The earthing system has a vital and critical function in the lightning protection system. It must be capable of discharging huge value of electricity into the earth, during lightning strikes. The down conductors efficiently conduct lightning current to the earth electrode. An effective, low-impedance path is the key element of a perfect earthing system. It is most important for human safety, as well as protection for vital equipment.

The earth resistance is the resistance of soil to the passage of electric current. The soil is a relatively poor conductor than copper. However, the effective area of the current path is large. Therefore resistance can be quite low and the earth can be a good conductor. The earth resistivity of the site must be calculated before effective earthing systems can be designed. The size and number of earth electrodes are calculated based on the soil resistivity value at each location.