I can't answer your question directly because I don't know where you are. But in the U.S. you can not (by national electrical code) ground some things to some other things.
Most notably, you cannot ground a chassis to a neutral, nor can you use a grounded conductor to carry current
This can get confusing, because in reality, "ground" ground and the "mains" neutral are the same electrical point at one place........where the mains comes into the house at the main power / meter panel. again, I'm speaking "American" LOL
So an example..................
You have a typical U.S. electric kitchen range which (in this case) uses no 120V circuits, and therefore needs no neutral for actual operation. These used to be wired up with a three wire plug...........a ground, and 2 240V hot wires. The ground was purely for safety, and connects to the range housing / case.
So let's change this some...........you are building a ham radio homebrew amplifier operating on 240V, and it DOES have some 120V components, for controls, etc
You can NOT use a 3 wire plug in this case, and you can NOT use the case as the neutral for the 120V circuits.
If you are in the UK, example, I have no idea how this affects
Here in the US there used to exist small cheap kitchen / table radios called the "all American five" because they mostly all used the same tubes with series wired filaments (heaters) across the 120V line. These were usually in plastic cabinets, and "supposedly" the metal chassis was "isolated."
BUT THEY HAD capacitors to the metal chassis from one side of the line, and the leakage current in these caps could be dangerous. Depending on which way the (older style) line plug was inserted, the chassis could be "hot."