The 3UG5643-2CS20 is a digital monitoring relay from the Siemens SIRIUS 3UG5 family, designed to monitor current, active current, voltage, power factor, and power in a single device. It operates from a 90 to 690 V AC/DC internal power supply and accepts a measuring input of 0.05 to 10 A. Two changeover contacts with spring-loaded terminals handle the output. This is an active, current-production part.
Supply and measurement share the same terminals — the relay is self-powered from the monitored circuit across 90 to 690 V AC/DC, so no auxiliary supply is needed. The 0.05 to 10 A current input covers most motor and feeder monitoring ranges without an external CT, though you can still use one if the primary current exceeds 10 A. On-delay and tripping delay are independently adjustable from 0.1 to 999.9 s, giving you flexibility to ride through inrush or transient events. Spring-loaded terminals accept 0.2 to 2.5 mm² solid or ferruled stranded wire; strip length 8 mm. The 127 x 111 x 38 mm package fits a standard DIN-rail footprint with room for adjacent devices in the panel.