Transformer Protection Breaker, SIRIUS Size S00
The Siemens SIRIUS 3RV1421-0FA10-ZW97 is a three-pole circuit breaker specifically designed for transformer protection, not general motor protection. Its adjustable overload release covers 0.35 to 0.5 A, with a fixed N-release (instantaneous magnetic trip) set at 10 A. This means the breaker protects the transformer primary against sustained overloads via the thermal element, while the magnetic trip handles short-circuits — but the 10 A magnetic threshold is deliberately high to avoid nuisance tripping on transformer inrush current, which can be several times the full-load rating for tens of milliseconds. The unit mounts via screw and snap-on onto 35 mm DIN rail per DIN EN 60715, fitting the standard S00 frame size (45 mm wide, 90 mm high, 75 mm deep). Screw terminals accept 2x (0.5 to 1.5 mm²) solid or 2x (0.75 to 2.5 mm²) finely stranded with ferrule. Torque the main and auxiliary contacts to 0.8-1.2 N·m using a Pozidriv size 2 tip. The rocker switch provides visual switching status indication.
The Substance Prohibitance date of 01.05.2012 indicates RoHS compliance per EU Directive 2011/65/EU, with no restricted substances above threshold limits as of that date.
Panel Fit & Integration
This breaker occupies the same S00 footprint as the motor-protection siblings (3RV1011-0GA10, 3RV1011-0HA10, 3RV1011-1AA15) — same 45 mm width, same DIN-rail clip, same terminal layout. If a panel was originally wired for a 3RV1011 motor-protective breaker, the 3RV1421 will drop into the same mounting hole and busbar arrangement without rewiring. The difference is internal: the overload release curve is tailored for transformer inrush, not motor starting characteristics (no Class 10 trip class). The auxiliary switch option (product extension auxiliary switch = Yes) allows adding a remote status contact, though this variant ships without one fitted. The auxiliary contact slot accepts standard SIRIUS S00 auxiliary switch blocks.