The service outlets in IBM mainframe machines were derived from an ungrounded secondary so on a scope, the two ungrounded conductors were roughly 60v above ground but the EGC was connected normally. Touching either conductor might give you a slight tingle but barely even noticeable. Certainly not enough to operate a GFCI.
In the 360 days and before, the design specs were that no neutral was even brought to computer room panels. All loads were line to line, either 240 or 208, depending on the service.(delta or wye). The insulated neutral bus was used for the isolated ground that was only tied to the GEC in the service disconnect enclosure. All of that IG foolishness went away in our design specs in the early 70s when the 370 line was introduced. The legend that it actually fixed anything went on long after that. It turned out the "noise" they were trying to isolate was actually coming from the switching power supplies in our machines, not elevators fluorescent ballasts or any of the other usual suspects. I am not sure we ever admitted it tho. Anyone with an AM radio figured it out pretty fast.
