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Thread: Subpanel in Separate Building

  1. #1
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    Subpanel in Separate Building

    I recently asked a question about neutral and ground in a subpanel in the same building structure. Now suppose the subpanel is in a remote structure (100 ft away, this is a situation at my brothers house). In this particular case the subpanel was installed with (1) GEC to grounding rods at the remote build, (2) 3 wires and a ground running from the main panel, and (3) the ground and neutral tied together at the subpanel. Are the neutral and ground supposed to be tied together at the remote subpanel when remote grounding rods are used? What about when remote grounding rods are not used? Are the remote grounding rods required?

  2. #2
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    If an EGC was run with the circuit to the separate building then neutral and ground are not tied together. The grounding electrode(s) are bonded to the EGC. A grounding electrode is required if there's a subpanel with multiple circuits as you seem to describe.

    There's an exception that allows an existing feeder run without an EGC to be used as is. In that case EGC and grounding electrode are both bonded to neutral as would be be done at a service. But that doesn't match your description.

  3. #3
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    E, a sub-panel should never have the neutrals and grounding tied together, regardless of whether in an attached or detached structure. The only thing different is that a detached structure needs a grounding electrode system, tied to the equipment grounding system.

    Treat the neutral as if it was energized, other than having no over-current protection. The exception Ben mentioned is only for existing situations, and then only if there are no other metallic pathways between the structures. If you have four conductors, separate the neutral.
    Code references based on 2005 NEC
    Larry B. Fine
    Master Electrician
    Electrical Contractor
    Richmond, VA

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