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. It includes thermal overload protection, so it doubles as an overload protector for the downstream circuit, not just a ground-fault interrupter.
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 4-pole design (3 phases + neutral) with neutral switching means it disconnects all live conductors on a fault.
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 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.
What the approvals tell you
The design complies with overvoltage category III per IEC/EN standards, which covers fixed-installation equipment. 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.