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Grounding a base antenna?? Lightning

Discussion in 'CB Antennas' started by hammer0630, Sep 1, 2013.

  1. hammer0630

    hammer0630 Active Member

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    OK this is a subject that has been talked about a lot but I still am not sure of some of the basics of grounding a base antenna against lightning strikes. If you use the proper copper wire? how many feet into the ground is needed to achieve a earth ground and how do you check that you have achieved a proper ground into the dirt or is there another way to ground possibly through your house electrical ground? And this is the one I am most concerned about when it comes to properly grounding a base antenna If you are hit directly with a lightning strike to your antenna what happens to your radio does it save your equipment? I once attached a ground wire from the chassis of my radio and inserted it into the ground receptacle on my wall socket and it removed some of the hash buzzing on my receive and also I could turn my power mic up quite a bit louder before it would squeal so can you achieve a proper ground by simply using your house ground? Any comments greatly appreciated!!


     

  2. Robb

    Robb Yup

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    The whole idea is this, if you can be sure that the least path of resistance to a lightning strike can be contained to the outside of the house rather than in it, then you might survive and your house not burn down.

    How to accomplish this is not that problematic. First of all, the house ground in its electrical system has a ground rod. Is it enough to redirect some +150k amps of lightning current safely into the ground? No; that is more than one single ground rod can provide for that much pulsed current. It was put in to be a reference ground for your power service; not for dealing with lightning.

    Copper strapping at three points close to the mast is the usual method. Will your fiberglass antenna survive? Probably not. How about an aluminum antenna? Maybe/maybe not. The antenna will need to have a DC ground to the mast too. These CB antennas really were not designed to survive a lightning strike. Keep the antenna off of the roof.

    Running a single 10ga strand of copper wire will evaporate in the same millisecond the lightning hits your antenna. Why? Because it will turn it into a fuse and stop being a continuous electrical path for lighting pulses since it can/will not handle that massive amount of heat and current. So, you must create the least path of resistance that can handle that much current w/o melting or evaporating. Takes some pretty large gauge stuff to do that.

    Lightning > Antenna > Tower/Mast > Ground rods(3) bolted to copper strapping/mast > Lightning into the ground.

    [​IMG]
     
    #2 Robb, Sep 1, 2013
    Last edited: Sep 1, 2013
    rabbiporkchop and hammer0630 like this.
  3. Captain Kilowatt

    Captain Kilowatt Professional Amateur
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    Robb: Is that one of Tom W8JI's towers? It looks like it.

    There is a fair amount of knowledge required to basically lightning proof your installation. The actual work is not that bad but you have to know what to do and how do it right. In a nutshell you need to provide a large heavy conductor (minimum 6 gauge bigger is better) from the antenna mounting point to no less than three ground rods driven to a depth of 8 feet and spaced at least four feet apart. The coax should be grounded to the antenna at one end and also grounded to the mast/ground rods at the bottom with no sharp bends in it.It should also be grounded where it enters the house.The ground rods should also be tied to the main electrical service entrance ground at one point and one point only. This ensures that all grounds are actually at the same voltage potential in the event of a strike. There is more to it but this is a point to start from.

    Here is the base of my tower.

    [​IMG]

    Here is the ground cable used. It is 000 gauge (Triple ought)

    [​IMG]


    Coax cables protected by these.

    [​IMG]


    Rotator and switch control leads protected by this.

    [​IMG]

    There is a very heavy gauge copper cable leaving the tower base and running completely around the house forming a complete loop with ground rods every so often along the way. This is tied to the main electrical service panel as well. No guarantee I will be able to leave my gear connected during a lightning strike and be unharmed but it is a step in the right direction. many people refuse to believe that you can leave gear connected and survive a direct strike but having worked in the broadcasting industry for 22 years I can say I have had transmitter sites take a hit and all that has happened was the transmitter high SWR protection circuit tripped the TX off and then reset the transmitter bringing it right back on the air. Then there are the other times that I still don't want to talk about. :cry:
     
    #3 Captain Kilowatt, Sep 1, 2013
    Last edited: Sep 1, 2013
  4. hammer0630

    hammer0630 Active Member

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    cb

    cb
     
  5. Robb

    Robb Yup

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    Principles are the same; of course lightning doesn't know the difference between a CB, Ham radio tower, or your house. I forgot about the electrical service tie-in and the coax, my mistake.
     
  6. Captain Kilowatt

    Captain Kilowatt Professional Amateur
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    An antenna is an antenna and a lightning strike is a lightning strike. The only difference between ham and CB is that most CBers' seem to think a single four foot ground rod and a piece of 12 gauge housewire will save them while slightly fewer hams feel the same way. :D Then there are those that know what it really takes to do the job, regardless of the radio service.
     
    #6 Captain Kilowatt, Sep 1, 2013
    Last edited: Sep 1, 2013
    222DBFL and The DB like this.
  7. johnny9

    johnny9 Active Member

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    good teachings in these posts,;) picking up 2 23ft sections tomorrow with a 4 ft apex,and has the tilting bottom,with a winch for raising and lowering and these pics made me understand much more than my single ground rod i have now,thanks,j9
     
  8. Lil'Yeshua

    Lil'Yeshua .......

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    Several years ago I'd experienced a close lightning strike. I had just shut my eyes to go to sleep that night. There it wasn't just one loud bang but five bangs in quick succession as the lightning hit the tree twenty feet off of the corner of my parents house. The lightning blew the (big)tree's trunk bark off if it. The two metal rods propped up against the tree's trunk,the ground had circular rings around the rods where the lightning had disturbed the dirt resembling anthill granulated dirt. All of the appliances electronic parts in the house had been zapped and had to be replaced. The water oak tree became firewood three years later. Last but not least,there was the fragrance of ozone(I think)in the air or maybe it was the attic fan pulling all of the crispy electronics smells past my nose.
    Good grounding practices are a must if you like not paying for everything over and over again including your house
     
    #8 Lil'Yeshua, Dec 26, 2013
    Last edited: Dec 26, 2013
  9. Captain Kilowatt

    Captain Kilowatt Professional Amateur
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    years ago at another location I was laying in bed and three things happened at the same time.

    #1-the bedroom lit up like daylight.

    #2- the entire house was shaken by an extremely loud BOOM!

    #3-there was a very distinct frying sound at the time the above two events happened.

    After I started breathing again and checked the bed for signs of having been soiled I looked out the window at the tower. Everything was still there so I ran to the basement to check the gear. All was fine. The next morning I checked the tower and found a couple burn marks where the ground cable was connected to it and the grass/ground was torn up a bit around each of three ground rods. No positive proof however this all indicates a direct strike on the tower. The radio gear and rotator came thru unscathed. Surviving a direct strike is certainly possible but you need more than just a single ground rod and a piece of wire. My new installation pictured above at this location is far above what it was at the former location so even while I feel comfortable I will still disconnect my transceivers if a storm is nearby. I don't believe in pushing my luck. Yeah I am a tiny bit paranoid about lightning strikes.Radio gear is one thing, the house is another.
     
    222DBFL likes this.
  10. Jay in the Mojave

    Jay in the Mojave Active Member

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    Hello All: Great info and pictures here.

    Not much can be done for a direct lightening strike, but precautions can be taken.

    While servicing radios on top of a local mountain top over looking the Southern California area, I noticed a new tower being installed, and the installation crew was coiling the coaxes in 3 to 4 turns while each end of the coil, a ground rod was attached. I asked what the coils of coax Heliax was all for. They told me that lightening didn't like to pass thru a coil and it was a last ditch effort to save the radio equipment inside the utility shack. They also installed commercial lightening protection equipment, as the coaxes entered the utility shack.

    I noticed that the coaxes coming down from the antennas on the tower were also connected to a large bus bar assembly that the coax shields were connected to on the tower base, and massive ground wires attached. They were really serious about lightening strikes taking out there equipment, and doing a finial and complete computer reset of the controllers.

    Jay in the Mojave
     
  11. Captain Kilowatt

    Captain Kilowatt Professional Amateur
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    Those coils of transmission line have to be aligned so that they are in the same plane as a direct line to the tower. This means you should not be able to look thru the loop and see the tower. This is to reduce the transformer effect of inducing an electric field into the transmission line from the surge field generated in the tower itself during a strike. As the energy moves out from the tower and intersects the loop it can generate a voltage in the transmission line and this is what you want to avoid.
     
  12. Limeybastard

    Limeybastard Active Member

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    On a slightly different subject, so those small lightening rods some homes have on their roof is pretty useless?
     
  13. Robb

    Robb Yup

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    On the family farm/barn and on other barns close to us w/metal roofs, there are some that use lightning rods. They alone do not carry the current; the very large gauge wire/rope is attached to ground rods below to redirect that large flow of pulsed current thru the lightning rod. I've seen a barn that didn't have a sufficient grounding system, and it caught fire and was heavily damaged.

    A lightning rod is an attractive nuisance and a potential danger to life and property if not properly installed. You live in Florida IIRC; the lightning capital/state of the US. You need to be aware and informed of lightning hazards since it occurs there with greater regularity - IMO. Having a vertical antenna w/o lightning protocols is a formula for real danger! No rod on the house!
     
    #13 Robb, Jun 14, 2017
    Last edited: Jun 14, 2017
    Limeybastard likes this.
  14. The DB

    The DB Sr. Member

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    They are not useless, but they don't work like most people thing lightening rods work. They are actually designed to repel lightening, not attract it. However, it is possible for storm conditions to overload the lightening rod systems's ability to repel lightening and cause a strike anyway.






    The DB
     
  15. Captain Kilowatt

    Captain Kilowatt Professional Amateur
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    Exactly. Lightning rods are intended to bleed off a charge safely before it builds up to the point of a strike. When it cannot do that fast enough lightning strikes the rod and the energy is safely routed to ground if the rod is installed properly. Contrary to popular myth they do not attract lightning unless it was bound to hit there anyway. The key, like ANY good lightning protection system is to make sure it is installed PROPERLY.
     
    #15 Captain Kilowatt, Jun 14, 2017
    Last edited: Jun 15, 2017

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