Thermal derating and real-world fit
The 5SM9122-6KK01: The 40 A rating holds at 40 °C and 45 °C (37.2 A at both), then begins a gentle slope: 36 A at 50 °C, 34.8 A at 55 °C, 34 A at 60 °C, 33.2 A at 65 °C, and 32 A at 70 °C.
The short-time delayed characteristic (selectivity class) lets it coordinate with downstream RCDs, avoiding nuisance trips on transient leakage from motor starts or capacitor inrush. The 10 mA trip threshold is sensitive enough for personnel protection (direct contact) in wet or medical-adjacent zones, but the delay prevents false tripping on normal equipment leakage.
Panel integration
This is a 2-pole modular device in the SENTRON 5SM9 design, sized for standard DIN-rail mounting in a distribution board or sub-panel. The 230/400 V AC supply voltage covers both single-phase and line-to-line feeds. No neutral conductor switching — it's a 2-pole RC unit, so it switches both phase conductors on a single-phase circuit or two phases on a three-phase system.
Lifecycle status is current — no phase-out, no last-time-buy window. No official successor exists because none is needed.