Sharing Ground Rods

[LarryFine]

250.32. The separate structure needs its own GES.

If it's physically distant enough to make that more economical, you're certainly allowed to.

But, if they're close enough, one system may be shared, just like when you have two mains.

 

[david]

250.32. The separate structure needs its own GES.

Take into consideration a city metal water pipe system as a grounding electrode for each service

Also consider a metal water pipe run from the building with the service to the building supplied by a feeder

 

[LarryFine]

One reason we only bond to the neutral in one place is so paralleled grounding and electrode connections do not contribute to improper neutral current pathways (ideally speaking).

 

[jaggedben]

If it's physically distant enough to make that more economical, you're certainly allowed to.

But, if they're close enough, one system may be shared, just like when you have two mains.

That's not how I read it.

 

[david]

That's not how I read it.

250.53 (B) is what I found tonight but the code use to say something like if two electrodes were less than 6 ft apart they had to be bonded together.

If two ground rods were driven at the OP pedestal do you see anything in 250 part lll that would prevent a bond between the pedestal ground rod and the service ground rod
I will agree with your reading that the pedestal has to have a code compliant grounding electrode

Once that happens though I see nothing in 250 part lll that would prevent the two systems from being bonded together

I would argue if there was four ground rods total on the same premise and they were closer than 6ft from each other they would have to be bonded together

 

[Dennis Alwon]

250.32. The separate structure needs its own GES.

Yes 250.32 says that a separate structure needs a grounding electrode system . Where does it say it needs its own?

 

[david]

That's not how I read it.

You made me go back and read 250.50 five times and it is a short paragraph

 

[jaggedben]

Yes 250.32 says that a separate structure needs a grounding electrode system . Where does it say it needs its own?

What would be the point of the section otherwise? What other possible meaning could the requirement have?

 

[LarryFine]

What would be the point of the section otherwise? What other possible meaning could the requirement have?

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

An electrode system within practicable reach would be such an existing electrode.

 

[david]

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

An electrode system within practicable reach would be such an existing electrode.

I can't go there. Because than my answer to the OP would of had to been, you didn't need to drive any electrodes at the pedestal.

However you are required to install a grounding electrode conductor connected to the ground rod at the service

I can't agree that the service electrodes are required for the pedestal

I can't agree that the electrodes at the pedestal are not permited to bond to the electrodes at the service

Intent or language of the code section. Could an inspector except what the OP ask. I would say yes

Could an inspector require the service electrodes to be used or a near by detached garage or any other structure, I would say no.

 

[wwhitney]

What would be the point of the section otherwise? What other possible meaning could the requirement have?

The EGC in the supply to the building or structure will always provide a conductive path back to the supplying building's GES. If 250.32(A) were not there, that would be the only required path for mitigating say lightning induced voltages. By requiring a GEC connected to a GES, the minimum size of the conductive path (minimum GEC is #8 Cu) is greater (minimum EGC could be #14 Cu).

Regardless, 250.32(A) has no language about exclusivity of the GES or proximity to the building supplied.

Cheers, Wayne

P.S. Devil's advocate: 250.50 starts off: "All grounding electrodes as described in 250.52(A)(1) through (A)(7) that are present at each building or structure served shall be bonded together to form the grounding electrode system. Where none of these grounding electrodes exist, one or more of the grounding electrodes specified in 250.52(A)(4) through (A)(8) shall be installed and used."

So one could argue that as the 1st sentence says "at each building or structure served", the 2nd sentence implicitly has the same modifier, and a remote electrode would not satisfy 250.50.

 

[Jaysee62]

Thank you all for sharing your experience & thoughts on this. The first ground rod is about one foot away from the metal poles my sub panel is mounted on. Considering the idea/requirement for the second ground rod be at least 6 feet away from the other rod, it seemed convenient to share the house service ground rod which is about 10 feet from the first rod nearest the sub panel.

 

[jaggedben]

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

An electrode system within practicable reach would be such an existing electrode.

I think that second sentence is reasonable and it's pretty close to what I said in my first reply to this thread, where I put it in terms of whether the pool equipment is really at a separate structure. Ultimately the relevant distance is not specified in the NEC and up to the AHJ's judgment. 'Shall have' is pretty vague. But within the context of 250.32 existing, it's clear that a building or structure can't 'have' a GES at a remote building. Because then the grounding requirement for services would allow all outbuildings to 'have' the GES at the service and 250.32 would be a meaningless and unnecessary requirement.

 

[LarryFine]

The first ground rod is about one foot away from the metal poles my sub panel is mounted on.

So, all you need to do is connect to the closer rod; the existing jumper between them does the rest.

 

[jaggedben]

Thank you all for sharing your experience & thoughts on this. The first ground rod is about one foot away from the metal poles my sub panel is mounted on. Considering the idea/requirement for the second ground rod be at least 6 feet away from the other rod, it seemed convenient to share the house service ground rod which is about 10 feet from the first rod nearest the sub panel.

I'm inclined to agree that with everything at that kind of distance you can share the electrodes. Your subpanel and service share the vicinity where the grounding electrodes for either would be installed.

 

[LarryFine]

I'm inclined to agree that with everything at that kind of distance you can share the electrodes. Your subpanel and service share the vicinity where the grounding electrodes for either would be installed.

Agreed. Besides, with the sub-panel that close, even if you drove separate electrodes, they would still have to be connected to the existing ones, effectively providing four where only two are required.

 

[Jaysee62]

Another question: In Mike Holt's video on Grounding and Bonding, he states " we take the metal enclosure and connect to the earth" showing the connection to the ground rod.
My question is, do we connect the #6 bare wire going to the ground rod to the ground bar inside the sub panel OR connect it directly to the sub panel enclosure?

 

[Jaysee62]

Here is my installation. About 4 feet from the house.

 

[LarryFine]

Either is adequate.

 

[roger]

I'm late to the party and haven't read all the posts but IMO, I see the length of the conductor in contact with the earth simply being a GE itself and the longer it is between the service bonding and the first Electrode the better it is