yet another detached structure grounding question

[electrofelon]

Can I use a main structure's grounding electrode system to also serve as the GE system for a detached structure?

 

[electrofelon]

...assume there are no existing electrodes at the detached structure.

 

[charlie b]

I would say no.

This may be an exception to the commonly-believed rule of thumb that if the NEC does not prohibit something, then that something is allowed. In this case, I can't find anything in the NEC that says you can't share electrodes. But I don't concluded that you can. Rather, I see statements that the house and the separate garage each need a GES. Since neither statement says that you can take credit for a GES that serves another building, I conclude that you cannot.

 

[Pierre C Belarge]

I tend to agree with Charlie.
Also, 250.32(A)... the end of the paragraph.

"... Where there is no existing grounding electrode, the grounding electrode(s) required in 250.50 shall be installed."

 

[iwire]

I also agree with Charlie and Pierre.

I relate it to installing separately derived systems like transformers, we do not get to use the EGC as the the GEC for the derived neutral.

 

[electrofelon]

I tend to agree with all of you, however it could get tricky depending on what you consider an "existing" electrode. Is a ground rod a few feet from a structure an existing electrode for that structure? What about 10 feet away? Say the two structures are in close proximity and the two rods for the main structure are actually closer to the detached structure? So you pound two new rods, now do you have to bond both systems together sinceall available electrode must be used? I have never run into a situation where it would save labor and materials to do this even if it is permitted, but its just an academic question ive been thinking about.

 

[tonyi]

I can't find anything in the NEC that says you can't share electrodes. But I don't concluded that you can.

Scenario (real one I worked on a few years ago):

Two buildings share a common well. Several lengths of metallic piping run between the buildings to pipe water around -- ~15' between the structures.

Of necessity, all that shared metallic piping had to be included in each building's GES and the the pipes were common between them.

The code demands I include all that common pipe in the buildings GES's.

There are situations where it is unavoidable.