What it is and what it does
The Siemens 3RV1021-1JA10-ZX95 is a SIRIUS motor protection circuit breaker — a 3-pole device rated for 10 A continuous current with a CLASS 10 trip characteristic. It detects phase failure — a common cause of single-phasing motor burnout — and provides adjustable thermal-magnetic overload protection for motors up to 4 kW at 400 V. The breaker snaps onto a 35 mm DIN rail per DIN EN 50022 and accepts screw-type terminals on both main and auxiliary circuits, with wire capacity for 2x (1 to 2.5 mm²) solid or stranded, and 2x (2.5 to 6 mm²). Its breaking capacity reaches 100 kA at 400 V AC, which means it can safely interrupt a bolted fault up to that level without upstream fuses — useful for high-SCCR panel designs.
Where it goes in the panel
Mounts in any orientation on a standard 35 mm DIN rail; the 45 mm width and 97 mm height fit a standard motor starter combination with a contactor alongside. Depth is 96 mm, so plan for gland-plate clearance if the breaker is near the enclosure back wall. No side or backward spacing required — you can butt it against adjacent devices without derating, which simplifies layout in dense control panels. Front IP20 protects against finger contact; suitable for enclosed panel use, not for washdown environments.
Signal integrity and noise considerations
No ground-fault detection — if your motor circuit needs GF protection, add an external RCD or a separate ground-fault module. The breaker's own surge withstand is 6 kV, so it can handle transient spikes from contactor switching without nuisance tripping. Power dissipation at rated load is 9.25 W total, 3.1 W per pole — negligible for panel thermal rise, but worth noting if the enclosure is tightly sealed with multiple breakers.