Deals with the requirements of Surge Protective Devices (SPDs) standardized by IEC 61643-1. These SPDs are installed according to the Lightning Protection Zones concept given by IEC 61312-1.

First, starting from primary relevant threats, gives instructions for the determination of the stress for individual SPDs.

For SPDs installed within a complex system, it is admissible to divide the system into simple basic arrangements, observing the rules described. When the values and directions of the partial lightining currents flowing within the system are known, the appropriate SPDs can be selected.

Also deals with basic questions of the energy coordination of SPDs among each other and between SPDs and the threat at the respective place of installation are to be considered for effective coordination. The proof of the coordination of SPDs installed in a system, is described briefly.