[TowerTalk] ground rod depth problem due to rocky soil -- solutions?

[K1TTT]

My program doesn't do strap, so instead of 2" strap that the OP has, I
substituted 1" wire which gives a slightly smaller surface area... the OP
said he was going have 700' of buried stuff so that is what I used... of
course you can't bury in rock, but I can simulate it as a worst case, the 1'
of topsoil on top shows there isn't much difference.



David Robbins K1TTT
e-mail: mailto:k1ttt at arrl.net
web: http://wiki.k1ttt.net
AR-Cluster node: 145.69MHz or telnet://k1ttt.net


-----Original Message-----
From: Michael Goins [mailto:wmgoins at gmail.com] 
Sent: Friday, November 16, 2012 15:28
To: Jim Lux
Cc: towertalk at contesting.com
Subject: Re: [TowerTalk] ground rod depth problem due to rocky soil --
solutions?

Impractical analysis because where are you going to get 1" wires and who
could possibly afford 700 feet of it? Plus the cost of getting it a foot
down in rock?

I'm on pretty much solid rock here, 1800 feet up on the side of a hill, and
that would cost a fortune to do.

Still not clear about the need/reason. Why not just totally disconnect and
reconnect the tower when you operate? That's what I do here and the tower is
not grounded other than by its proximity due to the factory base 5 feet deep
in solid rock. My station is completely broken from the tower when I am not
operating and I don't operate in storms. There is nowhere for lightning to
go that would harm my station.

Michael Goins, k5wmg
Professor, Writing
University of Texas at San Antonio




On Fri, Nov 16, 2012 at 8:57 AM, Jim Lux <jimlux at earthlink.net> wrote:

> On 11/16/12 6:46 AM, K1TTT wrote:
>
>> 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.
>>
>>
>>
>
> This brings up an interesting question...  Off hand, I would expect 
> that laying a bunch of radials (not too long, but lots of them) of not 
> very big wire (AWG14 or AWG12) might be a better lightning ground for 
> the dollar than any of the other strategies (except concrete and 
> wire.. great ground, and concrete is cheaper than copper)
>
> Time consuming to install (compared to driving a single rod)
>
>
>
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