The Siemens 5SU1374-7DK82 is a 4-pole RCBO from the SENTRON 5SU1 series, combining overcurrent protection and residual current detection in a single 11-module-wide unit. It is rated 125 A at 30 °C ambient, with a C tripping curve for moderate inrush loads like motor starters or transformer banks, and a Type B+ fault current characteristic that detects smooth DC residual currents up to 2 kHz — critical for variable-speed drives and UPS-fed circuits where standard AC/DC-sensitive RCDs may blind. Overvoltage category III means it is rated for fixed-installation distribution boards, not just downstream equipment.
Current derating and ambient limits
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.
Conductor sizing and termination
For a 125 A circuit, 35 mm² or 50 mm² copper is typical depending on installation method and ambient; the terminal range covers both without need for pin lugs.