The Siemens 5SU1344-2RC40 is a 4-pole RCBO (residual current circuit breaker with overcurrent protection) rated at 40 A with a D tripping characteristic and 30 mA Type AC residual current sensitivity. It occupies 8 module widths on a DIN rail, making it a direct fit for standard panel distribution boards where both overcurrent and earth leakage protection must be combined in a single device.
The 8-module width (roughly 144 mm on a standard DIN-rail grid) determines the enclosure space required. In a panel with multiple RCBOs, the cumulative width drives the rail length and cabinet depth. The D characteristic (10–20× In magnetic trip) is specified for loads with high inrush — typically motor circuits, transformers, or discharge lighting — where a B or C curve would nuisance-trip on startup. The 30 mA Type AC residual sensitivity covers sinusoidal AC fault currents; for pulsating DC or smooth DC fault types, a Type A or F device would be required instead.
The 40 A rating at 4 poles means this RCBO protects all three phases plus neutral in a single unit. For a 230/400 V three-phase supply, it handles line currents up to 40 A per phase while providing earth leakage protection on the same physical package. This consolidates what would otherwise require a separate MCB and RCCD, saving one DIN position compared to two discrete devices.