The only reasons for those recommended separations is to make it hard to create an installation where your victim can be caught straddling 2 zones that may be at different voltages - if humans were smaller and had shorter limbs, the recommended distances would be less. Equally the separations would not be good enough for horses or cows, but lickily for us they do not write the regs. Similar consideration applies to the distances for sockets in UK bathrooms (though why is not clear as the rest of the planet has no issue).

For a vertical rod electrode, in more or less uniform soil - note comments about surface finish - most of the volt drop is within one rod length of the centre - the diameter of the live 'carrot' shape of earth around it scales with length.  A short high impedance electrode (like on the rod tester) has a zone of influence that may be a few inches across.  We are not always sinking 8 ft DNO sized rods - in a domestic setting it may be lucky to be more than a couple of feet and less than a hundred ohms.


In the car case it becomes more complex, as we have two mobile electrodes, weakly grounded, namely the user, and the car, as well as the more obvious fixed ones associated with the supply and the armour of cables and so on, as well as probably various items like gate posts, fences and so on that bring the average of the terra-firma potential beneath them to places it may not otherwise be  accessible to touch.

The only reasons for those recommended separations is to make it hard to create an installation where your victim can be caught straddling 2 zones that may be at different voltages - if humans were smaller and had shorter limbs, the recommended distances would be less. Equally the separations would not be good enough for horses or cows, but lickily for us they do not write the regs. Similar consideration applies to the distances for sockets in UK bathrooms (though why is not clear as the rest of the planet has no issue).

For a vertical rod electrode, in more or less uniform soil - note comments about surface finish - most of the volt drop is within one rod length of the centre - the diameter of the live 'carrot' shape of earth around it scales with length.  A short high impedance electrode (like on the rod tester) has a zone of influence that may be a few inches across.  We are not always sinking 8 ft DNO sized rods - in a domestic setting it may be lucky to be more than a couple of feet and less than a hundred ohms.


In the car case it becomes more complex, as we have two mobile electrodes, weakly grounded, namely the user, and the car, as well as the more obvious fixed ones associated with the supply and the armour of cables and so on, as well as probably various items like gate posts, fences and so on that bring the average of the terra-firma potential beneath them to places it may not otherwise be  accessible to touch.