[TowerTalk] Tower lightning ground system layout

[K9MA]

This is exactly the scenario I've imagined. Thankfully, it hasn't 
happened here yet. I think it's virtually impossible to completely 
protect the equipment, at least without building a new house, but I also 
have insurance. Replacing equipment is a nuisance, but not a disaster. A 
fire is a disaster, and that is what Keith's grounding system apparently 
prevented.

No doubt, in Keith's case, the strike to the tower induced currents in 
the power lines, which caused the damage. I've arranged my station so I 
can easily disconnect all the antennas and control lines, as well as the 
AC power. I know disconnecting the power is no guarantee, but it can't hurt.

73,
Scott K9MA



On 5/19/2020 06:48, Keith Dutson wrote:
> Art,
>
> My tower had a direct lightning hit the evening of May 9, 2019.  This was
> observed visually by my daughter who lives on my place of 16 acres.  She
> sent me a text asking if I knew lightning had struck the tower.  She said
> sparks flew in all directions.  I was inside the shack and felt a concussion
> like I had experienced during basic combat training in the military.
> Virtually everything in my shack was destroyed.  No antennas were attached
> to any equipment as I was in the process of moving the operating desk.
> Transceivers were connected to the Internet and computers for initial
> software setup.
>
> Upon investigation by the insurance adjuster, it was determined the problem
> was caused by AC power surges.  Virtually all breakers in the panel were
> tripped, although they are still in use today.  There was severe arcing
> everywhere with a connection to AC power, including televisions monitors and
> computers.
>
> I have subsequentially collected more than $20K insurance payment for
> damages, and am now in the process of rebuilding the multi-two station.
>
> The tower suffered no visible damage, but the 40-20-15-10 Yagi on top is
> toast, along with the rotor.  This is at 150 feet.  There is a Force-12 C-3
> at 120 feet turned by a TIC Ringrotor that is okay, but the 213 coax is
> toast.  The rest of the tower was clear for earlier re-build of Yagi's.
>
> I will add to the tower grounding system.  Grounding effectiveness is highly
> dependent on soil conditions.  My soil is mainly sandy loam (from an old
> farm), plus iron ore clay and gravel down below 3 feet.  The ground rods are
> 8 feet straight down, one at each leg, then going out 16 feet to the second
> rod, and 32 feet to the last rod.  All are connected with #2 tinned solid
> copper wire, as used by the power company on power line poles.  Erico
> Cadweld Oneshot for #1-2 solid are used to connect the wire and rods.  This
> system is also connected to another ground rod at the shack entrance, below
> a KF7P custom entrance panel.  A three inch copper strap connects the ground
> rod to the entrance panel.  This shack ground rod is also connected to the
> AC power service ground rod at the breaker panel.
>
> My college degree is in physics and math.  I have studied lightning and
> found quite a bit of information, especially from work done in Florida.
> Keep in mind that lightning is basically a huge collection of electrons
> flowing through a plasma until it reaches ground.  Those electrons are
> looking for places to flow, once they get to earth.  They will follow the
> paths of lowest impedance.  When there is not a path, they will arc over to
> complete the path.  I think 32 feet is a reasonable length in my case to
> dissipate the bulk of electrons.
>
> Good luck with your plans and installation.
>
> 73, Keith NM5G
>
> -----Original Message-----
> From: TowerTalk <towertalk-bounces at contesting.com> On Behalf Of Art
> Greenberg
> Sent: Monday, May 18, 2020 2:29 PM
> To: TowerTalk at contesting.com
> Subject: [TowerTalk] Tower lightning ground system layout
>
> I am working on the layout for my tower lightning ground system.
>
> I have on hand about 275 feet of #2 bare solid copper. I also have 17 8-foot
> ground rods.
>
> I've read that lightning protection "radials" reach the point of rapidly
> diminishing returns at lengths beyond about 70 feet.
>
> Originally I planned to have three runs of 50 feet about 120 degrees apart
> and make a fourth run go to my entrance panel and mains ground. But it seems
> my distance estimating skills are lacking. I just measured that distance and
> its more than 100 feet, and well beyond being an effective length.
>
> If I instead go with four runs of about 65 feet spaced at about 90 degrees,
> the fourth run will be limited in length by a driveway. I can't rotate the
> whole pattern very much to improve that due to another obstacle. My apparent
> options:
>
> 1 - I can abandon the idea of equal angular spacing to make that run a bit
> longer. I think I can get the full 65 feet but I'll be going into a wooded
> area with the possibility of having to deal with shallow tree roots and I
> definitely won't be able to make a perfectly straight line of it.
>
> 2 - I can turn it into two or three shorter runs in a fan configuration
> (also abandoning equal angular spacing), but the angular spacing between the
> fan runs will result in the set ground rods on each run that are 16 feet
> from the base of the tower being much less than 16 feet apart. I imagine the
> optimal spacing rule of 2 times rod length still applies.
>
> 3 - I can put a bend in a single run to turn it parallel to the driveway to
> get the full 65 feet. I would have to abandon equal angular spacing to avoid
> an acute (less than 90 degrees) bend. What would be the best way to lay out
> this bend (e.g., multiple gentler bends vs. a single bend, smooth curve or
> something else, what about ground rod placement, etc.)?
>
> Any of these options means acquiring more ground rods. I think I have a
> sufficient number of Uni-Shots already.
>
> I'm thinking option 1 is best, but I'm uncertain. Is there a clear advantage
> to one approach vs. the other?
>
> While I'm asking ... Should I be thinking about using more shorter runs, say
> 5 runs of 55-ish feet spaced 70 degrees apart, or 6 runs of 45-ish feet
> spaced 60 degrees apart?
>
> Yeah, I'm probably over thinking this. But I live in Florida and summer
> thunderstorm season is about to begin.
>
> Thanks.
>

-- 
Scott  K9MA

k9ma at sdellington.us