Transformer-protection circuit breaker, 8 A, CLASS 10
The Siemens 3RV1421-1HA15 is a SIRIUS circuit breaker specifically designed for transformer protection, rated at 8 A continuous current with a CLASS 10 trip characteristic. It delivers 100 kA breaking capacity at 400 V AC, meaning it can safely interrupt fault currents up to that level without upstream devices needing to clear the fault — critical for selectivity in distribution panels feeding transformer loads. The CLASS 10 trip class means it will disconnect within 10 seconds at 7.2× rated current, fast enough to protect transformers from sustained overloads while riding through inrush.
Breaking capacity and coordination
Breaking capacity is 100 kA at 240 V and 400 V AC, dropping to 42 kA at 500 V and 6 kA at 690 V. The 100 kA SCCR at 400 V means this breaker can be used in high-fault panels without requiring a current-limiting upstream fuse — a real advantage when coordinating with a 100 kA-rated transformer feeder. Phase failure detection is built in, so it will trip on loss of any phase, protecting the transformer from single-phasing.
Mounting and integration
Mounts via screw or snap-on onto 35 mm DIN rail per EN 50022. Width is 45 mm, height 97 mm, depth 96 mm — fits standard 45 mm module spacing in control panels. Screw-type terminals for the main circuit accept 2x (0.5–1.5 mm²) solid or 2x (1–2.5 mm²) stranded; auxiliary terminals accept 2x (0.75–2.5 mm²) solid. IP20 on the front face, suitable for enclosed panel mounting. Any mounting position allowed. Operating temperature range -20 to +60 °C; storage -50 to +80 °C.