The Siemens 5SU1624-0KK82 is a 2-pole RCBO (residual current circuit breaker with overcurrent protection) from the SENTRON family, rated 125 A at 30 °C, B-curve, with a 300 mA residual trip and a 10 kA breaking capacity per both EN 60898 and IEC 60947-2. That 300 mA sensitivity is sized for equipment protection rather than personal shock protection — it catches ground-leakage faults on fixed machinery or distribution subfeeds where a 30 mA device would nuisance-trip on cable capacitance.
This RCBO is rated 125 A at 30 °C, but the continuous current drops as the enclosure heats up: 115.62 A at 40 °C, 111.25 A at 45 °C, 106.25 A at 50 °C, 101.25 A at 55 °C, and 96.25 A at 60 °C. That derating curve is the one you size the load against — if the panel ambient hits 50 °C, you can't pull the full 125 A through it. The unit is 2 modular width units (MW) wide, installs in any mounting position, and accepts supply from either top or bottom. Installation depth is 70 mm. Touch protection is built in on the line-side terminals.
The 10 kA breaking capacity at both EN 60898 and IEC 60947-2 means it can safely interrupt a fault current up to 10,000 A — standard for residential and light commercial distribution boards. Pollution degree 2 (non-conductive pollution that becomes conductive only when condensation occurs) is the typical indoor panel condition. Operating frequency is 50 Hz only — not suitable for 60 Hz grids without derating verification. The insulation voltage (Ui) is rated 440 V, so it's fine on 230/400 V three-phase systems. Maximum ambient temperature is 75 °C; minimum is -40 °C, which covers cold storage or unheated substations.