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Station Grounding Question

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by KB5CC, Mar 3, 2019.

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  1. KB5CC

    KB5CC Premium Subscriber QRZ Page

    Hopefully, my first question to the forum will not be an obviously dumb one. I read the three "Grounding Do's Don'ts & Why" posts and definitely plan to study them closer. I've also watch several videos on Youtube (selecting ones that seem to have mostly positive comments) but I am stuck on something... I understand that not only do I need to ground my radio to a copper rod outside of my house but I should also then bond that grounding rod to the already existing grounding rod near the electrical service panel. So, ground the gear to a rod and then bond the rods together effectively creating a single point.

    Here's my question... why not just ground the radio straight to the already existing grounding rod?

    Greg H
    Austin, TX
     
    Last edited: Mar 3, 2019
  2. WA7ARK

    WA7ARK Ham Member QRZ Page

    Presumably, the grounding rod just outside your ham shack is in the direct coax path from antenna/mast/tower to ham shack, while the electrical service ground rod could be some distance away around the house. You want a short, direct path for the lightning surge.

    I have four ground rods around the base of my tower, then one near the building under where the coax cables enter the building through a bulkhead, then that is cross tied to the electrical service ground, and then goes further to a ground-rod near my well-head and finally to the metal well-casing (21ft of steel pipe going straight down...)

    The antenna grounding system being cross-tied to the electrical service ground is what is mandated by Code.
     
  3. K6CLS

    K6CLS Ham Member QRZ Page

    Exactly that worked out perfectly for me at one QTH. The shortest path was from the radio desk, out a hole in the wall, a couple feet to the rod.

    But lightning is very rare here.

    Do you have a similar situation?
     
  4. KB5CC

    KB5CC Premium Subscriber QRZ Page

    Possibly similar situation but it would be my second choice for where to have the radio. It would be in my living room and I think I should be able to run the coax out the same hole where the TV cable used to come in. Then from there it would run outside the house about 20 ft to where the electrical service ground rod is located.

    My first choice is in a back room which is the exact opposite corner of where the electrical service grounding rod is located. I would have to run the grounding cable around the entire back of the house and then up the side... a total of roughly 80 ft.

    If I make a short run from that back room to a new grounding rod right outside the window (call it Point B) and then connect that new rod to the grounding rod already up near the front of the house (call it Point A)... how is that really different than simply grounding the radio directly to Point A?
     
  5. KB5CC

    KB5CC Premium Subscriber QRZ Page

    Thank you! I think the obvious finally clicked in my brain. You want the surge to have the shortest path possible to earth. You certainly would not have that if you ran a long grounding wire half way around the house to the electrical service ground. I think the idea of bonding the two rods to effectively make them a single point is what had me hung up on "Well, if it's a single point why not just have one rod?" I think I get now why that would be a bad idea.
     
  6. WB5WPA

    WB5WPA Ham Member QRZ Page

    Are you planning on being on-the-air during an electrical (thunder) storm?

    Is your station being designed to survive a direct lightning strike while all the equipment is connected (but in the "off" state)?

    There *are* certain minimum things that need to be done, whether or not you are designing a station to survive a lightning strike or not ... LIKE providing a bleed-off path to earth ground FOR static charges that WILL build up on conductive structures (antenna or tower) UNDER a statically-charged "thundercloud" (cumulonimbus; towering, rain-producing cloud mass).
     
  7. WA7ARK

    WA7ARK Ham Member QRZ Page

    It doesn't much matter if you are "on-the-air" at the instant the lightning strikes, or not! The antenna will likely always be there regardless if you are in the shack, or even home at the time.

    The goal is to do enough so that if your antenna is struck, you minimize the damage to your house and its contents.
     
    K0UO likes this.
  8. WB5WPA

    WB5WPA Ham Member QRZ Page

    I'm just asking the question, as, I WANT TO KNOW WHAT IS IN THE MIND OF THE OP.

    I DON'T expect a serious answer of YES to the question "Are you planning ... during ... storm".

    Let me further "virtue signal" (seems to be needed on occasion): I DON'T OPERATE DURING LIGHTNING STORMS, but, MY UHF REPEATER DOES.

    I notice no comment on the "meat" of my prev post, to wit: "There *are* certain minimum things that need to be done, whether or not you are designing a station to survive a lightning strike or not ... LIKE providing a bleed-off path to earth ground FOR static charges that WILL build up on conductive structures (antenna or tower) UNDER a statically-charged "thundercloud" (cumulonimbus; towering, rain-producing cloud mass)."

    Now, where were we?
     
    Last edited: Mar 3, 2019
  9. WR2E

    WR2E Ham Member QRZ Page

    I think OP may be missing the part about "step voltage" during a surge event which IMO is the main reason that NEC demands that multiple ground rods be bonded together.

    At the instant of an 'event' where a surge is headed to ground, the voltage at that ground is raised to a much higher voltage for an instant. In other words, relative to ground, that point is no longer ground, for an instant.

    If there are two 'grounds' which are not bonded with as low an impedance bond as possible surge energy will flow away from the higher voltage point to the lower voltage point through any means it can find. This could be through the safety ground wiring in the home.

    The idea of bonding multiple ground rods together is to keep that energy OUTSIDE the home.

    Yes, of course ANY connection will exhibit an impedance to a fast rising surge, and that includes the 6ga bonding wire between rods, but this impedance is certainly much less than the circuitous ground path that weaves throughout the home.

    One can never prevent damage completely, the idea is to MINIMIZE damage as much as humanly possible.

    @KB5ZZT

    PS: I have first hand experience of the effects of a DIRECT strike to a 10 meter vertical antenna.
     
    Last edited: Mar 3, 2019
    W6KCS, WB5YUZ, WA7ARK and 1 other person like this.
  10. WB5YUZ

    WB5YUZ Ham Member QRZ Page

    Actually, in order to comply with NEC, you will want to ground the shield of any coax that enters the building at the point of entry. That ground should be bonded to the electrical ground of your home's system. The most convenient way of doing this is to bring the coax into the building physically close to the electrical system ground when that is possible.

    In addition, the third prong of your radios/power supplies will effectively ground your equipment for shock prevention purposes, provided your home's electrical ground was installed properly.

    As for a so-called "RF" ground, one probably won't be necessary. Search for WB2BIK's posts on this topic. In my own experience, I built an RF ground system with a ground rod and a 7' connection to ground. I knew this connection would be too long to be effective on 17m and shorter waves, but eventually I found it wasn't necessary on any band. As far as I could determine, it never caused a problem nor cured one when I had them (my "RF in the shack" problems have all been due to either bad shield connections or misunderstanding of how common-mode current behaves. Every one).

    Certainly, you can try building your station without one, and see what happens.
     
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