The Siemens 5SP3716-0 is a 1-pole main conductor circuit-breaker (SHU) rated 16 A at 230/400 V. It's a DIN-rail mounted device for protecting branch circuits in distribution panels — the kind of part you spec into a sub-distribution board or backup as a critical spare for an existing install.
Snap-on DIN-rail mounting for standard 35 mm rail. The 1-pole form factor occupies one module width, keeping panel fill factor tight. Rated 16 A at 230/400 V covers single-phase or line-to-neutral branch protection in a 400 V three-phase system.