Separation distances for air termination systems in proximity to large conductive areas

In case of a direct lightning strike to a building dangerous sparking may occur between the external lightning protection system and conductive parts inside or at the building. To avoid such side flashes a minimum separation distance between these parts has to be kept. The standard IEC 62305-3 provides an equation and parameters to determine the necessary separation distance. The parameters given there were developed for large loops, many meters wide. Nowadays, it often occurs that the air termination system is to be placed relatively close to large conductive areas. Typical examples are air termination wires placed on a metal roof or on a reinforced concrete structure. For such cases, it has to be expected that the parameters are different to those given in IEC 62305-3. Objective of this paper is to experimentally determine these parameters.