What this RCCB is and where it fits
The Siemens 5SM3446-0LA is a 4-pole residual current operated circuit breaker (RCCB) from the SENTRON 5SM3 series, designed for 400 V AC, 50 Hz systems. It's a type AC device — meaning it trips on sinusoidal AC residual currents — rated at 63 A load current with a 100 mA sensitivity. The 10 kA short-circuit current rating (SCCR) means it can safely interrupt fault currents up to that level without failing catastrophically, which is the figure you need for coordination with the upstream protective device. It includes thermal overload protection, so it doubles as an overload protector for the downstream circuit, not just a ground-fault interrupter.
Key ratings and what they mean for fit
The 63 A rated current (In) sets the continuous load capacity — sized for a main feeder or a large sub-distribution board on a 400 V three-phase system. The 100 mA rated residual current (IΔn) is the trip threshold for earth leakage; at 100 mA it's above the 30 mA personal-protection level, so it's typically used for fire protection or equipment protection rather than direct shock protection. The 10 kA SCCR at 400 V AC means it can handle fault currents up to that level without rupturing — important for verifying selectivity with the upstream breaker. The 4-pole design (3 phases + neutral) with neutral switching means it disconnects all live conductors on a fault.
Mounting and panel integration
Snaps onto DIN rail (REG profile) and occupies 4 width units (about 72 mm at 18 mm per unit). Installation depth is 70 mm, which fits standard distribution boards. Mounting position is any — no restriction on orientation. The IP20 rating means it's protected against solid objects larger than 12.5 mm (finger-safe) but not against moisture; it's intended for installation inside a distribution board with connected conductors. The terminals accept solid or stranded conductors from 1.5 to 25 mm², with a tightening torque of 2.5 to 3 N·m. Supply can come from top or bottom. The overvoltage category III rating confirms it's suitable for fixed installation downstream of the main distribution board.
What the approvals tell you
The design complies with overvoltage category III per IEC/EN standards, which covers fixed-installation equipment. The IP20 rating with connected conductors is standard for panel-mount devices. The silicon-free designation matters for applications where silicone outgassing can contaminate sensitive surfaces — e.g., in paint shops or electronics assembly areas. The finger and back-of-hand safe protection means the terminals are touch-safe when installed per the manufacturer's instructions.