The ground design begins with site analysis, collecting geological data, and soil resistivity in the area. Usually, the field engineer or equipment manufacturer will specify the ground resistance. When designing a grounding system, the difficulty and cost are multiplied as the target grounding resistance approaches the unattainable zero-ohm goal.

Once the requirements are identified, data collection begins. Soil resistivity tests, geological surveys, and test boreholes provide the basis for all grounding designs. For example, a three-point potentiometric drop can be used to test a follower at that location, or an inductive frequency test can be performed with a clamp-on ground resistance meter.

Using all available data, sophisticated computer programs can begin to provide soil models that show soil resistivity in ohmic tables and at various layer depths. Knowing at what depth the most conductive soil at the site is located enables the design engineer to model the system to meet the requirements of the application.

Soil resistivity is a key factor to determine the resistance or performance of electrical grounding systems. This is the starting point for any electrical grounding design. Soil resistivity varies widely throughout the world and is greatly affected by electrolyte content, moisture, minerals, densification, and temperature.