Surly the path  of the rod back to the star point needs to be low enough to operate the protective device. 

Also, in regards to three phase generators, if one of the lines comes into contact with mass of earth ( True earth) how does the value of the electrode influence potential neutral inversion ? 

Although slightly of topic , this incident is still somewhat relevant. Recently, I became aware of a 630mm single neutral conductor from a transformer to a store being severed and stolen. Remarkably, the electrical supply remained uninterrupted, and the theft was only discovered upon review of CCTV footage. The Distribution Network Operator subsequently visited the site and isolated the supply. I am astounded by the expertise of these thieves, who specifically targeted the neutral conductor.

How about let’s say HO7RNF generator tails on the surface. What happens if they get cut and exposed copper touches the ground?

All depends on the soil resistance and the contact area. As a for instance, let's imagine that the soil is of a type where a 4' x 3/8" rod (so surface area about 30,000 mm²) gives a resistance of 200Ω - and say the gash in the cable exposed say 20x1 mm of conductor (20mm²) - then as a very simple approximation you might imagine that the fault would gave a resistance about 1500x higher than the rod (30,000/20) - so around 30kΩ.. (All very rough, if the soil eas dryer near the surface it could be a lot higher, of if in a puddle it might be lower) Anyhow 230V and 30kΩ would mean a fault current of less than 8mA - so nothing trips, not even a 30mA RCD,

Cue comments about choosing a cable that's suitable for the environment. RN sheathed is pretty robust and isn't easily cut into by the usual blunt trauma - but if sharp implements are a credible risk and other precautions aren't sufficient, then consider armoured (or at least braided) cables instead.

  - Andy.