Sizing Grounding Electrode Bonding Jumper

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Jim_SWFL

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A potential contractor raised a question about a design regarding sizing of grounding electrode conductors

Design in question consists of a 5000A service entrance main, with its neutral bus bonded to a building main ground bus via a #3/0 grounding electrode conductor, sized per table 250.66.

The main ground bus is to be bonded to:

-main water supply pipe via #3/0 (sized per table 250.66), and
-building rebar via #4 (max size required per 250.66(B)
-triad ground via #6 (see below)

My interpretation of 250.53(D)(2), is that using a water pipe as a grounding electrode, requires a supplemental electrode. This supplemental electrode can be the building structural metal (covered by bonding the rebar) or a ground rod. I believe this #6 is permitted as the maximum size per 250.53(E), and possibly 250.66(A).

The contractor is suggesting the triad needs to be tied together using #3/0 all the way to the building main bus bar to carry fault current. I contest that it is a waste of materials and labor, and isn't required by code, and isn't the intended or designed path of fault current which would be via the grounded conductor back to the utility.

I'm obviously biased by my own position, but I'd like some input, especially if my interpretations of the code are incorrect, or if I'm designing something that would be unsafe.

:thumbsup: or :thumbsdown:

-Jim
 
You must follow 250.66 for all bonding and connections to grounding electrode conductor's. The exception is the wire to a ground rod, ground ring or a concrete encased electrode. So yes you can go from the rod to the panel with a #6 but you cannot continue on with 3/0. The rod would be a sole connection and all the steel beams and water pipes would be 3/0 back to the panel. Of course, you can use a bonding jumper from the water pipe to the steel since it is connected with the 3/0
 
Jim_SWFL said:
My interpretation of 250.53(D)(2), is that using a water pipe as a grounding electrode, requires a supplemental electrode. This supplemental electrode can be the building structural metal (covered by bonding the rebar) or a ground rod. I believe this #6 is permitted as the maximum size per 250.53(E), and possibly 250.66(A).
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You are correct but the CEE or the rods would have been enough without any other supplemental electrodes but then again all electrodes present need to be used

Jim_SWFL said:
The contractor is suggesting the triad needs to be tied together using #3/0 all the way to the building main bus bar to carry fault current. I contest that it is a waste of materials and labor, and isn't required by code, and isn't the intended or designed path of fault current which would be via the grounded conductor back to the utility.
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The contractor needs to do some refreshing of code and theory.

Jim_SWFL said:
I'm obviously biased by my own position, but I'd like some input, especially if my interpretations of the code are incorrect, or if I'm designing something that would be unsafe.
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Your design is fine.

Roger
 
Perhaps the contractor was thinking if you start from the panel to the ground rod and continue on from there, then the 3/0 is required to the rod. Only when the ground rod is the sole connection can a #6 be used.
 
Dennis Alwon said:
Perhaps the contractor was thinking if you start from the panel to the ground rod and continue on from there, then the 3/0 is required to the rod. Only when the ground rod is the sole connection can a #6 be used.
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What if the service only required a #6 GEC to the other electrodes?
 
infinity said:
What if the service only required a #6 GEC to the other electrodes?
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Are you all trying to give the new guy a hard time? :D

Well that is a different story but technically before the 2014 it was not compliant but so damncrazy yankee wrote a proposal that got accepted. He added a (s) and that covered it. I think

250.66(A) Connections to a Rod, Pipe, or Plate Electrode(s).
Where the grounding electrode conductor is connected to
a single or multiple rod, pipe, or plate electrode(s), or any
combination thereof, as permitted in 250.52(A)(5) or (A)(7),
that portion of the conductor that is the sole connection to the
grounding electrode(s) shall not be required to be larger than
6 AWG copper wire or 4 AWG aluminum wire.
Click to expand...
 
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Dennis Alwon said:
Are you all trying to give the new guy a hard time? :D

Well that is a different story but technically before the 2014 it was not compliant but so damncrazyyankee wrote a proposal that got accepted. He added a (s) and that covered it. I think
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I thought it was some damn Yankee desertin' Reb', now a Carolina transplant. :happyyes:
 
Jim_SWFL said:
...Design in question consists of a 5000A service entrance main, with its neutral bus bonded to a building main ground bus via a #3/0 grounding electrode conductor, sized per table 250.66. ...
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The only conductor permitted to bond a service neutral and grounding buses is called the Main Bonding Jumper (MBJ).
 
Dennis Alwon said:
Perhaps the contractor was thinking if you start from the panel to the ground rod and continue on from there, then the 3/0 is required to the rod. Only when the ground rod is the sole connection can a #6 be used.
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If the GEC connects any electrode other than rod, pipe, or plate after the rod(s), pipe(s), or plate(s), the GEC to the rod(s), pipe(s), or plate(s) must be sized per Table 250.66. Right? :D
 
Smart $ said:
If the GEC connects any electrode other than rod, pipe, or plate after the rod(s), pipe(s), or plate(s), the GEC to the rod(s), pipe(s), or plate(s) must be sized per Table 250.66. Right? :D
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I think that we all think so, and I for one wish that they had said that to be size bounded the GEC would have to connect to rod(s) only rather than being the only connection to the rod.

Although on further thought, it does seem that a GEC (or jumper) that connects to first one rod and then on to another probably should be bounded at #4 instead of #6, since it could be carrying twice the current that a single rod would see. (Assuming, of course, that the current is limited by the rod to earth resistance.)
 
GoldDigger said:
I think that we all think so, and I for one wish that they had said that to be size bounded the GEC would have to connect to rod(s) only rather than being the only connection to the rod.

Although on further thought, it does seem that a GEC (or jumper) that connects to first one rod and then on to another probably should be bounded at #4 instead of #6, since it could be carrying twice the current that a single rod would see. (Assuming, of course, that the current is limited by the rod to earth resistance.)
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Prior to 2014, I always thought we had to use a Table-sized GEC to a rod, pipe, or plate if other electrodes were jumpered to it (i.e. the rod, pipe, or plate is not the sole electrode connected). Now we can connect a whole gaggle of 'em and only have to use #6.

Damn that yankee deserter done went and messed with my mind. :rant:
 
A MBJ for a 5000 amp service would be bigger than #3/0. It would need to 12.5% of the total circular mil area of the SEC's. {250.102(C)}

Are you using an external ground bus mounted somewhere in the room where all of the GEC's and bonding jumpers connect to it?
 
Jim_SWFL said:
You are referring to the Main Bonding Jumper, that would normally be inside the service equipment, and sized by a different table, right?
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Not "normally". The MBJ is required to be inside the Service Disconnecting Means (SDM) enclosure of all grounded services.

If the grounding bus you are referring to is as Rob (infinity) describes, that is not the grounding bus of the SDM. It is a grounding electrode conductor bus permitted under the rules for more than one SDM enclosure. It is a commonplace "fixture" in industrial electrical rooms... some commercial. What you have between that bus and the SDM enclosure is called a GEC tap. See 250.62(D).
 
Smart $ said:
Not "normally". The MBJ is required to be inside the Service Disconnecting Means (SDM) enclosure of all grounded services.

If the grounding bus you are referring to is as Rob (infinity) describes, that is not the grounding bus of the SDM. It is a grounding electrode conductor bus permitted under the rules for more than one SDM enclosure. It is a commonplace "fixture" in industrial electrical rooms... some commercial. What you have between that bus and the SDM enclosure is called a GEC tap. See 250.62(D).
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Sorry, the "normally" was my error.

I thought in the my first post I mentioned a external ground bar (bus) being part of the design, and specifically had a question regarding the ground electrode conductor from the SDM (5000A) to the bus bar, and then a GEC or bonding jumper from that bus bar to a ground rod via #6.
 
Jim_SWFL said:
Sorry, the "normally" was my error.

I thought in the my first post I mentioned a external ground bar (bus) being part of the design, and specifically had a question regarding the ground electrode conductor from the SDM (5000A) to the bus bar, and then a GEC or bonding jumper from that bus bar to a ground rod via #6.
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As previously mentioned, the conductor from the SDM to the bus bar to is a grounding electrode conductor tap under 250.62(D).

On the other, you specifically mentioned a "triad". That is not Code terminology and there is no Code equivalent. Under Code, a triad is simply considered three ground rods.

Under 2014 edition of 250.66(A), a #6 GEC to the "triad" is all that is required. Under 2011 and prior Code, the same conductor can be interpreted as requiring a full-sized GEC per Table 250.66. Some will say the 2014 Code provides the clarification that #6 is all that is needed. Only your AHJ can tell you for certain.
 
I believe you meant 250.64(D). If so, I agree that this section covers my arrangement.

This would be under the 2011 code, and I agree with your interpretation. We haven't had an AHJ push back on this, only this one contractor, and after looking at his question, I thought it merited consideration to make sure we weren't just following a habit.
 
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