The Siemens 5SU1356-0KK25 is a SENTRON RCBO combining overcurrent protection and residual current detection in a single 2-module-width (36 mm) package. It's rated 25 A with a B-curve trip characteristic and Type AC residual current sensitivity, making it a standard choice for residential and commercial final circuits where both short-circuit and earth-fault protection are required in one device. Breaking capacity is 6 kA per EN 60898 and 15 kA per IEC 60947-2 — the higher figure applies when the RCBO is used as a distribution board main or where the prospective fault current exceeds 6 kA. The 1P+N configuration switches the phase only; the neutral is switched internally for isolation but not protected against overcurrent.
Thermal derating and mounting
At 30 °C ambient the unit carries the full 25 A; at 40 °C it derates to 23.5 A, at 50 °C to 21.75 A, and at 70 °C to 18.25 A. If the panel runs hot — say a crowded DIN rail near a transformer — size the upstream protection for the actual ambient, not the 30 °C nameplate. Mounting position is unrestricted, and the supply can enter from top or bottom, which simplifies busbar routing in a distribution board. Installation depth is 70 mm (77 mm overall), fitting standard flush-mount enclosures. IP20 applies only with the distribution board closed and conductors connected — the front face is finger-safe, but the terminals are not touch-proof with the cover open.