What it is and what it does
The Siemens 3RV2031-4JA10-0BA0 is a SIRIUS motor protection circuit breaker in the size S2 frame, designed specifically for motor protection duty. It combines a circuit breaker and overload relay in one device, saving panel space and wiring time over a separate breaker-plus-overload combination. The Class 10 trip characteristic means it will disconnect within 10 seconds at 7.2× the thermal setting — fast enough to protect standard induction motors during a locked-rotor event without nuisance tripping on normal starting inrush. Rated breaking capacity hits 30 kA at 400 V AC, which covers most industrial distribution panels fed by a typical 1 MVA transformer. At 230 V it's rated 100 kA, and at 690 V it still holds 4 kA — so it's suitable for 400 V lineups without worrying about upstream fuse coordination. Phase failure detection is built in, so a lost phase on the line side will trip the breaker before single-phasing cooks the motor winding. Temperature compensation is active from -20 to +60 °C, keeping the thermal curve accurate across the panel's ambient range.
Mounting and integration
Mounts on 35 mm DIN rail per EN 60715 with a screw-and-snap mechanism — the screw secures it against vibration, the snap lets you remove it without tools. Any mounting position is allowed, so it fits in tight enclosures or vertical bus risers. At 55 mm wide and 149 mm deep, the S2 frame takes up one standard 55 mm module on the rail. Clearance requirements are 50 mm above and below, 10 mm to the side — plan your gland plate and wireway accordingly. Main circuit terminals accept up to 2× 35 mm² or 1× 50 mm² solid/stranded copper. Use a Pozidriv size 2 bit with a 5–6 mm shaft diameter for the screw terminals — torque spec isn't listed here, but M6 studs on the main contacts suggest a standard 6–8 Nm range typical for this frame size.
Backup fuse coordination
When the available fault current exceeds the breaker's rated breaking capacity, you need backup fuses upstream. At 400 V, a gG 160 A fuse is required; at 500 V step down to gG 125 A, and at 690 V to gG 100 A. At 240 V no backup fuse is needed — the breaker's 100 kA rating covers virtually any service entrance.