Properly sizing grounding electrode cond.

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jrob

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In 250.66 it states that the grounding electrode conductor is to be sized according to table 250.66. With the exception certain electrodes. Particularly ground rods. In 250.66 (A) it states that the electrode conductor need not be bigger than #6 copper. Does this apply to all ground rods? For example, would this apply to MDPS' or just subpanels. Looking for some clarification.
 
jrob said:
In 250.66 it states that the grounding electrode conductor is to be sized according to table 250.66. With the exception certain electrodes. Particularly ground rods. In 250.66 (A) it states that the electrode conductor need not be bigger than #6 copper. Does this apply to all ground rods? For example, would this apply to MDPS' or just subpanels. Looking for some clarification.
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I don't understand what you mean by sub panels. No ground rod is required for sub panels. The main service must have 2 ground rods unless you can get 25 ohms with one or use a CEE. The conductor does not need to be any larger than a #6.
 
In the area that I'm working we have MDPS' in one location, and subpanels on the outside of buildings around the site. These subpanels needs need ground rods. From what I understand you don't need to have larger than a number 6 to any ground rod, but my coworked has always gone off of table 250.66 to size his electrode conductor to ground rods. My question is does it make a difference what size the service panel or subpanel is, or is #6 efficient no matter what size.
 
As a rule you're not supposed to ground the neutral on the load side of the service unless the sub panels are in a separate building with a disconnect as outlined in 250.32(A). I would think that 250.66(A) would apply to all ground rods regardless of size. As you can see there are no exceptions written into the code on this matter.
 
jrob said:
In the area that I'm working we have MDPS' in one location, and subpanels on the outside of buildings around the site. These subpanels needs need ground rods. From what I understand you don't need to have larger than a number 6 to any ground rod, but my coworked has always gone off of table 250.66 to size his electrode conductor to ground rods. My question is does it make a difference what size the service panel or subpanel is, or is #6 efficient no matter what size.
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That is for electrodes other then ground rods. Such as metal cold water lines.
 
I'm not grounding the neutral on the subpanel. I'm grounding encloser of the panel to earth, because it is on the outside of a building. I was 99% about the #6 to ground rods, but I was just looking for some other input, because my coworker had a different opinion.
 
jrob said:
I'm not grounding the neutral on the subpanel. I'm grounding encloser of the panel to earth, because it is on the outside of a building. I was 99% about the #6 to ground rods, but I was just looking for some other input, because my coworker had a different opinion.
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agree on the #6 equirement. are you also installing an equipment ground to each panel ?
 
jrob said:
In the area that I'm working we have MDPS' in one location, and subpanels on the outside of buildings around the site. These subpanels needs need ground rods. From what I understand you don't need to have larger than a number 6 to any ground rod, but my coworked has always gone off of table 250.66 to size his electrode conductor to ground rods. My question is does it make a difference what size the service panel or subpanel is, or is #6 efficient no matter what size.
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I realized after I posted this morning and left for work that you may have had sub panels at other buildings. The requirements for the ground rods are the same as for the service ground rods (#6 max). Also, as you stated, you bond the can not the neutral assuming you have an equipment ground.
 
Jrob,

250.66 vs. 250.122 Check the definitions in the NEC handbook.

#6 GEC is for lightning, HV transient and HV fault characteristics.
Always #6, per .66.

The GEC is not for bonding (standard grounding) and EGC, per .122.

That advice helped me differentiate between .122 and .66 tables.

I've always thought that the use of 'grounding' was vague.
Maybe some term like "GECing" and "EGCing" would communicate better.
We even have a forum dedicated to the subject.
NEC is clarifying its use of these kinds of words.

Hope you find this forum useful.
 
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According to our AHJ, We can use a #6 GEC on a 100 amp service, however where it is subject to damage it would have to be mechanically protected (i.e. - running down the side of a building out to the rods). However, if we use a #4 - then we can run it down & out to the rods w/o having to sleeve it in pipe.
 
resistance said:
Couldn't have put it better! :D
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MDP....... L ... .......R
| ....| ..| .. | ...| ...|
| ....| ..| ...| ...| ...|
| ....|--|___|...| ...|
| ....|--------- |___|
|___|
.|
.|
.|<- 3/0
.|
.|_________
.| ............ | Ground
.| ......... ...|
.0 ............ -

h20

Inspector asked why I use 3/0 ! I could only answer, "Well let me show you the drawing".
 
An inspector failed an installation today. It's a 600 amp service for an RV park. We grounded the equipment with a #4awg copper wire to the ground rod. He said we need a 1 ought conductor going to the rod. I'll do what he's asking.
 
gigahertz said:
An inspector failed an installation today. It's a 600 amp service for an RV park. We grounded the equipment with a #4awg copper wire to the ground rod. He said we need a 1 ought conductor going to the rod. I'll do what he's asking.
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I would have asked for code Ref. If he sited a local I would install
a 1/0.Then I would of come home and read all locals to see
if I had made a mistake in my homework.Live,learn,Question everything.
 
Kdawg67 said:
According to our AHJ, We can use a #6 GEC on a 100 amp service, however where it is subject to damage it would have to be mechanically protected (i.e. - running down the side of a building out to the rods). However, if we use a #4 - then we can run it down & out to the rods w/o having to sleeve it in pipe.
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Kdawg,

In Memphis, per the AHJ,
we MUST run a residential GEC (#6 or #4) inside of protection
( like RNMC or EMT).
I guess that simplifies the inspectors job.

Thanks for the comment.
 
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