[TowerTalk] Grounding Wire/Strip

[DavidC]

> The water table here in west central Florida is 18-19 feet, or so I am
told.
> Is your understanding that I should drive a rod down to that depth to
> which to ground the tower?
> Not necessarily.  You don't really need to hit the water table with the
> ground rod although it probably would help in your case.  What is your
soil?
> If it is sandy or other poorly conductive material, you would be better
off
> hitting the water table.
> Realize that one of the purposes of the ground rod is to get some of the
> surge current into other (deeper) conductive layers.

I am told by informed sources that the soil in this immediate area is mostly
sand just about down to the water table (18-19 feet down), though there are
traces of clay starting to mix in down below 9 feet or so.

> My tower will be about 100 feet from the shared ground for everything in
> the house & shack.  If I run one of my lines as 1" 75 ohm CATV coax and
> ground the heavy shell at the tower base and at the shared ground point
> do I really need to run an additional ground-only wire to the house?
> No.  Once your tower and the house single point ground are separated
> by more than about 75' they can be treated as separate systems and tieing
> them together is unnecessary unless you want to do so anyway.  Nothing is
> really gained or lost.  However, you must establish a good ground system
> at the tower as well as one at the single-point ground location.

Understood, thanks!

> There is a common fallacy that underground cables are somehow immune
> to lightning surge currents.  I would suggest keeping the parallel cables
as far
> apart as possible.

My concern is if I have 100 plus feet of coax and rotor control line running
outside, above or below ground, and at least 50 feet of that is run in close
proximity (less than 3 feet) parallel to the foundation of my
concrete-block-
on-a-slab-home (all wiring is above ground but some plumbing, at least
drains,
are beside and under the slab) that there *may* be a possibility of
lightning
energy that gets into the antenna and rotor lines coupling into the house
wiring.

I do intend to protect all antenna and rotor lines at the tower and
shack-entry points.

> Another common error is to have protected and unprotected lines in
parallel
> and close together after the protection.  Surge current from the
unprotected line
> can be induced into the protected line under these circumstances.

I intend to protect every single line and have some of the Polyphaser
devices
already.  A request to them for clarification as to the additional specific
devices
I need went unresponded to ... though it could have been lost when my E-mail
Inbox self-deleted ... I will resend it to them.  There sure are lots of
pieces to
the lightning protection puzzle when done correctly!

> For lightning protection purposes, the ground rods should be about twice
> the distance apart that they are in good conductive soil.  So, if you have
an 8'
> rod and 4' is in good conductive soil, the spacing should be 8'; if all 8'
were in
> good conductive soil, the spacing would be 16'.  I personally have
advocated
> a 1.5:1 rather than 2:1 spacing since it is usually difficult to know how
much of
> the rod is in conductive soil unless [extensice] soil samples have been
taken.
> CADWeld(TM) is a trademark and should be noted as such.  However, it
> has taken the place of the more generic exothermic welding and, like
Xerox(TM)
> for photocopying and Kleenex(TM) for tissues, is used to mean that even if
you
> are using another brand of welding, photocopier, or tissue.

OK, will take a closer look at that ... and will use copper strip or 2/0 to
bond them.

> A last suggestion.  Sandy soil can be glassified (petrified) by a
lightning surge.
> Then you've lost the ability to get the surge current into the ground.
Periodically
> mechanically test your system by pulling up on the rods.  I'd suggest
quarterly and
> not less than semi-annually in your case.  Hopefully, you've got "useful"
soil under
> the sand.   73, Bob AA0CY

Sure ... down 19 feet at the water table ...!  ;-)

Perhaps I need a single 20 foot ground rod at the entry point as well as at
the tower?

Thanks again! & 73, DavidC  K1YP


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