What it is and what it does
The Siemens 5SU1353-7KK08 is a 2-pole (1P+N) RCBO from the SENTRON 5SU1 series, combining overcurrent protection and residual current detection in a single 36 mm-wide module. Rated 8 A with a Type C tripping characteristic and a Type A fault current sensitivity, it breaks fault currents up to 4.5 kA per EN 60898. That Type A rating means it catches pulsating DC fault currents — the kind rectified loads like switch-mode supplies and VFDs can produce — not just pure AC sine-wave faults. If your panel feeds electronics, this is the right residual-current class.
Ratings that matter for the panel
The 8 A rating is at 30 °C ambient. Above that, the continuous current derates: 7.52 A at 40 °C, 7.28 A at 45 °C, 6.96 A at 50 °C, 6.48 A at 55 °C, 6.48 A at 60 °C, 6.16 A at 65 °C, and 5.84 A at 70 °C. If your enclosure runs hot — say a packed panel with drives — size the load to the derated figure at your actual ambient, not the 30 °C headline. The RCBO itself is rated for ambient -25 to +55 °C operating, with storage from -40 to +75 °C. Conductor termination accepts solid or stranded wire from 0.75 mm² up to 35 mm², so it handles both the small control-circuit tails and the heavier power feeds. The 77 mm depth and 70 mm installation depth fit standard 36 mm-wide DIN-rail enclosures; mounting position is any orientation. Power supply can enter from top or bottom — no forced busbar routing.