The Siemens SENTRON 5SU1674-7BK82 is a selective RCBO — a combined residual-current circuit breaker with overcurrent protection — built for 4-pole (3L+N) circuits. It's rated 125 A at 30 °C with a C tripping characteristic and a 300 mA Type B residual-current trip, meaning it catches smooth DC fault currents as well as AC and pulsed DC, which is what you need on VFD-fed circuits or UPS-backed loads where pure sine-wave residual current isn't guaranteed. The 10 kA breaking capacity per EN 60898 and IEC 60947-2 gives it enough fault-clearing headroom for most commercial and light-industrial distribution boards.
Thermal derating and panel fit
This is an 11-module-wide unit (198 mm wide, 90 mm tall, 77 mm deep plus 70 mm installation depth) that mounts in any position on a DIN rail inside an IP20 distribution board. The 125 A rating is at 30 °C ambient; at 40 °C it's 115.62 A, at 50 °C it's 106.25 A, and at 60 °C it's 96.25 A. If your panel runs warm — and most enclosed boards do — size the upstream feeder for the derated figure, not the 30 °C headline number. Supply can enter from top or bottom, which simplifies busbar routing.