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.
That's well into industrial-grade territory, not just residential backup. 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.
Standard rail mount, 35 mm DIN. Saddle terminals (not cage clamps) give a solid bite on larger conductors. 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.