Method of the Protected Volume LPZ0B of Lightning Air-Termination Systems

The protection system for the structures against lightning is basically constituted by means of an air termination system, down-conductors and a ground-termination system. The IEC standard 62305 introduces the rolling sphere method to analyze and to design the protected volumes of air-termination systems with a complex configuration. In order to avoid the exposure of equipment and elements on the building roof to direct lightning in the design and the following operation with new exigencies, the identification of the protected volumes LPZ0B allows taking corrective measures if needed. The suggested method assumes as reference element a pair of rods for the air termination system and proposes to identify the protected volume combining the two IEC methods of the graphical rolling sphere with the protective angle. The protected volume method proposes, as simpler first step, the mathematical calculation of the minimum protection height of prospected profile described by the rolling sphere, useful for a preliminary evaluation. As second step, the method completes the definition of the protected volume section, describing a cautionary model that replaces the circular sector of the rolling sphere with a “vase section” shape, applying the protective angle method.