I can't see evidence of an external earthing point on the mill or the electrical cabinet; is there a best place for this and can I simply take a cable and run to ground? (Concrete floor or wall?)

USB issue seems to be resolved by the Windows setting... We'll see!

E-stop issue was the 'axis limit switch override'... I pressed it by mistake last week and it must be faulty as I had to link it out to clear the e-stop alarm...
Question is what is its purpose and do I need to keep it? I could replace the switch or do away with it!?