Selective RCBO for feeder protection
The Siemens 5SU1874-7BK82 is a 4-pole selective RCBO from the SENTRON 5SU1 series, combining overcurrent protection and residual current detection in a single 11-module-wide unit. Rated 125 A at 230/400 V AC with a C tripping characteristic, it delivers a 10 kA breaking capacity certified to both EN 60898 and IEC 60947-2 — the dual standard covering domestic and industrial installations. The Type B fault-current detection handles smooth DC, pulsed DC, and AC residual currents, which matters for variable-speed drives, UPS systems, and EV charging infrastructure where pure AC-sensing RCDs would blind. Because it is selective (time-delayed), the 5SU1874-7BK82 coordinates with downstream RCDs so that a fault on a sub-circuit trips the local device first — the main stays in, keeping the rest of the distribution board live. That selectivity is the difference between one machine dropping out and a whole panel going dark.
Thermal derating and mounting flexibility
The 125 A rating holds at 30 °C ambient; at 40 °C it derates to 115.62 A, at 50 °C to 106.25 A, and at 60 °C to 96.25 A. Installation depth is 70 mm (overall depth 77 mm), width 198 mm (11 width units), height 90 mm.