Not Required To Be Larger

[Francis Vineyard]

How do you size the grounding conductors per 250.64(D)(1) [or 2005 250.64(D)] and (F)(3) [or 2005 250.64©(3)]when using made electrodes; 25066(A) and (B); where none of the other electrodes exist?

In the scenario above the “sole connection” only applies to bonding jumpers?

 

[raider1]

Very good question, the code can be a little vague in this aspect.

Here goes, in regards to 250.64(D)(1) where there are multiple service disconnecting means and one grounding electrode conductor that you will tap off to each disconnect, I would say that the GEC would need to be sized from 250.66 based on the size of the service entrance conductors. This GEC would terminate at the first electrode and then the individual bonding jumpers connecting the other electrodes to the GEC could be sized on 250.66(A) and (B) depending on what electrode the GEC was connected to.

Chris

 

[Francis Vineyard]

Chris thanks for the quick response. As I understand in this scenario the GEC would be size as though the first rod is a metal underground water pipe. But if they had a concrete-encased electrode then the #4 copper would be too small?

 

[raider1]

Chris thanks for the quick response. As I understand in this scenario the GEC would be size as though the first rod is a metal underground water pipe. But if they had a concrete-encased electrode then the #4 copper would be too small?

Because the grounding electrode conductor connects multiple types of electrodes and is not the sole connection it must be sized in accordance to 250.66 (Not (A),(B)or©) So the size would be based on the service entrance conductors.

Now this may require that the GEC be larger than the #4 for the UFER ground but because it also connects ground rods you could not use 250.66(B) and just use a #4.

Hope this helps.

Chris

 

[peach]

This is an example of why the NEC confuses me: If there is one ground rod, 250.66 (A) doesn't require anything bigger than #6 CU ... now, if we drive a second rod (for the same stray voltage.. not a fault - that's what we size EGC for).. we have to upsize the GEC?

doesn't make any sense.

 

[raider1]

This is an example of why the NEC confuses me: If there is one ground rod, 250.66 (A) doesn't require anything bigger than #6 CU ... now, if we drive a second rod (for the same stray voltage.. not a fault - that's what we size EGC for).. we have to upsize the GEC?doesn't make any sense.

Who says the NEC ever makes sense.

Chris

 

[peach]

Amen, brother Raider..

 

[paul hardy]

for those who use the IRC this is from the 06 notice it states that two or more electrodes shall be considered one system then allows that system to have a conductor not larger than a #6.

E3508.3 Rod, pipe and plate electrode requirements.

Where practicable, rod, pipe and plate electrodes shall be embedded below permanent moisture level. Such electrodes shall be free from nonconductive coatings such as paint or enamel. Where more than one such electrode is used, each electrode of one grounding system shall be not less than 6 feet (1829 mm) from any other electrode of another grounding system. [/Two or more grounding electrodes that are effectively bonded together shall be considered as a single grounding electrode system. That portion of a bonding jumper that is the sole connection to a rod, pipe or plate electrode shall not be required to be larger than 6 AWG copper or 4 AWG aluminum wire.

TABLE E3503.1 SERVICE CONDUCTOR AND GROUNDING ELECTRODE CONDUCTOR SIZING

d. Where the sole grounding electrode system is a ground rod or pipe as covered in Section E3508.2, the grounding electrode conductor shall not be required to be larger than 6 AWG copper or 4 AWG aluminum. Where the sole grounding electrode system is the footing steel as covered in Section E3508.1.2, the grounding electrode conductor shall not be required to be larger than 4 AWG copper conductor.

 

[raider1]

for those who use the IRC this is from the 06 notice it states that two or more electrodes shall be considered one system then allows that system to have a conductor not larger than a #6.E3508.3 Rod, pipe and plate electrode requirements.

Where practicable, rod, pipe and plate electrodes shall be embedded below permanent moisture level. Such electrodes shall be free from nonconductive coatings such as paint or enamel. Where more than one such electrode is used, each electrode of one grounding system shall be not less than 6 feet (1829 mm) from any other electrode of another grounding system. [/Two or more grounding electrodes that are effectively bonded together shall be considered as a single grounding electrode system. That portion of a bonding jumper that is the sole connection to a rod, pipe or plate electrode shall not be required to be larger than 6 AWG copper or 4 AWG aluminum wire.

TABLE E3503.1 SERVICE CONDUCTOR AND GROUNDING ELECTRODE CONDUCTOR SIZING

d. Where the sole grounding electrode system is a ground rod or pipe as covered in Section E3508.2, the grounding electrode conductor shall not be required to be larger than 6 AWG copper or 4 AWG aluminum. Where the sole grounding electrode system is the footing steel as covered in Section E3508.1.2, the grounding electrode conductor shall not be required to be larger than 4 AWG copper conductor.

Paul, That section only applies to two or more rods, pipes or plates. It does not apply to a grounding electrode system that is comprised of a concrete encased electrode and a ground rod.

Chris

 

[Francis Vineyard]

My main purpose of this thread was to clarify the difference of “that portion of a bonding jumper that is the sole conductor”, “the sole grounding electrode system” from the “common grounding electrode conductor”.

The IRC covers wiring methods most commonly encountered where each dwelling has its own separately wired service disconnecting means and each with its own “sole grounding electrode conductor” to the grounding electrode system albeit the same grounding electrode system. The confusion is when for expample where the "singular" grounding electrode system serves more than one disconnecting means at a condo or two family dwelling, it is not the "sole" grounding electrode system.

The safety violation occurs when the “common” grounding electrode conductor is sized as a “sole” grounding electrode conductor for two or more service disconnecting means.

Note I choose the words “same” and “singular” instead of “sole”. The ambiguity is the use of the word sole; it is not defined but instructs how it is installed.

In the scope of the IRC invites that electrical systems not specifically covered in these chapters shall comply with the applicable provisions of NFPA 70.

 

[paul hardy]

raider

I understand that I was replying to peaches statment that if two rods were driven that the conductor would need to be sized differently, as long as is is the sole connection to the system it does not need to be larger than #6 but the rest of the system will need to be sized according to the sevice entrance size.

 

[peach]

paul.. the rest of the system is bonding, not grounding.

for a 200 amp house service, #6 is all that's required for the GEC, #4 is required for the water bonding.

For a 2000 amp service, #6 is all that's required for the GEC, 750 MCM may be required for the bonding.

Different purposes. One is stray current (the GEC).. one is fault (EGC).