The Siemens 5SU1324-2RC40 is a combined residual-current circuit breaker with overcurrent protection — an RCBO — rated 40 A, 2-pole, 4-module width, D characteristic, Type AC, 30 mA trip sensitivity.
The 4-module width (roughly 72 mm on a standard DIN rail) means it occupies four adjacent 18 mm positions in the consumer unit or distribution board — factor this into your fill plan, especially when grouping multiple RCBOs in a compact enclosure. D-curve coordination: upstream MCB or fuse must be sized to handle the let-through energy of a 40 A D-curve device at prospective short-circuit current; typical selectivity tables from the manufacturer should be consulted for the specific fault level at the installation point.