SIRIUS motor protection circuit breaker, S0 frame, Trip Class 10
The Siemens 3RV2021-4AA20-0BA0 is a SIRIUS motor protection circuit breaker in the S0 frame size, designed to protect three-phase motors against overload, short-circuit, and phase failure. It carries a Trip Class 10 rating, meaning it will trip within 10 seconds at 7.2× the thermal setting — the standard for standard-duty motor starting applications where the acceleration time is under a few seconds. The spring-loaded terminals accept 2x (1... 10 mm²) solid or stranded conductors, so no lug crimping on the line side for typical motor branch circuits up to that cross-section. This breaker mounts on 35 mm DIN rail per DIN EN 60715, with screw and snap-on fastening. The 45 mm width and 97 mm depth fit the standard S0 footprint — it occupies one 45 mm slot in the panel, leaving the adjacent spaces free for contactors or auxiliary blocks. Mounting position is any, which simplifies layout in crowded enclosures.
Breaking capacity and coordination
The interrupting ratings are given for both ultimate (Icu) and service (Ics) breaking capacity across voltages. At 400 V AC, the rated ultimate breaking capacity is 25 kA, and the service breaking capacity is 55 kA — the higher Ics figure at the same voltage indicates this breaker can clear faults repeatedly without derating, which matters for high-fault locations like motor control centers fed by large transformers. At 240 V AC, the Icu is 100 kA and Ics is 100 kA, so it holds up even on low-voltage distribution with high available fault current. The gG fuse backup ratings are also specified: at 400 V, the maximum gG fuse is 63 A; at 500 V it drops to 50 A; at 690 V to 40 A. These values define the upstream fuse limit for selective coordination. Phase failure detection is built in, so the breaker will trip if one phase drops out — a common cause of single-phasing damage on delta-connected motors. Ground fault detection is not included; that function would need an external residual-current device or a separate ground-fault relay.
Integration and wiring
The spring-loaded terminals are the main-circuit connection type. They accept solid or stranded conductors from 1 mm² up to 10 mm² per conductor, with two conductors per clamp. The screwdriver shaft diameter is 3 mm, and the tip size is 3.0 x 0.5 mm — a standard Pozidriv or slotted bit. Clearance distances: 50 mm upwards, 50 mm downwards, 30 mm at the sides, and 0 mm forwards and backwards. The zero forward/backward clearance means the breaker can be mounted flush against the back panel or enclosure wall, saving depth in shallow enclosures.