The Siemens SIRIUS 3RV2321-4BC10 is a circuit breaker designed specifically for starter combinations — meaning it integrates directly into a motor starter assembly, handling both short-circuit and overload protection in one footprint. It mounts on a 35 mm DIN rail per DIN EN 60715, using either screw or snap-on fastening, and accepts any mounting position. The screw-type terminals on the main current circuit accept up to 2x 10 mm² solid or stranded conductors.
Breaking capacity — what the numbers mean for panel coordination
At 240 V AC this breaker interrupts 100 kA — a figure that covers most industrial service-entrance fault levels without needing an upstream current-limiting fuse. At 400 V the rating drops to 25 kA, and at 690 V to 2 kA. For a 400 V panel fed from a typical 1 MVA transformer (prospective fault around 25 kA), this breaker coordinates cleanly. The 690 V rating is lower, so verify the available fault current if the breaker lands in a 690 V circuit.
Mounting and clearances
The breaker measures 45 mm wide, 97 mm deep, and 97 mm tall. Required clearances: 50 mm above and below, 30 mm to the side, zero forward and backward. That 50 mm vertical gap is the one that catches panel layouts — if you're stacking breakers in a row, leave room for the arc-chamber venting. The 45 mm width matches the standard SIRIUS double-module footprint, so it fits alongside contactors and overload relays on the same DIN rail without adapters.