I have a somewhat unique situation. I had a separate 200A service run to my garage a few years ago to run my welders and compressor. My house still has 60A service. I am now moving my wood shop from a commercial space into my basement and will need more power down there. I was advised by the electrician who installed the 200A panel in the garage that at some point I could pull 100A off that panel and go underground to the house. I have no problems with the existing 60A service in the house so simplest approach would seem to just install a sub-panel in the basement to feed all the woodworking machinery and leave the existing house wiring as is. I intend to run 2/2/2/4 THHN/THWN wires in conduit to feed the sub-panel.
Reading up on this I find much confusing info regarding grounding and bonding and of course it's all addressing a sub-panel from the house to the garage, not the way I'm going. So a few questions...
Am even I allowed to have two panels in the house with separate feeds?
Unlike most garages the house is full of 'metallic pathways' and I assume the existing 60A panel is grounded so how would one properly deal with bonding and grounding the new 100A sub-panel in the basement?
I understand the ground and neutral in the sub-panel should not be bonded but I'm confused about the grounding. Some say grounding electrode, others say the #4 equipment ground is good, some say I need an additional grounding electrode at the main panel in the garage...
Any clarification would be much appreciated.