The Siemens 5SU1444-2RC40 is a combined residual current device and miniature circuit breaker (RCBO) rated at 40 A, 4-pole, occupying 8 module widths on a DIN rail. The Type AC residual sensing detects sinusoidal AC fault currents down to 100 mA, covering basic shock protection and fire prevention in standard commercial and industrial final circuits.
The 40 A rating governs the overcurrent protection threshold — sized for a 40 A final circuit feeding motor starters or distribution sub-panels. The D characteristic (tripping between 10× and 20× In) avoids nuisance trips on starting surges from pumps, compressors, or small transformers. The 100 mA residual sensitivity is less sensitive than the 30 mA required for personal shock protection in socket-outlet circuits; it is intended for equipment protection or fire prevention where the earth-leakage path is higher impedance. The 4-pole (3P+N) construction suits three-phase loads with neutral, common in European-style panelboards.
Panel integration
At 8 modules (144 mm wide), it occupies a standard 8-MCB slot in a distribution board. The busbar comb bridges across the line-side terminals; the neutral is switched internally, so no separate neutral bar connection is needed downstream.