The Siemens 5SL4250-8 is a 2-pole SENTRON miniature circuit breaker rated 50 A at 30 °C with a D tripping characteristic. The D curve means it tolerates inrush currents 10–20× rated — sized for motor and transformer branch circuits where the starting surge would nuisance-trip a B or C curve breaker. Breaking capacity is 10 kA per both EN 60898 and IEC 60947-2, so it clears faults up to that level without upstream coordination issues in residential or light commercial panels. Rated voltage is 400 V AC, with a maximum multi-phase operating voltage of 440 V AC. The 2-pole configuration (2P) switches both phase conductors; neutral conductor switching is not included, so the neutral bar remains continuous through the panel. The breaker occupies 2 modular width units (36 mm total) on a DIN rail. Mounting position is unrestricted — vertical, horizontal, or inverted — which simplifies layout in crowded enclosures.
Thermal derating and ambient limits
The 50 A rating holds at 30 °C ambient. At 40 °C the breaker must be derated to 46.19 A; at 45 °C to 44 A; at 55 °C to 39.81 A. These are per the manufacturer's published curve — panel builders should apply the derating factor for the enclosure's internal temperature rise, not the room ambient. The breaker is rated for ambient temperatures from -40 °C to +75 °C, with a maximum 95 % humidity at 55 °C. Degree of pollution is 2 (non-conductive pollution that may become conductive due to condensation), which covers most indoor panel environments.
Physical fit and panel integration
Dimensions are 76 mm depth, 36 mm width (2 MW), 90 mm height. Installation depth is 70 mm — the extra 6 mm accounts for the terminal screw clearance behind the DIN rail. The housing is halogen-free and silicon-free, which matters for panels in clean-room or sensitive electronics environments where outgassing can contaminate contacts. Sealable with a lead seal or lockout tag; touch protection is integrated on the line-side terminals. IP20 with connected conductors — suitable for enclosed distribution boards, not for wet or washdown locations.