What the SIRIUS 3RF2320-1AA04 is, and where it lands in a panel
The Siemens SIRIUS 3RF2320-1AA04 is a single-phase solid-state contactor with a 20 A AC-51 rating and a 48 to 460 V operating range at 50/60 Hz, designed for zero-point switching of resistive and slightly inductive loads in control panels. It lives in the 22.5 mm SIRIUS housing family — 120 mm deep, 95 mm tall — and snaps onto a standard 35 mm mounting rail per IEC 60715, with side-by-side mounting allowed so the bin can stack multiple units on the same rail without derating between neighbours.
20 A AC-51 continuous, 17.6 A per UL 508
The headline current rating is 20 A in AC-51 duty (resistive or weakly inductive), which is the figure that should govern heater banks and similar steady loads; under UL 508 the same device is listed at 17.6 A, and that lower figure is the binding number for any panel being built to a North American inspection path. Dissipation in the hot operating state runs to 20 W at AC full load, and the unit is derated from 40 °C ambient upward — meaning inside a sealed cabinet above that threshold the continuous current must be reduced against the manufacturer's derating curve rather than run flat to the nameplate.
Zero-point switching means the thyristor fires at the AC voltage zero-cross rather than at a random phase angle — keeping the inrush transient low on lamp and heater loads and reducing electrical noise on the supply. The trade-off is the 10 mA off-state leakage typical of inverse-parallel thyristors, which matters where a downstream earth-leakage trip is sensitive.
Control-side draw and minimum load
The control input draws 13 mA at the 30 V DC rated voltage — light enough that a standard PLC transistor output can switch several of these contactors in parallel off one output card, provided the card's per-point current budget covers it. Turn-on and turn-off delay each sit at 1 ms plus a maximum of one additional half-wave, so the contactor tracks the control signal close enough for heater control loops but is not the right pick for phase-angle timing or fast-pulse applications. A 500 mA minimum operational current is required for reliable thyristor commutation — below that threshold the device should not be specified.
Wiring, fusing and the bin-side realities
Specified back-up fuses are DIAZED 5SB2711, NEOZED 5SE2320, or NH 3NA6807 depending on the cabinet standard. I²t maximum is 1 800 A²·s, which is the figure to cross-check against the chosen semiconductor fuse let-through to confirm coordination; pollution degree 3 is rated, so the contactor is built for typical industrial atmospheres without extra enclosure sealing beyond the cabinet itself.