I will google "Jan Axelson's Serial Port Complete" tomorrow. Im off to bed now.

What exactly do you mean by "isolate it completely" is that having each device isolated from the rest of them or having each device isolated from the mains using a transformer?

You seem to be saying that i shouldnt have the 3rd wire in this case but then you say the easiest thing is to have one. I think i might have misunderstood on of those paragraphs.

You really wernt joking when you said "Ground loops are very difficult for most people to understand". I definately fit in the "most people" category