The Siemens SENTRON 5SM3345-6 is a 4-pole Type A residual current circuit breaker (RCCB) rated for 125 A with a 30 mA trip sensitivity, operating at 400 V AC and 50 Hz.
Panel integration
Snap-on DIN rail (REG) mounting per. Occupies 4 modular width units (72 mm wide, 77 mm deep, 90 mm tall) — plan for that 4-MU slot in the distribution board. The IP20 rating applies once the board is installed with conductors connected; the front face is touch-safe, but the terminals are not finger-proof until wired.
The 125 A rating on a 4-pole RCCB is a heavy feeder or submain device — not a final-circuit unit. At 125 A and 400 V, the per-pole power loss in hot operating state is 8.9 W, so four poles dissipate about 35.6 W inside the enclosure; factor that into the thermal budget, especially if the board is densely populated. The 30 mA sensitivity is standard for personnel protection (shock hazard) under IEC 61008-1. The device is instantaneous (no short-time delay), so it trips immediately on a residual fault; it cannot be used for selective coordination with downstream RCDs unless you add a time-delay module upstream.
Rated for ambient temperatures from -25 °C to +45 °C, with storage down to -40 °C. Overvoltage category III (distribution-level). Silicon-free construction — relevant for automotive or paint-shop environments where silicone outgassing causes adhesion failures.