UFER Ground as sole electrode in larger service sizes

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SouthwestSparky

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Reno, Nevada, USA
Would like to get a clear answer on concrete encased electrodes ( UFER Ground) as the sole electrode in a system.
NEC 250.52 States that you can use a Piece of rebar 20’ or more and minimum of ½” diameter or 20’ of “bare copper conductor not smaller than 4 AWG” as the “Electrode”. This implies that you may need to use a larger wire size but you can not use a smaller one.
NEC 250.66 Has the table for sizing Grounding Electrode conductors. Exception B notes that where the portion of the GEC is connected to a UFER that portion of the conductor that is the sole connection to the UFER shall not be required to be larger than #4 AWG copper.

There are hundreds of examples showing a 200A service with water pipes, ground rods etc as the “Grounding Electrode system”. However, in modern practice we rarely ever have more than the UFER ground on a site as the electrode. However, there are wildly different theories and requirements on what size UFER ground is required. We have local jurisdictions require 1/0 for a 400A service while others require #2. We have seen plans from engineers specify 3/0 for a 1200A service and a few specify 500MCM for a 2000A service.

My understanding is when using a UFER ground you need 20’ of #4 Copper or 1/2” Rebar minimum in the concrete and are not required to have larger than #4 AWG copper between the electrode and the main service no matter what the service size is. Please correct me if I am wrong.


My questions:

Since 250.52 states “not smaller than” are there times where a concrete encased electrode would be required to be larger than #4? If so what would they be?


If the concrete encased electrode is the only electrode in the system does this require that the Grounding equipment conductor be sized per table 250.66 or that the portion between the electrode (UFER) and the service equipment be sized per the table?
 
The sections you are citing are very clear.
250.52 says not smaller than 4AWG that means use 4, you can use larger it you want or is speced.
250.66 (B) says shall not be required to be larger than 4AWG.

I don't know where the confusion is or why anybody would spec a conductor larger than 4AWG for a CCE.
 
Might be questionable if the embedded conductor that is the electrode can be smaller, but IMO you can run a smaller GEC/bonding jumper to rebar if T250.66 allows a smaller GEC. Many run 4 AWG anyway, if you ever upgraded the service/feeder it will still work regardless if you upgraded to 150 amps or 2000 amps.
 
I agree it is very clear. I cannot understand why an engineer would specify something larger unless there was a valid reason, building departments I understand as they are typically handling multiple trades in my area and they go from inspecting drywall to electric and plumbing in the same 40 minutes.
 
I think the confusion is there for the same reason it confuses me... We have situations where we are required to run EGC's that are way larger than a number 4 wire, in raceways etc... yet we only need to bond from the main panel to the ground rod or Ufer with a number four wire. Confuses me, but surely someone knows why and wherefore. My own thought would be that it is fine but in USA you now cannot have a reduced size egc on 14-8 guage wires anymore yet here in UK it is still normal, especially in the UK version of NM-B wire, for the 2.5mm wire to have a 1.5 or 1.0 mm ground wire.

So much to learn so little sticks sometimes.
 
Adamjamma said:
I think the confusion is there for the same reason it confuses me... We have situations where we are required to run EGC's that are way larger than a number 4 wire, in raceways etc... yet we only need to bond from the main panel to the ground rod or Ufer with a number four wire. Confuses me, but surely someone knows why and wherefore. My own thought would be that it is fine but in USA you now cannot have a reduced size egc on 14-8 guage wires anymore yet here in UK it is still normal, especially in the UK version of NM-B wire, for the 2.5mm wire to have a 1.5 or 1.0 mm ground wire.

So much to learn so little sticks sometimes.
Click to expand...
Because EGC and GEC have different functions. A rod or pipe electrode never needs more than 6 AWG copper run to it because the electrode will not dissipate any more energy into the earth than a 6AWG can deliver to it, they just don't have low enough resistance to earth to do that. Same with the CEE, except they do have lower resistance than a rod or pipe but never low enough that more than a 4 AWG is necessary. I don't know who determined this but that is basically why you never need larger than those sizes as the sole connection to said electrodes.
 
Totally agree. Yet we are confronted with this all the time. We work in multiple states and counties and deal with multiple engineers. Below is an excerpt from a county we work in.
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If I'm paying for it the CEE gets a #4 and that's it. I see engineers who get all warm and fuzzy when they run #3/0 to twenty points on the footing.
 
kwired said:
Because EGC and GEC have different functions. A rod or pipe electrode never needs more than 6 AWG copper run to it because the electrode will not dissipate any more energy into the earth than a 6AWG can deliver to it, they just don't have low enough resistance to earth to do that. Same with the CEE, except they do have lower resistance than a rod or pipe but never low enough that more than a 4 AWG is necessary. I don't know who determined this but that is basically why you never need larger than those sizes as the sole connection to said electrodes.
Click to expand...

The energy that a 6 or 4 can dissipate is limited by its impedance - particularly at lightning frequencies. At high frequencies there is little difference between a 6 and 3/0. Plus the ground rod or ufer is limited...probably whats somewhat more important is stabilizing the voltage.

However in the long run, our GEs don't really do that much in a lightning event. If you want lightning protection then a full blown lightning system is needed.

Drive two and go home, or use the Ufer. Our focus should be on bonding.
 
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