SIRIUS motor-protective circuit breaker, 40 A, CLASS 20
The Siemens 3RV1042-4FB10 is a SIRIUS motor-protective circuit breaker designed for motor protection, rated at 40 A continuous current with a CLASS 20 trip characteristic — meaning it allows a 20-second overload at 7.2× rated current before tripping, matching the thermal time constant of standard induction motors. It carries an 18.5 kW motor rating at 400 V AC and delivers 100 kA breaking capacity at 400 V, so it can safely clear a high-fault bolted short without upstream coordination gymnastics.
Breaking capacity is 100 kA at 240 V and 400 V AC, dropping to 18 kA at 500 V and 12 kA at 690 V.
Main current circuit uses screw-type box terminals. Solid conductors: 2x (2.5 to 16 mm²). Stranded: 2x (10 to 50 mm²) or 1x (10 to 70 mm²). Finely stranded with ferrule: 2x (2.5 to 35 mm²) or 2.5 to 50 mm². AWG equivalents: 2x (10 to 1) or 1x (10 to 2). That range covers most motor feeder cables up to 70 mm² — plenty for a 40 A circuit. Auxiliary and control circuit terminals are also screw-type. An auxiliary switch can be added via the product extension.
Mounting position is any. Zero clearance required backwards and at the sides — no derating for side-by-side installation on the rail. Shock resistance 25g for 11 ms. Dimensions: 70 mm wide, 165 mm high, 174 mm deep. That 174 mm depth is the body depth behind the panel — check it clears the enclosure depth before wiring.