This is a question faced by specialists designing circuits with the installed SDPs in the lightning protection systems. A simplified answer can be as follows: the lightning current is equally divided between the ground terminal of the building where the lightning has got and its metal utilities (cables, pipelines, etc.). However, unconsidered transient processes of a short-term lightning pulse make this approach unsuitable.
Linear capacitance, current collectors and utilities inductance, and resistance of the ground terminals begin to restrain the current dramatically, which, in turn, leads to increased surges.
To design a truly reliable system for surge protection, you should directly calculate the distribution of lightning currents in the SDP circuits. The complexity of this problem is mostly apparent. If the problem algorithm is properly developed, any calculation using an average modern PC will hardly take more than a minute.
This is what a guru of lightning protection theory and practice thinks, Prof. of ENIN E. M. Bazelyan.
Read the article to know more about the calculation method recommended by E.M. Bazelyan.
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