The Siemens SIRIUS 3RV1421-4AA10-ZW96 is a 3-pole circuit breaker purpose-built for transformer protection, rated 16 A continuous with a CLASS 10 trip characteristic. That CLASS 10 rating means it clears overloads within 10 seconds at 7.2× rated current — fast enough to protect transformer windings from sustained inrush during energization, but coordinated to ride through the magnetizing inrush pulse without nuisance tripping. Interrupting capacity hits 50 kA at 400 V AC, 100 kA at 240 V AC, and still holds 4 kA at 690 V AC — giving solid selectivity headroom downstream of a larger feeder breaker.
Occupies 45 mm width on the rail. Depth is 96 mm, height 97 mm. Backwards and side clearances are 0 mm.