250.66(B) says that the "portion of the conductor that is the sole connection to the grounding electrode shall not be required to be larger than #4 copper wire"

If I have a 400 amp service and my only grounding electrode is the Ufer, do I need to use #2 copper per the table (250.66)?

No, it "Shall not be required to be larger than #4 copper wire".
The paradox is, if you have metal water pipes in the house, that connection needs to be sized to 250.66, even if you think it might be plastic where it goes into the ground.

Thank You Greg. This is new construction with Pex, and no gas at all. So the Ufer is the only grounding electrode. Our local AHJ seems to think there must be at least one GEC in the system sized to table 250.66, so if there is only one grounding electrode they consider it the "main grounding electrode" and want the GEC sized to the table regardless of the grounding electrode type. They will only allow the #4 to the Ufer as a tap from another GEC sized to table 250.66.

What would that other electrode be?

Your AHJ is not wrong (according to 90-4) but he is certainly confused.

I guess it's easier for me: the EE calls out the GEC system conductors.

As a general principle most AHJ are not going to allow downsizing bonding connections in the GEC System.

So if you have a Ufer using # 2 then that self same #2 is expected to be brought up to the GEC bonding/grounding rail in the Service.

Strictly speaking, a Ufer is a concrete encased electrode. Yet, it is commonplace for 'Ground Ring' sized conductors to be encased in concrete, too. Strict construction of the terms would require Ground Rings to be set bare into the soil, underneath the pour. I never see that.

-------

Out my way, #4 Ufers are explicitly mandated for 200 A Services. No ifs, ands or buts.

-------

Since one is expected to have an UNBROKEN CONDUCTOR RUN from the GEC up into the Service any effort to complicate it by downsizing with an irreverseable ( Cadweld/ultra-compression connector ) connector are entirely uneconomic.

--------

All of which makes me wonder why such brain matter is focused upon shaving that last itsy-bitsy bit of copper out of a job.

To my mind, the very short runs involved with GEC Systems make them no place to concentrate ones energies.

Instead, focus on clean, quick installations. That's where one makes it or breaks it.

I’m not sure I’m following this. Is the inspector saying that a GEC sized per Table 250.66 is required to be run and connected to the #4 CU for the Ufer?
If so, I would think that since 250.66[A] clearly says that portion of the conductor that is the sole connection to the CEE/Ufer only needs to be sized at #4 CU, the #4 from the Ufer should be able to be run to the main service equipment and connected to the neutral bus as is without issue.
Don’t we basically do the same thing with #6 CU and ground rods?

I suspect the inspector is confused because there is no metal water pipe in there.

We are not trying to save copper. What happened was a #4 solid got used to attach to the re bar in the slab before the pour, we were not in the picture yet.

Now we come along with a 400 amp service and the inspector says we need either a #2 to the re bar and if not we need to drive 2 ground rods and attach a #2 to them.

BigB:
Depending on how much time you have on this job, you may just decide to drive the 2 rods & get on.

Or, take the 'good fight'! A conversation with the inspector, book in hand. Or, a conversation with the Chief Inspector, again book in hand.

Here in NJ, you could go further via the Board of Appeals; $150 filing fee, 30-90 days to get on the docket & if you are anything other then a sole proprietor, bring the lawyer.

IMHO, the conversation route is the best shot, & if not helpful...drive the rods.

It's not conceeding defeat, its making the best decission.

Your inspector is just further confirming his confusion about 250.66. At a certain point you should just do what he says and get on with your life. You might prevail in an appeal but I doubt you will win.

It would be a shame not to utilize that ufer. Would a one-shot Cadweld work for that #2 to #4 connection or are those only for rods. I know that Burndy makes the Hylink compression connectors that are listed for grounding, but I’m not sure if they make a #2 CU to #4 CU connector.

The inspector will never forgive you for your being right.

Overwhelmingly, inspectors only accept engineering handed down from higher authorities -- and a contractor is at the wrong end of the food chain.

------

There once was a general forman, a true genius, he was...

He made the mistake of trying to help out green foremen, green superintendents...

The latter NEVER forgave him.

At the end, EVERYONE involved was fired: both genius and greenhorns.

The super ran off the genius -- too much of an intellectual threat...

Then the super blew up the entire job -- running everything 'backwards'...

( He hadn't a CLUE as to where the priorities were. )

This caused ALL of the subs ( that's an astounding achievement ) to lose buckets of money and chronically fail their inspections.

After creating an 'instant legend' -- subs would discuss the horror for many months afterward all over the greater metropolitan area -- he had the guts to request job recommendations from the very contractors he burned for big money. (!)

------

Which is all to say: you can't afford to be right all the time; ESPECIALLY if you are. It drives the other guy crazy.

------

As for the case at hand...

Check to see if the #4 solid GEC is bonded to the re-bar above the grade. This is VERY commonly done. If so, expose it and switch conductors.

We're starting to see epoxy-coated re-bar. It would make for a useless GEC element. The Code is going to have to address this ASAP.

The Code, especially the Handbook, should have a Table of GEC Elements.

Within that table Ufers, Ground Rings, Ground Rods would be spelled out in crystal clear terms.

System elements that are required to be bonded in, if present, should be detailed.

The Grounding Path and the Elements that need to be Bonded to it so as to establish an Equipotential Plane can then be driven home.

And, lastly, some attempt can be made to clean up the difference between grounding and bonding.

( Grounding paths carry residual current ( +/- ) down into the Earth at all times. )

[ Bonding connections establish an equipotential plane for conducting elements -- with voltage potential flowing up and down -- normally, trivially -- with the bonded elements functioning in a Capacitive capacity -- NOT Conductive capacity. That is, they fill up with electro-potential and then bounce it back into the system - - just like a capacitor.]

The GEC into the earth, in contrast, bleeds electro-potential into the planet -- operating as a conductor for that purpose.

In Teslas words...

"The inspector will never forgive you for your being right."

Some of us are human, and have been known to make mis-judgements, bad calls, incorrect fails, being late for dinner, and who knows what else.

Any contractor, foreman, journeyman, apprentice, helper, etc. is always welcome to talk, question, debate, etc.

The Ufer is a required thing these days in Florida, at least around here. If you are using epoxy rebar they would have you dropping in a stick or two of uncoated for the electrode.

As I understand it, through the research done during the development of CEE/Ufer systems, it was determined that conductors larger than #4CU had no verifiable effect on increased ability to clear fault current, so this would seem to indicate that increasing the size of the GEC to the ufer is basically just giving the inspector a warm fuzzy feeling with no actual benefit to anyone.

How to keep the steel from corroding given the chemical exposure and likely levels of electrical current during storms (they have those in Florida)? My guess would be that titanium nitride would work great since it bonds well to steel, resists corrosion well enough for medical implants (unless heated to 800C), and conducts electricity well enough for tiny electrical circuits (unless chilled to near absolute zero) despite being chemically a ceramic. Of course it is expensive.

http://en.wikipedia.org/wiki/Titanium_nitride

They allow the turned up rebar connection inside a wall with a cover over it in most jurisdictions here. That #4 copper pigtail had a bad habit of disappearing, either by job site damage or just theft.

This is a typical Ufer