The Siemens 3RQ4052-1SM40 is an output optocoupler relay from the SIRIUS 3RQ4 family of narrow-design coupling relays. It switches a single normally-open (NO) contact rated for a thermal current of 3 A, controlled by a 24 V DC input. The 6.2 mm width is the key space-saving feature — it packs into a dense DIN-rail terminal block arrangement where every millimeter of panel width matters.
The 3 A thermal current (Ith) is the continuous current the NO contact can carry in free air at 40 °C ambient. For switching inductive loads like small contactor coils or solenoid valves, derate to roughly 1.5–2 A depending on the load power factor and switching frequency. The 24 V DC input is the control side — it powers the internal LED that drives the optocoupler output, providing galvanic isolation between the PLC or controller output and the switched circuit. The 6.2 mm housing width matches the standard SIRIUS 3RQ4 footprint, so it occupies one slot on a DIN-rail terminal block assembly. No special tooling needed — a standard slotted screwdriver for the terminals and a flat-blade for the DIN-rail clip.
RoHS compliant since 26 September 2024. Export classification is AL: N / ECCN: EAR99, meaning no special export licensing for most destinations.