The Siemens SIRIUS 3RV1421-0HA10-ZX95 is a transformer-protection circuit breaker rated at 0.8 A continuous current with a 100 kA breaking capacity at 400 V AC — that's the same interrupting rating across 240 V through 690 V, so it clears faults up to that level without cascading upstream.
Snaps onto a 35 mm DIN rail per EN 50022 and accepts screw-type terminals on the main circuit — 2x (1–2.5 mm²) solid or stranded, or 2x (2.5–6 mm²) for heavier tails. The 45 mm wide body leaves room for adjacent breakers in a crowded panel; depth is 96 mm, height 97 mm.
Environmental and electrical margins
Surge voltage resistance is 6 000 V, and the unit withstands 25 g / 11 ms shock. Phase-failure detection is built in; ground-fault detection is not. The auxiliary switch option is present on this variant (0 factory-fitted auxiliary contacts, but the slot is there for field addition).