These measures to protect against life hazards have top priority when installing power
supply systems. All other protective measures such as lightning and surge protection
of electrical systems and installations are secondary to the protective measures taken
against indirect contact with protective conductors under consideration of the system
configuration and the protective device. The latter must not be overridden by the use of
protective devices for lightning and surge protection. The occurrence of a fault in an
SPD, unlikely as it may be, should also be taken into account. This has particular
significance because the SPDs are always installed between active conductor (L1,
L2, L3, N) and protective conductor (PE, PEN).