The Siemens 5SU1374-8DK81 is a 4-pole RCBO from the SENTRON series, combining overcurrent protection with residual current detection in a single modular device. It carries a Type B+ residual current sensitivity of 30 mA and a D tripping characteristic for the overcurrent element, rated at 100 A at 30 °C ambient.
The 100 A rating holds at 30 °C; at 40 °C it derates to 92.5 A, at 50 °C to 85 A, and at 60 °C to 77 A.
Residual current type and application
Type B+ residual current protection detects AC, pulsating DC, smooth DC, and high-frequency AC fault currents up to 1 kHz. This makes it suitable for circuits with variable-speed drives, UPS systems, EV chargers, and other equipment that can generate mixed-frequency or DC residual currents. The D tripping characteristic handles high inrush loads like motors and transformers without nuisance tripping.