I meant to Save not Send this post, but am seeking advice about proper
use and pitfalls of these types of measurements, as well as any comments
about what they mean.
Thanks,
Grant
On 8/12/2015 10:18 AM, Grant Saviers wrote:
I'm using a clamp on ground resistance tester Duoyi DY1000A to measure
some new ground rods and Ufer grounds.
New ground rods driven into bone dry soil 8' x 5/8 rods, #6 to tower
base
south 85 ohms
north 0.05 ohms since connection is a loop and rod end is buried
west 88 ohms
2x#6 Cu in 45' trench 8" deep 65 ohms (some watered soil)
Interpretation: as I understand how the instrument works, if I
don't have a very low resistance ground in the network, I am measuring
the sum of the resistances, or nearly so, of an isolated branch. So,
it seems likely that the actual ground rods are around 40 to 50 ohms
each.
Old tower ufer measurements
east tower (18 yards concrete 6 x 10' x 8') 1.5 ohms, known wet
spot, water table was about 5' down in fine clay this time of year,
partially touching an abandoned septic tank
west tower (5x5x8) 16 ohms, didn't hit the water table with this
foundation
Interpretation: The difference is a bit surprising. For both
towers, the reference ground resistance is only coax braids and AC
earth return paths to the shop
Ufer rebar out of foundation near mains entrance (250' perimeter x 12"
wide down 16") 0.041ohms
three #4 connections from Ufer rebar to power panels 0.034, 0.009,
0.009 ohms
two exterior 8' ground rods to power panel 0.023, 0.024ohms
Intepretation: these all seem way too low, particularly the two
exterior ground rod measurements.
Ufer rebar out of foundation at radios
measures >1000 ohms, instrument overload. Not good as equipment
is bonded to the #4 wire so there is a return path through the AC
earth wire
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