63 A, 100 mA, short-time delayed — what that means on the line
The Siemens SENTRON 5SM3446-0LB01 is a 4-pole residual current circuit breaker (RCCB) rated for 63 A continuous at 230 V AC, with a 100 mA trip sensitivity and a short-time delayed switching function. That 100 mA threshold means it's sized for equipment protection or fire prevention rather than personnel shock protection — the human-body let-go threshold is 30 mA, so this unit trips above that, intended for circuits where nuisance tripping on normal leakage (long cable runs, VFDs, heaters) would be a problem. The short-time delay (type S / selective) lets it ride out transient earth faults downstream while coordinating with a 30 mA RCCB closer to the load, so only the faulted branch clears. Rated short-circuit current withstand is 10 kA, and surge current resistance is 3 kA — figures that tell you this RCCB can survive a bolted fault on a 230/400 V distribution board without rupturing, and it won't false-trip on lightning or capacitor-switching surges. Overvoltage category III confirms it's rated for fixed-installation distribution panels, not just downstream socket circuits.
DIN-rail fit and panel integration
Mounts on DIN rail (REG), occupies 4 width units (roughly 72 mm), installation depth 70 mm. The supply cord position is top or bottom — no forced orientation, which saves wire-bending radius in a crowded enclosure. IP20 with connected conductors, so it's intended for a distribution board interior, not a washdown environment. Finger and back-of-hand safe per the protection-against-electrical-shock rating. Ambient operating range is -5 °C to 45 °C; storage range -40 °C to 75 °C. That -5 °C floor means it's not rated for unheated outdoor cabinets in freezing climates — if the panel sits in a cold warehouse, you'll need a space heater or a different RCCB rated for lower ambients. Silicon-free construction, which matters for potting and conformal-coating compatibility in sealed assemblies.