Siemens 5SN6304-8CP — 3-pole C-curve MCB for panel protection
It's rated at 400 V AC, 50 Hz, and carries a 6 kA breaking capacity per EN 60898 and 30 kA per IEC 60947-2 — the IEC 60947-2 figure is the one you use for industrial panel coordination, since it covers the higher fault currents you'd see downstream of a transformer.
Three modular width units (54 mm wide, 90 mm tall, 76 mm deep with 70 mm installation depth) — it occupies three standard 18 mm DIN-rail slots, so check your panel layout if you're swapping in for a narrower 1- or 2-pole unit. The 72 V DC maximum rating means it can also switch DC control circuits up to that voltage, but the primary duty is AC. Maximum solid conductor cross-section is 35 mm², which handles feeder and branch wiring without a separate terminal adapter.
Snap-on DIN-rail mount, 3-pole design — it clips into any standard 35 mm rail. Terminal screws accept solid or stranded up to 35 mm², and the neutral bus can be fed from either end.