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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...

  1. Am even I allowed to have two panels in the house with separate feeds?

  2. 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.

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2 Answers 2

National Electrical Code 2014

Chapter 2 Wiring and Protection

Article 230 Services

I. General

230.2 Number of Services. A building or other structure served shall be supplied by only one service...

If you live in an area covered by NEC, you're only option is to upgrade the service to the house.

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Thanks, Can't get any clearer than that. So if I upgrade the panel does that mean I also have to upgrade the wiring? It's a 1937 Bungalow with flex conduit (one guy referred to it as knob and tube??) two wire, two prong outlets. Old fabric looking insulation. I have upgraded some of the outlets with three prongers and grounded them with a jumper to the metal box with green jumpers and holes in the metal box tapped for 'official' green ground screws. I have no idea if that is code but I was told some inspectors will allow it. –  RoscoP Jun 2 at 12:09
    
As long as the wiring that enters the panel is code compliant, there should be no reason to upgrade all the wiring in the house. Though depending on the condition of the wire, the Electrician that does the upgrade may want to upgrade some or all of the circuits. –  Tester101 Jun 2 at 12:13

Bottom line is NO, you cannot have two separate panels fed from two different sources at a single structure.

Your easiest bet is to either upgrade the service to the house, or abandon the existing service to the house and run a new 100A sub-panel from the garage.

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Thank you. I was afraid of that. I guess the electrician who installed the new service in the garage gave me some bad advice. If I have to upgrade the house I would rather go to a 200A because I have some big machinery. Would have made more sense to upgrade the house and go the garage with 100A subpanel. Plus wouldn't the power company likely pay for the wire from the pole to the house? Guess I'll have to make a call... –  RoscoP Jun 2 at 12:10

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