AEMC 3640 - Effect of Ground Electrode Size and Depth on Resistance

Digital Ground Resistance Tester Model 3640 and 4610 15
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
1/25/8 3/411 1/41 1/21 3/4
Rod Diameter (inches)
Resistance in %
Figure 4
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%.
5 15 25 3540 50 60 70
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 5