The Siemens 5SY3105-7 is a 1-pole SENTRON miniature circuit breaker with a C-curve trip characteristic rated at 0.5 A at 400 V AC. At 0.5 A it is sized for control transformers, signal circuits, or very small auxiliary loads, not main power distribution. Breaking capacity is rated at 4.5 kA per EN 60898 and 6 kA per IEC 60947-2. Either way, this breaker is meant for low-fault installations — if your panel's SCCR exceeds 6 kA at 400 V, step up to a higher-rated frame. For DC circuits the maximum rated voltage is 72 V, with a DC breaking capacity of 15 kA per IEC 60947-2. That makes it usable in 48 V or 60 V DC control buses, telecom rectifier outputs, or battery-backed auxiliary supplies — but not for 110 V DC traction battery strings. The breaker carries a UL 1077 and CSA C22.2 No. 235 supplementary protection rating at 5 kA / 400 V AC. That means it is recognized as a supplementary protector in North American panels — not a branch-circuit rated breaker per UL 489, so it must be backed by a listed branch-circuit OCPD upstream.
Width is 18 mm — one modular unit (1 MW) on a standard DIN rail. The quick-assembly mounting system snaps onto the rail without tools. That is unusually wide for a 0.5 A breaker — it lets you land larger incoming tails or loop through a busbar while the protection element stays small. Both top and bottom terminals are combined (line/load reversible), and the terminals are touch-protected per IP20 with conductors connected. The breaker is sealable, halogen-free, and silicon-free — relevant for food-processing, pharmaceutical, or clean-room panels where outgassing or tamper evidence matters.