Transformer-protection circuit breaker, SIRIUS
The Siemens 3RV2421-4CA10 is a SIRIUS-brand circuit breaker explicitly designed for transformer protection, not general motor or cable duty. This means its trip curve and short-circuit ratings are tuned to handle the inrush and overload profile of a transformer primary — a distinction that matters when coordinating with downstream protection. Rated operating voltage spans 20 to 690 V, with breaking capacities that drop as voltage rises: 100 kA at 240 V, 25 kA at 400 V, 5 kA at 500 V, and 2 kA at 690 V. At 400 V the unit coordinates with a gL/gG fuse rated 63 A; at 500 V and 690 V that drops to 50 A gL/gG.
Width is 45 mm (roughly 2.5 modular spaces), depth 97 mm, height 97 mm. Mounting position is any orientation. Clearance requirements: 50 mm upwards and downwards, 30 mm at the sides, 0 mm forwards and backwards — so it can sit flush against the back panel or enclosure wall. Main circuit terminals are M4 screw-type, accepting 2×(1–2.5 mm²) or 2×(2.5–10 mm²) solid or stranded copper. The terminal layout and pitch match the standard SIRIUS 3RV2 footprint, so a panel wired for a 3RV2023-4CA10 will accept this unit without rewiring — same screw positions, same DIN rail clip.