The Siemens SIRIUS 3RV2721-4BD10 is a size S0 circuit breaker for system protection, designed for screw and snap-on mounting onto 35 mm DIN rail per DIN EN 60715. It carries a 25 kA interrupting rating at 400 V AC and is UL 489 / CSA C22.2 No. 5 listed, making it suitable for North American panel builds where branch-circuit protection is required. The 45 mm width and 144 mm height fit standard S0 footprint, and the 97 mm depth leaves room for wiring behind the rail.
Ratings and what they mean for your panel
The 25 kA SCCR at 400 V AC tells you this breaker can safely interrupt a fault current up to that level without upstream fuses having to clear — critical for coordination studies. At 500 V the rating drops to 5 kA, and at 690 V to 2 kA, so if your line voltage is higher than 400 V, verify the available fault current is within these limits. The gG fuse backup ratings (63 A at 400 V, 50 A at 500/690 V) define the maximum upstream fuse for selectivity; exceed those and the breaker may not coordinate. Rated operational voltage spans 20...690 V, covering most low-voltage industrial supplies. The 5.5 kW motor rating at 230 V gives a quick sizing reference for direct-on-line motor starting at that voltage.
Mounting and integration
Snap-on onto 35 mm DIN rail per DIN EN 60715 — no tools needed for the rail mount, though the screw-type terminals for the main circuit require a Pozidriv size 2 tip (shaft diameter 5 to 6 mm). Accepts 1...10 mm² solid or stranded, up to 2x 10 mm². Clearance requirements: 70 mm above and below, 30 mm to the side, 0 mm forward and backward — so you can butt it against the back panel or a busbar without extra spacing.