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.
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.
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.