The CM-UFD.M31 grid feed-in monitoring relay monitors voltage and frequency in single-phase and three-phase networks. In conjunction with inverters with integrated island network detection, it meets the conditions for NA protection according to VDE-AR-N 4105:2018-11 (generation systems on the low-voltage network) or VDE-AR-N 4110:2018-11 (generation systems on the medium-voltage network). For use in old systems, the setting values according to VDE-AR-N 4105:2011 or BDEW (feed-in to the medium-voltage network) can also be selected. The last 99 shutdown causes and their respective times are stored in an alarm memory. The connected coupling switches are also monitored, vector shift detection and ROCOF frequency gradient monitoring are carried out.