The Siemens 5SU9306-0DV20 is a combined residual current device and miniature circuit breaker (RCBO) in a single 1+N-pole module. It provides both overcurrent protection (B-curve, 20 A rated current) and residual current protection (Type AC, 30 mA sensitivity) in one DIN-rail mounted unit.
The B-curve characteristic means the magnetic trip operates at 3 to 5 times rated current (60–100 A for this 20 A unit), so it's sized for resistive and general-purpose loads — lighting, socket outlets, small appliances — not high-inrush motor circuits that would nuisance-trip a B-curve.