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From: DavidC[SMTP:eDoc@netzero.net]
Sent: Wednesday, December 08, 1999 6:36 PM
To: towertalk@contesting.com
Subject: [TowerTalk] Three Lightning Protection Clarifications Please?
I think I know the answers to these three questions from my perusal
of the TT archives I saved ... but better safe than sorry!
1. Ground rods:
I am supplementing the existing service panel ground rod by adding one
more rod off to the north and three to the south at 16 foot
separations.
A local phone company guy who is supposed to know these things
told me that since the service panel rod had been "megged out" that
I could use galvanized just as well as copper for the extra rods.
True?
Not true. Megged out is to use a Megger(TM) or equivalent device to
measure the resistance of the ground rod. This is done at about 100 Hz
and has no bearing on the resistance/impedance at RF. While there are
surge currents up to at least 1000 MHz in a lightning-induced surge, most
of the damage is done at dc and the lower frequencies. To avoid a dissimilar
metals problem (corrosion), use the same material for your additional rods as
what is there already. You may want to do a pH test, as previously discussed,
but regardless of the results, you need to use the same material as what's
there already.
2. Ground wire between rods:
I understand that 0/0 is the best choice, though one needs to be
Hercules
to work with it. I have some of what I believe to be 0/2 or 0/3
available that
I'd just need the local metal recycler to run through his stripper. Is
that
acceptable? (What is the thickness of 0/2 and 0/3? Mine is only
identified
600v.) Is it OK to use two lengths of wire if the ends are joined at a
CADweld?
OK #00 is also written as 2/0; 000 as 3/0 and 0000 as 4/0. #2 is "thinner"
than #0 (1/0), so 2/0 is thicker than 1/0, 3/0 thicker than 2/0 etc. The
thicker
the wire, the less inductance it has and the more surface area it provides. The
name of the game in creating a good lightning ground system is lowest
inductance and the most surface area (the ground system surface area should
equal or exceed that of all the RF coaxial cables being grounded at that
location). This is the reason why PolyPhaser recommends wide copper strap
over round member devices.
3. CADweld
The best sources (price) of the CADweld kits are Erico, Ron Block or
DavisRF? What is the best price, with reasonable shipping charges
included, that folks have found, please?
The rods and wire go down this week, CADwelds when I get them. Then
on to the tower!
- Thanks! & 73, DavidC K1YP in lightning-alley ... Hudson, Florida
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