Motor protection circuit breaker — 3RV1031-4FA10-ZW98
The Siemens 3RV1031-4FA10-ZW98 is a SIRIUS-series motor protection circuit breaker, rated 40 A continuous current and 18.5 kW at 400 V AC. It's a Class 10 trip device, meaning it will disconnect within 10 seconds at 7.2× the thermal setting — fast enough to protect standard induction motors during a stall or locked-rotor event without nuisance tripping on normal start-up. Phase failure detection is built in, so a lost phase won't cook the winding while the other two legs still draw current. Breaking capacity runs 100 kA at 240 V AC, 50 kA at 400 V AC, 10 kA at 500 V AC, and 4 kA at 690 V AC (–). That 50 kA at 400 V is the number most panel builders will check first — it means this breaker can clear a bolted fault on a 400 V distribution board without upstream fuses needing to intervene, as long as the available fault current stays under that threshold.
Mounting and wiring
Mounts on 35 mm DIN rail per DIN EN 50022, either snapped on or screwed down. The 55 mm width and 140 mm height leave room for adjacent contactors or overloads in a motor starter lineup. Screw-type box terminals on the main circuit accept 2x (0.75–16 mm²) solid or 2x (0.75–25 mm²) stranded, with a single termination up to 35 mm². That's enough for 40 A motor feeds with standard THHN or PVC cable. Auxiliary and control circuits also use screw terminals, and the breaker accepts an auxiliary switch add-on.