The Siemens 5SU1644-1KK82 is a SENTRON RCBO — a combined residual-current circuit breaker with overcurrent protection — rated 125 A at 30 °C, 4-pole, C-curve trip characteristic, and 300 mA residual-current sensitivity. The C-curve means it holds through motor inrush up to about 5–10× rated current, then trips fast — sized for mixed resistive-inductive loads like pump circuits or compressor feeds.
Mounts on DIN rail, any position. At 11 modular width units (roughly 198 mm), it occupies a standard panel slot. Installation depth is 70 mm. IP20 with conductors connected and distribution board installed, so it lives inside a closed enclosure, not exposed to washdown.
Thermal derating is published: 125 A at 30 °C drops to 115.62 A at 40 °C, 111.25 A at 45 °C, 106.25 A at 50 °C, 101.25 A at 55 °C, and 96.25 A at 60 °C.