The Siemens 3RV1042-4JA10 is a SIRIUS motor-protection circuit breaker — a three-pole, screw-terminal device sized for 63 A continuous current and rated 30 kW at 400 V. It's built for the main current circuit of a motor branch, not a distribution feeder. Phase-failure detection is included, so a lost phase on the line side won't cook the winding while the motor tries to single-phase run. Ground-fault detection is not built in — that's a separate module if your circuit needs it.
Breaking capacity — the real-world fault limit
The interrupting rating drops with system voltage: 100 kA at 240 V and 400 V AC, then 15 kA at 500 V, and 7.5 kA at 690 V.
Zero clearance needed at the back or sides — you can butt it against adjacent devices on the rail. Dimensions are 70 mm wide, 165 mm high, 174 mm deep.
Terminal wiring capacity
Main circuit terminals accept solid conductors 2x (2.5 to 16 mm²) and stranded 2x (10 to 50 mm²) or 1x (10 to 70 mm²). AWG equivalents for the main contacts are 2x (10 to 1) solid, 1x (10 to 2) stranded. Auxiliary and control circuit terminals are also screw-type. Finely stranded with core-end processing goes 2x (2.5 to 35 mm²) or 2.5 to 50 mm². That covers everything from a 4 mm² motor lead up to a 70 mm² feeder.
Thermal behavior and operating limits
Power dissipation in hot operating state is 34 W total, 11.3 W per pole. Shock resistance is 25 g for 11 ms. Maximum switching frequency in AC-3 duty is 15 operations per hour, so it's sized for motor starting cycles, not rapid jogging.