What it is and what it does
The Siemens SIRIUS 3RV2021-4BA15-ZX95 is a motor protection circuit breaker designed to protect three-phase motors against overload and short-circuit. It is part of the SIRIUS brand, a widely used industrial control component family. The breaker is rated for a voltage range of 20 to 690 V and offers a Class 10 trip characteristic, meaning it will trip within 10 seconds at 7.2x the thermal setting — fast enough to protect standard induction motors during a locked-rotor event without nuisance tripping on normal starts. Phase failure detection is built in, so if one phase drops out the breaker will trip, preventing single-phasing damage to the motor windings. Ground fault detection is not included, so for applications requiring ground-fault protection, an external GFCI or residual-current device would need to be added downstream.
Mounting and integration
Mounts via screw or snap-on onto 35 mm DIN rail per DIN EN 60715. The 45 mm width matches the standard 45 mm modular device footprint, so it drops into a panel alongside contactors, overloads, and terminal blocks without wasting rail space. Depth is 97 mm, height 97 mm — a compact cube that fits in shallow enclosures. Mounting position is any orientation, which simplifies layout in tight cabinets. Clearance distances: 50 mm upwards and downwards, 30 mm at the sides, 0 mm forwards and backwards. That means you can butt it against the back panel and adjacent devices on the sides, but need breathing room above and below for arc venting and heat dissipation.
Breaking capacity and selectivity
Short-circuit breaking capacity is 100 kA at 240 V, 25 kA at 400 V, 5 kA at 500 V, and 2 kA at 690 V. At 480 V it is rated for 20 A continuous, and at 600 V also 20 A. The 100 kA at 240 V is high enough to handle most fault currents at that voltage without requiring an upstream current-limiting fuse — useful for panel builders who want to avoid a separate fuse holder. At 400 V, 25 kA covers typical industrial service-entrance fault levels. For backup protection with gL/gG fuses: 63 A at 400 V, 50 A at 500 V and 690 V. This coordination data lets you size the upstream fuse to clear before the breaker reaches its breaking limit, maintaining selectivity in a distribution panel.
Environmental and lifecycle
Auxiliary contact ratings: 1 A at 24 V, 0.5 A at 120/125/230 V, 0.15 A at 60 V. These are for the internal auxiliary switch used to signal the breaker's status to a PLC or indicator light. The main contact terminals accept M4 screws and 2x (0.5 to 1.5 mm²) or 2x (0.75 to 2.5 mm²) solid or stranded wire.