AEMC 4500 User Manual

26 Digital Ground Resistance Tester Model 4500X-Y DistanceResistanceReading VariationEffective ResistanceAreas (Overlapping)X Y' Y Y'' ZFigure 10On the other hand, if the auxiliary potential rod Y is located outside ofthe effective resistance areas, as Y is moved back and forth the readingvariation is minimal. The readings taken should be relatively close to eachother, and are the best values for the resistance to ground of the ground X.The readings should be plotted to ensure that they lie in a “plateau” regionas shown in Figure 11.X-Y DistanceResistanceReading VariationEffective ResistanceAreas (No Overlap)X Y' Y Y'' ZFigure 114.4 Measuring Resistance of Ground Electrodes(62% Method)The 62% method has been adopted after graphical consideration andafter actual test. It is the most accurate method but is limited by the factthat the ground tested is a single unit. This method applies only when allthree electrodes are in a straight line and the ground is a single electrode,pipe, or plate, etc., as in Figure 12.