What it is and what it does
The Siemens SIRIUS 3RV2021-1JA20-ZW96 is a motor protection circuit breaker designed for the main current circuit of a motor branch. Its job is to combine overload and short-circuit protection in one device, saving a panel row and a set of fuses. The Trip Class 10 rating means it trips within 10 seconds at 7.2× the thermal setting — fast enough to protect standard induction motors against locked-rotor heat buildup without nuisance tripping on normal starting inrush. Rated breaking capacity hits 100 kA at 400 V AC, which covers most industrial distribution panels in Europe and Asia. At 690 V it still interrupts 4 kA, fine for the occasional 690 V motor circuit. Phase failure detection is built in — if one phase drops, the breaker opens the circuit, preventing single-phasing damage to the motor. Mounts on 35 mm DIN rail per DIN EN 60715, either snap-on or screw-fastened for vibration resistance. The 45 mm width (three module spaces) is standard for this class — fits a typical motor starter lineup without crowding. Spring-loaded terminals accept up to 2×10 mm² solid or stranded, so no ferrule crimping needed for most panel wiring.
Clearance and mounting
The breaker needs 50 mm clearance above and below for air circulation and arc-quenching — no side clearance required (0 mm left/right). No forward or backward clearance is specified either, so it can sit flush against a backplate or gland plate. Any mounting position is allowed, which simplifies layout in tight enclosures.