The Siemens 3RV1421-4AA15 is a SIRIUS circuit breaker specifically designed for transformer protection — meaning its trip curve and thermal memory are tuned to handle the inrush and sustained overload profile of a transformer primary, not a motor start. Breaking capacity is 100 kA at 240 V AC, 50 kA at 400 V AC, 10 kA at 500 V AC, and 4 kA at 690 V AC — so in a 400 V panel it handles high-fault-current scenarios without cascading upstream. No ground fault detection on this variant.
Width is 45 mm, height 97 mm, depth 96 mm — fits standard panel layout with no side clearance needed (0 mm backwards and at the side). Any mounting position allowed. Main circuit terminals accept solid 2x (0.5–1.5 mm²) and 2x (0.75–2.5 mm²), stranded 2x (1–2.5 mm²) and 2x (2.5–6 mm²), or AWG 2x (14–10). Auxiliary and control circuit terminals are also screw type. The auxiliary switch is transverse design and field-addable.
RoHS compliance date is 01.05.2012.