The Siemens 5SY5120-6CC12 is a 1-pole miniature circuit breaker from the 5SY5 series, rated for 220V DC with a 10kA interrupting capacity and a B20 tripping curve. It's a DIN-rail mount component built for DC branch-circuit protection in control panels, switchgear, and distribution boards—typical for isolating and protecting DC loads like drives, power supplies, and fieldbus slices where a quick trip on overload is needed.
The B20 curve means the breaker trips magnetically between 3x and 5x rated current (60 A to 100 A for a 20 A frame), which is standard for resistive and low-inductance DC loads—good for power supplies and control transformers, not for motor starting where inrush would nuisance-trip it. The 220V DC rating is specific: DC arcs are harder to extinguish than AC, so this breaker's internal arc chamber is designed for that voltage.
The 1-pole width is one module (approx. 18 mm), so it fits tight gland-plate layouts. Terminal clamps accept up to 25 mm² conductor—enough for the 20 A rating with some headroom. No special derating for side-by-side mounting at 30 °C ambient, but above 40 °C consult the thermal derating curve in the full datasheet.