Lightning protection with the mesh method: Some models for the effectiveness analysis

Lightning protection of structures using the Mesh Method is based on long-term experience but does not involve any theoretical background. This paper proposes to prove the effectiveness of the Mesh Method using modified electro-geometrical theory. A roof constructed from insulating or low-conductivity material has been treated as permeable for the ‘rolling sphere’. The analysis confirms the high efficiency of low-suspended or roof mounted horizontal air terminals. In particular, when any conducting elements in the object interior are not closer to the meshwork surface than half the length of the square mesh side, the mean value of the protection unreliability coefficient falls in the range 5×10−5 to about 10−7 (depending on the protection level). When conducting elements are placed directly below the roof surface, the protection effectiveness falls considerably. The calculated protection unreliability is strongly influenced by mean lightning parameters. Considerable discrepancy between the data in references makes it impossible to obtain unambiguous, quantitative evaluation of the efficiency of the low-suspended terminals.