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MILHDBK419A
Figure 28. Earth Resistance Shells Surrounding a Vertical Earth Electrode
Equation 220 permits the area of influence of a single rod to be determined. For example, consider a 10foot
long, linch diameter rod at distance x =
= 0.15
The ratio of 0.15 indicates that 85 percent of the total resistance to earth of a 10foot long ground rod is
established within 10 feet of the rod. For a 100foot rod, 89 percent of the grounding resistance is obtained
within 100 feet of the rod.
220


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