Martin as an electrician and a cert. lighting ground installer in New York
might I suggest the following.
First when seccureing your wire for lightning use only copper or aluminium
nails and straps.all others will not work.Second do not bend sharp angles in
the ground wire(sweeps only)the speed at wich lightning travels will cause it
not to make a sharp turn.
As for being on granite if you run a bare copper ground(#4
recommended)burried 2 ft or so run it as long as possible.the increase in the
surface area in contact with the ground will help disipate the charge.Hope this
helps NY6DX
Martin Ewing <martin@aa6e.net> wrote:
>Folks,
>
>Having invested in a SteppIR, a roof-top tower, a
>rotor, and several wire antennas, I find I have a lot
>of copper running out to the sky from my shack. ?Too
>much to easily disconnect when I hear thunder. ?Time
>to think about a better protective ground system.
>
>Inside the shack, I am thinking of a single-point
>ground plane near the feedline entrances. ?All
>connections including AC power, telephone, computer,
>SteppIR/rotor control, etc. pass through surge devices
>on that plane, and all equipment is hopefully
>connected by low inductance strapping to the SPG.
>
>My problem is how to get a good "earth ground" for the
>SPG. ?My house is on a granite ledge with only 1-2 ft
>of soil nearby. We are about 80 ft from salt water,
>but that doesn't help. The house does have lightning
>rods with 3 or 4 downleads (more on this in a moment).
> The 20-ft rooftop tower is connected to a lightning
>rod ground, but feedlines are not.
>
>I was wondering how the lightning rod grounds were set
>up, so I partly excavated one. ?The results are
>visible on my web site:
>http://www.aa6e.net/aa6e/grounding .
>
>Is this approach - dual buried horizontal ground rods
>- good enough even for home protection? ?Should I do
>something like this for my station? (The shack is not
>near any of the existing ground connections.)
>
>It's clear that not even an "excellent" ground
>connection can prevent kilovolt surges from a near
>hit, because that is what happens to the earth itself.
>And full protection from a direct hit to the house is
>hard to achieve (IMO) no matter how you try in a
>typical home retrofit. The whole shack should be
>inside a grounded metal box...
>
>My philosophy now is to concentrate on the SPG system
>and not to obsess on the low-Z ground, which must be
>pretty hard to realize over rock. ?(I would put in
>something like what I see on the existing lightning
>rod system.) If the SPG is really good, and the
>equipment is all referred to that carefully, then it
>shouldn't matter if the whole system floats up and
>down by kilovolts. ?(Hopefully the op is elsewhere!)
>
>The "kilovolt" scenario doesn't quite catch the full
>impact of a direct hit to the antenna. ?10,000 amps
>into a one ohm ground (?) is 10 kV. ?No one expects
>the Spanish Inquisition! (i.e., worst-case event)
>
>I would appreciate suggestions, especially from anyone
>who has faced a similar problem -- and survived the
>worst.
>
>73, Martin, AA6E
>
>p.s. Fortunately here in CT, we have fairly low
>lightning incidence. ?Even so, we had a close strike a
>couple of years ago. ?A BIG crack, and both my close
>neighbors lost their telephones and other electronics.
> We had no troubles here. ?My tower was down then;
>maybe our lightning rods actually caught one. Thank
>you, Ben Franklin.
>
>
>_______________________________________________
>
>See: http://www.mscomputer.com ?for "Self Supporting Towers", "Wireless
>Weather Stations", and lot's more. ?Call Toll Free, 1-800-333-9041 with any
>questions and ask for Sherman, W2FLA.
>
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_______________________________________________
See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless Weather
Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any questions
and ask for Sherman, W2FLA.
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