[TowerTalk] [Bulk] Re: RF Ground is a Myth

[Jim Lux]

On 1/21/15 1:41 PM, Jim Brown wrote:
> On Wed,1/21/2015 1:01 PM, Patrick Greenlee wrote:
>> I'm confused...    (still, yet, again...)
>>
>> There are recommendations to place ground rods (8 footers) 8 ft apart
>> in a circle (octagon.) If my 14 ft apart Ufer grounds are too close
>> together so as to act as a single point, what about the 8 ft rods 8 ft
>> apart?
>
> Forget about "single point" with respect to these various earth
> electrodes. Multiple electrodes (rods, Ufer, etc.) simply provides
> multiple paths in parallel to discharge a strike. Each of those paths is
> R + jwL, and the impedances to earth of the combination of those paths
> adds like any other combination of resistance and inductance, except to
> the extent that mutual coupling between the electrodes increases the
> combined impedance.
>
> Lightning is NOT a DC event, it is an RF event, with the energy
> concentrated in very broad spectrum, roughly centered (on a log
> frequency scale) around 1 MHz (in other words, spread roughly between 50
> kHz and 20 MHz). Thus, the inductance dominates the impedance.
> Resistance matters primarily to the extent that we would like the
> conductor to carry as much as possible of the strike current before it
> vaporizes. :)
>

And just plain old redundancy.  Install 3 rods of various length in 
various parts of your yard with manky old clamps cobbled together out of 
stuff you found in the parts bin in your garage, don't look at them for 
10 years, and hopefully not all the clamps have fallen off.  I have used 
stainless steel hose clamps to connect ground wires to a rod.  Clearly 
not to code, clearly not a good long term solution, but hey, I'm pretty 
sure that if something "bad" had happened while I had it hooked up, it 
would have been a heck of a lot better than nothing.