The Siemens 3RF3340-1AA02 is a 1-pole solid-state contactor from the SIRIUS 3RF33 family, rated for AC-1 resistive loads at 40 A with a 40 °C ambient. Control voltage spans 24-230 V AC and accepts 24 V DC, terminated via screw terminals. This is a zero-crossing switching device — it turns on and off at the voltage zero crossing, which minimizes electrical noise and inrush on resistive heater, lighting, or transformer loads.
Mounts on standard DIN rail. The 105 x 27 x 122 mm envelope fits a single-module width — useful when you're packing multiple contactors into a crowded enclosure. Screw terminals accept up to 6 mm² wire; torque to 1.2 Nm per the terminal marking. No heatsink calculation needed at 40 A in a 40 °C cabinet, but if your enclosure runs hotter, you'll need to derate or add forced air — the 40 °C rating is the reference point, not a ceiling.