What this breaker does on the line
The Siemens SIRIUS 3RV2021-4AA20-ZW96 is a motor protection circuit breaker in the size S0 footprint, rated at 16 A operational current with a CLASS 10 trip characteristic.
Breaking capacity — what the ratings mean for your panel
The interrupting rating varies sharply with system voltage, and that's the number that decides whether this breaker coordinates with your upstream protection. At 240 V AC it clears 100 kA; at 400 V AC it's rated 55 kA; at 500 V AC it drops to 10 kA; at 690 V AC it's 4 kA. The DC ratings are lower: 25 kA at 400 V, 5 kA at 500 V, 2 kA at 690 V. For a 400 V panel fed from a transformer with 65 kA available fault current, this breaker needs an upstream current-limiting device — it won't self-protect. The auxiliary contact block (1 NO + 1 NC) is rated C300 / R300 per UL, fine for signaling a PLC input or dropping out a contactor coil.
Panel integration notes
Mounts on 35 mm DIN rail per DIN EN 60715 — snap-on, no tools needed. The spring-type terminals accept 2 × (0.5...2.5 mm²) solid or stranded, or 2 × (0.5...1.5 mm²) finely stranded with ferrules. Side-by-side mounting at 0 mm clearance means you can pack them tight on the rail, but keep the 30 mm clearance above and below for airflow and handle access. The S0 frame is 45 mm wide, 97 mm deep, 119 mm tall. Combines directly with S00 and S0 contactors from the same SIRIUS family.