AEMC 4500 - Effect of Electrode Size;Depth on Resistance

Digital Ground Resistance Tester Model 4500 17
4.1.1 Effect of Ground Electrode Size and Depth on
Resistance
Size: Increasing the diameter of the rod does not materially reduce its
resistance. Doubling the diameter reduces resistance by less than 10%.
0
25
50
75
100
1/2 5/8 3/4 11 1/4 1 1/2
1 3/4
Rod Diameter (inches)
Resistance in %
Figure 5
Depth: As a ground rod is driven deeper into the earth, its resistance
is substantially reduced. In general, doubling the rod length reduces the
resistance by an additional 40%.
515253540506
070
1
2
3
4
5
6
8
10
20
30
40
60
80
100
200
Driven Depth in Feet
Ground Resistance Versus Ground Rod Depth
Resistance in Ohms
1/2" dia.1" dia.
Figure 6