[TowerTalk] Tower lightning ground system layout

[wc1m73 at gmail.com]

I had a similar experience. A stack match was the only item on the tower
that was damaged -- relays fused, PCB trace vaporized. But everything
connected to my shack computer was damaged or destroyed. The insurance
didn't have to pay as much because I did a lot of troubleshooting and repair
myself instead of declaring everything dead.

Also, my tower didn't take a direct hit. An induced surge was caused by a
massive strike in the woods several hundred feet away.

The tower was installed with Ufer ground connected to three 1/0 radials,
each 50 feet long, with 8-foot ground rods Cadwelded every 16 feet. The
tower is 225 feet away from the shack, so I didn't use a separate ground
wire between them. The shack end has a single-point ground with its own
ground rods. The SPG ground is bonded to every utility ground that enters
the house. Every non-ground wire is connected to a surge suppressor at the
tower end and at the shack end. Polyphaser coax surge protectors are used on
RF cables and suppressor boards are used on all the low-voltage rotor,
switch, etc. wires. The suppressor boards have two MOVs and a fuse for each
wire (total of four per wire.)

Further analysis suggested that the surge came in on the control leads for
my three SteppIR antennas, and from the control boxes to the computer, and
from the computer to everything else. Being selected for higher-voltage
rotor cables, the MOV trigger voltages were too high to catch the surge, and
the fuses weren't fast enough to blow, before the damage was done. I changed
the MOVs to lower voltage, but it's tricky because you can't use MOVs that
are too close to the operating voltages of the attached equipment.

My point is, don't rely on the ground system and/or suppressors to keep you
safe from a lightning strike. After my incident, I built a patch panel
behind the SPG panel that allows me to disconnect every cable and wire
leading to the towers, antennas, rotors, switches, etc. There are also
disconnect boxes for the AC to the shack and the amps.

I wouldn't jinx myself by declaring victory, but I haven't had any lightning
damage in the 13 years since building the patch panel.

73, Dick WC1M

-----Original Message-----
From: Keith Dutson <kdutson at sbcglobal.net> 
Sent: Tuesday, May 19, 2020 7:49 AM
To: Tower Talk <towertalk at contesting.com>
Subject: Re: [TowerTalk] Tower lightning ground system layout

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.

--
Art Greenberg
WA2LLN
art at artg.tv
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