Common Grounding Electrode Conductor

[inspector141]

In 250.64(D)(1), a common grounding electrode conductor must be sized based on the circular mil area of the largest service entrance conductor(s). However, there are some interpretations that this common grounding electrode conductor also applies to 250.66 (A)(B) and(C). That is, if your two service disconnects are supplied with 500kcmil service conductors for each service disconnect, you would need a min 2/0 to the concrete encased electrode based on Table 250.66 using 1000kcmil.

I do not believe this is correct. Just because 250.64 references the gec must be sized based on 250.66, does not mean you ignore 250.66 A,B & C. Also, 250.64 does not say use Table 250.66, it simply says to use 250.66.

For example, if you had a 2000 amp service disconnect with a concrete encased electrode, 250.66(B) only requires a #4cu gec.

However, if you had two 400 amp service disconnect switches (500kcmil)with a concrete encased electrode, according to some, a 2/0 would be required.

It's very clear if the grounding electrode is building steel or metal water pipe, then Table 250.66 must be used, but 250.66 A, B or C would still apply for multiple service disconnects.

I would like to know what other code professionals and experts think...

 

[Dennis Alwon]

As long as the conductor to the CEE is the sole connection then a #4 is all that is required no matter what size the service.

 

[Dennis Alwon]

Do these same experts think you need more than a #6 to a ground rod?

 

[inspector141]

Do these same experts think you need more than a #6 to a ground rod?

Yes!

 

[Dennis Alwon]

Well, I have heard the arguments and don't agree. I think the articles are very clear. If it is the sole connection then #6 for the rod and #4 to the CEE. Now if you go to a rod first then to other electrodes then the conductor to the rod must be sized based on 250.66.

 

[inspector141]

here is a great graphic!

 

[roger]

The problem is that many people (even so called experts) see Table 250.66 as being all of 250.66 and the text doesn't mean anything to them.

This kind of like those claiming they buy Playboy for the articles, they may say that but we know better and if you ask them about a particular article most won't have a clue as to what was in print.

Roger

 

[infinity]

Well, I have heard the arguments and don't agree. I think the articles are very clear. If it is the sole connection then #6 for the rod and #4 to the CEE. Now if you go to a rod first then to other electrodes then the conductor to the rod must be sized based on 250.66.

I agree. This is pretty clear IMO.

 

[Dennis Alwon]

If you read art. 250.64(D) as it is written then I can see why there is confusion. This article basically refers you to 250.66 however art. 250.66(B) clearly states a #4 is all that is required to a CEE.

I think Mike's graphic is incorrect or deceptive in that he is showing a CEE. If I use that same graphic and connect to the trough above then I am only required one cee (#4) to the trough so why would I need more then that with a tap.

 

[infinity]

I think Mike's graphic is incorrect or deceptive in that he is showing a CEE. If I use that same graphic and connect to the trough above then I am only required one cee (#4) to the trough so why would I need more then that with a tap.

I would go with deceiving, because there are no conductor sizes listed. The GEC to the CEE isn't required to be larger than #4. IMO the use of a CEE is this graphic is a poor choice due to it's rather small maximum size requirement.

 

[inspector141]

Thanks for the replies. And yes, I agree completely.

Perhaps some are getting this "common grounding electrode conductor" confused with the requirement for multiple transformers in 250.30(A)(6). But this article, in (A)(1), is very clear....it requires the gec to be a minimum 3/0cu without referencing 250.66 or Table 250.66.

It's frustrating when teaching a code class and a few inspectors are requiring a larger conductor than what is required.:happysad: