The sole purpose of the design exercise for grounding systems is to make the performance predictable upon installation. For ground system designs, there are several options for the design process or the method of manipulating the data by formulas, spreadsheets, or software. Likewise, there are alternatives for the design result or the actual instructions showing locations, models and quantity of grounding electrodes required to achieve the grounding system performance indicated by the design.
For utilities designing site-specific grounding systems, soil resistivity testing is an absolutely necessary step. Soil resistivity data is required for the ground system to meet a specific performance requirement. With resistivity data, the design becomes predictable so that you know the final ground resistance to expect after installation.