The Siemens SIRIUS 3UG4511-2BP20 is a single-function phase monitoring relay that monitors AC three-phase systems for phase loss and phase sequence. It detects the presence and correct rotation of all three phases and switches its output contacts accordingly. Rated for a supply voltage of 320 to 500 VAC at both 50 Hz and 60 Hz, it covers the common 400 V industrial mains without needing a separate control transformer. The output relay is rated to switch 3 A at 250 V or 400 V (50/60 Hz), and derates to 1 A at 24 V, 0.2 A at 125 V, and 0.1 A at 250 V for DC loads. The relay offers an auto-reset function, meaning it automatically re-energizes its output when the monitored phases return to normal after a fault. A delayed switching of 2 seconds is built in to ride through brief dips or transients without nuisance tripping.
Housed in a 22.5 mm wide enclosure (94 mm high, 91 mm deep), it snaps directly onto a standard DIN rail. Clearance of 0 mm is required on all sides (up, down, forward, backward, and side), so it can be packed tightly against other devices. A green LED indicates the operating status.