The Siemens SENTRON 5SY5120-7CC11 is a 1-pole miniature circuit breaker rated 20 A with a C tripping characteristic, designed specifically for DC circuits up to 250 V and carrying a 10 kA breaking capacity at 220 V DC per IEC 60947-2. This is not a general-purpose AC-only MCB — the DC rating and the railway designation mean it is built for the vibration profile, temperature extremes, and polarity-aware wiring of rail applications. The 18 mm width (1 MW) fits standard DIN-rail distribution boards, and the quick-assembly fastening system lets it snap into place without tools.
What the DC rating means for your circuit
DC arcs are harder to extinguish than AC arcs because there is no natural zero-crossing. The 5SY5120-7CC11 is tested to IEC 60947-2 for DC interruption, achieving 10 kA at 220 V DC. That 10 kA figure is the prospective short-circuit current it can safely break — if your DC bus can deliver more fault current (e.g., a large battery bank or rectified supply), you need to verify coordination upstream. The C-curve means magnetic trip occurs at 5 to 10 times rated current, so a 20 A breaker trips magnetically between 100 A and 200 A. That suits moderate inrush loads like DC contactor coils, solenoids, or control transformers, but not highly capacitive loads that might cause nuisance trips.