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Grounding Electrode Conductor Sizing

Grounding Electrode Conductor Sizing

Grounding Electrode Conductor Sizing

(OP)
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

RE: Grounding Electrode Conductor Sizing

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.
 

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