Dear Mr. Ghali,
First off, i should thank you for the elaborated reply, basically i’m responsible to do the building design & cannot get such deep information before the actual operation, of course during the design we can estimate the percentage of the harmonics at the feeder or circuit, so if you are in my place where making the design, what is the ideal steps when sizing the grounding conductor? most of the designers always sizing the grounding conductor to half of the phase which is completly uneconomical, at the same time we don’t want to loose the protection by anyway because of some extra cost.