The Siemens 5SM3645-0 is a SENTRON residual current circuit breaker (RCCB), 4-pole, type AC, rated 125 A with 300 mA sensitivity on a 400 V AC supply. It's an instantaneous-trip device — no intentional delay — so it clears ground faults on the first half-cycle, which is what you want for personnel protection in a distribution board. That's standard for a domestic or light commercial panel; if your available fault current is higher, the RCCB needs an upstream backup fuse or MCB rated to coordinate.
IP20 with the distribution board installed and conductors connected. That's expected for a panel-mount device — no special gasketing, no washdown rating. The silicon-free construction matters if this board is in a painting or coating line where silicone outgassing causes fisheyes.
Rated per EN 60898 and IEC 61008-1, both at 1.25 kA. Overvoltage category III, ambient range -5 °C to +45 °C, storage down to -40 °C. Mechanical life 10 000 cycles typical.