The Siemens 3UG4815-2AA40 is a SIRIUS network monitoring relay with digital setting, built for AC phase monitoring. It packs five functions into a 22.5 mm wide housing — phase sequence, phase failure, asymmetry, undervoltage, and overvoltage — all configurable via the LCD display. The relay output is rated 3 A at 400 V (50/60 Hz), enough to drive a contactor coil or signal a PLC input directly. Snap-on mounting to DIN rail, IP20 finger-safe terminals, and any mounting position mean it fits into a crowded panel without special bracketing.
The 3 A switching capacity at 400 V covers the typical contactor coil or small load — don't plan to switch a motor directly. The relay contacts are rated 1 A at 24 V, 0.2 A at 125 V, and 0.1 A at 250 V for DC loads, so inductive DC circuits need derating. Asymmetry detection is built in, not an add-on. The start-up delay (0 to 999.9 s) lets you ride through momentary sags or generator ramp-up, and auto-reset (with optional external reset) means the relay can re-close after a cleared fault without a manual pushbutton. IO-Link COM2 (38.4 kBaud) is on board for parameter backup and remote monitoring — useful if the panel is part of a networked line. The LCD shows the measured voltage and fault code, so a tech can read the cause without a laptop.