In a properly installed electrical system NONE< in an improperly installed electrical system, MAYBE SOME. Improperly installed in this instance refers to downstream neutral ground connections.1) What 'earthly' good is isolated grounding?
In a single phase system triplen harmonics are not an issue, and unless the store has tons of electronics, (Best Buy etc.) harmonics are most likely not an issue, in either case the IG has nothing to do with this.2) If stores need them, why wouldn't I in my home?
Theory: harmonics from fluorescent ballasts affecting data somehow?
At the XO in the transformer from that point it should be isolated from other grounds (in most installations this is not the case)3) Does the IG electrode conductor (my term) stop at the transformer feeding my new service, or does it go all the way back to building steel?
NO see above.4) Does it have to attach to both building steel and a water line?
Sure from XO to electrode you have parallel paths, it is from XO downstream they need to be isolated.5) If instructed to place both the transformer's GEC and the IG conductor through the same hardware on the building steel and water line, is it really isolated?
Has nothing to do with anything, if you keep the separately derived systems SEPERATE. No crossed neutrals which is common, unfortunately.6) In a retail situation like this, with everybody connecting their respective grounds to the same structures, is it even possible to have "isolation"?