The 3RB1055-2FG0: The 50...200 A range covers a wide band of motor FLA — from a 50 A motor up to a 200 A motor — so it fits medium-to-large induction motors on pumps, fans, compressors, and conveyors. Class 20 means it allows 600% of set current for 20 seconds before tripping, which is the standard thermal curve for standard-start induction motors (NEMA Class 20). It won't nuisance-trip on a normal across-the-line start but still protects against sustained overload. Size S6 is the physical envelope: it's built to match the Siemens 3RT105 contactor frame. If you're retrofitting an existing panel that uses a 3RT105, this relay bolts directly on with the included connecting bars — no extra wiring. For standalone mounting, the 35 mm DIN-rail clip is already on the back.
Two installation paths: (1) Snap it onto a 35 mm top-hat DIN rail for standalone use — the fixing is manual-reset only (no remote reset option on this variant). (2) Bolt it directly to a 3RT105 contactor using the supplied connecting bars — that saves panel wiring and keeps the power loop short. The connecting bars are included, so no separate order for bus bars.