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I think this question gets close to answering my question, but I am not quite sure. I have a detached structure, powered by a feeder from the main panel where the ground and neutral are bonded. The ground there goes to a grounding electrode (and also to the water main).

On my detached structure, the ground busbar is connected to the main panel's ground busbar, but not to any other grounding source at the detached structure. If I have a copper water pipe coming in, would it be a bad idea to connect a jumper from it to the ground busbar in my detached structure's subpanel? I think that would be appropriate under NEC 250.52(A)(1) since it runs underground for more than 10'.

Also, if it is a good idea (or required) to bond it to my subpanel ground busbar, does it need to be a dedicated wire going from the bonding strap to the busbar, or can I connect it to the EGC on a nearby receptacle?

EDIT: I think I found that NEC 250.64(C) requires a continuous wire from the grounding strap on the electrode to the busbar in the subpanel, if I am reading it correctly.

Also, it looks like NEC 250.32(B)(1) should settle this question, but in one part it says

An equipment grounding conductor, as described in 250.188 shall be run with the supply conductors and be connected to the building or structure disconnecting means and to the grounding electrode(s).

...

Any installed neutral grounded conductor shall not be connected to the equipment grounding conductor or to the grounding electrode(s).

So this just makes it more confusing.

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  • I corrected your NEC quote from "NEC lawyerspeak" to common English. Does that help any? – Harper - Reinstate Monica Feb 7 '18 at 0:52
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    That is not a correct "correction." – Ecnerwal Feb 7 '18 at 1:00
  • I don't think that "neutral" can replace "equipment grounding conductor" in this context, given that it states it must meet the requirements of 250.188, which is for Equipment Grounding Conductors (EGCs), and lists such options as EMT. Looking at this again, perhaps you replaced the wrong term with "neutral" since "grounded conductor" fits the bill better – Hari Ganti Feb 7 '18 at 1:00
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    @Ecnerwal sorry, editing error. I did the wrong one. Fixed. – Harper - Reinstate Monica Feb 7 '18 at 1:04
  • The question would be what year was your detached structure built & powered. Code in this area has had quite a few changes in the last 19 or so years. – Ed Beal Feb 8 '18 at 0:23
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The grounded conductor is the white or gray Neutral. The Grounding conductor is the green or bare ground. The Grounded conductor is expected to carry current in normal service. The Grounding conductor only carries current in fault conditions.

For a (current/recent) detached structure they should be isolated all the way back to the single bond at the service entrance. That means removing any Neutral-Ground bond, and keeping all the neutral wires on a neutral buss that is isolated from the case. Grounding conductors should all be connected to the case and the grounding conductor (which may be metallic conduit) leading back to the service entrance connection.

The detached structure should have one (or more) grounding electrodes. If it has a concrete slab or footing in direct contact with the soil, that should have a UFER ground installed when poured these days, but often that detail is forgotten.

My building has 5 ground rods and a 100 foot well casing as grounding electrodes. The more, the merrier. But when the next building goes up, the neutral and ground remain separated all the way back the first building. And the next one will actually have the (required, actually, in this state) Ufer Ground.

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  • Somewhat based on @Harper's comment, I did realize that the second part of the quote is, as you said, referring to the neutral, not the ground. As such, it certainly makes sense now. – Hari Ganti Feb 7 '18 at 1:01
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    This is exactly why the "grounded conductor" term is a literary tire fire. – Harper - Reinstate Monica Feb 7 '18 at 1:08
  • Am I also correct in that the GEC must be continuous from grounding electrode system to the subpanel busbar? – Hari Ganti Feb 7 '18 at 18:53
  • The grounding electrode conductor can be spliced by listed iriversable means depending on the AHJ. – Ed Beal Feb 8 '18 at 0:26
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It's mandatory

We're talking new work here. Installations earlier than the 1990s are usually "grandfathered", but this has a pretty bad failure mode, so I recommend upgrading.

An outbuilding must have both local ground rods* or equivalent, and a hardwired ground wire** back to the main service.

Each of them do different jobs with wayward electricity: one returns human-generated electricity, the other nature-generated electricty like lightning.

This must be kept completely separated from neutral*** everywhere in the outbuilding.

* in NEC codebook lawyerspeak, this is called "grounding electrode system".

** ”equipment grounding conductor”

*** ”grounded conductor”. This confuses everybody.

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  • Mayby by today's standards but if it was built to code in the 90' S this was NOT required. Currently there is no requirement to update old services. But I agree most are confused by grounded and grounding. – Ed Beal Feb 8 '18 at 0:29
  • @EdBeal I happen to know Hari is doing an almost total rewire of an old property. Regardless even if this is grandfathered, it is one of the scary ones, and hence should be on the shortlist of things to correct even if grandfathered... even higher than NEMA 10 and for the same reason. – Harper - Reinstate Monica Feb 8 '18 at 0:49
  • You may happen to know but without that as part of the question or answer I stand by my comment. With that said in many jurisdictions there are levels lower than the current code that allow a lower level of code, for example in my current home I am expanding the home both bedrooms,kitchen and bath, my AHJ allows non AFCI and gfci's in all but areas within sinks and baths, although in most cases tamper resistant outlets are required. – Ed Beal Feb 8 '18 at 2:51
  • Probably the 20th answer I've read on the subject of grounding and sub-panels, and the first one to put a definitive, layman's definition on the three ground terms. Thank you for that. – DonBoitnott Aug 13 '20 at 12:19

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