The Siemens 5SU1323-1BB20 is a 2-pole RCBO (residual-current circuit breaker with overcurrent protection) from the SENTRON series, combining a C-curve miniature circuit breaker (20 A rated current) with a 30 mA Type AC residual-current device in a single 4-module-width unit. It is designed for residential and commercial final circuits where both overcurrent and earth-fault protection are needed in one device — saving a DIN-rail slot compared to separate MCB+RCCB. The 30 mA residual-current element (Type AC, sensitive to sinusoidal AC fault currents) provides personnel protection in standard domestic and commercial installations. Breaking capacity is 4.5 kA per EN 60898 (the standard for household MCBs) and 15 kA per IEC 60947-2 (the industrial standard) — the higher figure gives headroom for installations with higher prospective fault currents.
Tightening torque is 2.5 to 3 N·m.