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Add a #6 copper wire as a grounding electrode conductor from the two ground rods 8 inches apart around the house to the GEC from the panel to the other ground rods. Now the green #10 equipment grounding conductor becomes legitimate in that it ends at a point on the grounding electrode system.
Ignoring the difficulty of running a #6 wire from the double ground rods to the panel....

Suppose there is a strong surge that results in 1000 surge amps to the ground rods at the panel. And suppose that the resistance to earth of those rods is a near miraculous 10 ohms. The potential of the "ground"; at the service panel is 10,000V above 'absolute' earth potential. In general the voltage drop away from a ground rod is in the first 3 feet of the rod [so the second rod spaced 8 inches from the other distant rod is useless]. The distant rods will be far more than 7000V from the "ground" at the service. The neutral at the service (if installed correctly) is connected to the "ground" at the panel. So the power wiring will be over 7000V from the distant rods - not what you want. (If the attic j-box is also connected to the new service panel the j-box ground will be a fraction of 7000V from the power wires.)

But you suggest a #6 wire connecting the distant ground rods to the new ground rods. A surge from lightning is a very short event. As a result it has relatively high frequency current components. As a result the inductance of the wire is more important than the resistance. The IEEE surge guide (link has been provided) has an example with a ground wire from a cable entry protector to the earthing system that is 30 feet long with 10,000V between ends. A larger diameter wire can greatly lower the resistance, but not so much the inductance.

A nearby lightning strike can also result in the 2 sets of ground rods being thousands of volts apart.

Separate earthing systems are a bad idea. You want to combine all the earthing systems into a single system then connect at a common point to that single system. The distant rods should be abandoned and the ground at the attic j-box connected to the new panel (if it is not already connected).

The distant ground rods increase the risk of damage.

There is a table of sizes for GECs that is dependent on the amperage of the electrical system. The maximum GEC required going to ground rods is #6.
I agree. The connection to a ground rod only has to be #6 wire because a rod is a pretty crappy electrode. Ufer grounds only have to be #4. The wire size to connect a metal water service pipe goes up as the size of the electrical service increases.
 

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Discussion Starter · #22 ·
I have decided to cut and pull the wire out from the closely spaced ground rods as it will be difficult to run a wire from the new ground rods to the old due to a patio and landscaping in between. I did also consult a local electrician and he thought this was also a bad idea to use these. I traced the green wire back to one of the bedrooms where two of the outlets had been grounded off of it. This wire had been attached to the ground bar in the panel in the attic when the update was done, so this is now grounded in the new system. The remainder of the wire which I found went to the ground rods had been abandoned after the update.

I have everything I need to get this finished up now. I will be going with #6 solid copper instead of #4 with two 5/8" X 8' ground rods. The rods will be 8 feet apart which will put the second rod just in front of where my phone line comes in so I can ground this also. When I pulled on the ground wire for the phone service it pulled right out of the dirt. I never even found a rod after digging down there! :eek:

The distance to the first ground rod is right about 3-1/2'. It is a straight shot down from the breaker panel with only a very slight curve as it comes down to the ground rod. Hopefully I can get it all put in this morning.

Thanks everyone for the input. It has been a big help.
 
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