The Siemens 5SU1356-1DA25 is a combined residual current device and miniature circuit breaker (RCBO) — what Siemens calls an FI/LS protector.
The 30 mA sensitivity is the common touch-protection threshold; it covers the human body path to ground in a fault.
This is a 1+N-pole unit — it switches and protects the line conductor and switches the neutral, but the neutral is not overload-protected. The pigtail connection (factory-fitted neutral tail) simplifies wiring in DIN-rail distribution boards: the neutral bus bar connects to the pigtail, and the line side clips onto the bus bar or is fed from the upstream device. The 70 mm depth (D=70mm) is standard for Siemens 5SU series RCBOs, so it fits flush in a standard enclosure without protruding past the cover.