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A friend of mine is building a boat. On this boat, he has 12V batteries with a 230V/13A transformer.
Recently somebody suggested he should connect the null with the ground. With DC, this is common practice. But how would somebody suggest doing the same with AC?! Polarity switches continuously on AC.
I suspect he either misunderstood the advice or the advisor didn't understand it himself either.
What might the advisor have wanted to tell? There's no reason to assume malicious intent.
I think the "adviser" may have been talking about connecting the socket's earth to the inverter's neutral / cold / null point:
simulate this circuit – Schematic created using CircuitLab
With this arrangement, if there is a short or other fault causing current to flow through the earth connection, it will either cause enough current to flow to trip / blow the MCB or Fuse, or cause a mismatch in the live / neutral currents which would trip an RCD (GFCI). You could also add an ELCB into the mix as well, and that would function normally.
But how would somebody suggest doing the same with AC?! Polarity switches continuously on AC.
This is not advise or complete answer for your main question, just explanation about GND.
Voltage is difference between two terminals.
In the other words - there is no voltage in one terminal. Voltage must be between two terminals.
GND can be used as point of reference and sometimes as conductor in some cases (cars, boats) to reduce cost of wiring. It is also commonly used method. You can read more about grounding here: Where is the ground/negative for overhead power lines?
If you connect one terminal to GND and say "this is zero" - other terminal relatively to this will have variable voltage - sometimes positive, sometimes negative.
If you have a boat and you will connect 12V battery - to GND and say "this is zero" - other terminal will have +12V relatively to GND.
If you connect battery + to GND - other terminal will have -12V relatively to your ground.
The shore power neutral must not be connected to vessel ground. When the inverter is operating, the on-board neutral must be connected to vessel ground.
The shore power "safety ground" should be connected to the vessel ground, preferably through a Galvanic Isolator.
The above rules are from ABYC (USA) and CSA (Canada), but, according to a British book I have, apply there as well.
