On 11/16/12 7:46 AM, K1TTT wrote:
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.
From a transient behavior standpoint, I would imagine that the wire
could be insulated it and would work about the same. 700 feet x 1/3 foot
is around 230 square feet of surface area, or 22 square meters..
if it's separated by 1mm from the "earth", that's a capacitance of
8.85E-12* 22/1E-3 F or about .2 uF...
At a nominal 1 MHz (for lightning), that's an impedance of a bit less
than an ohm...
and, because I'm a fan of Ufer grounds.. a 3x3x3 foot cube of concrete
in soil with the top surface exposed has a surface area of 45 square
feet, so its capacitive impedance is about 4 ohms.. a 5x5x5 cube is
about 2 ohms.. so don't worry about the vapor barrier between concrete
and soil. The concrete has lower inductance than the wire radials, too..
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