The Siemens 3UG5816-2AA40 is a digitally adjustable monitoring relay from the SIRIUS line monitoring family, covering phase failure, phase sequence, asymmetry, frequency, overvoltage, and undervoltage on three-phase systems with or without a neutral conductor. It operates across 90-690 V AC at 15-70 Hz, making it suitable for 50/60 Hz networks worldwide. The single changeover contact is rated for general-purpose switching, and the spring-loaded terminals accept 0.2-2.5 mm² conductors — no screwdriver needed for termination. IO-Link connectivity gives the PLC direct access to the measured values and device diagnostics, which saves a panel scan for a separate analog input.
What the ratings mean for fit
The 90-690 V AC input range covers low-voltage networks from 110 V to 690 V line-to-line without needing a separate voltage tap. The 15-70 Hz frequency window catches both 50 Hz and 60 Hz grids and tolerates generator sets or variable-frequency supplies that drift outside nominal. Phase asymmetry detection triggers when the voltage imbalance exceeds the adjustable threshold — typically set at 5-10 % to catch a failing motor winding or a loose connection before the motor overheats. The single changeover contact (SPDT) is enough to drive a PLC digital input or a contactor coil; if you need two isolated signals, you will need an auxiliary relay block.
Integration notes
The relay snaps onto a 35 mm DIN rail per EN 60715. The spring-loaded terminals accept solid or ferruled stranded wire, 0.2-2.5 mm², with a strip length of 8-10 mm. The packaging dimensions (127 x 111 x 38 mm) give you the footprint for panel layout — it occupies roughly 4 module widths on the rail. IO-Link communication uses the standard M12 connector (not included); set the IO-Link address via the master or the onboard DIP switches. The relay's self-test and measured-value output can be polled cyclically, which eliminates the need for a separate analog input module for voltage monitoring.