If I stuck two earth rods in a uniform field (e.g. a big flat area with grass or whatever) at ever increasing distances (e.g. 10m, 20m, 30m ..., 1000m etc) how would the result vary as a function of distance? An obvious answer would be linear (i.e. of the form R = AL + B where B is the resistance of the rods themselves). But a field isn't a wire, it's a plane - and that's a bit beyond my intuition, and beyond any easy maths.
The distance between the earth rods is unimportant. The accepted view is that the general mass of earth has zero resistance and that the measured resistances are in fact a CONTACT resistance due to the limited area of contact.
Or put another way, the resistance between two earth rods would be the same if they are 100 yards apart or thousands of miles apart. (presuming similar sized rods and ground conditions in each case)
Earth return telegraph systems worked fine over thousands of miles, this not only saved the cost of a second wire, but gave half the circuit resistance of a two wire circuit.
Earth return power circuits are used in some places and give a lower resistance than two wires.
The cross channel power link normally operates as a two wire system with well insulated positive and negative cables. In the event of a cable fault, it may be operated at half capacity via the sound cable and an earth return.
The distance between the earth rods is unimportant. The accepted view is that the general mass of earth has zero resistance and that the measured resistances are in fact a CONTACT resistance due to the limited area of contact.
Or put another way, the resistance between two earth rods would be the same if they are 100 yards apart or thousands of miles apart. (presuming similar sized rods and ground conditions in each case)
Earth return telegraph systems worked fine over thousands of miles, this not only saved the cost of a second wire, but gave half the circuit resistance of a two wire circuit.
Earth return power circuits are used in some places and give a lower resistance than two wires.
The cross channel power link normally operates as a two wire system with well insulated positive and negative cables. In the event of a cable fault, it may be operated at half capacity via the sound cable and an earth return.
