What the ratings mean for fit
The Siemens 5SU1356-6KK25 is a SENTRON RCBO (residual current operated circuit breaker with integral overcurrent protection) in a 1P+N configuration — one protected pole plus a switched neutral. Rated 25 A at 30 °C with a B tripping characteristic, it trips instantaneously between 3 and 5 times rated current (75–125 A), which makes it the right choice for residential or light commercial final circuits where inrush is low — lighting, socket outlets, small appliances. The 6 kA breaking capacity per EN 60898 covers most domestic service-entrance fault levels; the 15 kA rating per IEC 60947-2 gives headroom for industrial panel applications where the prospective short-circuit current is higher, so you can specify it into a sub-distribution board without worrying about cascading failure upstream. Temperature derating is built in: at 40 °C it carries 23.5 A, at 50 °C it's 21.75 A, and at 70 °C it's 18.25 A. If your panel runs hot — say a packed enclosure with minimal airflow — plan the load accordingly. The 2 MW unit width (36 mm) per DIN 43880 means it occupies two standard 18 mm slots on the rail; at 77 mm depth plus 70 mm installation depth, it clears most domestic and light-industrial enclosures without a deep-can modification.
Panel integration notes
Snap-on mounting to 35 mm DIN rail per EN 60715, any position. Supply can land top or bottom — no orientation restriction, which simplifies wiring in tight enclosures. IP20 with connected conductors (the distribution board must be installed for the protection to be effective). Overvoltage category III and pollution degree 2 mean it's rated for fixed installation downstream of the main distribution board, not for outdoor or wet locations without additional enclosure sealing. Halogen-free and silicon-free construction matters if the panel is in a clean-room or process environment where outgassing could contaminate optics or contacts.