Grounding electrode conductor sizing

[wwebb]

Articles 250.66 (A), (B) are causing some confusion in our jurisdiction. These articles state: "that PORTION of the conductor that is the SOLE CONNECTION to the grounding electrode shall not be required to be larger thatn 6 AWG copper wire or 4 AWG aluminum wire".
Particularly in the case of rod electrodes (ground rods), this is a bit confusing. Most think that the grounding electrode conductor from the ground rod to the service must be sized using Table 250.66. Others feel that, no matter the size of the largest ungrounded service-entrance conductor, that, with 250.66 (A) they may only be required to use a 6AWG copper wire for this purpose.
Some consensus would be helpful here in settling this, as I am not quite sure how to justify, properly, this interpretation....for either argument.
Thanks for the assistance.

 

[bob]

Re: Grounding electrode conductor sizing

Read 250.66. It says that the GEC shall be sized according to table 250.66 except as permitted in 250.66(A) thru (C). Ground rods, encased electrodes and ground rings are exceptions the this rule.

 

[roger]

Re: Grounding electrode conductor sizing

Think about what the rod does and what it would carry at this low voltage even if it met 25 ohms.

Now think about the rods capability to discharge a high surge or lightning stroke.

Anything larger than a #6 cu or # 4 Al is a waste of materials

Roger

 

[derwith]

Re: Grounding electrode conductor sizing

Article 250.66 says to use Table 250.66. However there are exceptions. In exception A, you are not required to use anything larger than #6 awg for the conductor going to a ground rod.

 

[wwebb]

Re: Grounding electrode conductor sizing

If it is meant that the entire GEC be sized at #6, then why have the wordings "that portion" and "sole connection"? It seems to imply that either this is for a single ground rod connection only. If multiple rods or supplemental grounding electrodes are tied to the ground rod in addition to the conductor going to the service (ie: "T" type cadweld), would this negate this exception. Or is "that portion" refering to some sort of "tap" to the GEC? This is the wording that has been the source of our debate.

[ October 14, 2004, 12:57 PM: Message edited by: wwebb ]

 

[eprice]

Re: Grounding electrode conductor sizing

I believe the intent is that, if the GEC is run to a ground rod, then a bonding jumper is run from the rod to the water pipe, for example, then the GEC would need to be full sized from table 250.66 and the ground rod exception would not apply. (the bonding jumper to the water pipe would also need to be full sized of course). I guess there is room for the interpretation that, if the GEC runs to a ground rod, then a bonding jumper runs to a second ground rod, the GEC to the first rod would need to be full sized. But I think that would be a stretch, and I don't think that is the intent.

 

[physis]

Re: Grounding electrode conductor sizing

The only sense I can make from 250.66(A) is:

If you have a GEC that continues from a rod, pipe or plate to another electrode, then the GEC only has to be 6 awg up to the rod, pipe or plate. Thereafter it may be required to be larger. (A multidiameter conductor)?

 

[wwebb]

Re: Grounding electrode conductor sizing

keep these comments coming folks. It sounds, so far, like we (here) are not the only ones to find the interpretation of this article.....difficult!
I WONDER WHAT MR. HOLT MAY HAVE TO SAY ON THIS???

[ October 14, 2004, 03:50 PM: Message edited by: wwebb ]

 

[roger]

Re: Grounding electrode conductor sizing

Wweb, I will ask, what would putting a larger conductor on this poor excuse of a GE do?

A ground rod is simply a placebo.

I do know that Mike Holt doesn't put much merit in ground rods. Although not directly addressing this issue, go here and read his comments at the bottom of the page.

Roger

[ October 14, 2004, 04:26 PM: Message edited by: roger ]

 

[wwebb]

Re: Grounding electrode conductor sizing

Roger, I think you're missing the point....I'm not talking about putting more copper in the ground, I'm talking about an adequate path for fault current. If a #6 wire can be used as the sole GEC on a 277/480v 800a service, it makes me feel a little bit uncomfortable....although, I don't think any electrical engineer would EVER design that sort of system.

 

[physis]

Re: Grounding electrode conductor sizing

A ground rod is simply a placebo.

OK, I'll bite. Roger, you got some splainin to do.

 

[iwire]

Re: Grounding electrode conductor sizing

Originally posted by wwebb:
I'm talking about an adequate path for fault current.

What fault current our you talking about?

A ground rod plays no role in fault clearing of the premise wiring system.

Originally posted by wwebb:
If a #6 wire can be used as the sole GEC on a 277/480v 800a service, it makes me feel a little bit uncomfortable....

Lets say you lucky enough to get down to 10 ohms of combined resistance between the rod driven for the service and the grounding electrodes connected to the source.

Now place a ground fault on this rod.

277 volts / 10 ohms = 27.7 amps of current flow on the 6 AWG GEC.

 

[iwire]

Re: Grounding electrode conductor sizing

Originally posted by physis:

A ground rod is simply a placebo.

OK, I'll bite. Roger, you got some splainin to do.

Sam what would you say the ground rod is capable of?

 

[physis]

Re: Grounding electrode conductor sizing

Directing lighting to earth and keeping neutral voltage near equal to earth potential.

 

[physis]

Re: Grounding electrode conductor sizing

Bob, why would you say Roger said a ground rod is simply a placebo?

 

[sandsnow]

Re: Grounding electrode conductor sizing

At one of our recent IAEI chapter meetings the Code Clearing Committee was asked about the 2 ground rod issue and was of the opinion that the conductor from the first rod to the service would have to be per 250-66 and the conductor from the first to the second would be allowed to be #6.

It seems to me that #6 all the way would be fine.

I'd be curious as to other opinions.

 

[roger]

Re: Grounding electrode conductor sizing

Wwebb,

I'm talking about an adequate path for fault current.

this is kind of what I thought you were thinking, and as Iwire points out, fault clearing is not a function of this GE nor is protecting people or animals from shock. This would apply to a 60 amp 240/120 volt service or a multi thousand amp 480/277 volt service.

Sam,

Directing lighting to earth and keeping neutral voltage near equal to earth potential.

"directing lightning to earth" may not be the right term, and I question if a single or multiple rod system does this very well. "Keeping neutral voltage near equal to earth potential" is the only thing this type of a GE is capable of doing at any true level of competence.

Here are a couple of pertinent graphics from Mike Holt, the first one would go with Wwebbs last post and the second shows dangers associated with a ground rod.

Roger

 

[ryan_618]

Re: Grounding electrode conductor sizing

Originally posted by sandsnow:
...the Code Clearing Committee was asked about the 2 ground rod issue and was of the opinion that the conductor from the first rod to the service would have to be per 250-66 and the conductor from the first to the second would be allowed to be #6.

It seems to me that #6 all the way would be fine.

I disagree with the panel and I agree with you.

 

[roger]

Re: Grounding electrode conductor sizing

And I agree with both of you guys.

Roger

 

[derwith]

Re: Grounding electrode conductor sizing

The capability of a ground rod to dissapate the fault current into the earth is limited to what a #6 wire can deliver.