Phase monitoring relay for 320-500 VAC lines
The Siemens SIRIUS 3UG4511-1BP20 is a single-function phase monitoring relay designed for AC systems. It monitors a 320-500 VAC supply at 50 or 60 Hz and provides a switched output rated at 3 A at 250 V or 400 V (50/60 Hz). The unit has a single changeover contact (SPDT) rated 1 A at 24 V, 0.2 A at 125 V, and 0.1 A at 250 V for DC loads. An LED indicates the operating status, and the relay offers an auto-reset function after a fault clears — useful for unattended restart scenarios.
IP20 protection means it is suitable for installation inside a closed panel only.
The 3 A contact rating at 250/400 V AC is the thermal current (Ith) for resistive loads; for inductive or DC loads, derate to the values listed (1 A at 24 V DC, 0.2 A at 125 V DC, 0.1 A at 250 V DC). The relay does not detect asymmetry, overvoltage, or undervoltage — it only monitors phase loss or phase sequence on a three-phase supply. If your application requires asymmetry detection, you would need a different SIRIUS variant (e.g., 3UG4611).