Grounding and probe

[cropwell]

Some people think that single phase AC Neutral is synonymous with Ground (Earth). It is not! It is phase neutral for the live, which is one of the three phases used for domestic supply. Different houses in the same street can be supplied from different phases. That, however, is a digression. There is often a voltage difference between Neutral and a local earth. That voltage will depend on several factors. At my house it is 10v. Power supplies can be double insulated, but the output Ground should be connected to Earth, as should the whole machine. In some countries, the Earth terminal on the Mains socket can not be relied on to give protection from shock hazards and so a ground rod is desirable.