Like any of the design decisions or computational processes required in electrical earthing systems, the quality of the input data is essential. Once the relevant governing standard has been determined it is important for designers to know the variety of cable between the primary and secondary substation in a given system. They next will want to clarify the length of the cable along with the cross sectional area. With these data assets in hand the Earthing Services electrical earthing system design engineer will seek to learn the earth mat resistance at both the primary and secondary substations. It would be impossible to proceed with any meaningful fault current distribution analysis without being in possession of the phase to earth fault level, and for this to be processed a knowledge of the average soil resistivity for the area will need to be achieved.