GEC sizing question

Archive Public Archive
#1

Originally Posted By: escanlan
This post was automatically imported from our archived forum.


Re: 2003 IRC, Table 3503.1, Note “d”


Is this is a typo in the IRC? The note states:

"Where the sole grounding electrode system is a ground rod or pipe..."

But this does not match the NEC (all versions: 1999, 2002 or 2005, section 250.66(A. The NEC requires the "sole connection" of the GEC to the GE be full size as per NEC Table 250.66 which IRC table E3503.1 was derived from.

The IRC reworded the NEC from "sole connection" to "sole grounding electrode system".

If I'm interpreting this incorrectly I could use straightening out. Also if anyone could explain the technical reason behind the drop in GEC size it would be appreciated.

--
Manny (Emmanuel) Scanlan

Knowledge is power, but sharing knowledge brings peace!

#2

Originally Posted By: Greg Fretwell
This post was automatically imported from our archived forum.


The short answer is a rod is not that good of an electrode so they do not require more than a #6 go to it.


If this is supplimenting a better electrode the GEC going to the better electrode shall be sized by 250.66 and the portion that only serves the rod can be #6. The choice of wording to say this will be up to the code agency writing it.

#3

Originally Posted By: bbadger
This post was automatically imported from our archived forum.


I agree with Greg, their is no way to overload a 6 AWG running to a ground rod, it just does not connect to earth well enough.


A water line on the other hand (assuming a neighborhood with metal water lines) will be bonded multiple times so the GEC from a panel to a water line could be subjected to very high current if a service conductor faults to the panel enclosure.

I do not know anything about the IRC

--
Bob Badger
Electrical Construction & Maintenance
Moderator at ECN

#4

Originally Posted By: escanlan
This post was automatically imported from our archived forum.


Thanks for the info guys!!


Please excuse the follow-up but I was trying to keep the original post short and left out some of what I was a bit confused about.

Reading through the NEC (I use the NEC 2005 Handbook) I was under the impression that the primary connection from the SE to the Grounding Electrode must be sized fully as per NEC Table 250.66. As such if the GEC was run from the SE to the GE (Rod, Pipe or plate as in 250.66(A)) for a 200 Amp Service it would need to be a #4 copper. Then, anything bonded to it would not have to be larger than #6. Also, if the GEC ran to a water pipe first it would be #4 then the bonding from the water pipe to the rod, pipe or plate GE would require no larger than #6. This, I thought, would be the description of the supplemental electrode bonding size requirements and the requirement for the primary connection from SE to primary GE.

There was a current errata to the 2003 IRC that added additional confusion. The errata for IRC E3508.2 seems to specify this but Footnote "d" to Table E3503.1 was not changed in the errata which (at least for me) added a bit more confusion.

Not trying to debate what is written, just trying to properly understand the intention. That is where the NEC Handbook and commentaries included come in handy.

--
Manny (Emmanuel) Scanlan

Knowledge is power, but sharing knowledge brings peace!

#5

Originally Posted By: Greg Fretwell
This post was automatically imported from our archived forum.


If there is no suitable water pipe and the rod(s) was the only electrode the GEC could be #6. You only have to use the #4 if you have a better electrode and then, only to the good electrode.


This is from the handbook


[ Image: http://www.nachi.org/bbsystem/usrimages/I/Image111.jpg ]

#6

Originally Posted By: escanlan
This post was automatically imported from our archived forum.


Quote:
If the grounding electrode conductor from the service equipment was run, for example, to the ground rod first and then to the water pipe, the conductor to the ground rod would also have to be full size, per Table 250.66.


That would indicate that for 200 Amp service the "full size" of the GEC to the ground rod "shall not be less than" #4 Copper or #2 Aluminum. The way the "Note d", in the IRC states it is that the GEC does not have to be larger than #6 if run to a ground rod or pipe.

The wording in NEC, along with the NEC referenced subsections, does not appear to be completely interpreted by NFPA for inclusion into the IRC.

--
Manny (Emmanuel) Scanlan

Knowledge is power, but sharing knowledge brings peace!