A perfect quality of the earth termination system is a crucial element to ensure the efficiency of all lightning protection technologies (Single rods, Mesh cage, ESE lightning rod...).
In order to evaluate its quality, we measure the resistivity of the soil which is expressed in ohms (Ω). The lower the resistance value, the better the ground connection. NFC 17102 standard recommends soil resistance values lower than 10 Ω.
Due to the dispersion of the lightning current through the earthing system, the resistance value can increase considerably and affect efficiency of the entire lightning protection system.
Regular measurements of the soil resistivity must be carried out and especially after each lightning strike event.