Robin .. everything is earthed (by law AFAIK) apart from double insulated . All we are discussing is changing from supplied earth, to a local earth.
I know the theory of 'floating'potential' , but we just don't have it here in the UK ,unless you disconnect the earth at the main consumer board where the supply comes into the house (again illegal)

Yes, I have RCD from the house to the shop, and again at the shop dist' box.





From the manual.... it's the failure rate of the machine I don't wan't to happen ! I can't see how, but it says , so I'm asking !


5. Safety Grounding
Morn laser engraver uses fourth type of laser tube. The type of drive is
high-voltage-driven, so during users use the machine, they must comply with the
"Safety Note ". On the other hand, it asks stringent requirement about the safety
grounding to the users. The safe Line-to-Ground Resistance should be less than 5Ω.
Specific connection method are shown in Fig.F2-12, F2-13
F2-12

F2-13

10
User’s Manual of Laser Engraving / Cutting software
Attention please, bad grounding can cause high failure rate of equipment and at
the same time may cause other safety incidents! ! !
The company won’t assume any responsibility and obligation to the fault and the
accident caused by bad grounding!!!