What it is and what it does
The Siemens 5SU1356-1DV20 is a combined residual-current circuit breaker and miniature circuit breaker (RCBO) — an FI/LS-protector — in a single module. Type AC means it detects sinusoidal AC earth faults only (no pulsed DC or smooth DC components). Rated at 30 mA sensitivity (IFN) and 6 kA breaking capacity, with a C-curve 20 A overcurrent characteristic. The 1+N-pole configuration switches the line and monitors the neutral; the pig-tail (WS) variant simplifies wiring in distribution boards where the neutral bar is already present.
Where it fits
Snaps onto standard DIN rail in a residential or light-commercial distribution board. The 70 mm depth (D=70MM) matches the Siemens 5SV series RCBO footprint — no extra clearance needed behind the panel door. The pig-tail neutral connection means you land the neutral bar directly, not through a busbar slot; this is common in retrofit swaps where the existing neutral bar is fixed.