What this SIRIUS breaker does on the line
The Siemens 3RV1021-4DA15-ZW97 is a SIRIUS motor protection circuit breaker rated for 25 A continuous current with CLASS 10 trip characteristics, meaning it clears overloads fast enough to protect standard induction motors during start-up without nuisance tripping. It handles motor loads up to 11 kW at 400 V AC and carries a 50 kA breaking capacity at 400 V — enough to interrupt a bolted fault on most industrial distribution without upstream fuses needing to clear first. Phase failure detection is built in, so if one leg drops on a three-phase motor, the breaker trips before single-phasing cooks the winding. The auxiliary switch is transverse-mounted and field-addable, which lets you wire a remote trip indication or a PLC input without opening the main power circuit.
Mounting and wiring — what fits in the panel
Snaps onto 35 mm DIN rail per DIN EN 50022. Width is 45 mm, height 97 mm, depth 96 mm — a standard three-module footprint that leaves room for a contactor alongside in the motor starter row. Mounting position is any orientation, so vertical or horizontal rail layouts both work. Main circuit terminals accept solid conductors 2x (0.5…1.5 mm²) and 2x (0.75…2.5 mm²), or stranded 2x (1…2.5 mm²) and 2x (2.5…6 mm²). AWG equivalents for the main contacts are 2x (14…10). Auxiliary and control circuits use separate screw-type terminals. Clearance: zero mm backwards and zero mm at the side — no extra air gap needed between adjacent devices on the rail.
Breaking capacity and coordination
Rated short-circuit breaking capacity varies by line voltage: 100 kA at 240 V AC, 50 kA at 400 V AC, 10 kA at 500 V AC, and 4 kA at 690 V AC (–). At 400 V — the most common industrial supply — the 50 kA figure means this breaker can be applied upstream of most motor starters without requiring a current-limiting backup fuse, provided the available fault current at the panel doesn't exceed that level. The auxiliary switch is transverse-design and field-installable. If you're comparing against the 3RV6021-4DA10, note that the 3RV1021-4DA15-ZW97 uses screw-type terminals on both main and auxiliary circuits, whereas the 3RV6021 series uses spring-cage terminals. Panel wiring practices differ — if your shop standardizes on spring-cage, the 3RV6021-4DA10 is the closer fit without retraining the wire prep.
Environmental and compliance
RoHS compliance date is 01.05.2012 — the part meets the EU RoHS substance restrictions effective from that date. Operating temperature range is -20 to +60 °C; storage and transport range is -50 to +80 °C. Front face protection is IP20 — finger-safe from the front but not sealed against dust or moisture ingress into the enclosure.