What this RCBO is and what the ratings mean
The Siemens 5SU1674-7CK82 is a 4-pole RCBO from the SENTRON Super resistant K series — a combined overcurrent and residual current device that fits a standard DIN-rail distribution board. The Type B residual current detection handles smooth DC, pulsating DC, and AC fault currents up to 300 mA, which means it covers variable-speed drives, UPS systems, and EV charging circuits where pure AC or pulsating DC RCDs would be blind to a DC fault component. The C-curve tripping characteristic (125 A rated) is sized for motor and lighting circuits with moderate inrush; the 10 kA breaking capacity per both EN 60898 and IEC 60947-2 tells you it can safely interrupt a fault up to that level without upstream damage.
Temperature derating — the real continuous current
The 125 A rating holds at 30 °C. At 40 °C it derates to 115.62 A, at 45 °C to 111.25 A, at 50 °C to 106.25 A, at 55 °C to 101.25 A, and at 60 °C to 96.25 A. If the distribution board runs warm — typical in a crowded panel — the actual continuous current the RCBO can carry without nuisance tripping is lower than the label. Size the upstream conductor and load accordingly.
Mounting and integration
Mounts in any position on a DIN rail; the supply can enter from either top or bottom, which simplifies panel wiring. At 11 modular width units (198 mm wide, 77 mm deep, 90 mm tall), it takes up a full 11-pole slot on the rail. The IP20 rating applies once the distribution board is installed with connected conductors — it's protected against finger contact but not against water ingress, so keep it inside the enclosure.