Grounding and probe

[john swift]

For one of the supply wires to be "Neutral" it has to be connected to earth / ground other wise it would be just another line

the earth connection has to be a low enough impedance to ensure the fuse or circuit breaker opens fast enough to remove the danger when you have live to neutral or live to earth fault

Here in the UK
Depending on the wiring system used in towns and cities the utility company may supply the earth and neutral as separate earth and neutral conductors (TN-S system)
or as a combined earth & neutral (TN-C system) some times with multiple earths along its length

For rural supplies the you may have to supply your own earth (TT system)
even though the utility will have connected the neutral to earth at the transformer

It does not matter if the neutral / earth connection is 3 miles down the road at the supply transformer or the utility junction block next to your Kw/Hr meter

what matters is the neutral is earthed before it passes through the residual current circuit breaker ( RCCB)
what you see when measuring the difference between Earth and Neutral is the volt drop along the neutral wire when the 3 phase supply cable has an unbalanced load

when ever the neutral wire out of the RCCB is connected to the earth there is an imbalance between the live and neutral currents which trips the breaker - (you have an earth path in parallel with the neutral reducing the neutral current the RCCB sees)
usually the circuit breaker is designed to trip at 30mA
( depending on the application various trip currents are available )

In my part of South Lancashire my mains supply varies between 243V and 248V
depending on the time of day - just now its 245V

John