This paper deals with the efficiency of a coordinated system of surge protective devices (SPD), which is
indicated by the IEC standard 62305 as typical protection measure for electrical and electronic apparatus
against surges due to lightning. For practical applications, the probability of a given SPD system to reduce
the risk of failure of apparatus is a key point for its proper selection and installation. The paper aims to
give the rationale for the evaluation of such probability and shows application examples of different
types of SPD systems in the case of direct lightning stroke to the structure (source of damage S1).