7.2.3 Formation of equipotential surfaces as a reference plane for calculating the separation distance

different impedances of the current paths from the point of strike of the lightning discharge in the air-termination system to the common equipotential bonding level/earthing system, the lightning current is distributed unevenly across the individual down conductors. This is reflected in the value of the current distribution coefficient k_c determined in this way. The resulting separation distance s is referred to as the full separation distance in the local German supplement 1 to IEC 62305-3 (local application guide).

A reduction in the value of k_c and thus a reduction in the required separation distance s (reduced separation distance) can only be achieved if care is taken to ensure that the lightning current is distributed evenly across all existing current paths (down conductors) to the earthing system. This is the case when the air-termination system is part of an equipotential bonding system that ensures that the lightning current is distributed evenly across the existing down conductors, regardless of the point of strike in the air-termination system. This can only be achieved by means of a completely metal or very tightly intermeshed conductor structure in the area of the air-termination system. If this is the case, the current distribution coefficient k_c can be calculated using Equation 7.2.3.1: