14 www.megger.comDetermining a Good Electrode LocationA good, low-resistance earth electrode depends upon a low-resistivity soil in a spot where you can drive in your electrodes. There are two approaches to picking your location:1. Drive rods in various locations to such depths as may be required and test their resistances while they are being driven.2. Measure the earth resistivity before driving ground rods. Then calculate the number and length of rods required.To get a low-resistance electrode in an unfavorable location, lay out straight lines 10 ft apart, covering the area. Drive four stakes 10 ft apart, but not more than 6 in. deep, along a line a-b-d-c, as shown in Fig. 5. Measure the resistance R between stakes b and c, using the method described for earth resistivity. Then, shift the stakes along the line in question to points b-c-d-e, c-d-e-f, etc. (see Fig. 5) and test until the entire line has been covered. Next, move to the next line and repeat Fig. 5: Method of prospecting for best earth electrode location to a depth a. Location giving lowest reading on the Megger ground tester is the most desirable.
