The Siemens 3RB2055-1FC2 is a SIRIUS solid-state overload relay — a three-pole device that protects motor circuits against overload and phase imbalance by monitoring current and tripping within the CLASS 10E curve (typically 10 seconds at 7.2× Ie). It can be mounted directly onto a contactor or installed stand-alone in a panel, giving flexibility in cabinet layout.
The solid-state design means no heating elements to drift or replace; power dissipation per pole is only 0.02 W (0.05 W total for the main circuit), so it doesn't add significant heat inside the enclosure. Terminals accept solid conductors from 0.5 to 4 mm² (or 2× 0.5 to 2.5 mm²) and finely stranded with ferrules from 0.5 to 2.5 mm² (2× 0.5 to 1.5 mm²) — covers most control wiring gauges used in motor starter circuits. Dimensions are 120 mm wide, 119 mm high, 155 mm deep — fits standard 120 mm-wide DIN-rail or contactor-mounting footprints. Side clearance of 6 mm is required for ventilation; no clearance needed above, below, or behind the unit. The relay is rated for operation at altitudes up to 2 000 m without derating, and can operate in ambient temperatures from -25 to +60 °C with 100 % relative humidity — suitable for most indoor industrial environments.