The Siemens SIRIUS 3RV2021-1KA20-ZX95 is a motor protection circuit breaker designed for the main current circuit, with spring-loaded terminals and phase failure detection built in. Its Class 10 trip characteristic means it disconnects within 10 seconds at 7.2× the thermal setting — a standard fit for standard induction motor starting, where the inrush transient needs to ride through without nuisance tripping.
SCCR and breaking capacity
Rated short-circuit breaking capacity hits 100 kA at 240 V and 400 V AC, dropping to 42 kA at 500 V and 4 kA at 690 V. That 100 kA figure at 400 V is the one that matters for most North American and European panel builds — it lets you place this breaker downstream of a high-capacity transformer without needing a current-limiting fuse upstream for coordination.
Mounting and panel fit
Mounts via screw or snap-on onto 35 mm DIN rail per DIN EN 60715, in any position. The 45 mm width and 97 mm depth are the critical dimensions for panel layout — at 45 mm wide it occupies a single 45 mm module slot on the rail, leaving room alongside contactors or overloads in a motor starter column.