The Siemens 3RB2123-4RB0 is a SIRIUS-brand solid-state overload relay for three-phase motor protection in control panels. It mounts directly to a contactor (fastening method: contactor mounting) and uses screw-type terminals for both the main current circuit and auxiliary/control circuits. The relay is rated for 3 poles and carries ATEX certification (PTB 06 ATEX 3001 Ex II (2) GD), making it suitable for installation in potentially explosive atmospheres where motor protection is required.
Mechanical integration and wiring
Dimensions are 45 mm wide, 73 mm high, and 75 mm deep — a compact 45 mm footprint that occupies one standard DIN-rail mounting position when attached to a contactor. Mounting position is any orientation, with zero clearance required upwards, forwards, backwards, and downwards; 6 mm clearance needed at the side for airflow or wiring access. Main circuit terminals accept solid conductors from 0.5 to 4 mm² (or 2x 0.5 to 2.5 mm²), and AWG 14–10 for the main contacts. Auxiliary and control circuit terminals accept 2x AWG 20–14. Finely stranded wire with ferrule is supported: 0.5 to 2.5 mm² single, 2x 0.5 to 1.5 mm². This covers standard motor power wiring up to approximately 4 mm² (roughly 12 AWG) for the main circuit.
The product is RoHS compliant with substance prohibition date of 07/01/2006.