The 0.3 A rating is unusual for a 4-pole MCB — most panel builders reach for 1 A or higher for control circuits. The C-curve is the right choice here because a pure resistive load (heater, indicator lamp) would be fine on B-curve, but rail auxiliary panels often have a small transformer or a DC/DC converter input that pulls a brief inrush.
Deployment context
The 4-pole width (4 modules at 18 mm each) fits a standard rail distribution board inside a locomotive electrical cabinet or a trackside signal enclosure. The railway application marking on the order code means the breaker carries the vibration, shock, and temperature cycling qualification per EN 61373 and EN 50155 — not every 10 kA MCB on the shelf has that, so if you're replacing a part in a rail-certified panel, this is the one that keeps the type approval intact.