What this RCBO is and what it does
The Siemens 5SU9356-7KN25 is a 1P+N RCD-operated circuit breaker (RCBO) from the SENTRON 5SU9 series, combining overcurrent and residual-current protection in a single 36 mm-wide (2 MW) module. It's rated 25 A with a C tripping characteristic, meaning it handles moderate inrush from motor or lighting loads without nuisance trips. The Type A fault-current detection catches pulsating DC and AC residual currents — common on single-phase electronics, variable-speed drives, and switching power supplies. Breaking capacity is 6 kA per EN 60898 and 10 kA per IEC 60947-2, so it's sized for standard domestic and light commercial distribution boards where fault levels stay under those thresholds.
Ratings that matter for panel fit
Rated current is 25 A at 30 °C ambient, but the thermal derating curve is worth noting: at 40 °C it's 23.5 A, at 45 °C it's 22.75 A, and at 55 °C it drops to 20.25 A. If your panel runs warm — say, a packed enclosure with multiple breakers — size the load side accordingly. The ambient operating range is -25 to +45 °C, with storage from -40 to +75 °C. Solid and stranded conductors from 0.75 to 35 mm² are accepted — that covers everything from 1.5 mm² lighting circuits up to 10 mm² feeder tails. Installation depth is 70 mm, overall depth 77 mm, so it clears most standard distribution board gland plates. Mounting position is any, and power supply can enter from top or bottom, which helps when retrofitting into an existing board with fixed busbar orientation. Power loss is 1.5 W maximum — negligible for thermal budgeting in a populated board, but worth knowing if you're counting every watt in a sealed enclosure.
Compliance and approvals
The 5SU9356-7KN25 carries IP20 protection (finger-safe, with conductors connected and distribution board installed). Overvoltage category III, energy limiting class 3, and it's halogen-free and silicon-free — relevant for clean-room or low-smoke installations. Touch protection is built in. The design references EN 60898 and IEC 60947-2 for breaking capacity, and the component function code is F per DIN EN 61346-2 and DIN EN 81346-2.