The Siemens 3RF2440-1AC45 is a SIRIUS solid-state contactor designed for three-phase controlled switching with zero-point switching, rated at 40 A in AC-51 duty. This means it is sized for resistive or slightly inductive loads — typical for heating elements in furnaces or ovens where zero-point switching reduces inrush and RFI by turning on at the voltage zero crossing.
The AC-51 rated value of 40 A defines the continuous resistive load the contactor can handle. For motor loads, derating applies — the part carries a minimum operational current of 500 mA, so it will not drop out on lightly loaded circuits. The I²t maximum of 6,600 A²·s governs short-circuit withstand; the evidence recommends 3NA3812 fuses with a smaller rated current than the semiconductor relay for protection. Control current draw is 30 mA at the DC rated value of 30 V, with an ON-delay of 1 ms plus a maximum of one half-wave. This fast switching suits applications needing precise timing, such as thermal profiling in glass or ceramic furnaces where ramp and soak, repeatably, depend on consistent turn-on delay.
Mounts via screw fixing — not a snap-on DIN rail clip — so factor in panel drilling and hardware. Side-by-side mounting is permitted, which helps density in multi-contactor heater banks. The operating temperature range of -25 to +60 °C and storage range of -55 to +80 °C cover most cabinet environments, but derating begins at 40 °C, so forced ventilation or current reduction is needed above that threshold.