The 5SM34460 RCCB: The Siemens 5SM3446-0 is a 4-pole Residual Current Circuit Breaker (RCCB) rated for 63 A continuous current with a 300 mA earth leakage trip threshold. The 300 mA sensitivity is the deciding spec here — it's set above the 30 mA personal-protection threshold, so this RCCB is meant for equipment and fire protection on circuits where nuisance tripping on normal leakage would be a problem (think motor drives, heaters, or long cable runs). Not for socket-outlet circuits protecting people.
The 4-pole design lets it protect a three-phase plus neutral circuit in one device — no need to gang single-pole units. That simplifies the panel layout and keeps the wiring tidy for a 63 A sub-feed.