Necessary Separation Distances for Lightning Protection Systems - Iec 62305-3 Revisited

In case of direct lightning strike to a building dangerous sparking may occur between the external lightning protection system and conductive installations inside the building. To avoid such side flashes a minimum separation distance between conductive parts inside the building and the air termination or down conductor system is required. The standard IEC 62305-3 provides formulae to determine the necessary separation distance. Objective of the paper is to re-visit the determination of separation distances. The international standard IEC 62305-3 recommends using electrically conductive parts of a building or structure as so-called ‘natural components’ of the lightning protection system. The use of such extended metal parts can lead to significant reduction of the necessary separation distances. Objective of the paper is also to study the necessary separation distances for buildings using metal roofs, walls or attics as integral part of the lightning protection system. Such configurations are not yet covered by the IEC-standards.