Grounding Electrode conductor to rod

[Frederick S.]

I installed a 400 amp service, on a pole, as a temporary installation for some modular buildings. The only grounding electrode is 2 - 5/8 x 8' rods.
In accordance with article250.66 (A), I ran #6 solid copper as the sole grounding electrode conductor.
I was told that this was unacceptable, and that I should use 2/0, as required by Table 250.66, because although it goes to the rod, it is my primary, (not supplemental), grounding electrode conductor.
My contention is that if the conductor is connected to a rod, regardless of primary or supplemental, it is not required to be larger that #6. The rod is not capable of conducting more that 60 amps.
Am I correct?

 

[roger]

You are correct, a GEC to a rod or rods doesn't have to be larger than a # 6 CU regardless of the service size

Roger

 

[LarryFine]

You are correct, a GEC to a rod or rods doesn't have to be larger than a # 6 CU regardless of the service size.

Or whether it's the only electrode. Increasing the conductor beyond #6 would have absolutely zero electrical benefit.

 

[bphgravity]

The rod is not capable of conducting more that 60 amps.
Am I correct?

Try not to think of it like this. For one, don't think of a ground rod as conducting anything. And don't try to compare it to a current-carrying conductor.

Instead, think of the rod as a connector to earth. The rod only has so much surface area and along wth it's surge impedance, needs only a #6 awg CU GEC to peform its function.
That function is to ensure that any ground potential rise that may occur also occurs on the metal parts of the service and premise wiring. This action reduces the potential of hazardous currents flowing among the grounded parts.

 

[Dennis Alwon]

I installed a 400 amp service, on a pole, as a temporary installation for some modular buildings. The only grounding electrode is 2 - 5/8 x 8' rods.
In accordance with article250.66 (A), I ran #6 solid copper as the sole grounding electrode conductor.
I was told that this was unacceptable, and that I should use 2/0, as required by Table 250.66, because although it goes to the rod, it is my primary, (not supplemental), grounding electrode conductor.
My contention is that if the conductor is connected to a rod, regardless of primary or supplemental, it is not required to be larger that #6. The rod is not capable of conducting more that 60 amps.
Am I correct?

Check out art. 250.66(A)

(A) Connections to Rod, Pipe, or Plate Electrodes. Where the grounding electrode conductor is connected to rod, pipe, or plate electrodes as permitted in 250.52(A)(5) or (A)(7), 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 wire or 4 AWG aluminum wire.

T. 250.66 is for the main grounding electrodes such as a metallic water pipe or for bonding the metallic water pipes, building steel etc.

 

[Flex]

Does that mean any ground rod driven, even those for transformers, need only a 6 awg copper ground.

 

[Dennis Alwon]

Does that mean any ground rod driven, even those for transformers, need only a 6 awg copper ground.

Unless an engineer specs it that is all that is required. A larger wire will do no better attached to a rod.

 

[radiopet]

So it brings me to this.....

a.) What if the installation was using the grounding electrode conductor tap allowance of 250.64. Now, if they use ground rods......is the COMMON GROUNDING ELECTRODE for this section allowance supposed to be 6 AWG...or as 250.64 says and size it based on the sum of the circular mill area of the largest ungrounded service conductors and so on if more than one set......yada...yada

So in larry's response......and so in the example I pose above since it is not the sole connection to a ground rod...but actually a connection to the common grounding electrode allowed by 250.64(D)......would you still install a 6 AWG as the common grounding electrode conductor...lol

Lets here what ya say.....lol

FYI- We are assuming MULTIPLE service panels in my example

 

[Dennis Alwon]

Paul I don't believe the ground rod can only conduct as well as a #6 copper wire can. My understanding it does no good to upsize the conductor.

 

[480sparky]

Paul I don't believe the ground rod can only conduct as well as a #6 copper wire can. My understanding it does no good to upsize the conductor.

That's my understanding as well. Even the best 8' rod can only dissapate so much current, and that's less than #6 can carry.

 

[LarryFine]

Paul, the answer is the same for conductors that connect only to driven electrodes.

In fact, that job where we met, the one you did the final on for me (remember the rooftop Sealtites?), the only electrodes were two rods, one original and one I drove.

There were two exterior main breakers to the upstairs aqpartments' ML panels, and two panels downstarirs: one 200a 1-ph MB panel and one small 125a 3-ph ML panel.

The new incoming water main was plastic and there is a rule against bonding the sprinkler system. The entire GES was made of #6 solid copper split-bolted together.

I ran one unbroken length from the downstairs 200a panel to the first rod, and everything else tapped onto that.

 

[radiopet]

lol.....i was only inspecting what was on the list from a previous visit so I can't comment on the other.

So let me get this straight.......please define the term " Sole Connection" .

So lets look at this setup....

 

[don_resqcapt19]

Sole connection....a connection to a single grounding electrode. It doesn't matter how many taps are made off of the GEC....as long as it only goes to a rod, it doesn't have to be larger than #6.

 

[radiopet]

lol....dang you don.....I wanted this to drag on longer....lol

 

[radiopet]

OMG.....yes I remember now Larry....where have you been fella I have not seen you since big guy.

 

[radiopet]

Don,

Hope I did not steal the thread......I was just trying to get as many definitions of "Sole Connection" as possible for an article I am doing that explains 250.64(D) and how it does not apply to specific items of 250.66(A)-(C) and so on. But I then figured I only need one as it would simply drag out the article.

 

[mdshunk]

In the case of Paul's drawing above, I typically make the GEC connect directly to the furthermost panel, and that's one less tap to do. In that case of the example, that would only be two taps instead of three. Not code, obviously, but a good economic installation practice.

 

[radiopet]

mark,
I would agree and it is probably what we see the most in our area also. it also described larry's install listed above and while it is not to the letter of 250.64(D)....I don't believe anyone I have ran into have a problem with it.

My article was trying to show that while 250.64(D) gives a method for sizing the common grounding electrode and so on, that under 250.66(A) the sole connection is still simply the common grounding electode and since it is the sole connection to the ground rods in the example...6 AWG is all that is needed.

While I think it would be nicer if 250.64(D) said that cleaner versus giving the sizing information and then giving 250.66 with a comma after it and refering to sizing....gets students confused sometimes which is the basis for my article....

Anyway...i should have not hijacked the thread.....should have just asked guys to post their definition of "Sole Connection" but Don hit it best right out the gate and so I just figured it was futile to put it in the article.

 

[LarryFine]

Paul, I agree the text wording is less than optimal (In the NEC? Gasp!), but I take it to mean that the driven electrode is the sole electrode on this particular length of GEC.

 

[radiopet]

Yep.....I think what messes up some is that 250.64(D) specifically tried to tell you how to size the common grounding electrode conductor....and then it goes into the circular mils and what not.......then if makes the student TRY to determine what the "SOLE CONNECTION" means in 250.66(A).

Since 250.66 tells you how to size the GEC anyway and then gives you 250.66 (A),(B) and (C)...personally i think 250.64(D) makes it confusing for the student....should just stop right after it says to use 250.66 and be done with it......guess I should have proposed it...lol