Need some clarification on subpanels. I am moving my overhead 100ampservice (at the house) to underground 200amp service(at my detached garage). I will then install a new 200amp panel in the garage and feed my existing 100amp panel (at the house). So, my existing panel at the house will now be a subpanel. I need to understand the proper grounding for this set up. And also any necessary seperation of ground and neutrals (rules that usually apply to main and subpanels in the same structure). thanks.