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 MIL-HDBK-419A
At a distance equal to two ground rod lengths,
Thus 92 percent of the resistance of a lo-foot by l-inch rod is obtained in a 20-foot radius cylinder. Similarly,
94 percent of the resistance of a 100-foot by l-inch rod is obtained in a 200-foot radius cylinder. The
resistance distribution for representative vertical electrodes is tabulated in Table 2-4.
Table 2-4
Resistance Distribution for Vertical Electrodes
Approximate
Distance from Rod
Total Resistance
Type of Rod Electrode
(feet)
(%)
3/4-inch pipe,
90
6
driven 3-feet
95
12
deep
98
31
99
61
3/4-inch pipe,
90
9
driven 5-feet
95
18
deep
98
46
99
92
1-1/4-inch pipe,
90
18
driven 10-feet
95
35
98
88
99
176
2-1/2-inch pipe,
90
25
driven 20-feet
95
69
deep
98
173
99
345
2-21
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