Subpanel for an unattached building

EntlebucherDecember 1, 2011

I would like to install a subpanel in an out building. I plan on running individual conductors in PVC conduit. Can I run 2 hot leads and a neutral to the subpanel and use a ground rod at the out building instead of running a ground wire in the conduit?

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Ron Natalie

Depends what version of the electrical code your jurisdiction is operating under. Frankly, it is a very very good idea to do so even if you're on one of the older codes anyway.

If you're running more than one circuit in the outbuilding you will require a grounding system (which is probably more than ONE ground rod).

    Bookmark   December 1, 2011 at 6:11PM
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petey_racer

I wouldn't think there is any area left in the US still under the 2005 NEC, which allows the use of the neutral to also serve as the ground in some cases like this.

Entlebucher, you need two hots, a neutral AND an equipment ground conductor.
A ground while is required in either case, but has nothing to do with equipment grounding. It does not take the place of one nor does it serve nearly the same purpose.

    Bookmark   December 1, 2011 at 8:26PM
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Ron Natalie

Missouri (other than St. Louis),DC, Utah, and Connecticut appear to still be on 2005. Many of the major cities in areas that haven't got statewide adoption are still there: including Tuscon, Springfield, IL, most of Maine, a good deal of Maryland, etc...

That being said, if you have any metallic connections to the building other than the power, you can't use the exemption either. As I stated, even if you qualify (old code, no other metallic paths) it's still a really, really, good idea to run the ground between the structures.

    Bookmark   December 2, 2011 at 1:31PM
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btharmy

Don't forget to drive 2 ground rods at least 6ft apart as well. That is unless you can verify that the resistance to ground from only one rod is within specs.

    Bookmark   December 3, 2011 at 11:34PM
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dkenny

why not run all 4 wires?
and a ground rod for the ground near the remote panel.

running all 4 wires will guarantee the voltages will in reference to each other. and all the conductors that are intended to carry current--carry current. and those that aren't supposed to carry current DON'T.

the additional ground rod will add to the lightning protection...what happens if a bolt hits your out building..what's the current path to ground? back up the wire to your house? might not be a good plan.

-dkenny

ps..it it were me..i'd run 4 wires out to the out building.
but that's me.

    Bookmark   December 4, 2011 at 12:05AM
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Ron Natalie

Thank you Dkenny. You just got around to saying exactly what I said in the very first post. One rod itself is not likely to be an effective and legal ground.
It's highly advisable to run the grounds between the buildings. However, to assuage the pedantic here, there are still large chunks of the country that in certain situations you can legally get away with not running it. The major reason to do so would be COST.

    Bookmark   December 4, 2011 at 7:55AM
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