Motor-Protection Circuit Breaker for 40 A Lines
The Siemens 3RV1031-4FB15 is a SIRIUS motor-protection circuit breaker rated for 40 A continuous current and 18.5 kW at 400 V AC-3 duty. Its Trip Class 20 characteristic means it allows a 20-second overload before tripping at 7.2× rated current — sized for standard induction motor starting profiles without nuisance trips on moderate inertia loads. Breaking capacity reaches 100 kA at 240 V AC, 50 kA at 400 V, 10 kA at 500 V, and 4 kA at 690 V — sufficient for high-fault panels where the upstream transformer is large. Phase failure detection is built in, so a lost phase on the line side will trip the breaker, protecting the motor from single-phasing.
Mounting and Integration
Mounts via screw fixing or snap-on onto 35 mm standard mounting rail per DIN EN 50022. Any mounting position is permitted. Dimensions are 55 mm wide, 140 mm high, 149 mm deep — fits a standard 55 mm-wide DIN slot with no side clearance required (0 mm at the side, 0 mm backwards). Main circuit terminals accept solid conductors 2x (0.5…1.5 mm²) and 2x (0.75…2.5 mm²), or stranded 2x (0.75…25 mm²) and 1x (0.75…35 mm²). AWG equivalents for main contacts are 2x (18…2) and 1x (18…2). Auxiliary and control circuits use screw-type terminals with a transverse auxiliary switch design. The auxiliary switch is a factory-fitted extension.
Lifecycle and Compliance
Front protection class is IP20, suitable for installation inside a panel with a higher-rated enclosure. Power dissipation in hot operating state is 29 W at rated current — factor this into the panel thermal budget.