This innovative relay guarantees grid stability and seeks to prevent blackouts. If the voltage or frequency magnitudes of the public grid are outside the permited range, then the device changes status and acts to disconnect the renewable energy system from the public grid by sending a signal to a decoupling unit (e.g. contactor, switch disconnector or circuit breaker). As soon as the grid is stable again, the system may automatically reconnected. The CM-UFD.M31 provides different monitoring functions including over-/undervoltage and over-/underfrequency as well as rate of change of frequency (RoCoF) and vector shift monitoring functions, which detect a loss of mains event. This grid feed monitoring relay is certified in accordance to VDE-AR-N 4105, VDE-AR-N 4110 & VDE-AR-N 4120.