I am testing ground rods on a location with multiple portable buildings fed from a single panel. When the rods are isolated they may show a resistance of anywhere from 30 to as high as 150 ohms. When they are connected to the circuit they will test at 5 ohms or lower in most cases. My question is, can I consider the reading with the rod connected to the circuit as a good reading? Or do I have to add rods and attempt to lower the isolated reading.