The Siemens 3RF3025-1AA42 is a SIRIUS 3RF30 semiconductor relay — a 1-pole solid-state relay in a 45 mm housing, rated for 25 A continuous load current. The control input accepts 24-230 V AC/DC on the line side and 4-30 V DC on the logic side, terminated via screw terminals. This is a zero-crossing switching SSR, meaning it turns on near the voltage zero crossing to minimize inrush and EMI — suited for resistive and light inductive loads like heaters, lamps, and solenoid valves where silent, wear-free switching matters.
The 25 A rating is the continuous load current the SSR can switch at its rated voltage (24-230 V). For a solid-state relay, this is the thermal current rating — it assumes proper heatsinking and ambient temperature within the datasheet's derating curve. The dual control voltage range (24-230 V AC/DC line-side, 4-30 V DC logic-side) means it can be driven directly from a PLC digital output (24 V DC) or from a higher-voltage control circuit without an interposing relay.