What it is and what it does
The Siemens 3UG4633-2AL30 is a SIRIUS voltage monitoring relay with digital setting — it watches a supply line for undervoltage and overvoltage conditions and trips its output contacts when the measured voltage strays outside the programmed window. The monitored voltage range is 17 to 275 V AC/DC, covering most common control voltages from 24 VDC up to 230 VAC without needing a separate supply transformer.
Key ratings and what they mean for fit
The relay's output contacts are rated 1 A at 24 V, 0.2 A at 125 V, and 0.1 A at 250 V — these are the maximum switching currents for resistive loads at those voltages. For a typical PLC digital input or contactor coil, the 1 A at 24 V rating is the one that governs; it comfortably handles a bank of small relays or a single contactor coil, but not a motor starter directly. Relative repeat accuracy is 1 %, meaning the trip point will not drift more than 1 % of the set value from one cycle to the next — tight enough for protecting sensitive electronics or motor controls where a few volts of drift could cause nuisance trips. The 22.5 mm width and snap-on mounting (DIN rail) mean it fits the standard narrow-form-factor slot in a control panel, leaving room for other modules in the same row. IP20 protection means it is safe for dry indoor panels only — no washdown or dust ingress protection; mount it inside a cabinet with at least IP54 enclosure.
Where it is used
This class of relay is installed in control panels to protect downstream equipment from supply anomalies — undervoltage can cause contactors to drop out unpredictably, overvoltage can damage drives and power supplies. The 3UG4633-2AL30 is built for that role with both detection functions in one unit and an auto-reset option so the line restarts automatically when voltage returns to normal. The LCD display shows the actual measured voltage and the programmed thresholds, which helps during commissioning and troubleshooting without needing a handheld meter.