Kelly ve4xt wrote:
>>Here's an interesting question: if the concrete base is an effective
ground connection, do you get more value by placing the rods a rod length
away from the base? <<
Is concrete is an effective ground connection? I have not seen any data
regarding the measured _impedance_ between tower and remote earth via a
reinforced concrete base. I am skeptical of using DC theory or DC
measurements as a proxy for the impedance of a tower footing seen by the
RF-like lightning impulse.
It seems codes and practice are in a state of confusion with DC and
impedance. DC resistance traditionally is used to measure the quality of a
ground, yet low impedance is the design goal. For example TIA-222 suggests,
in their default grounding system, use of a star ground with wires having a
_surface area_ not less than #00. The surface area language tells me the
code writers were thinking about skin effect and impedance, not DC
resistance.
I concur with Grant KZ1W, best known practice is a star ground with rods at
20 feet separation minimum.
73 Jim K6OK
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