What it is and what it monitors
The Siemens 3UG5716-1CR20 is a digital monitoring relay from the Line monitoring family that watches three-phase mains for phase failure, phase sequence reversal, asymmetry, frequency deviation, overvoltage, and undervoltage — all in one unit. It covers 90 to 690 V AC line-to-line, 15 to 70 Hz, and reports status via two changeover contacts (screw terminals). The Bluetooth interface lets a service tech pull parameters and fault logs without opening the panel door.
Mounting and wiring
Packaged at 127 x 111 x 38 mm, this relay snaps onto a standard DIN rail. Spring-cage or screw terminals accept 0.2–2.5 mm² conductors; strip 8 mm for a clean connection. The Bluetooth pairing is done via the Siemens SIRIUS mobile app — no gateway hardware needed between the relay and a smartphone or tablet.