Motor protection breaker, S0 frame, 16 A
The Siemens SIRIUS 3RV2021-4AA20-ZX95 is a motor protection circuit breaker in the size S0 frame, designed for three-phase motor branch circuits. It combines a thermal overload relay and a magnetic short-circuit trip in one device, saving panel space over a separate contactor-and-relay pair. Rated operational current is 16 A, with an adjustable thermal overload release covering 10…16 A. The instantaneous short-circuit trip responds at 208 A, which coordinates with downstream contactors and starters to clear faults before they damage the load. Trip Class CLASS 10 means the overload element will trip within 10 seconds at 7.2× the set current — the standard for protecting standard induction motors during locked-rotor starts. For motors with longer acceleration times (high-inertia loads), a CLASS 20 or CLASS 30 breaker would be required.
Breaking capacity and coordination
Rated short-circuit breaking capacity is specified per IEC 60947-2 across the voltage range: 100 kA at 240 V AC, 55 kA at 400 V AC, 10 kA at 500 V AC, and 4 kA at 690 V AC. The 55 kA at 400 V gives substantial SCCR headroom for most industrial distribution panels without requiring upstream current-limiting fuses. The rated insulation voltage is 690 V, and the impulse withstand voltage is 6 kV, matching the standard requirements for 400 V and 690 V industrial networks.
Termination and mounting
Spring-type terminals on both main and auxiliary circuits — no screw torque to verify, no re-tightening on thermal cycles. Accepts 0.5…2.5 mm² solid or stranded, or 0.5…1.5 mm² finely stranded with ferrule. Snaps onto 35 mm DIN rail per DIN EN 60715; mounting position is any, which simplifies panel layout. The breaker occupies a 45 mm width on the DIN rail, same as the standard S0 frame. Side-by-side mounting with zero spacing is permitted at rated current, so no derating for ganging.
Lifecycle and compliance
The product carries RoHS compliance with a substance prohibition date of 10/01/2009, indicating it meets the EU RoHS directive. The SIRIUS series is UL/CSA listed and CE marked for the European market.