The Siemens SIRIUS 3UG4511-2AQ20 is a single-function phase monitoring relay for AC systems. It monitors a three-phase supply between 420 and 690 V at 50 or 60 Hz, with a rated contact current of 3 A at 400 V. The relay detects phase loss or incorrect phase sequence and switches its output accordingly — no asymmetry or over/undervoltage detection built in, so it's a straightforward phase-failure guard.
The screw terminals accept solid or stranded wire from 24 to 16 AWG (2 x 24...16 AWG for solid). IP20 rated — fine inside a cabinet, not for wet areas. Depth is 91 mm, so check clearance to the gland plate or door.