The Siemens 3RV1042-4AA10 is a SIRIUS motor protection circuit breaker rated for 16 A continuous current with a CLASS 10 trip characteristic — meaning it will trip within 10 seconds at 7.2× rated current, fast enough to protect standard induction motors from locked-rotor heat buildup without nuisance tripping during normal start-up. It's designed for the main current circuit of a three-phase motor branch, with phase failure detection built in so a dropped phase won't let the motor single-phase and cook the winding. Rated for 7.5 kW motor load at 400 V AC, this breaker snaps onto a 35 mm DIN rail per EN 50022 and takes up 70 mm of panel width. The screw-type box terminals accept solid conductors up to 2× 16 mm² or stranded up to 1× 70 mm² — heavy enough for the feeder side of a moderate motor branch.
SCCR headroom on the motor branch
Where this breaker earns its keep out in the panel is the short-circuit current ratings. At 240 V and 400 V AC it interrupts 100 kA, dropping to 30 kA at 500 V and 12 kA at 690 V. The 21 W power dissipation at rated load (7 W per pole) means you should account for the heat in a densely packed panel — keep ventilation slots clear and don't sandwich it between high-dissipation drives.
Zero clearance needed at the back or sides — you can butt it against adjacent devices without derating for spacing. Depth is 174 mm, height 165 mm, width 70 mm. The protection class on the front is IP20 — finger-safe for the panel face, but keep it inside an enclosure. Solid wire range is 2× (2.5 to 16 mm²); stranded with ferrule goes up to 2× 35 mm² or single 50 mm². That covers common motor feeder cables from 2.5 mm² for small motors up to 50 mm² for the 7.5 kW branch.