I have a 200amp main panel in my home, and my garage has a subpanel fed by a two pole 50amp breaker by approximately 85' of 6/3 plus ground cable. I use my garage as a workshop, greenhouse, and office. I'm planning to install a ventilation system and add more power for my workshop on the lower level. I'm also going to install a ductless minisplit system on both levels of the building; hence, I'd like to update the panel.
When I first opened the existing subpanel, I noticed that the ground and neutral wires were bonded, so I purchased a ground bar and separated everything. All looks good now. There's a #6 ground wire attached to a grounding rod a foot or so away from the building.
My goal has been to replace the 50amp panel with a 100amp panel, running 2-2-2-4cu thhn inside 1.5" pvc conduit, buried 18" deep, from the main panel, 85' to the new 100amp panel in the garage. That said, I'd like to utilize the existing 6/3 cable and grounding rod. My question is, how would I do so appropriately and most gainfully? Does it make sense to have a second panel in the garage despite the redundancy? Honestly, I'd like to be able to utilize close to 90 or so amps in addition to the existing 50 amps in my garage, if possible. Currently, I figure I should play it safe since I spend most of my time out there, and I seem to like to use energy sucking devices for work and play.
Perhaps the old subpanel can be used for the minisplit and 3 fan ventilation system while the new panel can take over the duties of the existing circuits plus new ones I plan on running? I know that the minisplit will need a disconnect, so I'm wondering the best way to do this. Does the new grounding rod need to be 6' away from the existing one? Any tips would be greatly appreciated.
Thanks in advance, Chris