The Siemens 3RF2450-1AC45 is a SIRIUS three-phase solid-state contactor with zero-point switching, rated 50 A in AC-51 duty (resistive loads) and 38 A per UL 508. It switches 48–600 VAC at 50/60 Hz, with a minimum operational current of 500 mA — so it handles everything from small heater banks up to 50 A resistive loads without the contact wear of a mechanical relay.
Mounts via screw fixing (no DIN-rail clip), sized 150 mm high × 119.5 mm wide × 130 mm deep — plan for a fixed backplate or sub-panel. Main circuit terminals accept 1.5–6 mm² solid/stranded (or 2× 14–10 AWG), control terminals take 0.5–2.5 mm² solid. Side-by-side mounting is allowed, but watch the derating above 40 °C ambient; the 50 A AC-51 rating holds at 40 °C, above that you'll need to space or reduce load.