What this RCCB is and where it fits
The Siemens SENTRON 5SM3646-6KK12 is a 4-pole residual current circuit breaker (RCCB) rated for 63 A at 400 V AC, 50 Hz. It's a Type A device, meaning it detects sinusoidal AC fault currents plus pulsating DC fault currents — the kind you get from rectified loads like VFDs, switched-mode power supplies, and single-phase drives. Out here in the grease, that's the difference between a nuisance trip and a real ground-fault catch on a mixed-load panel. Rated short-circuit current withstand is 10 kA, surge current resistance is 1 kA. I²t let-through is 70,000 A²s.
Temperature derating — the real-world current
This RCCB carries its full 63 A rating up to 45 °C ambient. Above that, it derates linearly: 60.48 A at 50 °C, 57.96 A at 55 °C, 55.44 A at 60 °C, 52.92 A at 65 °C, and 50.4 A at 70 °C. If your panel sits near a hot motor starter or a sunny wall, that 63 A nameplate won't hold — size the feeder accordingly.
Mounting and wiring
Snaps onto standard DIN rail (REG profile). Occupies 4 width units (72 mm wide), 90 mm tall, 77 mm deep — installation depth is 70 mm. Accepts solid or stranded copper from 1.5 mm² up to 25 mm². Mount in any position; supply connects to the bottom terminals. Finger and back-of-hand safe per IP20 when installed in a distribution board with conductors connected.