SIRIUS 3RV1021-0KA15 — Motor Protection Circuit Breaker, 1.25 A
The Siemens 3RV1021-0KA15 is a SIRIUS motor protection circuit breaker rated for 1.25 A continuous current with a Class 10 trip characteristic, meaning it protects motors against overload and short circuit by tripping within 10 seconds at 7.2× rated current — fast enough for standard induction motor starts without nuisance tripping. Rated for 690 V AC maximum, it delivers 100 kA breaking capacity across 240 V, 400 V, 500 V, and 690 V AC — sufficient to clear high-fault-current scenarios in industrial distribution without cascading upstream breakers. Mounts via screw or snap-on onto 35 mm DIN rail per EN 50022, with a 45 mm width footprint that fits standard panel layout grids. IP20 front protection means it is touch-safe for the panel interior but not rated for washdown environments.
Motor Duty and Trip Coordination
At 400 V AC-3 duty, this breaker supports a 0.37 kW motor load — the rating that governs real-world motor protection sizing, not the 1.25 A continuous current alone. The 1.25 A continuous rating sets the thermal overload threshold; the 0.37 kW figure tells you what motor frame it protects on a 400 V line. Phase failure detection is built in, so a lost phase on the supply side will trip the breaker — critical for preventing single-phasing damage on delta-connected motors. No ground fault detection, so that function must be handled separately downstream. Power dissipation at rated current in hot operating state is 7.25 W — factor this into enclosure thermal calculations if multiple breakers are ganged in a small cabinet.
Termination and Wiring
Main circuit terminals accept screw-type connections: solid conductors from 2x (0.5 to 1.5 mm²) up to 2x (0.75 to 2.5 mm²), and stranded conductors from 2x (1 to 2.5 mm²) up to 2x (2.5 to 6 mm²). AWG equivalents for main contacts are 2x (14 to 10). Auxiliary and control circuits also use screw terminals. Auxiliary switch extension is available as a product option, with a transverse design — allows adding a signal contact for remote status indication without replacing the breaker.
Environmental and Mechanical
Operating temperature range is -20 to +60 °C; storage and transport range is -50 to +80 °C. Shock resistance rated at 25 g for 11 ms — suitable for installation on machinery subject to vibration, such as conveyor drives or compressor skids. Mounting position is any orientation, and backwards and side clearances are 0 mm — meaning no mandatory air gap to adjacent devices, simplifying panel layout.