BEst practice

drwaltMarch 2, 2012

I presently have an outbuilding subpanel connected to a main service panel with #10 copper 2+G backfeeding a 30A breaker, w branch circuits - the G wire serves as neutral. The sub panel neutral buss is tied to a ground rod because there is no other metalic connector between the two buildings. This has worked well so far. Now I want to run a 100 Amp #2 aluminium wire to a new subpanel in the same outbuilding, from the same service panel. The aluminum wie is direct burial, 2-2-4, no ground. Here are my questions. Assuming the main service panel is properly grounded to two ground rods with #6 copper:

1) should I disconnect the present 30 Amp service and rewire the existing subpanel to a 30 Amp breaker in the New Panel?

2) should I connect the new panel to the existing ground rods on the existing 30 Amp subpanel , or would it be better to use the #10 wire to run the ground back to the main service panel?

3) presently the neutral and ground wires in the main service panel are on the same buss, this is also true in the existing 30 subpanel in the outbuilding. Should the subpanel neutrals and grounds be on separate busses or tied together?

Thanks, drwalt

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What version of the NEC are you under?

Around 2008 the 3-wire feed exception was removed, and a 4-wire feed is not required.

    Bookmark   March 2, 2012 at 10:12AM
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I don't know, where would I find out? What are the implications for my situation?

    Bookmark   March 2, 2012 at 10:15AM
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House was built in 1989, so I assume pre2008NEC.

    Bookmark   March 2, 2012 at 10:21AM
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But when you are modifying or adding to the electrical system, you have to conform to whatever code is currently being used in your area.

Brickeyee, did you mean "a 4-wire feed IS required"?

    Bookmark   March 2, 2012 at 10:46AM
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"I don't know, where would I find out? What are the implications for my situation?"

Whoever is responsible for inspections (city, county etc) in your area will gladly tell you what edition of the NEC has been adopted.

Depending on the department, the inspectors might be willing to answer specific questions directly.

    Bookmark   March 2, 2012 at 1:19PM
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Ron Natalie

Doesn't matter when the house was built. Your new work will need to correspond to the current code. If you tell us where you are, we can probably make a good guess as to NEC version (unless you're in CT, MO, HI, Reno, or Tuscon, it's probably a safe bet you're on 2008 or later).

As pointed out, the old code had an exemption to not run an equipment grounding conductor between buildings when there were no other metallic paths between the building. Your current 30A wiring appears to not be legal under any version of the code. You can't just use the ground wire in the cable for the required grounded (neutral) conductor.

I'd run the grounding conductor, it was always a good idea even under the old code.

    Bookmark   March 3, 2012 at 2:46AM
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