I don’t know how I missed this after all these years. A 1200 amp service fed with 4 runs of 400 kcmil copper. A grounding electrode conductor to the underground water pipe is required to be 3/0 copper per 250.66. However, 250.104 requires a 4/0 copper for metal water piping ran throughout the building. (Table 250.102(C)(1) So, I would require a 4/0 copper grounding electrode conductor. Correct? This size would also include fire sprinkler pipe as well. Correct?
sizing grounding electrode conductor
- Thread starter wyboy
- Start date
- Status
- Location
- New Jersey
- Occupation
- Journeyman Electrician
First you define what the conductor actually is, a GEC is never required to be larger than #3/0. I do not see #4/0 copper in Table 250.102(C)(1) maybe you can elaborate.
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
Is the waterpipe an electrode? If so then I would think you could use 3/0... but that is interesting.. I don't know why they changed that table
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
1600 x .125 = 200 kcm = 4/0
- Location
- New Jersey
- Occupation
- Journeyman Electrician
Are you saying that you're using that table for bonding a water pipe that is not a grounding electrode? Is that connection a supply side bonding jumper? That table as stated in the notes is for:
texie
Senior Member
- Location
- Fort Collins, Colorado
- Occupation
- Electrician, Contractor, Inspector
The GEC only needs to be 3/0 CU as that is the max. for any GEC. The bonding jumper, as you know, does not max out. In your case the bonding jumper works out to 4/0 CU.
Take notice of 250.104(A)(1)(3). This recognizes that this happens.
texie
Senior Member
- Location
- Fort Collins, Colorado
- Occupation
- Electrician, Contractor, Inspector
See 250.104(A)(1)(3)
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
I think the point is that 3/0 is sufficent as an electrode but the same water pipe not connected to the earth would need 4/0. The grounding electrode conductor does bond the water pipe when using it as an electrode but why the need for a larger size when it is bonded.
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
This what that says
Grounding electrode conductor if of sufficient size--
But the grounding electrode conductor is not of sufficient size for a water pipe bond so are you saying 4/0 is needed? That is what I think
- Location
- New Jersey
- Occupation
- Journeyman Electrician
How does the 12.5% apply when that table is only for the MBJ, SSBJ and SBJ?
texie
Senior Member
- Location
- Fort Collins, Colorado
- Occupation
- Electrician, Contractor, Inspector
Let's say that the water pipe electrode is isolated from the interior metallic piping. Then you could use a 3/0 to the pipe electrode but you would need a 4/0 to the interior piping.
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
It appears to say the grounding electrode conductor can be used as the bonding if it is of sufficient size. If the water pipe is an electrode and connected to the interior pipes wouldn't that require 4/0.
texie
Senior Member
- Location
- Fort Collins, Colorado
- Occupation
- Electrician, Contractor, Inspector
Yes, this would be the case in most installs.
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
I believe the water pipe bond is sized by T250.104
- Location
- New Jersey
- Occupation
- Journeyman Electrician
That is correct, I'm just wondering why the note to the table mentions that the term bonding jumper is meant only for the MBJ, SSBJ and SBJ.
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