The Siemens SENTRON 5SM1744-0 is a 4-pole residual current operated circuit breaker (RCCB) rated at 40 A and 400 V AC, with a 500 mA tripping residual current. It is a type AC instantaneous device, meaning it detects sinusoidal AC fault currents without intentional delay — suited for general-purpose protection where no DC or pulsed DC fault components are present. The 10 kA short-circuit current rating (SCCR) means it can safely interrupt fault currents up to that level without upstream damage, provided the prospective fault current at the installation point does not exceed it.
Current derating and thermal limits
This RCCB carries its full 40 A rating up to 45 °C ambient. Above that, the current must be derated: 38.4 A at 50 °C, 36.8 A at 55 °C, 35.2 A at 60 °C, 33.6 A at 65 °C, and 32 A at 70 °C. The operating ambient range is -5 to +45 °C, with storage from -40 to +60 °C. If the panel ambient exceeds 45 °C, the derated figure governs the continuous load — not the nameplate 40 A.
Mounting and wiring
Snaps onto DIN rail (REG) and occupies 4 width units (roughly 72 mm at 18 mm per unit). Installation depth is 55 mm. Accepts solid or stranded conductors from 1.5 to 25 mm². The screw terminals require a tightening torque of 2.5 to 3 N·m. Supply can enter from top or bottom. Mounting position is unrestricted. The IP20 rating applies when installed in a distribution board with connected conductors — not for open-panel or wet-area use.