The Siemens SIRIUS 3RF2420-1AC45 is a three-phase solid-state contactor with zero-point switching, rated 22 A in AC-51 duty (resistive load) and 15 A per UL 508. It switches loads between 48 and 600 V AC at 50/60 Hz, with a minimum operational current of 500 mA — so it handles everything from small resistive heaters up to a 22 A resistive three-phase bank. Zero-point switching means the thyristors turn on only when the AC waveform crosses zero, which minimizes inrush and electrical noise — a clean start for resistive loads like ovens or infrared heaters. The ON-delay is 1 ms plus at most one half-wave, so response is near-instantaneous for the control loop.
Dimensions are 74.5 mm wide, 100 mm tall, 119.5 mm deep, fitting a standard enclosure footprint. Main and control circuit connections are screw-type terminals, accepting 1x (0.5 to 2.5 mm²) solid or stranded, or 2x (0.5 to 1.0 mm²) — typical for panel wiring up to 14 AWG. The control circuit draws 22 mA at DC rated value (30 V) and 30 mA control current at DC rated value, so it's compatible with standard 24 VDC PLC outputs.
Thermal and electrical limits
The I²t value is 1800 A²s, which governs fuse coordination: the recommended upstream fuse is a 3NA3805 (rated below the semiconductor relay's current) for short-circuit protection up to 460 V.
RoHS compliance date is July 1, 2006, covering the EU RoHS scope. No other compliance flags are noted in the listing; the UL 508 rating (15 A) confirms acceptance for North American panel builds.