What it is and what it does
The Siemens 5SY4125-6CC is a SENTRON miniature circuit breaker — one pole, 25 A rated current, B-curve trip, designed to protect branch circuits in industrial control panels and distribution boards. The B characteristic (3–5× In magnetic trip) makes it a fit for resistive and general-purpose loads where inrush is modest; it clears overcurrents before they damage downstream wiring or equipment. Rated 400 V AC with a 10 kA breaking capacity per EN 60898, and 5 kA per UL 1077 / CSA C22.2 No. 235 — so it handles fault currents up to those levels without welding contacts or cascading upstream. The 72 V DC max rating covers control-circuit applications on DC rails.
Mounting and wiring
Snaps onto DIN rail via the quick-assembly system — 18 mm width (1 width unit), any mounting position, any supply-side orientation. Accepts solid or stranded copper from 0.75 mm² up to 35 mm² at the screw terminals; torque to 2.5–3.5 N·m. Combined top and bottom terminals let you loop feed-through without extra busbars. IP20 with conductors connected — fine inside a closed panel, not for wet or dusty environments. Ambient range -25 to +55 °C operating, storage from -40 to +75 °C. Sealable cover option for lockout/tagout compliance.