The Siemens 5SU1656-1KV20 is an FI/LS combination unit — an RCD and MCB in one 70mm-wide module. The Type AC residual-current detection (300mA IΔn) handles sinusoidal AC fault currents to ground; it's the standard choice for general-purpose socket-outlet circuits where no DC or pulsed DC fault content is expected. The 6kA breaking capacity (IEC 60898) covers most domestic and light-commercial distribution boards fed from a transformer up to that prospective fault level. The C-curve 20A thermal-magnetic trip means it holds inrush from motorized loads (pumps, compressors) up to about 10x rated current, then trips magnetically above that.
In a distribution board, it snaps onto the DIN rail and connects via the busbar system. The 1+N-pole configuration switches both line and neutral, with the neutral pole switching but not protected against overcurrent — standard for single-phase final circuits where neutral isolation is required.