The Siemens SIRIUS 3UG3041-1BP50 is a 45 mm monitoring relay for three-phase voltage supervision — it detects both undervoltage and overvoltage conditions on a 3x 400 V AC supply at 50/60 Hz. The two changeover contacts (2 W) give you one NO and one NC per channel, enough to signal a fault and drop a contactor coil in the same circuit.
Rated for 3x 400 V AC phase-to-phase — that is the standard European low-voltage three-phase network. The relay monitors all three phases simultaneously and trips on under- or overvoltage.
The 3UG3041-1BP50 is a standard catalog item in the SIRIUS range.
Panel fit and wiring note
The relay is self-powered from the monitored voltage; no auxiliary supply needed. Wire the three phases to L1, L2, L3 terminals, and the changeover contacts to your PLC input or contactor coil circuit.