Sizing the GEC

[TimNY]

It would hardly be worth coming to work if I never learned anything.

NY Residential Code Table E3503.1 footnote d states in part, "Where the sole grounding electrode system is the footing steel as covered in Section E3508.1.2, the grounding electrode conductor shall not be required to be larger than 4 AWG copper conductor"

Situation here is 300A service, two sets of 2/0.

Regarding footnote d, the CEE is not the sole system for this residence, as a metal underground water pipe will also be bonded and the local POCO requires rod electrodes. Therefore #2 Cu required per E3508.1.2.

However, NEC 2008 250.66(B) states that the portion of the GEC that is solely connected to the CEE need only be #4. So if individual GECs were run per 250.64(D)(2), the conductor to the CEE would only need to be #4.

I'm assuming it's just poor wording in the NY Code (and probably IRC)?

Also, electrician states he is running #4 to the metal underground water pipe; I see no exception allowing anything less that the #2 required by the tables.

Not an electrical inspector... just the guy who signs the C.O.'s and tries to keep everybody compliant.

Tim

 

[Dennis]

Basically if the #4 going to the concrete encased electrode starts at the service and goes to the rebar without continuing on to other electrodes then a #4 is all that is required no matter what the service size is unless the plans call for something larger. It does not mean if there are more than one electrode for the building. Think of it this way if the service requires a #2 grounding electrode conductor and you run #4 to the rebar then you cannot run #2 from the rebar to the water pipes. In that case the rebar is not the sole connection and a #2 would be needed. Hope that helps

 

[Francis Vineyard]

E3610.1 Depends "where electrodes are connected together to a common electrode conductor, the largest required size of the conductors will dictate the size of the common conductor. For example if a 6 AWG conductor ran from the service to a ground rod and a 4 AWG conductor was required to connect the ground rod to the CEE, the 6 AWG conductor would have to be upsized to a 4 AWG."

 

[TimNY]

Thank you Dennis and Francis. Without having referenced the NEC, I would have misconstrued the footnote.

It would seem that I was at least partially correct; the water main would need a #2 whereas the electrician stated he would use #4. #4 to the CEE is ok as long as they aren't going to use a bonding jumper to the water main from the CEE.

CEE's are a constant issue here. It seems I am the only one who attempts to enforce it. Most electricians have never installed one until they meet me. The electrical inspectors are getting on board, but we started from "you don't need it if you have rod electrodes". The electrician today was sizing it per 250.122.

Thanks again,

Tim

 

[Dennis]

I am amazed that licensed electricians don't know the difference between 250.66 and 250.122. I see that alot.