The Siemens 3RQ4118-1AB01 is an output coupler relay from the SIRIUS 3RQ4 family, designed as a narrow 6.2 mm interface between a control signal and a load circuit. It accepts a 24 V AC/DC coil supply and switches one change-over contact rated for a thermal current of 6 A. The hard gold-plated contacts are the key detail here: they handle low-level signals (milliamps, millivolts) reliably without oxidation issues, which standard silver-alloy contacts can develop when switching dry circuits in PLC or electronic load applications.
The plug-in relay base means the coil/contact module can be swapped without disturbing the wiring — a practical detail for commissioning or fault isolation on a populated rail. The 24 V AC/DC coil covers both common control voltages, so it works in AC-sourced panels or DC-supplied PLC cabinets without a separate coil voltage variant.