4 www.megger.com1 Four-terminal method of measuring earth resistivity ............................72 Earth resistivity survey of pipeline ...........................................................83 Graphs showing relation between soil and resistance ...........................94 Seasonal variation of earth resistance with an electrode ...................135 Method of prospecting for best earth electrode location ..................146 A simplified grounding system in an industrial plant...........................167 Example of an electrical circuit with too high an earth resistance ......188 Typical conditions to be considered in a plant ground system ............199 Components of earth resistances in an earth electrode .......................2210 Principle of an earth resistance test .......................................................2411 Fall-of-potential or three-terminal earth resistance test ......................2712 Dead earth method or two-point earth resistance test........................2713 Effect of C location on the earth resistance curve ................................3114 Example of how C location affects the earth resistance curve ............3215 Earth resistance decreases with depth of electrode in earth ...............3716 Diameter of a rod has little effect on its earth resistance ....................3817 Average results obtained from multiple-rod earth electrodes ............3918 Comparative resistance of multiple-rod earth electrodes ....................3919 Trench method of soil treatment ...........................................................4120 Chemical treatment of soil .....................................................................4121 Nomograph relating the basic factors affecting earth resistance .......4622 Basic clamp-on ground testing methodology .......................................4823 Pole ground application .........................................................................4924 Cellular tower application ......................................................................5225 Ground resistance measurement ...........................................................5326 Leakage current measurements .............................................................5427 Attached Rod Technique (ART) measurement ......................................5528 Earth resistance curve applicable to systems of a large area ...............5829 Earth resistance curves for a substation ................................................6030 Intersection curves for Fig. 29 ................................................................6031 Potential probe locations for using the slope method .........................6232 Four potential method test configuration ............................................6533 Star-Delta test configuration .................................................................6634 Making a two-point measurement ........................................................6735 Method of use for determining touch and step potential ...................70TABLE OF FIGURESFig. Page
