Direct Current Ground Electrode Behavior

The conducting of moderately high direct current through earth between variously sized electrodes installed in different types of soil has provided test data which, while in general agreement with expectations [1]-[3], places much more emphasis on the electrode-to-earth contact area than had been necessary in past designs, which were primarily used for conducting ground currents of short time duration. Analysis of the data indicates that the design of a grounding grid which is to carry current to earth continuously for several hours can be treated as two independent problems: The outer dimensions, or perimeter, should be based upon computed resistance to remote earth [4], with utilization of the low-resistivity valuesg usually measured at wide probe spacings. The contact area should be based upon the power dissipation value computed from the square of the proposed current density and from the measured soil-resistivity value at the electrode-to-soil interface.