The Siemens 5SJ6350-7 is a 3-pole miniature circuit breaker from the SENTRON 5SJ6 series, rated 50 A at 400 V AC with a C tripping characteristic. The C-curve means it holds through motor inrush (5–10× rated current) and trips on sustained overloads, so it's the usual pick for general-purpose loads like pumps, compressors, and lighting banks fed from a 400 V three-phase supply.
Three width units (3 x 18 mm = 54 mm) on the DIN rail — standard footprint for a 3-pole 5SJ6. Terminals accept 1.5 mm² to 2.5 mm² solid or stranded copper, which is fine for the 50 A rating if you keep the conductor length short and the ambient under 40 °C.