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  1. #1

    Default grounding source required for detached building

    For clarity I understand a grounding source (ground rods in our area) is required for a 4 wire feed to a detached building. If an existing 3 wire feed is present is it proper to install a ground rod if one is not present. Install was around 2000, I know I should dig up the yard and install a new feed but that is not economically feasible.

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  2. #2
    Join Date
    Mar 2007
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    Default Re: grounding source required for detached building

    Quote Originally Posted by Don Hawley View Post
    For clarity I understand a grounding source (ground rods in our area) is required for a 4 wire feed to a detached building. If an existing 3 wire feed is present is it proper to install a ground rod if one is not present. Install was around 2000, I know I should dig up the yard and install a new feed but that is not economically feasible.
    Hi Don,

    That depends.

    Prior to enforcement of the 2008 NEC (you would have to check enforcement dates for your area, but in this particular case, 2000 is clearly prior), it was acceptable to run a 3-wire feed (no equipment grounding conductor) to a panel at a detached building (neutral/ground would be bonded at this panel and a ground rod installed), if certain conditions were met. One was no equipment grounding conductor between the service equipment and this panel and I believe another was that it could not have GFCI protection for the circuit feeding the panel at the detached building. 250-32(2)

    The most pertinent requirement (in my opinion) was that there could be no continuous metallic path connecting the building in which the detached panel was located and the building where the service equipment was located. What constituted a "continuous metallic path" was up to interpretation, but clearly included copper water piping. I have heard it argued that this continuous metallic path could include a telephone line, TV cable, steel reinforcing in a concrete walkway, metal fencing, or pretty much any metal from one building to the other.

    The problem, from a home inspector's point of view, is that it is difficult to be certain that there is no continuous metallic patch between the two buildings.

    A grounding electrode (ground rod) is required, whether or not an equipment grounding conductor was provided. Unless there are significant changes to this outbuilding, I do not believe there are any requirements to upgrade the feed. Certainly, it would be safer.

    Best bet would be to become familiar with 2005 NEC 250-32(2) check with your local building department to find out how they interpret and enforce this.

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  3. #3
    Join Date
    Aug 2008
    Location
    Maryland
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    Default Re: grounding source required for detached building

    A 3 wire feed should have had a grounding system the same as a 4 wire feed.

    All answers based on unamended National Electrical codes.

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