Grounding Electrode Conductor Sizing

[dougjl]

NEC code 250.66 discusses the minimum sizing for the grounding electrode conductors. It shows that the largest size required as 3/0 when the area of the incoming service conductors exceed 1100 kcmil. 250.66(A) shows the minimum size for connecting ground rods, pipe & plates as 6 AWG. 250.66(B) shows the minimum size to be used when connecting to the foundation rebar as no less than 4 AWG.

I have seen several different facilities where all of the grounding of those items is done with bare 4/0 copper. I was curious if this is just a "tradition" or if there was a different code I have missed. I realize that code is calling out the minimum sizes and that nothing prevents me from using larger wire, but the cost of copper being what it is I want to make sure that extra expense has validity.

I have also seen a drawing for a new building construction that shows a 4/0 bare copper cable connecting via cadweld to a ground rod. And then shows a #6 jumper jumping between the 4/0 conductor and the ground rod (also connect via cadweld). That doesn't make sense to me. Is there a code reason for this?

Thanks for any input,
Doug

 

[7anoter4]

NEC art.250.66 is referring to: "that portion of the conductor that is the sole connection to the grounding electrode shall not be required to be larger than 6 awg copper or 4 awg aluminum."
The grounding electrode conductor connecting embedded concrete-encased electrode or grounding rings or similar is not conveying the main fault current and it is more protected from mechanical abuse .The Grounding System conductor -as per IEEE 80-is laid in an open field in a substation and has to support the fault current. In order to protect it from mechanical abuse minimum 2/0 is recommended. See IEEE-80 Annex B[B1]: "Based on this computation, a copper wire as small as size #4 AWG could be used, but due to the mechanical strength and ruggedness requirements, a larger 2/0 AWG stranded conductor with diameter d =0.0105 m (0.414 in) is usually preferred as a minimum"
In a large power station field the Grounding System buried 2-3 feet in the ground usually 4/0 will be the preferred conductor copper cross-section.