Soil resistivity Test is the most key factor in designing a grounding system for specific ohmic value required in electrical sytem . All soils conduct electrical current, with some soils having good electrical conductivity i.e. poor resistivity while the majority has poor electrical conductivity i.e. high resistivity. The resistivity of soils varies widely throughout the world and changes dramatically within small areas even at the same point in different direction i.e. anisotropically. Soil resistivity is primarily influenced by the type of soil (clay, shale, etc.) and its moisture content, the amount of electrolytes (mineral and   dissolved salts) and very nominally by temperature. When designing a grounding system

For a specific performance objective, it is necessary to accurately measure the soil resistivity of the site where the grounding to be installed. Grounding system design is an engineering process removing guesswork from earthing, leading to a more scientific approach to the grounding problem. The grounding process just gets a go from the very beginning which definitely results in cost saving, avoiding unnecessary expenditure.