The Siemens 3RV1421-0KA10-ZI41 is a size S0 circuit breaker from the SIRIUS 3RV1 family, designed specifically for transformer protection. It carries an A-release rated 0.9...1.25 A and a fixed short-circuit release set at 26 A, with screw terminals and standard switching capacity. This is a panel-mount device that snaps onto a DIN rail in a standard control cabinet.
The lifecycle stage for this order code is current, but the manufacturer's own description flags it as a phased-out product. The official successor is the SIRIUS 3RV2 series.