The Siemens SENTRON 5SY6120-8CC is a 1-pole miniature circuit breaker (MCB) with a D tripping characteristic, rated 6 kA per EN 60898 at 400 V AC. It's not for general lighting or resistive loads; those want B or C curves.
The interrupting rating is 6 kA per EN 60898 at 400 V AC, and 5 kA per UL 1077 and CSA C22.2 No.235. Rated operational voltage is 400 V AC single-phase, 440 V AC multi-phase. The DC rating tops out at 72 V, so don't spec it for a 125 V DC bus. Power loss per pole is 1.6 W in hot operating state — negligible for a single unit, but if you're packing 20 of these in a row, the cumulative heat matters for enclosure sizing.
The combined terminal at top and bottom accepts both busbar and conductor, and the breaker is sealable for tamper-proofing in metered or critical circuits. Ambient temperature range is -40 °C to 75 °C, with derating above 55 °C per the humidity curve (max 95% RH at 55 °C, dropping to 35% at 75 °C). Vibration resistance per IEC 60068-2-6: ±1 mm at 5–25 Hz, 50 m/s² at 25–150 Hz — survives typical machine vibration.