The Siemens 5SU1354-1LB20 is a SENTRON RCBO (residual current circuit breaker with overcurrent protection) in a 2-pole 1P+N configuration, rated 20 A with a C tripping characteristic and 30 mA AC residual current sensitivity.
The 30 mA AC residual current type catches sinusoidal earth faults only — not pulsating DC or smooth DC, so it's correct for general-purpose circuits but not for variable-speed drives or EV chargers that generate DC fault content. Rated current derates with ambient temperature: 20 A at 30 °C, 18.8 A at 40 °C, 14.6 A at 70 °C. In a crowded enclosure running warm, the actual continuous load should be sized against the derated figure, not the 20 A label. That matters in industrial panels where equipment start-up transients are routine.
Snaps onto DIN rail in any orientation.