I plugged that into my lightning modeling software... if I put 7 radial
wires(NO rods) 1" in diameter (a bit smaller surface area than 2" strap),
bury it 1' in solid rock (ignoring any advantage of topsoil above the rock)
and run them out 100' (to equal your 700') I get a ground resistance of
about 8 ohms... as good as 20 rods 8' long by 1" diameter in good loam...
still sounds like overkill to me. If I allow for 1' of topsoil on the rock
with the wires on the rock it goes down to under 6 ohms. To put that in
perspective, the 'normal' 2 rods in loam calculates out to over 70 ohms, in
common clay that reduces to 35 ohms.
David Robbins K1TTT
e-mail: mailto:k1ttt@arrl.net
web: http://wiki.k1ttt.net
AR-Cluster node: 145.69MHz or telnet://k1ttt.net
-----Original Message-----
From: Mat Eshpeter [mailto:kk1c@live.com]
Sent: Friday, November 16, 2012 14:17
To: Towertalk
Subject: Re: [TowerTalk] ground rod depth problem due to rocky soil --
solutions?
I have been reading the responses and have decided to try one last time to
get the rods as deep as possible. Last time around I rented a 20 lb Hilti
combination hammer drill/demo hammer. This time around I rented a 65lb
electric demo hammer -- a Hilti 3000. So I will attack the mountain tomorrow
and see what happens. I will be joining the rods together with 20 gauge 2"
copper strap so I think I will have quite a bit of contact with the soil --
just under 700 linear feet.
thanks for all your responses.
From: K7LXC@aol.com
Date: Tue, 13 Nov 2012 09:49:39 -0500
Subject: Re: [TowerTalk] ground rod depth problem due to rocky soil --
solutions?
To: towertalk@contesting.com; kk1c@live.com
> I am finally getting around to putting up my 60' AN
Wireless tower on top of a rocky ridge in WV. I rented a Hilti demo hammer
and got about 1/3 of my rods in to the ground at least 4' -- but the
majority are only 2 or 3 feet deep because of the rocks/ledges. I don't
think I have much of a choice other than to cut the rods off and drive the
remnants into the ground field and exothermically weld my 20 gauge copper
strap to all of these shallow rods.
Other than paying big money for a well drilling rig to drill some deep 6"
holes and filling them with bentonite (which may not be possible given the
slope of the land and the fact that I now have 8 trenches running 75' out
from the tower pad) do I have any other practical alternatives?
Sure. The rods can be installed horizontally.
Cheers,
Steve K7LXC
TOWER TECH
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