Transformer-protection breaker, 45 mm wide, 100 kA SCCR
The Siemens 3RV2421-1BA10 is a SIRIUS circuit breaker specifically designed for transformer protection — not a general-purpose motor-protective breaker. Mounts on 35 mm DIN rail per EN 60715; the 45 mm width and 97 mm depth fit a standard 4-module slot in a panel. Screw-type terminals on the main circuit accept 2x 1–2.5 mm² or 2x 2.5–10 mm² solid/stranded — no special lugs needed for transformer feeders up to that gauge.
Breaking capacity and fuse coordination
The 3RV2421-1BA10 is rated for 100 kA at 240 V, 400 V, and 500 V AC — that's a high interrupting rating for a 45 mm wide device, meaning it can be used on high-fault-capacity mains without a current-limiting fuse upstream. For selective coordination with downstream fuses, the spec lists maximum gL/gG fuse ratings: 25 A at 400 V and 500 V, 20 A at 690 V. That tells the panel builder the largest backup fuse that still lets the breaker trip first on a downstream fault.