The Siemens 3RQ4018-1AF00 is an output coupler from the SIRIUS 3RQ4 family, designed with an integrated relay for switching loads up to 6 A thermal current. It operates on 230 V AC/DC control voltage and provides a single change-over contact via screw terminals. The 6.2 mm narrow housing fits tight DIN-rail enclosures where panel space is at a premium — common in control cabinets for conveyor lines, pump stations, or HVAC zones where each millimeter of width per I/O point matters.
The 6 A thermal current (Ith) is the continuous carry rating through the change-over contact at ambient temperature — derate above 40°C per the Siemens thermal curve. The 230 V AC/DC coil means it accepts either supply without polarity concerns, simplifying wiring in mixed-voltage panels. One change-over contact (SPDT) handles a single signal or load path; for multi-load isolation, you stack multiple units or step up to a multi-pole relay in the same 3RQ4 family. The 6.2 mm width per channel is the key space constraint: a 32-channel bank occupies about 200 mm of DIN rail, leaving room for terminal blocks or a PLC slice next to it.