The Siemens 5SM2345-6KK12 is a 4-pole residual current circuit breaker (RCCB) rated 63 A at 400 V AC, 50 Hz, with a 30 mA trip threshold and Type A sensitivity. The 63 A rating at 40 °C (58.6 A) and 45 °C (58.59 A) means this device carries the full load of a three-phase sub-distribution board or a large machine infeed without nuisance tripping from leakage — the 30 mA threshold catches sinusoidal AC and pulsating DC fault currents, covering most modern electronic loads (switched-mode power supplies, VFDs, rectifiers). Type A is the standard choice for circuits with single-phase rectification downstream — think PLC power supplies, lighting ballasts, or small drives.
The 124 mm width (3 modular units) and 77 mm depth with 70 mm installation depth mean it occupies three 18 mm slots in a distribution board — check your enclosure fill factor before committing the BOM line.
Temperature derating — the real-world rating
The 63 A nominal rating holds at 40 °C ambient. Above that, the continuous current drops: 58.6 A at 40 °C, 56.7 A at 50 °C, 53.55 A at 60 °C, and 50.4 A at 70 °C.