it is not. that is why there is test equipment that does just that (measure earth resistance). resistance is function of resistivity, area of the corsssection and length of the medium. due sheer size of the electrodes placed in ground we can achieve large contact surface. undergroud water and minerals also reduce resistance. different applications may requre that earth resistance is below some limit. if the limit is small value, grounding will be big job and cost a lot. many new buildings have metal strips placed along foundations (to get large contact surface). dry soil is less conductive and values can vary quite a bit.
we use this concept in order to bypass the fault currents, as we know that fault currents are of high frequency. and also the equivalent circuit of the earth is the parallel combination of the resistor and capacitor,also capacitor acts as short circuit(i.e of least impedance). Xc1/(2*pie*frequency*capacitance)
A house is usually grounded through its piping systems that have generous contact with the damp earth, resulting in negligible resistance. An AC circuit alternately pushes electrons into the earth and draws them back out (60 times a second) for each separate phase similar to the power generation station. Electrons need not travel from power station to house and back full cycle. A separate ground wire (cable) would be required if the earth's resistance resulted in appreciable power losses.
No. If you put two proper grounding posts some distance apart you can measure a resistance between them. But the bulk of the earth - huge number of variant paths - makes it a good approximation. One place it definitely does not hold is in hospitals which are very careful to not have two grounding paths in the room for equipment connected into human bodies because the very small voltage drop between them can put enough current in the body to stop the heart.
The answer is no. There are resistances between electrodes placed in the ground anyplace on earth. The resistance varies with the composition of the soil. Grounding grids are engineered for industrial and commercial facilities. These usually consist of a grid of heavy gauge cable connected to a matrix of ground rods driven in the ground , sometimes to great depth. These ground rods are in a 6 to 12 inch diameter pipes at the ground level. There are special connectors which are used to test the resistance on scheduled periods. Individual electrical equipment and buildings are grounded directly to the grid using a method of welding the cables with a mold and a powder which is fired to create a short lived, very intense reaction. The individual cables connected to the structures and equipment is with a special split bolt which is threaded directly to the equipment. The cable is placed in the split and a nut is screwed on the free end of the bolt to compress the cable. Once while assisting in plant startup in Michigan, we had to drive the grid ground rods to a depth of 80 feet to obtain a satisfactory ground.
