What this part is and where it fits
The Siemens 3RB2045-1UB0 is a SIRIUS solid-state overload relay — a motor-protection device that monitors current and trips on overload, without bimetallic thermal lag. It mounts directly to a contactor (contactor mounting), saving a DIN-rail slot and keeping the motor branch compact. Trip class CLASS 10E means it will trip within 10 seconds at 7.2× rated current — fast enough to protect a standard induction motor during a stalled-rotor condition, without nuisance tripping on normal starting inrush. Rated for AC-3 duty up to 1000 V, so it handles the switched current profile of squirrel-cage motors — the most common load in industrial panels.
Integration and wiring
Main circuit terminals are screw-type, accepting solid wire 0.5 to 4 mm² (or 2× 0.5 to 2.5 mm²) and stranded up to 70 mm² — covers most motor leads from fractional-horsepower up to about 30 kW at 400 V. Mounts in any position; side clearance to adjacent devices is 6 mm. Depth is 124 mm, width 70 mm, height 106 mm — check that the contactor footprint leaves room for the relay body above it. Operating temperature range -25 to +60 °C, with 100 % relative humidity allowed — fine for non-condensing washdown areas but the IP00 front means it lives inside a panel, not on the machine frame.
Lifecycle and sourcing
ATEX certification PTB 06 ATEX 3001 Ex II (2) GD covers use in potentially explosive gas and dust atmospheres (Zone 1/2 gas, Zone 21/22 dust) when paired with an appropriate contactor and enclosure.