Multiple-driven-rod earth connection

The earthing system of a substation or power station usually includes a number of driven rods arranged around the periphery. It is necessary to estimate the total resistance of this set of rods and this presents certain difficulties. It is only possible to make approximate estimates of this value, and general formulas are developed to enable this to be done. The assumptions, on which these formulas are based, are discussed. Examples are given of the application of these formulas to specific sizes of rod.