Reference is now made FIG. 7D which illustrates a method, according to an embodiment of the present invention. In decision block 750, output power from inverter 104, 204 is constantly monitored. If output power is stopped, power converters 705 are shut down.

Reference is now made to FIG. 8, illustrating a system 80 according to other embodiments of the present invention for protection during an islanding condition. For simplicity, a single string 823 is shown of distributed power sources, e.g. solar panels 201 a-201 d connected to respective power converters 805 a-d. Serial string 823 is input to inverter 804 through wires 412 and 410. The output of inverter 804 is connected to and supplies electrical power to the electrical grid. Inverter 804, typically includes a monitoring and detection mechanism 701 which monitors one or more parameters of the electrical grid such as voltage and/or frequency. If one or more of the grid parameters is out of specification indicating an islanding condition, monitoring/detection mechanism 701 typically shuts down inverter 804 or disconnects from the grid, so that output power is no longer supplied by inverter 804 to the grid. During normal operation, a line communications transmitter 803 superimposes a keep-alive signal, for instance between 1 kilohertz to 100 Megahertz on direct current (DC) input lines 410 and 412 attached to serial string 823.