The Siemens 5SM9425-0KK is a SENTRON residual current (RC) unit — a 2-pole, type AC device rated for 63 A continuous at 230/400 V AC, 50 Hz, with a 100 mA tripping threshold. It's an instantaneous electronic RC unit, meaning no intentional time delay; it trips as soon as the residual current exceeds 100 mA. At 40 °C and 45 °C it carries the full 58.59 A without derating; from 50 °C upward the current capacity steps down gradually to 50.4 A at 70 °C.
What the ratings mean for fit
The 63 A rating governs the load it can pass continuously in a 40 °C ambient — sized for a submain or a large final circuit. The 100 mA residual sensitivity is less common than the standard 30 mA (personnel protection); 100 mA is typically specified for equipment protection or where nuisance tripping from leakage on long cable runs is a concern. Type AC means it detects sinusoidal AC residual currents only — not pulsed DC or smooth DC, so it's suited for conventional resistive and inductive AC loads, not VFDs, UPS systems, or EV chargers that generate DC fault components. The 2-pole construction (switching both phase and neutral) fits single-phase or split-phase panels where the neutral must be interrupted. Mounts on standard DIN rail in any position, occupying 2 width units (36 mm).