Siemens SENTRON - Page 70

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A.2.4 Summary
Residual current protective devices can be used in all network AC or three-phase
systems (TN, TT, or IT system, see  gure A6). The protection afforded by residual
current protective devices is superior to that offered by other approved protective
devices, because in addition to fault protection (protection in case of indirect
contact) when residual current protective devices with I
Δn
≤ 30 mA are used, they
also provide additional protection (protection in the event of direct contact), and
with their I
Δn
≤ 300 mA play an important role in preventive protection against
electrically ignited  res caused by ground fault currents.
Appendix
A
Figure A6: Residual current protective devices in all network systems