The Siemens SIRIUS 3RV2411-1FA20-0DA0 is a circuit breaker specifically designed for transformer protection, size S00. It's a current-production item, so no lifecycle concerns for a new BOM line. Rated at 1.1 kW at 230 V, it provides a Class 10 trip characteristic, meaning it will hold through motor inrush but trip quickly on a sustained overload — standard for protecting the transformer primary winding against secondary-side faults. Breaking capacity is 100 kA at 400 V AC, dropping to 6 kA at 690 V AC — check your available fault current at the panel's service voltage before specifying.
Mounting and integration
Snaps onto a 35 mm DIN rail per DIN EN 60715, or can be screw-mounted. The 45 mm width and 97 mm depth fit standard S00 footprint panels. Any mounting position is allowed. Spring-loaded terminals on the main circuit accept 2x 0.5 to 4 mm² solid or stranded wire. No need for ferrules, though they help on stranded — strip length is standard for the cage. Clearance: 50 mm above and below, 30 mm to the side, zero forward or backward. That's tight enough for most DIN-rail layouts, but watch the upward gap if you're stacking breakers.
What the ratings mean for the panel
The Class 10 trip curve is the key selection parameter here — it allows up to 10 seconds at 7.2x rated current before tripping, which covers transformer magnetizing inrush without nuisance trips. If your transformer has a higher inrush or you need coordination with downstream breakers, check the time-current curve. Rated insulation voltage is 20 to 690 V, so it's suitable for 400 V and 480 V systems common in industrial panels. The back-up fuse recommendation is gG 32 A at 400 V or 500 V, stepping down to gG 25 A at 690 V — size the upstream fuse accordingly. Operating temperature range is -20 to +60 °C, storage -50 to +80 °C. No derating needed in most ventilated enclosures, but if it's in a sealed box next to a transformer, watch the ambient. No ground fault or phase failure detection built in — this is a straight thermal-magnetic breaker. If you need those functions, you'd add a separate relay or move to a motor-protective circuit breaker variant.