Recently, thunderstorms are frequent, and the customer asks whether the protection grounding device of the machine room can be shared with the lightning surge protection grounding device to reduce the difficulty and cost of construction. The cabinet in the machine room of the customer's project is made of protection grounding, which is connected by 16mm² grounding cables in series, but he wants to confirm whether the ground cable of the lightning surge protection device (SPD) can be shared with the protection grounding device or not.

From this field case, first of all, it is necessary to confirm whether there is a grounding busbar used as lightning surge protection grounding to ground the lightning surge protection device (The result is no), and whether the protection grounding of the machine room is connected to the lightning surge protection grounding lead line (The result is yes). These investigations are to determine the feasibility of the final solution.

Actually, the lightning surge protection specification provides a clear explanation on whether the grounding system can be shared. Apart from buildings, other lightning surge protection systems, such as lightning rod grounding, could be shared with the lightning surge protection grounding system in the machine room. The grounding resistance should be the minimum value of each grounding system, which should be less than 4Ω.

When not sharing grounding, the distance between the two devices shall be calculated according to the site conditions, but the distance between the lightning rod grounding system and the lightning surge protection grounding system of the machine room shall not be less than 2 meters.

After the improvement of these measures, as long as the SPD is properly selected and installed and the connection can meet the requirements of the equal potential, it can play a good lightning surge protection role.