The Siemens 5SP3850-3 is a 3-pole main miniature circuit breaker from the SENTRON line, rated 50 A at 30 °C with an E tripping characteristic — a delayed curve designed for transformer and motor-start inrush where a standard B or C curve would nuisance-trip. The 25 kA breaking capacity at 400 V AC (EN 60898) means it can safely interrupt a fault current up to that level without upstream cascading, sized for service entrance or sub-distribution in residential and infrastructure panels. It clips onto standard 35 mm DIN rail per EN 60715 and occupies 4.5 modular width units.
Derating and thermal reality
At 40 °C it derates to 47.5 A, at 45 °C to 46.25 A, at 50 °C to 45 A, and at 55 °C to 43.75 A.
Saddle terminals accept solid or stranded copper from 2.5 mm² up to 50 mm² — enough for the full 50 A feed without pigtailing. Infeed can land at either the box terminal or the saddle; supply position is arbitrary, which simplifies busbar routing. The integrated locking slide accepts a padlock, wire seal, or cable tie for lockout/tagout. IP40 with conductors connected — fine for a dry indoor enclosure, not for washdown.