The Siemens 5SU9307-7QS50 is an RCBO from the Crabtree Polestar range — a combined residual-current device and miniature circuit breaker in one DIN-rail module. It carries a 16 kA breaking capacity, type A residual-current sensitivity at 30 mA, and a C50 thermal-magnetic trip characteristic. The 'Long Tail' variant extends the neutral conductor for panel wiring convenience.
What the ratings mean for fit
The C50 curve means the thermal trip holds up to 5× rated current (250 A) for short overloads, then snaps — sized for motor or lighting circuits with moderate inrush. The 30 mA type A residual-current element catches both sinusoidal AC fault currents and pulsating DC fault currents, which covers modern electronics and variable-speed drives downstream. The 16 kA breaking capacity at the service entrance or sub-distribution board means it can clear a bolted fault up to that level without welding its contacts shut.