[TowerTalk] understanding ground resistance measurements

[Grant Saviers]

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