The Siemens 5SU9306-0KK40 is a 1P+N RCD-operated circuit breaker (RCBO) from the SENTRON 5SU9 series, combining overcurrent protection and residual current detection in a single 18 mm wide module. The instantaneous design (no intentional delay) means it trips on the first half-cycle of a fault — suited for direct protection of final circuits where fast disconnection is required.
Supply can enter from either top or bottom, which simplifies busbar routing in a crowded panel. The IP20 rating applies once the distribution board is installed with connected conductors — treat it as a panel-internal device, not a surface-mount standalone.
Thermal behaviour and derating
At 40 °C it derates to 37.6 A, at 45 °C to 36.4 A, at 50 °C to 34.8 A, and at 55 °C to 32.4 A — a roughly 19 % reduction from 30 °C to 55 °C that must be factored into the circuit design if the enclosure runs warm.