The Siemens 5SY5102-6 is a SENTRON miniature circuit breaker, B-curve, rated 2 A at 230/400 V AC with a 10 kA breaking capacity per IEC/EN 60898-2 and UL1077. One-pole design, single-module width (18 mm), and a depth of 76 mm — fits standard DIN-rail enclosures without overhang. Tripping characteristic B means it holds 3–5× rated current for short overloads, then trips fast on a hard short; that's the go-to curve for general-purpose lighting and receptacle circuits where you want nuisance-free operation from inrush but still need fast fault clearing.
The 2 A rating is the continuous current at 35 °C ambient; derate to 1.9 A at 40 °C, 1.8 A at 50 °C, and 1.7 A at 60 °C. The 10 kA breaking capacity at 230/400 V AC (and 10 kA DC per EN 60898-2) means it can safely interrupt a fault up to that level without welding contacts or cascading upstream. The B-curve (3–5× In magnetic trip) is the right choice for resistive loads, small lighting circuits, and control transformers where you don't want the breaker to pop on a motor's starting inrush.
Snap-on DIN-rail mount, any position. Halogen-free and silicon-free construction — important for clean-room or semiconductor-adjacent panels where outgassing can contaminate optics or contacts.