Grounding Do's Don'ts & Why Part 3

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by AI5DH, Mar 19, 2012.

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  1. KD0CAC

    KD0CAC Ham Member QRZ Page

    Some guess - estimates .
    Lightning is one of those things we do not have completely figured out .
    I say that because of what I have read & watch , PBS TV at least a couple of Nova etc. programs on lightning , that even though they know a lot about lightning , during experiments & testing it is not totally predictable .
    One perspective that I did not see posted , at least not in the terms I want to use is ,
    What well grounded stations are doing is kind of a reverse faraday cage - to keep lightning out .
    I wander if one of the aspects of lightning that makes it a little unpredictable is that lightning has aspects of both AC & DC and that at what ever part of the lightning at any number of frequencies it can be resonant to something it hits or is near by and could be part of the reason that it will jump one way or the other , or radiate between hits ?
    I can understand that some stations can run during lightning storms and hits and not damage the equipment in the shack , but I can not understand how it the antenna or any small part that cannot carry the current / voltage of a hit be damaged .
    I do some tower work and some of that for several repeater clubs and have replaced more than one antenna that took a hit ?
    To my thinking the lack of damage would be where there is enough conductor to carry away the lightning strike , so like a vertical and some length of feed-line at the top of a tower would be fried but the tower would be OK ?
    I would have to go back through to be sure if this was the grounding thread that someone mentioned the mixing up of radials & grounds , if so we have to remember that radials are manipulating the RF and the grounds [ deeper electrodes ] are dealing with the lightning , not that there is not some interaction , but there is a need to have radials at or near the surface and ground as deep as possible .
     
  2. W3CSR

    W3CSR Ham Member QRZ Page

    I got it. Thanks. That really does explain it.

    Yes, I understand now. Thanks to each of you for being patient and explaining it to me and directing me to good links where it was explained well. For me, I do disconnect my antennas from the radios and from the house, because it is something I can do easily, but some guys are fortunate enough to have set ups that would not permit that due to their complexity.

    I did have lightening hit once. I was upstairs in bed and a crash came down from "above" right outside my bedroom window and probably hit the cable TV wires and propagated down to my house. My dog (a 115 pound German Shepherd) lept up off the floor and onto the bed in one quick, purposeful, but somehow graceful movement that would make an Olympic gymnast jealous. My jump was less graceful. Anyway, we lost the cable TV and Interwebs access. The total damage came down exclusively to the cable multiplexer connector outside the house. That was grounded to outside cold water faucet, as was the telephone network interface box located right next to the cable connector. The phones were fine. The cable boxes and modems were fine. The only damage was that little $1 connector for the cable wires.

    Some hams, like me, can very easily go right out the back door of the house, disconnect the antennas from the cables that go in through a crack in the window, and physically separate the radios from the antenna system when not using the radio. That's what I do. Yes, lightening can hit my power lines miles away from me, before I even know that there is a storm around, and then destroy my radios (and me, since I'd be sitting right in front of them) but that is a very small risk. I'm generally aware of the weather and impending storms. I have a ham transceiver and antenna tuner, a shortwave receiver, a 2meter/440 transceiver, and that's it. I have 4 6-foot cables that go out under the window sill, of which 2 feet is inside and 4 feet outside the house. Those 4 cables connect inside to Alpha Delta antenna switches that then go to short cables that connect to the tuner and radios. Outside, those 4 cables each go to an Alpha Delta lightening arrestor mounted to an 8 foot ground rod that is pounded 5 feet down into clay-type earth about 3 1/2 feet from the outside of the window. From the other side of each arrestor, another cable arises up to an antenna. I have a 12 foot tall 4x4 post that is sunk 3 feet into concrete, with 9 feet sticking up. The post is about 2 feet from the ground rod. At the top of the post is a section about 4 feet long of 2x6 lumber horizontally at the top of the post. From that arises a 10 foot section of 1 1/2 inch PVC pipe to serve as a mast for a 2meter/440 antenna. Lower down on the post, at waist height, are two 4:1 current baluns (on opposite sides of the 4x4 post). Each one of the baluns is fed with a 3 foot cable that connects to one of the lightening arrestors. Going up into the sky from each balun is a section of ladder line that goes up to one of my two doublets at about 65 feet in the air. The fourth lightening arrestor has a cable going to a balun further up the 4x4 post that gives rise on one side to a random length wire of about 55 feet length that rises up to the top of a tree about 25 feet away from the post. The other end of the balun gives rise to a counterpoise wire that is alternatively connected to the ground rod (I know, I know, but it works for me) or I can run it over to the top of a fence from where I have a network of unscientifically and rather randomly spread out ground radials.

    So, in summary, those four antennas come down to lightening arrestors mounted to a ground rod. When I am not using the radios, the 4 6-foot cables that go into the radio room are disconnected from the lightening arrestors, and moved over to a container at the window edge. When I want to use the radios, I just walk out a door right next to the radios, connect any or all of my antennas and go back inside. When I am done with the radios, and I want to turn them off, I go right out the door, disconnect my radios from the world, and go back inside. I can do this in the rain, snow, sleet, heat, cold, wind, day, night, etc.

    My ONLY concern is that if a blast of lightening comes down the antennas and goes to my ground rod, that will be happening right outside my window and I suppose that electrical energy from the lightening will be flowing around the surface of the ground near the ground rod. That will be about 3 1/2 feet from my window and that will be kind of close. I am worried about induced electrical charges being formed in those four "dangling" cables that go into my house. They don't just dangle down at ground level. When not in use, they each connect to 3-way female SO-239's (just to keep water and stuff from getting into the cable PL-259 connectors) and then they are pulled over to the window edge. That's at waist height, about 3 1/2 feet away from the set up of lightening arrestors connected to the ground rod. I need a better way to insulate those four cables from induced charges.
     
    Last edited: Jul 20, 2013
  3. K1VTY

    K1VTY Ham Member QRZ Page

    I firmly disagree with KD5SPX and his position on this. You can take a direct hit on the tower and still have your equipment survive. I have seen it myself. Had a 500 foot tower in Slidell, LA take a direct hit during a storm. Saw the tower take the hit. Saw the tower legs produce steam in the rain after the strike. Thought for sure all the radio equipment in the building would be black and belly up.

    Went inside the building and everything was just playing away just fine. However, there was one ham repeater that had the smell of electronic death coming out of it. The site owner had been trying for months to get the hams to ground the cabinet and coax to the facility ground system. The technical geek for the hams just stood his ground and refused. So they deserve all the damage they took.

    With a properly designed grounding system, you can protect your electronics. Remember I said a grounding system. It takes more than just putting a single ground wire from a tower leg to a single ground rod. It also takes surge protection on both the power feeds and the telephone lines.

    Those that keep supporting the position that you can't survive a lightning strike are just plain wrong. I have built cellular sites and commercial tower sites. If you do your homework, you can survive a strike. Have been on location and seen a number of towers hit and everything stays up and functional. It's not a fairytale.

    Jim
     
    Last edited: Oct 15, 2013
    W1ADE likes this.
  4. W6OGC

    W6OGC Ham Member QRZ Page

    So what is a practical solution for effective grounding?

    I have an outbuilding ~16x20 that I am remodeling for a shack. It is about 100' more or less from the house and separate garage. I just had electrical service beefed up by an electrician for 120 and 240 VAC 40 amp. service. I presume it is grounded per code.

    The soil is very rocky, probably so that an 8' ground rod will be impossible. Even trenching can be fraught with difficulties here.

    Should I put in copper pipe below the surface and tie everything to that? Copper strap? A dozen ground rods of 12-18" spaced around tied together somehow?

    I'd appreciate any insights on how to actually do this.
     
  5. AI5DH

    AI5DH Ham Member

    A real effective means in rocky soils is ground rings and lateral radials. Contrary to popular belief and myths rods do very little in a lightning strike. It is the lateral runs that dissipate the brunt of the energy..


    As for your new shack electrical system a lot depends on how your electrician applied the rules to article 250.32. Ask your EC if he treated the structure as a Service or Breaker Panel extension. In other words ask him if he ran an Equipment Ground Conductor or not. That will determine what you should and should not do.

    If he does not understand th equestion just ask him if he ran 3 or 4 wires from the main panel in the house, and what were those wires. If he ran 4 wires of L1, L2, N, and Equipment Ground Conductor he wired it as a sub panel. If he only ran 3 wires of L1, L2, and N then he ran it as a service. Running as a service is the preferred way in this application.
     
  6. W6OGC

    W6OGC Ham Member QRZ Page

    4 wire, black, red, white and green, two hots, neutral and ground.
     
  7. W6OGC

    W6OGC Ham Member QRZ Page

  8. AI5DH

    AI5DH Ham Member

    Pretty much how telephone, wireless carriers, and commercial broadcast do it. But htat is generally well beyond the means of DIY and hams. However you can use some of the same principles and techniques. All of it is code compliant and required.

    The most important thing for you to do is to properly bond the tower, coaxes and use coax surge protectors at the entry point into the shack. It would also be advisable since your shack electric service is 4-wire vs 3-wire is install a good quality 5 mode TVSS at the breaker panel in the shack.
     
  9. W6OGC

    W6OGC Ham Member QRZ Page

    What's a "TVSS?"
     
  10. AI5DH

    AI5DH Ham Member

    TVSS = Transient Voltage Surge Protector
     

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