7.3.7 Rating of cross-sectional areas and backup protection of SPDs
Connecting leads of arresters can be subjected to loads from impulse currents, operat- ing currents and short-circuit currents. The individual loads depend on various factors:
† Type of protective circuit: One-port (Figure 7.65) or two-port (Figure 7.66)
† Type of arrester: Lightning current arrester, combined lightning current and surge
arrester, SPDs
† Performance of the arrester on follow currents: Follow current extinction/follow
current limitation
If SPDs are installed as shown in Figure 7.65, the S2 and S3 connecting cables must only be rated on the criteria of short-circuit protection according to IEC 60364-5-53 and the impulse current carrying capability (the data sheet of the protective device provides the maximum permissible overcurrent protection that can be used in this application as backup protection for the arrester). When installing the devices, it must be ensured that the short-circuit current actually flowing is able to trip the