The Siemens SENTRON 5SY5103-7KK11 is a 1-pole miniature circuit breaker rated 3 A with a C tripping characteristic, breaking 10 kA per EN 60898. It's designed for universal current operation — AC or DC — making it a straight drop-in for general-purpose branch circuit protection in control panels, distribution boards, and railway auxiliary systems. The 18 mm width (1 modular unit) snaps onto DIN rail, and the quick-assembly fastening means it clicks in without tools.
The 3 A rating is at 35 °C ambient. At 40 °C it derates to 2.82 A, at 50 °C to 2.62 A, and at 60 °C to 2.41 A (–). The C-curve trips magnetically at 5–10× rated current, so it's sized for circuits where the connected load draws a brief startup surge under 30 A. The 10 kA breaking capacity at 230/400 V AC is the standard domestic/light-commercial SCCR; for DC circuits it's rated 10 kA per EN 60898-2 at 220 V DC. That DC rating matters if you're protecting a 220 VDC control bus or railway auxiliary supply — most general-purpose MCBs don't carry a published DC kA.
Panel integration
The 18 mm width takes one modular space — useful when filling a crowded sub-distribution board. Combined top and bottom terminals let you feed from either direction without flipping the breaker. The sealable design allows a lock-on tag for lockout/tagout procedures.