Grounding Electrode Conductor sizing

[hbeery10]

I am installing a new 320 amp single phase service (underground) to a building. The service entrance conductors go into a meterbase and then split into two 200 amp disconnects. I have a ufer ground and also a single ground rod (ground rod was required by the POCO). I had run a #4 from the neutral/ground bond point in the meterbase to the ufer sized per 250.66(B). The inspector failed the inspection because he said I needed a grounding electrode conductor sized per table 250.66 (he wanted me to have a 1/0 GEC). I didn't think the sizing in 250.66(B) had anything to do with the size of the service, just run a #4 regardless of the size of service?

Thanks,
Garth

 

[mopowr steve]

You are right ,

#4 is all that is required to the Ufer
and #6 is all that's required to the rod.
Unless you attached to the waterline via one of these then he would have a point, now you would need that 1/0 if attaching to waterline or structural steel.

I would kindly have him open the book with you and state your case.
I've done it on a couple occasions sometimes I win sometime I learn something.

 

[hbeery10]

You are right ,

#4 is all that is required to the Ufer
and #6 is all that's required to the rod.
Unless you attached to the waterline via one of these then he would have a point, now you would need that 1/0 if attaching to waterline or structural steel.

No metal waterline or structural steel. I get the feeling he sizes everything off of the table in 250.66 and isn't aware of the rest of the section. In the past he has made us run a 1/0 to the two ground rods before in a similar install having no other GE's.

 

[mopowr steve]

I believe that is the case.
And for years this has been a typical mis-understanding/awareness. In years past I too, have followed his misunderstanding also.

 

[infinity]

No metal waterline or structural steel. I get the feeling he sizes everything off of the table in 250.66 and isn't aware of the rest of the section. In the past he has made us run a 1/0 to the two ground rods before in a similar install having no other GE's.

Sounds like he doesn't know much beyond that table. 250.66(B) is pretty clear.

250.66(B) Connections to Concrete-Encased Electrodes. Where the grounding electrode conductor is connected to a single or multiple concrete-encased electrode(s) as permitted in 250.52(A)(3), that portion of the conductor that is the sole connection to the grounding electrode(s) shall not be required to be larger than 4 AWG copper wire.

 

[Knuckle Dragger]

You are right ,

#4 is all that is required to the Ufer
and #6 is all that's required to the rod.
Unless you attached to the waterline via one of these then he would have a point, now you would need that 1/0 if attaching to waterline or structural steel.

Sorry to jump in so late in the conversation but I am dealing with a very similar situation right now .
Are you saying that if the OP ran two sets of parallel 250mcm aluminum conductors (from the one meter), one set to each 200amp main breaker panel. If it went to the metal water main, for an EGC he would have to install a 1/0 instead #4 AWG copper?

 

[hbeery10]

I did not have a metal water pipe to go to so I didn't need to follow the table at all in 250.66. My understanding is that with a metal water pipe you would have to use the table to size the GEC. With parallel conductors you would have to take the total circular mils of both runs and use that total for the 250.66 table.

Aluminum 250 kcmil x2 = 500 kcmil

500 kcmil would need a #2 cu or 1/0 AL.

Sent from my SM-S920L using Tapatalk

 

[Dennis Alwon]

I am installing a new 320 amp single phase service (underground) to a building. The service entrance conductors go into a meterbase and then split into two 200 amp disconnects. I have a ufer ground and also a single ground rod (ground rod was required by the POCO). I had run a #4 from the neutral/ground bond point in the meterbase to the ufer sized per 250.66(B). The inspector failed the inspection because he said I needed a grounding electrode conductor sized per table 250.66 (he wanted me to have a 1/0 GEC). I didn't think the sizing in 250.66(B) had anything to do with the size of the service, just run a #4 regardless of the size of service?

Thanks,
Garth

First off 250.66(B) is clear as you surmised that a concrete encased electrode does not need to be larger than a #4

250.66(B) Connections to Concrete-Encased Electrodes. Where
the grounding electrode conductor is connected to a single
or multiple concrete-encased electrode(s) as permitted in
250.52(A)(3), that portion of the conductor that is the sole
connection to the grounding electrode(s) shall not be required
to be larger than 4 AWG copper wire.

Secondly, Table 250.66 is based on the size of your service conductors as in Note 1. Usually with 2 - 200 amp disconnects you would only need a #2 conductor as the grounding electrode conductor but that would be to other electrodes such as water pipe. You would need to use #2 if you had to bond the water pipes.

Note 1 states that you take the cir mil of the service conductors and size the grounding electrode conductor based on the sum of those conductors. Look at 3/0 copper--167800 x 2 = 335,600 . This is equivalent to 350 KCM. The table states #2 for 350 kcm.

If you had a meter main-- no service conductors then you would use Note 2 and then you would be required to use a 1/0 gec

 

[david]

Note 1 states that you take the cir mil of the service conductors and size the grounding electrode conductor based on the sum of those conductors. Look at 3/0 copper--167800 x 2 = 335,600 . This is equivalent to 350 KCM. The table states #2 for 350 kcm.

"Notes:
1. Where multiple sets of service-entrance conductors are used as permitted in 230.40, Exception No. 2, the equivalent size of the largest service-entrance conductor shall be determined by the largest sum of the areas of the corresponding conductors of each set."

"largest sum of the areas of the corresponding conductors of each set."

The largest sum of the tne cir. mil area of each set is a little different than the sum of the cir mil area of the sets of service entrance conductors