What it is and what it does
The Siemens 3RV1021-1KA15 is a SIRIUS motor-protective circuit breaker rated for 12.5 A continuous current with a CLASS 10 trip curve, sized for a 5.5 kW motor at 400 V AC. It protects against overload and phase failure, and its 100 kA breaking capacity at 400 V means it can safely interrupt a fault up to that level without needing an upstream fuse or larger breaker — a real advantage in high-fault panels where coordination is tight.
Mounting and wiring
Snaps onto a 35 mm DIN rail per EN 50022 and accepts screw-type terminals for the main circuit — 2x (0.5…1.5 mm²) solid or 2x (1…2.5 mm²) stranded, with the larger 2.5…6 mm² stranded for heavier feeds. The auxiliary switch is transverse-mounted and field-addable; the part ships without one, but the extension slot is ready. Zero clearance needed at the sides or rear, so it packs tight in a crowded panel.
Breaking capacity by voltage — the real derating story
The 100 kA SCCR holds at 240 V and 400 V AC, then drops to 42 kA at 500 V and 6 kA at 690 V. That 6 kA at 690 V is the number to watch if you're feeding a 690 V motor circuit — it's still adequate for most industrial installations, but verify your available fault current before committing the BOM line.