What it is and where it fits
The Siemens SENTRON 5SP3250-3 is a 2-pole miniature circuit breaker (MCB) from the 5SP3 series, rated 50 A at 400 V AC with an E tripping characteristic. It snaps onto a standard 35 mm DIN rail per EN 60715, taking up 3 width units (roughly 54 mm) in the panel.
Key ratings and what they mean for fit
The 25 kA breaking capacity (per EN 60898) at 400 V AC is the big one — this MCB can safely interrupt a fault current up to 25 kA without welding contacts or cascading failure upstream. That's well into industrial-grade territory, not just residential backup. The E tripping curve means it's designed for loads that see short, high inrush spikes — think transformer primaries, motor circuits with soft starts, or capacitor banks — where a B or C curve would nuisance-trip on magnetizing inrush. Pollution degree 3 and overvoltage category IV tell you it's meant for the main distribution panel, not a clean-room subpanel. It handles conductive dust and transient overvoltages up to 6 kV, which is what you get at the service entrance or in an industrial environment with switching surges.
Mounting and wiring
Standard rail mount, 35 mm DIN. Terminals accept solid or stranded copper from 2.5 mm² up to 50 mm² — that's a wide range, so it handles both the feed from a transformer and the branch wiring. Saddle terminals (not cage clamps) give a solid bite on larger conductors. The enclosure is IP40 with conductors connected; fine for a dry indoor panel but not for washdown areas. Depth is 76.3 mm, height 128 mm — fits standard shallow enclosures. The integrated locking slide accepts a padlock, wire seal, or cable tie for lockout/tagout.