The grounding or earth termination system is a part of an external lightning protection system (ESE, Faraday…) which is intended to conduct and disperse lightning current into the earth.
One grounding must be provided for each lightning down-conductor and shall be assured a certain contact surface with the soil in order to facilitate the lightning current dispersion in a short time.
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
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.
Unless there is a real impossibility, earth termination systems should always be directed outward from the buildings. Each down-conductor will be connected into the pit inspection which is interconnected with the general earthing system to ensure equipotential bonding. The earth connection can be performing with mechanical connectors (EN 50164) or exothermic welding.
Each down-conductor should be provided with a test joint in order to disconnect any other conductive component when performing resistivity measurements.
Thanks to the “Lightning Strike Alert” provide by “Contact@ir System”, a reactive maintenance can be performed on grounding system when resistance value becomes the most critical.
“An outside protection against lightning with a lightning rod must be checked every year and after each lightning strike to ensure its good working order.”
Source NFC 17-102 – September 2011.
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