All mine sites have grounded electrical systems, so that in the event of a lightning strike or utility overvoltage or ground fault, the current would be able to find a safe path to earth or the neutral of the transformer. To ensure a reliable connection to earth, electrical codes, engineering standards, and local standards often specify a minimum resistance for the ground electrodes. This method involves passing a current into the electrode to be measured and measuring the voltage between the ground electrode under test and a test potential electrode (P). A test current electrode (C) is driven into the earth to permit passing a current into the electrode to be tested.