SIRIUS 3RV1421-0FA10 — transformer-protection circuit breaker, 0.5 A, Class 10
Its 0.5 A continuous rated current and Class 10 trip characteristic mean it opens fast enough to protect small control transformers from sustained overloads without nuisance tripping on inrush — a common pain point when a general-purpose breaker is used instead. Rated breaking capacity holds at 100 kA across the full AC voltage range — 240 V, 400 V, 500 V, and 690 V — so it handles high-fault-current scenarios without cascading upstream. Phase-failure detection is built in, which matters for three-phase transformer banks where losing one phase can overheat the remaining windings. At 45 mm wide and 97 mm tall, it takes a single 45 mm slot in a standard panel layout. Screw terminals accept 1 to 6 mm² solid or stranded — 2x conductors per clamp — so paralleling feeds or daisy-chaining to downstream terminals is straightforward.
Depth is 96 mm — check clearance behind the DIN rail, especially in shallow enclosures. The IP20 finger-safe front means it can sit in a panel without additional shrouding, but the rear terminals are live when the breaker is on. Shock-rated to 25g / 11 ms, so it survives shipping and moderate vibration in the panel.