On Fri, 25 Feb 2005 14:40:36 -0800 (PST), Martin AA6E wrote:
>Potentially (no pun), that's a good thing
>if you want an isolated system.
You do NOT want an isolated ground system in the sense you seem to
be thinking of. All grounds MUST be bonded together. The manner in
which you tie them together is important. Remember -- wire has
inductance, and the peak of energy in lightning is in the AM
broadcast band. Wire SIZE does not matter (except to the extent that
bigger wire takes slightly longer to vaporize when lightning hits
it, and thus might last long enough to discharge your hit, depending
on how close and how big). INDUCTANCE is the only thing that counts
in determining the impedance to earth. Dale, WA9ENA, who is an EMC
engineer at Collins, gave some excellent advice on the voltage
gradients established in "ground" under lightning hit conditions.
See also my White Paper on Power and Grounding to understand what an
isolated ground system really is, why it is good, and why what you
are thinking of is bad.
http://audiosystemsgroup.com/SurgeXPowerGround.pdf
Also see some of the references in the paper, especially Morrison
(Grounding and Shielding in Facilities), the IEEE Green Book and
IEEE Emerald Book.
And I fully subscribe to Tom Rauch's advice on facilities grounding.
Jim Brown K9YC
_______________________________________________
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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