We use isolated ground on some sensitive serial data systems in critical applications, where a small difference in ground potential between two pieces of equiment would lead to problems. (Such a small difference in potential could easily be caused by a fault an unrelated system) So, we had a completely isolated system ground from the standard chassis ground. This is rapidly becoming obsolete, though, as new equipment is far less sensitive.
All the equipment had two grounds- one for electrical reference, and a 2nd for safety. The reference ground was only actually grounded at one point.
[This message has been edited by SteveFehr (edited 10-16-2006).]
