The Siemens 3RF3320-1DA24 is a 1-pole SIRIUS 3RF33 solid-state contactor rated for AC-1 resistive loads at 20 A continuous at 40 °C ambient. That 20 A figure is the thermal current — the load it carries without a heatsink derate — so for a resistive heater bank or lighting string at 40 °C panel ambient, this is the number that governs the circuit. The load voltage range spans 48-460 V AC, and the control coil is 110-230 V AC. The part is specified as short-circuit-proof when paired with a B-curve miniature circuit breaker, meaning the MCB clears a fault before the SSR fails — a coordination detail that saves replacing the contactor after a short. It belongs to the SIRIUS 3RF33 family, Siemens' compact solid-state contactor line for resistive and light inductive switching where silent, wear-free operation matters — no coil hum, no contact bounce, and no arc erosion over millions of cycles.
Integration notes
Screw terminals, 1-pole form factor. Packaging dimensions 105 x 27 x 122 mm — it's a narrow DIN-rail footprint, 27 mm wide, so it fits a standard 18 mm pitch rail with room for a neighboring device. The control voltage is 110-230 V AC, so verify your panel's control transformer taps before wiring. The short-circuit-proof coordination with a B-curve MCB means the upstream protection is sized to the contactor's let-through, not the full fault current — check the Siemens coordination tables if you're replacing a different brand's SSR.