46 www.megger.comAnother way to reduce the earth resistance would be to lower the earth resistivity. Note in Fig. 21 that if you draw a line from a reference point 1 (leaving rod depth and diameter unchanged), you would need to reduce earth resistivity to about 1000 ohm-cm to give the required 4-Ω earth resistance. You could do this by chemical treatment, as described earlier, but normally the deeper rod is the easier way.Fig. 21: Nomograph relating the basic factors affecting earth resistance.
