The Siemens 3RQ4018-2AM08-0AA0 is an output coupler with an integrated relay from the SIRIUS 3RQ4 family, designed in a narrow 6.2 mm housing. It operates on a 24 V DC coil (pick-up range 0.7–1.25 x Us) and provides a single change-over contact rated for a thermal current of 6 A. This part belongs to the SIRIUS 3RQ4 series of coupling relays, a line Siemens positions for space-constrained control cabinets. The 6.2 mm width per channel lets you pack more isolation points per meter of DIN rail compared to a standard 14 mm interface relay.
The 6 A thermal current (Ith) is the continuous carry rating through the contacts at ambient temperature. For a coupling relay this size, that figure governs the resistive load it can switch directly—think solenoid valves, indicator lamps, or small contactor coils. If your load draws more than 6 A steady-state, you need an interposing contactor, not this relay. The 24 V DC coil with a 0.7–1.25 x Us operating range means it picks up reliably between about 16.8 V and 30 V. That tolerance covers a sagging 24 V supply in a cabinet with multiple loads switching simultaneously. Below 16.8 V the relay drops out, which is typical for DC coils—plan your voltage drop across long cable runs accordingly. The single change-over contact (1 CO) gives you one normally-open and one normally-closed set from the same common. That is enough to switch a load and signal its state back to a PLC input, or to interlock two circuits, but not enough for redundant safety paths—those need force-guided contacts in a different housing.