The Siemens 5SU1653-7KK40 is a SENTRON RCBO — a combined residual-current device and miniature circuit breaker in a single 2-module (36 mm wide) package, 1P+N, rated 40 A at 30 °C with a C tripping characteristic. The C-curve means it holds up to 5–10× rated current momentarily, sized for motor or lighting loads that draw a moderate inrush without nuisance tripping. Type A fault-current detection catches both sinusoidal AC and pulsating DC residual currents — the standard choice for circuits with single-phase rectifiers, switched-mode supplies, or VFDs feeding the load side.
The 40 A rating holds only at 30 °C ambient. At 40 °C it derates to 37.6 A; at 50 °C to 34.8 A; at 60 °C to 32.4 A; at 70 °C to 29.2 A. The maximum power dissipation is 15.6 W, which adds to the enclosure's internal heat rise; factor that into the thermal calculation when grouping several units.
Width is 36 mm (2 width units), depth 77 mm, installation depth 70 mm, height 90 mm.