The Siemens SIRIUS 3UG3501-1AG20 is a level monitoring relay in the 22.5 mm housing — a standard footprint for DIN-rail panels. It monitors conductive liquid levels (or any resistive path) via two probes, with adjustable sensitivity from 5 to 100 kΩ, so you can tune out fouling or long cable runs. The single changeover contact (1 CO) switches at the set high or low level. Control supply is AC, rated 102–132 V at both 50 and 60 Hz, meaning it runs on a standard 120 V control transformer without frequency derating.
The screw-type terminals accept 2 x (20–14 AWG) solid or stranded, or 0.5–2.5 mm² finely stranded with ferrule. That covers standard panel wire up to 2.5 mm². No special tooling needed; strip and torque per Siemens terminal specs.