GEC sizing for Detached Building

[Josuea1990]

So, if you are requiered to establish a grounding electrode system on a detach building because you are bringing feeders to power a remote distribiuton panel for this detach building, and one of your existing electrodes in this building like a water pipe uses 250.66 table to size the GEC. ¿Do you still have to size your GEC based on the service entrance conductors?. Altought the feeders that you are bringing to feed this building are not service conductors? , i mean, they are feeders and they have their own OCPD. How do you do the sizing on this scenario for GEC?

[admin]

Greetings,

I believe I responded to your original question via email. However, I will explain here as well.

When you installed the GEC in a detached structure you would size the GEC based on the conductors feeding the detached structure and not the service conductors in an unrelated structure. The rules in 250.32(A) say the following:

(A) Grounding Electrode System and Grounding Electrode Conductor.
A building(s) or structure(s) supplied by a feeder(s) or branch circuit(s) shall have a grounding electrode system and grounding electrode conductor installed in accordance with Part III of Article 250.

Exception:
A grounding electrode system and grounding electrode conductor shall not be required if only a single branch circuit, including a multiwire branch circuit, supplies the building or structure and the branch circuit includes an equipment grounding conductor for grounding the normally non-current-carrying metal parts of equipment.

If you look at Part III of Article 250, most notably Table 250.66 for sizing GEC you will see the following:

Size of Largest Ungrounded Conductor or Equivalent Area for Parallel Conductors
(AWG/kcmil)

So, in this case, it's simply about the Largest Ungrounded Conductors and not specifically dedicated to the service conductors as feeders are not such conductors but they are indeed “ungrounded” conductors in this application. Keep in mind the allowances in 250.66(A), (B), and (C) also apply as well , where applicable.

Hope this is helpful.

[Josuea1990]

Most certainly you did, thank you very much!
Also, Sir! So 250.52 (A) (5) (a) says: Grounding electrodes of pipe or conduit shall not be smaller than metric designator 21 (trade size 3/4) and, where of steel,shall have the outer surface galvanized or otherwise metal-coated for corrosion protection.
Now it seems to me that the company i work for, look at the underground water pipe wich is normally a copper wich is a 3/4 metal pipe, they see it as the (A) (5) (a) type of electrode and they always run #6 to it and i even have made my numbers because for me that is an (A) (1) type of electrode so i use table 250.66 and come up with a with larger size than #6 but still they run the #6 to it, all the time.
The question is: ¿How dou you distinguish (A) (1) from (A) (5) (a)

[admin]

Well, one is used as an Underground water pipe and one is not. If it's supplies water to the house and it meets the 10' length rule in contact with the earth then its (A)(1).