The Siemens 5SY6308-8 is a 3-pole SENTRON miniature circuit breaker with a D tripping characteristic rated at 8 A and 400 V AC. The 6 kA breaking capacity per EN 60898 covers most residential and light commercial panelboards; the 15 kA per IEC 60947-2 gives headroom for industrial distribution where fault currents run higher. The 5 kA UL 1077 / CSA C22.2 No. 235 rating means it's accepted for North American supplementary protection applications, though it's not a branch-circuit rated UL 489 device.
Occupies 3 width units (54 mm). Accepts solid or stranded copper from 0.75 mm² up to 35 mm², which covers everything from control-circuit tails to feeder-sized conductors. Combined terminals top and bottom simplify busbar or daisy-chain wiring. IP20 with conductors connected; install in any orientation, and the sealable cover allows lockout/tagout on the panel door.