikes the antenna structure, some of the current goes to earth where the coax cables enter the shack (shack entry ground), but more than half of the surge follows the coax to the rig, comes out the green wire in the line cord, and flows through all of the ham equipment and house wiring in an attempt to get to the utility ground on the other side of the house. The utility ground system has a lower impedance to earth than the shack entry ground, so the strike energy is trying to get to the utility ground via the house wiring (a bad thing).

    During the surge event, one side of your house is tens of thousands of volts from the other side. The requirement to bond the two grounds together outside the house is an attempt to prevent the current surge from flowing in the house wiring by providing a lower impedance external path..., and to equalize the voltage from one side of the house to the other.

    To a lesser extent, if the antenna ground is not bonded to the utility ground per code, then if the power line is struck, the reverse happens; the surge enters from the utility, but is trying to find earth via the shack entry ground by flowing through your rig and other stuff in your ham shack.

    The advice to dispose of the shack entry ground is bogus. Now if the antenna takes the strike, all of the surge has to get from one side of the house to the other only on the house wiring. Leaving that ground rod in place is better than removing it.
     
    Last edited: Mar 9, 2018
    N0TZU likes this.
  6. AF7TS

    AF7TS Ham Member QRZ Page

    I should have said 'An issue' rather than 'the issue'. As you describe above, with a lightning strike to the tower, you end up with a potential difference between the two grounding electrode systems (antenna system on one side of the house, utility system on the other side of the house) and current going through conductors inside of the house.

    With a lightning strike in the vicinity, you will have current flowing through the soil and potential differences between non-bonded grounding electrodes, which can again cause current flow inside of the house. We can argue about the relative risk between direct versus nearby strikes, but both are an issue.

    Lightning is not the only issue. I've read reports (granted, from the internet, but on electrician's fora) of _grounded_ metal causing shocks, associated with utility caused earth currents and the associated potential difference. An example would be someone getting shocked touching a hose bib; all metal internal piping which is bonded to the electrical system ground, with grounding electrodes on the other side of the house. The potential between the patch of soil near the hose bib and the grounding electrode system is enough to shock someone (with wet bare feet and hands).

    For what its worth, I've personally encountered discharge damage to phone wiring inside a building where the incoming phone line passed through some sort of lightning/surge arrestor which had an isolated ground rod. There was no evidence of a lightning strike anywhere on the building, and replacing the wire was enough to fix everything; no high currents flowed on the external wiring coming in to the building. But the _internal_ damaged wire clearly suffered a severe insult. There were jagged points of copper ejected from the wire every few inches, each ending on a charred section of wall.

    73
    Jon
    AF7TS
     
  7. N7WR

    N7WR Premium Subscriber QRZ Page

    I live where we get lightning though probably not as much as you do at your location. My tower is 150 feet from the entrance to my radio room and the entrance panel there is about 75 feet and around a corner from the service entry ground rod. It was expensive (1 time expense) but when I built the station 15 years ago I installed three ground rods (one for each leg) at the base of the tower. Using #2 copper stranded wire I ran underground from the base of the tower to a ground rod just below the (grounded) entry panel where the coax, rotator cable and remote antenna switch cable come into the radio room. That ground rod was grounded (using the same size wire) to the service entry ground rod. In other words, a single point ground system.

    The coax, remote switch and rotator cables are all protected inside a weather proof box at the base of the tower using polyphazers which, of course, are grounded to the ground rods at the tower base. At the entry panel into the radio room those same cables are again protected by grounded polyphazers.

    As I said that was not inexpensive however dividing the total cost over the time frame the system has been up (and it isn't done yet) made the expense easier to digest. Having watched lightning strike the ground just a few yards from the base of the tower multiple times over the years and never having had any damage I'm glad I went to the time/trouble/and expense of doing the install the way I did.
     
  8. W6KCS

    W6KCS Ham Member QRZ Page

    I don't think anyone suggested that he remove the coax entry ground, or if we did, it was a typo/miscommunication. It sounds like he has a ground rod at the shack with the sole purpose of connecting the equipment chassis to ground, but not the coax entry. If that's true, it should be removed, because it a) Doesn't serve the purpose of keeping the coax surge currents out of the shack, and b) creates a dangerous situation in the event of a nearby strike, where large currents spreading out from the strike point travel through the ground, and if he has two ground rods that are unbonded, they will be at very different potentials and will try to equalize through his equipment EGC conductors and coax. The EGCs are there to clear allow the breakers to clear fault currents, not carry lightning surges.

    I'm not certain about his entry ground being there or not because I don't think he ever answered the question, but if that shack ground rod does have the coax ground bonded to it, then it should stay as you said, but must be bonded to the other grounds or all hell will break loose if a nearby strike occurs.
     
    Last edited: Mar 10, 2018
  9. AE0AQ

    AE0AQ Ham Member QRZ Page

    Thanks so much again. You all have been a great help, even though it seems that there are some differing opinions on grounding. I have only been licensed for a couple of months so this whole hobby is new to me. I have talked to some local hams but they seem equally divided on the value of grounding with and without universal bonding. Each side seems to have facts and experiences to back up their claims. It seems very confusing but I believe that here at QRZ I have received a consensus opinion that I will go with. I am going to have my entire system bonded to my electrical entrance ground (though I am still working on how I will do it) and though I do not have my coax yet grounded I will do that also. I assumed that happened at the chassis ground.

    Honestly, it seems that after 100+ years of hamming that there would be hard and fast scientific proof that one way is vastly superior to any other way. But I guess like any other endeavor opinions abound and that is what being part of the human race is about.

    So my thanks to all of you. I appreciate the time you have taken to help educate me. I will continue to learn about grounding and all other things HAM as time goes on.
     
  10. K4SAV

    K4SAV Ham Member QRZ Page

    Exactly true. The proof is there, but there are others that have opinions directly opposite that. Your job is to separate the facts from the fiction.

    Jerry, K4SAV
     

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