What it is and what it does
The Siemens 3RV2021-4AA25-ZW96 is a SIRIUS motor protection circuit breaker designed for motor protection, with a Class 10 trip characteristic that matches standard induction motor startup curves — it holds through the inrush and trips before the winding gets hot. Rated breaking capacity hits 100 kA at 240 V and 25 kA at 400 V, so it handles high-fault-current panels without needing an upstream fuse for most industrial installations. Phase failure detection is built in — if one leg drops out, the breaker trips, which keeps a three-phase motor from single-phasing and burning up on the remaining two phases.
Panel fit and wiring
Mounts via screw or snap-on onto 35 mm DIN rail per DIN EN 60715, in any position. At 45 mm wide and 97 mm deep, it fits standard motor-starter slots without crowding the gland plate. Main circuit connections use spring-loaded terminals that accept 2x (0.5 to 2.5 mm²) solid or stranded wire — no screw torque to verify, just strip and push. Clearance distances: 50 mm above and below, 30 mm to the side, zero front and back. That keeps the arc-quenching zone clear and the heat path open.