On 1/21/2015 9:15 AM, Jim Lux wrote:
On 1/21/15 5:29 AM, Patrick Greenlee wrote:
I have a triangular tower with legs on 14 ft centers, yes, 14 feet, not
inches. I built it with three separate concrete foundations, one per
leg. It is currently tilted over so one leg is not touching its
concrete embedded mechanical connection/mount.
Am I missing something? Will a simple ohm meter test give a reasonable
measure of Ufer ground quality, sufficient to decide the question of
whether or not multiple copper clad ground rods need to be installed and
interconnected?
You need to use an AC source for the measurement: a DC source will
cause polarization and the reading will be low resistance at first and
then rise (think as if it were an electrolytic capacitor). The other
thing is that a typical solid state multimeter uses such low
current/voltage that you're going to see strange readings.
if you have something like a 12-24V AC transformer around (12.6V
filament transformer, landscape lighting, bell transformer), you can
use it: measure voltage and current, and you can go from there. You
can even use 110V (with an isolation transformer from the line, please!)
Is it too much of a leap of faith or otherwise to assume the inter-leg
resistance is an adequate predictor of tower mount to Mother Earth
conductivity?
Nope.. that's pretty much how they do it.
Jim, I am glad you mentioned using AC as a source. I once observed a
crew from the electric company installing new ground rods. They used a
device that had a "zero center" meter on it to measure the ground rod's
"resistance", and, as I recall, the "AC source" must have been somewhere
around 1 Hz or so, based on my observation of the meter swinging back
and forth. The rod they used were threaded on each end, and they could
couple on another section and drive it further down if they didn't like
the readings they got.
As for the electrolytic action...that's my understanding as to why
multiple ground rods are used, and why the separation between them-- in
the event of a strike, the ground around the rod rapidly loses its
ability to further "charge" the ground around it (and dissipate the
energy) because of electrolytic action, and a rod too near to it would
suffer the same effect.
Randy
KZ4RV
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