250.66

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charlie b

charlie b

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OK OK, perhaps I am just being obtuse. I run service conductors from the outdoor transformer to a switchgear inside the building. The N-G bond is inside the switchgear. The service conductors are four sets of 500 MCM copper. I put a ground bar on the wall next to the switchgear. I put two ground rods outside the building. Table 250.66 tells me the wire from the switchgear's internal ground bus to the ground bar on the wall needs to be 3/0 copper. But does 250.66(A) allow me to use only a #6 copper from the ground bar on the wall to the ground rods outside the building? And if I run from the ground bar on the wall to the water service pipe, am I back to a 3/0?
 
The conductor to the rods isn't required to be larger than #6, as you've stated the water pipe is sized according to 250.66 which means a #3/0 in your example. The main bonding jumper would be 12.5% of the 4*500 kcmil.
 
I certainly may be mistaken, but to me that appears to be covered by 250.64(F)(3) {'14} and, IMO, your conductor to your buss from your gear would need to be a 3/0 in this situation.
 
Well, now the plot sickens - no I mean thickens.

From the article that Gus cited, I am tending to believe that,
  • The conductor from the neutral bar inside the switchgear to the ground bar on the wall is properly called a "grounding electrode conductor," but
  • The conductor from the ground bar on the wall to the ground rod outside the building is not properly called a "grounding electrode conductor." Rather, that conductor is properly called a "bonding jumper."
  • If that is true, then 250.66(A) would not apply.
  • Therefore, the conductor from the ground bar on the wall to the ground rod outside the building could not be a #6. It too would have to be 3/0.

What does the membership have to say?
 
I took a closer look at the definition of "grounding electrode conductor." You have a neutral wire coming into the switchgear. It lands on the neutral bus. You run a wire from that point to the ground bar on the wall. That wire meets the definition. But the wire that goes from the ground bar to the ground rod does not. Am I reading this right?
 
To me they are both "grounding electrode conductors", falling under 250.64.
According to 250.66 each would be sized from table 250.66, with a 3/0 maximum and a #6 to the rod per 250.66(A).
 
charlie b said:
I took a closer look at the definition of "grounding electrode conductor." You have a neutral wire coming into the switchgear. It lands on the neutral bus. You run a wire from that point to the ground bar on the wall. That wire meets the definition. But the wire that goes from the ground bar to the ground rod does not. Am I reading this right?
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augie47 said:
To me they are both "grounding electrode conductors", falling under 250.64.
According to 250.66 each would be sized from table 250.66, with a 3/0 maximum and a #6 to the rod per 250.66(A).
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Charlie has a point if we interpret literally. 250.64(F)(3) makes the rod to wall conductors "bonding jumpers" per the Code section itself. Size alleviations under 250.66 subsections do not cover bonding jumpers... only grounding electrode conductors.

I tend to look at GES bonding jumpers that same as "permitted GEC jumpers"... i.e. not subject to the irreversible connection requirement. I think intent has us sizing these "jumpers" no different than GEC's [250.53(C)].
 
charlie b said:
OK OK, perhaps I am just being obtuse. I run service conductors from the outdoor transformer to a switchgear inside the building. The N-G bond is inside the switchgear. The service conductors are four sets of 500 MCM copper. I put a ground bar on the wall next to the switchgear. I put two ground rods outside the building. Table 250.66 tells me the wire from the switchgear's internal ground bus to the ground bar on the wall needs to be 3/0 copper. But does 250.66(A) allow me to use only a #6 copper from the ground bar on the wall to the ground rods outside the building? And if I run from the ground bar on the wall to the water service pipe, am I back to a 3/0?
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all that depends on where you run "the" grounding electrode conductor to, 250.64(F)gives you permission to put the ground bar on the wall. 250.64(F) also gives you permission bond the different electrodes to the bar you placed on the wall.
instead of bonding electrodes to each other.

250.64(f)also gives you permission to connect "the" grounding electrode conductor to that bar instead of to one of the bonded electrodes.

250.64(f) does not mandate "the" grounding electrode conductor be run to the bonding bar.

you still have the option of connecting "the" grounding electrode conductor to any of the electrodes in a properly sized bonded system, for example to the ground rods

Edit: and if you run the grounding electrode conductor to the ground rod it goes without saying as you already know that would effect the bonding size from the rod to the bar
 
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ActionDave said:
I think if you try to make me run 3/0 to a ground rod you are crazy. Even the whacko specs for cell towers don't go larger than #2 and everywhere else I have been #6 to the ground rod was just fine.
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Many plans are designed with 3/0 to the rod. I have heard members mention that more than a few times.
 
electrofelon said:
I am not sure I see the external ground bar as code compliant. What am I missing?
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I am sure you see these all the time. You drill a bunch of holes in a flat bar and mount it on the wall. It becomes a common connection point for anything that needs to find its way to planet Earth. There will be wires running from similar bars in electrical rooms and telecomm rooms throughout the building, all of them tied to the bar in the main electrical room. It is not a substitute for the ground bar in the main panel. Indeed it is not for connection of equipment grounding conductors.

 
The definition of GEC does not start at planet Earth and work back towards the incoming service conductors. It starts at the service neutral, and does one of two things. It either lands on an electrode (the definition of which puts it in contact with dirt) or lands on a "point on the grounding electrode system." If we take that literally, a wire does not get to be called a GEC unless it "shakes hands with" the service neutral. It can't wave "hello" from the end of the hallway; it has to physically touch it. The wire from the ground bar on the wall to the ground rod does not physically touch the service neutral, but rather waves "hello" from a distance. Pardon the silly analogy, but I am trying to understand what is, and what is not, a GEC.

On one side if the discussion there is 250.64(F) and the definition of a GEC. There is also the notion that the wire ("bonding jumper"?) from ground bar to ground rod is separated from the service neutral by another conductor (i.e., "the real GEC").

On the other side of the discussion there is metal-to-metal-to-metal contact all the way from the ground rod to the service neutral. They are essentially the same electrical point. There is also the notion that the GEC and the service neutral are not actually spliced to each other anyway. They are separated by some (small) distance by virtue of being bolted to the same neutral bus bar internal to the main switchboard. So how is this different from their being separated by an intervening wire?
 
ActionDave said:
I think if you try to make me run 3/0 to a ground rod you are crazy.
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This is for a real project, one that has the very unusual circumstance that my client is the electrical contractor. We usually work for the architect, but this time my duty requires me to protect the EC's interests (i.e., consider the EC's costs). So I don't want to tell the EC that he has to use a 3/0 instead of a #6, unless I am certain of the code requirements.

 
charlie b said:
This is for a real project, one that has the very unusual circumstance that my client is the electrical contractor. We usually work for the architect, but this time my duty requires me to protect the EC's interests (i.e., consider the EC's costs). So I don't want to tell the EC that he has to use a 3/0 instead of a #6, unless I am certain of the code requirements.
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On a side note, I haven't seen a water pipe that qualifies as a grounding electrode conductor in at least ten years. And that includes several University and school projects. As such, a conductor sized to carry the current that the water pipe may become energized with is adequate.
 
charlie b said:
This is for a real project, one that has the very unusual circumstance that my client is the electrical contractor. We usually work for the architect, but this time my duty requires me to protect the EC's interests (i.e., consider the EC's costs). So I don't want to tell the EC that he has to use a 3/0 instead of a #6, unless I am certain of the code requirements.
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in application the section treats the bar just the same as you would one of the grounding electrode that are required to be bonded together.
in a grounding electrode system. you can run the grounding electrode conductor to any grounding electrode that is bonded.

just treat the same way if you went to building steel with your grounding electrode conductor than from building steel to a ground rod.

the bonding jumper definitions has not changed in this application.

All the rule says you are permitted to provide a bar to run your bonding to. picture it in a central location in a building instead of close to the service.

if building steel is next to the service you might chose to run "the" grounding electrode to building steel next to the service.

the building steel in the center location to the central bar
 
David, while I do sincerely appreciate your comments (I'll say the same to the rest of you as well), please allow me to say that I am not certain how you stand on my key question. So let me state the key question more clearly. I know I can do all the things that are being described (e.g., put bars on walls and attach wires to building steel). At issue is the size of the wire that connects directly to the ground rod. So here is the question:
  • Is the wire from the ground bar on the wall to the ground rod a "grounding electrode conductor," thus allowing it to be sized at #6, or
  • Is that wire a "bonding jumper," thus requiring it to be sized at 3/0?
 
The answer to that question depends to some extent on whether you have any other electrodes.
If the only electrode is the rod, the GEC starts at the rod and ends at the location of the ground to neutral bond. That conductor must be continuous (With a small exception for bud bar.)
It is not clear to ms that the configuration you describe I'd even compliant regardless of wire size.
Now if you have more than one electrode the wire you describe might be classifiable as a bonding jumper, but only if there is a continuous wire connection from the other electrode to the bonding point, making it the compliant GEC.
 
GoldDigger, please let me ask you to review that comment in light of 250.64(F)(3). I think it allows what I am describing, and it does not seem to me to matter whether there is a single electrode or several electrodes. My reading of that article tells me that the wire from the ground rod to the ground bar on the wall is a bonding jumper, and the wire from the ground bar on the wall to the N-G bond is the GEC.
 
While we are continuing to confuse ourselves over this issue, let me toss in another point of confusion (to me, at least). When 250.66(A) mentions the "portion of the conductor that is the sole connection to the grounding electrode," what does it mean? If I were to weld a wire to a chunk of metal, I should think that the end of the wire that gets welded is the "sole connection" point. :?
 
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