What this RCBO does and where it fits
The Siemens 5SU1344-6KK82 is a 4-pole residual current circuit breaker with overcurrent protection (RCBO) from the SENTRON family, rated 125 A at 30 °C and 115.62 A at 40 °C — the 40 °C figure is the one that governs a typical panel ambient, so that is the number to size against for continuous load.
Supply can enter from either top or bottom, which simplifies panel wiring when busbar orientation is fixed. Mounting position is any, so vertical or horizontal panel layouts both work.
Thermal derating and environmental range
The rated current derates from 125 A at 30 °C down to 96.25 A at 60 °C, following a linear curve. For a panel running at 45 °C, the usable rating is 111.25 A; at 50 °C it is 106.25 A. This matters when the RCBO is grouped with other heat-generating devices in a confined enclosure.