# GEC sizing



## aj13 (Oct 12, 2010)

Had an inspector question my grounding. I have 3000A UG service, my GEC is sized per table 250.66 per 250.24(D) at a 3/0. Inspector is telling me I should have used table 250.122 and used 400 MCM, this table relates to Equipment Grounding Conductors not Grounding Electrode Conductors. Any insight would be appreciated.


----------



## 480sparky (Sep 20, 2007)

Inspector has the tables mixed up. 250.66 is the correct one for GEC.

Did he 'just question' it, or fail it?


----------



## NasonElectric (Dec 21, 2010)

480sparky is right on. Unless you are mistaken about what a GEC is. Just don't think the inspector would think you need 400 going to a ground rod or building steal etc.,,, I he did he must be new or just dumb.


----------



## McClary’s Electrical (Feb 21, 2009)

Is the op written correctly? Did you mix up tables? 250.122 would give a smaller wire than 250.66. I'm not following you.


----------



## jwjrw (Jan 14, 2010)

mcclary's electrical said:


> Is the op written correctly? Did you mix up tables? 250.122 would give a smaller wire than 250.66. I'm not following you.




I think he has it right. 

Over 1100 Over 1750 3/0 copper 250Al (250.66)
3000a 400mcm cu 600mcm al (250.122)


----------



## 480sparky (Sep 20, 2007)

NasonElectric said:


> 480sparky is right on. Unless you are mistaken about what a GEC is. Just don't think the inspector would think you need 400 going to a ground rod or building steal etc.,,, I he did he must be new or just dumb.



400 to a *rod*?


----------



## NasonElectric (Dec 21, 2010)

250.122 says for a 3000A service you need a 400 copper or 600 aluminum ground. 250.66 says you need a 3/0. Not sure how you r not following. 250.122 to be smaller than a 3/0 would have to go all the way down to 1000A for copper or 500A in aluminum he states a 3000A service.


----------



## NasonElectric (Dec 21, 2010)

400A to a rod ... thats on bad a%^ acorn.


----------



## jwjrw (Jan 14, 2010)

480sparky said:


> 400 to a *rod*?



I caught that too but thought everyone has his own way of doing things.:001_huh:


----------



## Al13Cu29 (Nov 2, 2010)

NasonElectric said:


> 400A to a rod ... thats on bad a%^ acorn.


:laughing::lol:


----------



## 480sparky (Sep 20, 2007)

NasonElectric said:


> 250.122 says for a 3000A service you need a 400 copper or 600 aluminum ground. 250.66 says you need a 3/0. Not sure how you r not following. 250.122 to be smaller than a 3/0 would have to go all the way down to 1000A for copper or 500A in aluminum he states a 3000A service.



250.122 does not apply. That's for _equipment grounding conductors_.

OP is referring to _grounding electrode conductors_... 250.66. 3/0 CU - 250 Al is the largest you will ever need, even if the service is 1,000,000 amps.


----------



## Dennis Alwon (May 9, 2009)

The op has it correct. 3/0 is the largest GEC that is required no matter how large the service is. 250.122 req. 400kcm for a 3000 amp breaker but that is for EGC. Inspector has been smoking the wacky weed.


----------



## raider1 (Jan 22, 2007)

I agree with the others, a 3/0 is the largest GEC that is required.

Depending on the electrode you may only need a #6 or #4.:thumbsup:

Chris


----------



## amptech (Sep 21, 2007)

raider1 said:


> I agree with the others, a 3/0 is the largest GEC that is required.
> 
> Depending on the electrode you may only need a #6 or #4.:thumbsup:
> 
> Chris


I thought the largest ever required to a rod was #6 cu and #4 cu to a CEE.


----------



## McClary’s Electrical (Feb 21, 2009)

amptech said:


> I thought the largest ever required to a rod was #6 cu and #4 cu to a CEE.


 

That exactly what he meant by saying "depending on the electrode"


----------



## erics37 (May 7, 2009)

amptech said:


> I thought the largest ever required to a rod was #6 cu and #4 cu to a CEE.


Largest required or _smallest permitted_ depending on how you look at it I 'spose :thumbsup:


----------



## aj13 (Oct 12, 2010)

Thanks for the info. And yes he was going to fail the service until I explained the difference between the 2 tables and it passed. I just wanted to make sure I was correct.


----------



## elecpatsfan (Oct 1, 2010)

I was going to mention 250.66(A) but you guys beat me to it


----------

