charlie b said:
Isn?t it more accurate to say that the Earth is a very low impedance path, but there is a high impedance in the connections between the power system and the Earth? That is, it is the interface between the ground rod and the surrounding ground that has high impedance (i.e., on the order of ohms).
The way I look at it, if you put two resistors in parallel, the net resistance is lower than either of the two. If you put a billion resistors in parallel, the net resistance becomes very low indeed. I think that there are billions of parallel paths between any two ground rods. These include paths in a straight line from one to the other, and paths that go through the center of the planet, and paths that go from my house to my neighbor?s house (in Seattle) via Mike Holt?s offices (in Florida). A box of dirt may have a high impedance, but a planet?s worth of dirt will not.
Am I off-base in this way of thinking?
Charlie B.,
When we say earth is a poor conductor, we mean that its resisitivity is much higher than that of copper. If it were practical to obtain a huge cross sectional area we might obtain a satisfactorily low impedance, but that, as you know, is seldom the case.
Then too, the conductive soil layer is often thin which exacerbates the problem. In these cases we must consider "sheet resistivity" in ohms/square rather than using bulk resisivity in ohm-meters..
