The Siemens SIRIUS 3RV2021-4NA10-ZX95 is a motor protection circuit breaker designed for protecting three-phase induction motors against overload and short-circuit faults. Its Trip Class 10 thermal overload curve matches standard motor starting profiles, so it will not nuisance-trip during a normal start but still clears a stalled rotor before the motor windings overheat. The 25 kA breaking capacity at 400 V is the key short-circuit rating — it safely interrupts fault currents up to that level without upstream fuses needing to clear first, which simplifies panel coordination in a 400 V distribution system.
Mounting and integration
Mounts via screw or snap-on onto 35 mm DIN rail per DIN EN 60715. The 45 mm width and 97 mm depth mean it occupies a single 45 mm module on the rail — standard for this class of motor-protective device. Any mounting position is permitted, so it can be laid flat in a shallow enclosure or stood vertically without derating. Terminal capacity is 2x (1…2.5 mm²) or 2x (2.5…10 mm²) solid or stranded, accepting both control wiring and motor power conductors directly without intermediate terminal blocks.
Short-circuit coordination
Breaking capacity is rated at 25 kA at 400 V, 100 kA at 240 V, 5 kA at 500 V, and 2 kA at 690 V. The 25 kA at 400 V is the figure that governs most European 400 V distribution panels — it allows Type 1 or Type 2 coordination with downstream contactors without needing upstream fuses for fault currents below that threshold. The 100 kA at 240 V covers North American 240 V delta systems where available fault current can be high. The gL/gG fuse backup ratings at 400 V, 500 V, and 690 V are all 63 A, providing a clear selectivity boundary with upstream fuse-links.