What it is and what it does
The Siemens SIRIUS 3RV2021-4PA10-ZX95 is a motor protection circuit breaker designed to protect three-phase induction motors against overload and short-circuit faults. It trips in Class 10, meaning it disconnects within 10 seconds at 7.2× the thermal setting — fast enough to protect standard IEC motors during a stalled-rotor event. The 10 kA breaking capacity at 400 V AC handles most industrial distribution faults without needing an upstream current-limiting fuse, though the spec also shows a 100 kA rating at 240 V for high-fault panels on lower voltages. Phase failure detection is built in — if one line drops, the breaker trips on the remaining two phases, preventing single-phasing damage. Ground fault detection is not included, so if that's needed, a separate ground-fault relay or a different 3RV variant is the call.
Mounting and panel fit
Mounts via screw and snap-on onto 35 mm DIN rail per DIN EN 60715. The 45 mm width means it occupies one standard 45 mm module slot — a 12-way enclosure holds twelve of these side by side. Depth is 97 mm, height 97 mm. Clearance: 70 mm above and below, 30 mm at the sides, zero forwards or backwards. Mounting position is any, so vertical or horizontal rail orientation works.
Wiring and connections
Main circuit terminals are screw-type, M4 thread. Accepts 2× (1 to 2.5 mm²) or 2× (2.5 to 10 mm²) solid or stranded copper. That covers standard motor power wiring up to 10 mm² — enough for a 36 A rated load at 480 V or 600 V. The gG fuse backup at 400 V, 500 V, and 690 V is 63 A, so upstream fuse sizing is straightforward.