Current Flow From Two Closely Spaced Electrodes

In practice, we will need to place the two current electrodes close to each other. In doing so, however, the current distribution and equipotentials produced within a homogeneous earth become more complicated than those shown previously.

Instead of the current flowing radially out from the current electrodes, it now flows along curved paths connecting the two current electrodes. Six current paths are shown (red lines). Between the surface of the earth and any current path we can compute the total proportion of current encompassed. The table below shows this proportion for the six paths shown above. Current paths are labeled 1 through 6 starting with the top-most path and proceeding to the bottom-most path.

Current Path% of Total Current

From these calculations and the graph of the current flow shown above, notice that almost 50% of the current placed into the ground flows through rock at depths shallower or equal to the current electrode spacing.