The Siemens 5SM1644-6 is a 4-pole residual current circuit breaker (RCCB) from the SENTRON series, rated 40 A at 40 °C and 400 V AC at 50 Hz. It trips on Type A fault currents at 300 mA, covering pulsating DC and sinusoidal AC residual currents — the standard choice for circuits with single-phase rectifiers, switched-mode supplies, or electronic loads that generate smooth DC fault components.
Rated current holds at 40 A up to 45 °C ambient. Above that, derate linearly: 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 4.8 W maximum power loss is manageable in a standard enclosure but should be factored into thermal calculations for densely populated DIN-rail assemblies.
Fault current ratings and selectivity
Short-circuit current rating is 10 kA. Per EN 60898 the rated breaking capacity is 0.8 kA; per IEC 61008-1 it is also 0.8 kA. Surge current resistance is 1 kA. The 300 mA trip threshold suits circuits where a 30 mA device would nuisance-trip due to cumulative leakage from multiple loads — common on distribution sub-mains, EV chargers, or industrial socket circuits with long cable runs.
Mechanical and installation data
Mounts on DIN rail (REG) in any position. Occupies 4 width units, size 1 per DIN 43880. Installation depth is 55 mm. Protection class IP20 with distribution board installed and conductors connected. Finger and back-of-hand safe. Silicon-free construction.