The Siemens Betagard 5SL7120-3RC is a 1-pole miniature circuit breaker rated 20 A at AC with a K tripping characteristic, breaking capacity of 15 kA per both EN 60898 and IEC 60947-2. The K characteristic means it is designed for motor and transformer circuits where inrush currents are higher than resistive loads — the magnetic trip threshold is typically 8–12x rated current, so it holds through startup surges without nuisance tripping on a 20 A line feeding a small motor or inductive load.
Temperature derating and real-world current
The 20 A rating is at 50 °C ambient. At 30 °C the breaker can carry 21.8 A continuously; at 40 °C it handles 20.9 A; at 45 °C it's 20.5 A; at 55 °C it derates to 19.5 A; at 60 °C it carries 19 A. This matters when the breaker is packed into a warm panel alongside other heat sources — the actual trip point shifts with the thermal element, so a 20 A breaker in a 60 °C cabinet is effectively a 19 A device. Plan your load margin accordingly.