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Some countries call it Earth, some countries call it Ground, some people call just the outside soil connection Ground. In my view those two words are interchangable...use either of them, Ground or Earth, for the same thing.
If we wish to differentiate between reference points, then we need more than one symbol. In EC there is only one Earth symbol available, so I suggest that we all use a simple double Earth symbol on EC to draw attention to different reference points. (Triple symbols if reqd) ... In that way, EC will work, and viewers' attention is drawn to the possibility of a separate reference.
Electronics users should bear in mind that little home transformers are generally well designed with double insulation to keep the low v output in such a way that it has a no-mains-earth. Any output-side-Earth on those double insulated transformer circuits should not generally be connected to the mains-Earth (it is a mistaken view that it would increase safety to put an additional output metal part to the mains-earth).
Top... a little home transformer (rectification and specific v not considered here).. Any earth on the right refers to its own non-input-earthing (e.g. non-mains) circuit reference....now seen due to the double earth symbols.
Middle... a system where input and output coils have the same earth reference (e.g. some car ignition coils).
Bottom ... same as the middle, just shown differently ... a viewer is not drawn to consider a different earth ref. The one and only same-earth here is shown three times before the switch. It is however, depicting where that single earth should be joined in this OP schematic.
Bottom Right, after switch ... a different earth to that of the left switching section (e.g. as a mentioned opto-coupler etc), and it is also a different earth to the very top circuit where the two earth symbols are seen.
SO .... Let's all use multi-earth symbols for different EC earth references? ... a suggestion for debate, with a view to avoiding misunderstanding between each viewer's Earth interpretation.
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