What this RCD-operated circuit breaker does
The Siemens 5SU9354-8KK25 is a 2-pole (1P+N) RCD-operated circuit breaker from the SENTRON 5SU9 series, combining overcurrent protection and residual-current detection in a single 36 mm-wide module. The Type A fault-current detection handles pulsating DC residual currents — common on single-phase rectified loads like VFDs and switched-mode supplies — so it's suited for mixed-load panels where standard AC-only RCDs would miss a fault. The energy limiting class is 3, so it lets through less let-through energy than a Class 1 or 2 device — that matters when you want to protect downstream wiring and connected equipment during a short-circuit event.
Terminals accept solid or stranded conductors from 0.75 mm² up to 35 mm² — that covers everything from 1.5 mm² lighting circuits up to 10 mm² feeder tails.
At 40 °C it derates to 23.5 A, at 45 °C to 22.75 A, and at 50 °C to 21.75 A.