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There are many posts everywhere about this, but I'm still not clear on one thing. I have a separate building about 90 feet from the house where a buried 10-2 UF cable (2 conductors and a ground wire) supplies 110v electricity for lighting and receptacles. I am going to install a sub panel in that building and convert from 110v to 220v so I can install multiple circuits, one being 220v and 3 110v. So, in the 10-2 UF supply cable, I will use the white and black wires as conductors, and the ground wire as neutral. There are no other connections, pipes, telephone lines etc. between the buildings. I understand I must install a ground rod at the outbuilding to properly ground the subpanel. In the subpanel, should the ground bus and neutral bus be connected?

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    10 AWG conductors aren't going to allow you to run much other than some lights and general purpose receptacles. If you're looking to do more than that, you should consider upgrading to larger conductors.
    – Tester101
    Mar 10, 2015 at 20:20
  • What is the 240V load you're trying to run?
    – Tester101
    Mar 10, 2015 at 20:43

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You cannot do this under current code. You USED to be able to do this. I suspect that proved to be a poor idea, since now you need to run a 4th conductor (hot or neutral) and maintain separated ground and neutral all the way to the service entrance.

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    You only need to run 4 conductors if you're installing new conductors. If the OP uses the existing conductors, it's possible to have only 3 conductors (see the exception for 250.32 (B)). The bigger problem (in my opinion), is using 10 AWG conductors to feed a panel.
    – Tester101
    Mar 10, 2015 at 20:40
  • Thank you Tester101. I have read many posts on this and other sites about grounding a subpanel, but none of them answer the question I asked. In the scenario I described should the ground bus and neutral bus be connected or kept separate?
    – Dan
    Mar 11, 2015 at 12:57

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