The Siemens SENTRON 5SQ2570-2YA04 is a 2-pole miniature circuit breaker (1+N) rated 4 A with a C tripping characteristic, designed for 400 V AC, 50 Hz systems. The 3 kA breaking capacity per EN 60898 covers most domestic fault levels; for industrial panels with higher prospective short-circuit current, you'd step up to the 6 kA or 10 kA class in the same SENTRON 5SQ family.
Compared to the 3-pole 5SQ2370-2YA04 (same 4 A C-curve, same 3 kA breaking capacity, same 55 mm depth), this 2-pole unit adds neutral switching and occupies 2 width units instead of 3. The 5SQ2370-2YA04 does not switch the neutral — it's a 3-pole device for three-phase loads without neutral. If your panel was laid out for the 3-pole variant, the 2-pole 5SQ2570-2YA04 will not drop in without rewiring: the pole count and busbar arrangement differ. For a 4-pole alternative with neutral switching at 16 A, see the 5SQ2670-2YA16.
Two width units (18 mm each) means a 36 mm DIN rail footprint. The C-curve (5–10× In) handles motor inrush and transformer loads better than a B-curve; for purely resistive lighting or heating circuits, a B-curve would trip faster on short-circuit but the C-curve is the common choice for mixed loads.