The Siemens SIRIUS 3RV1042-4KB10 is a motor-protection circuit breaker rated for 75 A continuous current and 37 kW at 400 V, with a CLASS 20 trip curve that allows moderate overload duration before opening — typical for standard induction motor starts on pumps, fans, and conveyors where the start transient lasts up to 20 seconds. It carries a 100 kA breaking capacity at 240 V and 400 V, dropping to 10 kA at 500 V and 6 kA at 690 V, so the available fault current at the panel determines whether this breaker clears the fault alone or needs an upstream current-limiting device.
Main circuit terminals are screw-type box terminals accepting 2x (2.5 … 16 mm²) solid or 2x (10 … 50 mm²) stranded; auxiliary/control circuit uses separate screw terminals.
Protection features and operating limits
Phase-failure detection is built in — the breaker trips if one phase drops out, preventing single-phasing motor damage. Ground-fault detection is not included, so a separate ground-fault relay is needed for that function. Maximum operating frequency in AC-3 duty is 15 operations per hour — fine for infrequent starts, but a contactor or soft starter handles higher cycling. Shock resistance rated at 25g / 11 ms, suitable for mobile or vibration-prone installations.