The Siemens 3RV1321-0JC10 is a SIRIUS motor-protective circuit breaker designed for starter combinations — the class of breaker that sits ahead of a contactor to provide short-circuit and overload protection for a motor branch. The real headline here is the breaking capacity: 100 kA at 240 V, 400 V, 500 V, and 690 V AC.
Main circuit terminals accept solid or stranded wire: 2x (1…2.5 mm²) or 2x (2.5…6 mm²), with AWG equivalents 2x (14…10). Clearance: zero mm backwards, zero mm at the sides — you can butt it against adjacent devices without derating.
That saves panel space and a fuse holder. Rated for AC-3 duty (switching motors) up to 690 V, with a maximum of 15 operations per hour. That's fine for a pump or conveyor that cycles a few times an hour, not for a high-speed indexing machine. Power dissipation at rated current: 7.25 W total, 2.4 W per pole. In a dense panel, that adds up — keep an eye on the thermal budget if you're packing a row of these. Shock rated at 25 g for 11 ms — survives the vibration of a motor starter panel mounted on a machine frame.