>Sorry Rod, I didn't see the part about your size limitations but I
>still think your better off with the flashing strips even if they are
>not the width we would like to see. I've got somewhere a paper written
>within the last couple of year by a NASA group that studies lightning
>at the Kennedy Space Center. Real up to date info describing alot of
>reason to change our current methods of dissipating lighting. Among
>other things they strongly discourage the us of ground rod for a
>system of shallow placed wire much like a radial ground plane. This is
>much more effective in dissipating the charge due to the fact that a
>strike wants to spread out radially like the waves in a pool of water
>after a stone is tossed in. If you like send me your snail mail address
>and I'll see that you get a copy. It's rather long, I'm a lousy typist
>and I don't have a scanner otherwise I'd post it for all to see.
________________________________________________________________________
I am sure that you are correct regards copper strips being better
than braid for lightning disappation because of the lessened inductance
and therefor less L di/dt voltage drop across the length of the strip or
braid.
However, the situation here is such that the tower is well grounded and
250 feet from the hamshack. The PolyPhaser devices and the aluminum
plate to which they are attached (with Penetrox and star washers)are
inside the shack only 6 inches away from the 12" long 3" wide PVC that
joins the inside of the hamshack and the outside world. The ground
system initial ground rod (for the station ground) is only 4 ft below
the PVC. I only need to make a short run of braid (or some good
conductive material) from the aluminum plate to the ground rod.
The grounding system at the hamshack is a different one altogether from
the grounding system at the tower (on PolyPhaser's suggestion: they said
that if the tower is over 100 feet from the hamshack, there is a need
for a separate ground system.
Part of the coax that comes in from the tower is aluminum jacketed CATV
coax that is direct-buried (we have acidic soil here that is kind to
aluminum and tough on copper). The remaining charge that reaches the
hamshack is only a small fractional value of that which hits the tower
with its lightning rod at the 150 foot level. The 6 each 8 foot ground
rods afford a reasonably good grounding system for the tower and antennas.
The remaining charge that comes into the shack has only been sufficient
to blow a chip or two in the DRSI board TNC or to have (1 of 3 strikes)
hurt the Alinco transceivers (they were rebuildable for a reasonable sum
by Alinco) that are connected to the DRSI board in the PacketCluster Node
computer.
I am simply trying to bleed off the remaining charge that hits the hamshack
via the coax to the Alincos. I always disconnect the HF gear when not in
use and it is not in use if I can see lightning or hear thunder, no matter
how distant. (That's not foolproof: one of the 3 strikes at this location
came on a day in which all other symptoms of storm were so far distant that
only the faintest rumblings were audible... it was the only lightning strike
in this county, that day.... my bad luck... fortunately, it was not a really
major strike and only blew a trap on the 402CD and the direction sensing
potentiometer on the TT2. I had no lightning protection at all when that
happened, having lived in Florida for 15 years with a floating tower and
antenna system that was never hit by lightning down there. Now I even
disconnect the rotor control box cables via Radio Shack quick-disconnect 6
conductor connectors).
I took a very major hit at Paris, TN at a digipeater location which I had
installed just 2 weeks earlier. In this case, there was only one ground
rod that had been installed by the host. I installed the Astron power
supply, the Alinco DR1200, the TNC with its AC wallplug power module, and
my ground system. My ground system consisted of 3/4" braid attached
securely to the Astron power supply's external ground lug, and to the
PolyPhaser IS-50UX-C1 device that interceded the coax line to the DR-1200.
The braid went directly (5 feet away with most of the braid on the inside
of the metal building) to the two new ground rods I had installed 8 feet
apart.
When I heard about the lightning strike, my heart sank. I went the 60 miles
to the site and found the host's electrical distribution box innards blown
all over the small metal building that held the other repeater equipment.
The host's approach to lightning protection was a PolyPhaser IS-50UX-C1
attached to the metal wall that was then in turn connected to his lone
ground rod by a wire I considered too small. The host's PolyPhaser device
had a very large (6 inch diameter), completely blackened area on the wall
radiating outward from where the device had been attached (with no Penetrox).
The telephone line input box was also blown apart. The AC plug from the
Astron power supply that I had inserted into the wall plug had a similar
large, completely blackened area around where it joined the wall plug.
When I pulled the AC plug out of the wall plug, I noticed the ground lug
had a very large chunk of the lug missing with symptoms of a severe arc
having taken place. There was also carbon black on the back of the Astron
power supply where the braid had been connected and another one where the
AC power ground was attached on the inside of the power supply (as I found
out later).
I knew the equipment was as useless as the several racks of host's
equipment and so delayed even putting it all together to see what the
symptoms were. After replacing the fuse in the power supply I was amazed
to see that all, repeat all, of the equipment was functional. The 3/4"
braid and 2 ground rods became the return path for a major portion of the
bolt. The PolyPhaser device had protected the Alinco DR-1200. The heavy
braid had taken the current and shorted it to ground with no loss of
equipment!!!!!!
THEREFORE, braid in and of itself is a decent ground. It displays low
inductance and, if of sufficient size, will carry considerable current.
It may not be as effective as 9" wide copper strips, but when forced into
use by physical circumstances such as the situation here at my hamshack,
I am convinced it will handle the small amount of residual voltage/current
250 feet from the well-grounded tower.
My prime question was, "Is tinned copper braid a detriment because of the
tin covering over the copper?". I believe I have received some very good
information regarding the oxide that tin may become covered with when
exposed to the elements.
Therefore, my approach to the situation is to use solder to make a "solid"
end (at both ends) to preclude the possibility of corrosion between the
individual strands (and hence diode contact) and I will apply lots of
Penetrox at both junctions. Further, I will cover the new braid for its
full 4 foot length (outside the wall and extending inside the wall a foot)
and over the end of the ground rod that is annointed with Penetrox A, with
heatshrink material so as to prevent excessive weathering from moisture.
For those that wish to see a summary of the responses I received, please
let me know directly as opposed to the reflector and I will be glad to
oblige.
Thanks for the response and the help in solving this predicament that I
found myself in by the circumstances presented by the small PVC pipe
joining the inside wall of the hamshack with the outside wall of the
house.
Best Regards,
Rod, N5HV
w5hvv@aeneas.net
P.S. This is my signoff message in this regard.
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