George this 'clean' ground still must be tired into the systems grounded conductor at some point.
What exactly is going on here?
The instllation consist of a subpanel fed with 100a conductors in a metal raceway and the contractor want's to have a "clean ground" for electronics. This ground would be connected to the Service panel and then to be used as a reference at the sub panel end. (I think) I agree that it must be tied down at the Service but it can be floating at the sub panel end as long as the raceway is being used as the EGC for the sub panel.
I think there is more to be gained by having this "clean ground" inside the raceway than having it outside the raceway aand subject to stray electrical noise in the plant.
