What this part is and what it does
The Siemens 3RV1021-1JA38-1KT1 is a SIRIUS motor protection circuit breaker, designed specifically for motor protection duty. It provides overload and short-circuit protection for motors up to 4 kW at 400 V, with a CLASS 10 trip characteristic — meaning it trips within 10 seconds at 7.2× the set current, fast enough to protect standard induction motors during stall or locked-rotor conditions. Phase failure detection is built in, so a lost phase on the supply side trips the breaker before single-phasing damages the motor windings. Rated continuous current is 10 A, which sets the overload protection threshold. The breaker handles 100 kA prospective short-circuit current at 400 V AC — typical for high-fault industrial panels fed by a large transformer — and 42 kA at 500 V, dropping to 6 kA at 690 V. The 100 kA rating at 240 V AC is relevant for single-phase motor circuits or control transformers. That 100 kA SCCR means this breaker can clear a bolted fault without rupturing, even on a stiff network.
Mounting and integration
Mounts via screw fixing or snaps onto 35 mm standard DIN rail per EN 50022. Footprint: 45 mm wide × 97 mm high × 96 mm deep — a standard 45 mm module width, so it fits a typical 45 mm slot in a motor control center (MCC) bucket or enclosure row. Any mounting position is allowed, which helps when panel space is tight. IP20 on the front means finger-safe from the front; the wiring side inside the panel is unprotected, which is normal for this class.
Auxiliary switch and wiring
The breaker includes a transverse auxiliary switch with screw-type terminals on the main circuit. Main circuit terminals accept 2x (0.25 … 2.5 mm²) solid or stranded, or 2x AWG 24…14. The auxiliary contacts are rated at 1 A at 24 V, 0.15 A at 60 V, and 0.5 A at 230 V — sufficient for signaling to a PLC input or contactor coil. No ground-fault detection; that's a separate device.
Environmental and mechanical limits
Operating temperature range -20 … +60 °C; storage and transport -50 … +80 °C. Shock rated at 25g for 11 ms — survives typical shipping and panel-door slams. Maximum operating altitude 2 000 m without derating. Mechanical endurance of main contacts typically 100 000 operations. Power dissipation at AC in hot operating state is 9.25 W — factor that into enclosure thermal calculations.