The Siemens 5SL3350-7MB is a SENTRON 3-pole miniature circuit breaker with a C tripping characteristic, rated 50 A at 400 V AC and a 4.5 kA breaking capacity per EN 60898.
The 4.5 kA breaking capacity is the maximum prospective fault current it can safely interrupt at 400 V AC; if your service entrance or sub-panel has a higher available fault current, you need the 10 kA variant (5SL4363-7) or an upstream current-limiting device. At 50 A and 400 V three-phase, each pole dissipates 3.5 W in the hot operating state. In a densely packed enclosure, that adds up — three poles means 10.5 W total from this breaker alone, so keep an eye on internal ambient temperature rise, especially if adjacent MCBs are also loaded near their rating. It is also sealable, allowing the panel builder to lock the toggle position with a lead seal or a Siemens sealing cap.
Mounts in any position. Installation depth 70 mm. IP20 with connected conductors. Supplementary devices clip onto the right side without increasing DIN width. Sealable cover allows lockout/tagout.