What this RCCB is and what it does
The Siemens 5SM3326-4KK14 is a 2-pole residual current circuit breaker (RCCB) from the SENTRON 5SM3 series, rated 63 A at 40 °C and 230 V AC. It's a short-time delayed design (type B+), meaning it handles smooth DC fault currents and high-frequency AC residuals that a standard AC type would miss — think variable-speed drives, UPS systems, or PV inverters dumping DC onto the line. The 10 kA short-circuit current rating (SCCR) means it can interrupt a fault up to that level without welding contacts or cascading upstream. Mounts on DIN rail, takes up 4 width units (72 mm wide), and accepts solid or stranded conductors from 1.5 up to 25 mm².
Thermal derating — the real-world current rating
The 63 A rating holds at 40 °C and even at 45 °C, but above that you lose headroom fast: 59.2 A at 50 °C, 55.4 A at 55 °C, 51.7 A at 60 °C, 47.8 A at 65 °C, and 44 A at 70 °C. If this RCCB sits in a crowded panel or next to a heat source, size the load against the derated figure, not the nameplate. The ambient operating range is -25 to +45 °C; storage range is -40 to +75 °C.
B+ fault current type — what it catches
Type B+ RCCBs detect smooth DC fault currents plus AC and pulsating DC residuals. The short-time delayed characteristic prevents nuisance tripping from transient surges. The I²t withstand is 70,000 A²s.
Mounting and wiring in the panel
Snaps onto standard DIN rail (mounting type REG). Any mounting position works. The supply can come from top or bottom; for the SIGRES function, the bottom connection stays live even when switched off. The IP20 rating applies once the distribution board is installed with conductors connected — it's not sealed for wet environments. Overvoltage category III means it's rated for fixed installation downstream of the main distribution board. Finger and back-of-hand safe terminals reduce the chance of accidental contact during wiring.