Siemens 3RV2321-4PC10 SIRIUS Circuit Breaker, 10 kA at 400 V

The Siemens 3RV2321-4PC10 is a SIRIUS circuit breaker designed for starter combinations — meaning it integrates directly into a motor starter assembly, providing short-circuit and overload protection in one compact package. This is not a general-purpose branch breaker; it is sized and coordinated for use with a contactor and overload relay in a motor control center or standalone starter. Rated 10 kA at 400 V AC, this breaker safely interrupts fault currents up to that level without cascading upstream — essential for meeting the SCCR (short-circuit current rating) requirements of the panel label per UL 508A and IEC 60947-2. At 690 V the interrupting rating drops to 2 kA, so verify the available fault current at the point of installation. Mounting is screw and snap-on onto a 35 mm DIN rail per DIN EN 60715, with a 45 mm width that occupies a single modular space. The 97 mm depth and height keep the profile tight for shallow enclosures. Any mounting position is permitted, and the clearance requirements are: 50 mm above and below, 30 mm to the sides, zero forward and backward — so the breaker can sit flush against the back panel without derating. Terminals accept solid or stranded conductors: 2x 1–2.5 mm² or 2x 2.5–10 mm², with M4 screw-type connections on the main contacts. No ground-fault or phase-failure detection onboard — this is a straightforward thermal-magnetic or electronic trip unit for motor overload and short-circuit protection only.