What it is and what it does
The Siemens 5SU9354-8KK10 is a 1P+N RCD-operated circuit breaker (RCBO) from the SENTRON 5SU9 family. It combines overcurrent protection with residual current detection in a single 36 mm wide unit — that's two width units on a DIN rail. Rated 10 A with a D tripping characteristic, it handles high inrush loads like small motors, transformers, or solenoid banks without nuisance tripping. The Type A fault current detection catches pulsating DC residual currents, which standard AC-only RCDs miss. Breaking capacity is 10 kA per both EN 60898 and IEC 60947-2, so it clears faults up to that level without upstream coordination issues in most final-distribution panels. Ambient temperature range is -25 to +45 °C, with derating above 40 °C — at 45 °C it carries 9.1 A, at 50 °C it's 8.7 A. That's the figure to watch if the breaker sits near other heat sources in a crowded enclosure.
Mounting and wiring
Mounts on DIN rail in any position. Installation depth is 70 mm, overall depth 77 mm — that's the dimension to check against gland-plate clearance if you're retrofitting into a shallow enclosure. Terminals accept 0.75 to 35 mm² solid or stranded copper, so it handles both panel feed conductors and downstream distribution tails without adapters. Supply can land on either top or bottom terminals; no polarity restriction on the line side.