The Siemens 5 SN1 NG10A is a 1-pole miniature circuit breaker rated for 3 A switching current at 220 V supply voltage. As a miniature circuit breaker, it protects downstream wiring and loads from overcurrent and short-circuit faults in a control panel or distribution board.
The 3 A rated current suits a small branch circuit such as a control transformer or a single motor starter coil. It is not for a main feeder or a multi-load subpanel. The single-pole construction (1-pole) switches only the line conductor. For a 3-phase or double-insulated application, you would need a multi-pole variant.