600 amp service grounding electrode conductor sizing

[stew]

for a 600 amp service fed with 2 each 500 mcm al conductors table 250.66 calls for a gec size of 2/0 copper. The confusing part is that 250.66(A) says that the portion of the conductor that is the sole connection to grounding electrode is not required to be larger than 6 cu. can anyone explain this a bit further to clear up my muddied mind?

 

[iwire]

Re: 600 amp service grounding electrode conductor sizing

The ground rod can not "connect" to the earth enough to need more than a 6 AWG.

The GEC to a common metal water piping system may have to take the full fault current of the POCO transformer.

 

[hassaf]

Re: 600 amp service grounding electrode conductor sizing

the GEC is sized using table 250.66 based on largest service entrance conductors.

But, for sizing the GEC to a ground rod, then you use 250.66(A). See also 250.52(A)(5)(b).

If you're using Concrete-encased electrode (UFER) then, GEC not required to be bigger than #4, 250.66(B). See also 250.52(A)(3).

If you're using a ground plate as your grounding electrode, which is a 1/4" thick with 2 sq.ft area, then the grounding electorde conductor to that is not required to be more than #6.

All other electrode systems, the GEC are sized per table 205.66.

So, each different electrode seems to have a different way of sizing the GEC to it.

 

[stew]

Re: 600 amp service grounding electrode conductor sizing

Iwire this is an outside pole mounted service that will have only 2 driven ground rods for the ground electrode system. I guess where I am confused is if I run a #4 cu from the ground in the panel to the electrodes what is the 2/0 going to terminate to?

 

[don_resqcapt19]

Re: 600 amp service grounding electrode conductor sizing

Stew,
If the rods are the only grounding electordes, there is no need for 2/0. The GEC can be #6.
Don

 

[stew]

Re: 600 amp service grounding electrode conductor sizing

Don Thats what I thought but I had an inspector redline my 4cu and insert the 2/0 from the table. I believe he is wrong but I may just have to use 2/0 if he wont budge.

 

[dereckbc]

Re: 600 amp service grounding electrode conductor sizing

Stew, the inspector is wrong. But on the other hand a 2/0 will not hurt anything other than your bottom line.

 

[electricmanscott]

Re: 600 amp service grounding electrode conductor sizing

Stew show him 250.66 A. #6 AWG is all you need.

 

[ryan_618]

Re: 600 amp service grounding electrode conductor sizing

Originally posted by stew:
Don Thats what I thought but I had an inspector redline my 4cu and insert the 2/0 from the table.

It sounds to me like your inspector is practicing unlicensed engineering. Did you give your consent to have the design altered? Is the inspector now taking the position of engineer of record?

After you show him 250.66(A), tell him to leave the design the h*ll alone or he can talk to your attorney. Have a nice day.

 

[stew]

Re: 600 amp service grounding electrode conductor sizing

By golly with all this support Im gonna still use my #4 cu!!!!

 

[peter d]

Re: 600 amp service grounding electrode conductor sizing

Stew, why are you using #4? I assume this is so you don't have to protect the GEC with conduit?

 

[luke warmwater]

Re: 600 amp service grounding electrode conductor sizing

Originally posted by peter d:
Stew, why are you using #4? I assume this is so you don't have to protect the GEC with conduit?

I asked this question in the old forum.

I personally think that alot of people get the tables confused (not necessarily Stew in this case).

It could be the protection issue, although I just don't think that in alot of cases it is.

It could be that is what is on the truck and it is easier to just stock one size wire. (I think this is much more the case.)

I also think that it is possible that alot of guys are just told from the beginning to use #4 and that's what's in their head. We've all been there at one point, where we were taught to do something and it actually was beyond CODE, but we didn't know until later. Sometimes years...

 

[peter d]

Re: 600 amp service grounding electrode conductor sizing

Todd, I think you are right on. Most everyone in my area uses #4 for the GEC (200 amp serivces). Unfortunately, I also hear a lot of "The inpsector told me to do it that way."

[ June 03, 2004, 05:17 PM: Message edited by: peter d ]

 

[stew]

Re: 600 amp service grounding electrode conductor sizing

protection is exactly the reason I always use #4 and I never seem to get a gripe from an inspector.In addition when you have a 2/0 or 3/0 cu or 4/0 al for say a 200 amp service the bonding jumper on the service side needs to be #4 anyway. Simplicity of stock on the truck also.

[ June 04, 2004, 12:13 AM: Message edited by: stew ]