When driving two ground rods can I

[qcroanoke]

take 1 #6 and series through the ground rods or do I need to run a #6 to each rod?

 

[xformer]

take 1 #6 and series through the ground rods or do I need to run a #6 to each rod?

Look at 250.50

 

[tkb]

Yes you can. It is done all the time, and code compliant.

 

[Hendrix]

Yes you can. It is done all the time, and code compliant.

And make sure that they are between 6' and 12' apart.

 

[infinity]

You can do it this way as well:

And make sure that they are between 6' and 12' apart.

Why 12'?

 

[tkb]

Here is from the 2008 NECHB

 

[480sparky]

Why 12'?

Yes.......... What's so special about 12'?

 

[brian john]

And make sure that they are between 6' and 12' apart.

6' per code, after that anything goes...250' if that floats your boat.

 

[ptonsparky]

Yes.......... What's so special about 12'?

You're using 6' rods??

I figure the zone of influence is the length of rods installed. 8' rods get 8'of separation. 10' get 10'.

 

[Dennis Alwon]

I have heard the further apart the better. Some engineers feel that it should be twice the length of the ground rod. I also heard 1.5 time the length of the rod. That may be where he is getting the 12' but that is not a limitation at all.

 

[Hendrix]

Yes.......... What's so special about 12'?

I don't know. Must be the Flexril for the pinched nerve in my neck.

 

[480sparky]

You're using 6' rods??

6' rods would be a violation. 250.52(A)(5).

I figure the zone of influence is the length of rods installed. 8' rods get 8'of separation. 10' get 10'.

What is the 'zone of influence'?

 

[ptonsparky]

Basically the area or section of earth that the ground rod uses to pass current. From what I remember it is determined by the length of the rod. 8' rod would have a zone of influence within a 4' radius of the rod. Putting another rod within that region cuts the effectivness of the second.

 

[Hendrix]

I don't know. Must be the Flexril for the pinched nerve in my neck.

I should have said "make sure they are at least 6' apart".:roll:

 

[marti smith]

This is a little tid-bit I found a while back. The illustration would not paste, but heck, your great minds don't need it...

Ground rod spacing. Suppose you drive the first ground rod for a system. If it has a ground resistance of 25 ohms or more, 250.56 of the 2005 NEC requires you to drive a second rod. But many contractors don't bother measuring the ground resistance. They simply plan on driving two rods because doing so will meet the requirements of 250.56, regardless of actual ground resistance. Thus, two-rod installations are common, but are they necessarily correct?
Fig. 2b. Non-overlapping effective resistance areas reduce net resistance.
The Code requires you to space rods at least 6 feet apart [250.53(B)]. However, this spacing is a minimum ? and far from ideal. When using the typical 8-foot or 10-foot ground rod, you get the best results by spacing the rods at least 16 or 20 feet apart, respectively. This is much greater than the Code minimum 6-foot spacing.
Ground rods spaced less than two rod-lengths apart will interfere with each other because their effective resistance areas will overlap (Fig. 2a above). For reference, see IEEE-142 and Soares Book on Grounding. The overlap increases the net resistance of each rod, making the grounding electrode system less effective than if the rods were spaced farther apart (Fig. 2b above).

 

[ptonsparky]

6' rods would be a violation. 250.52(A)(5).

Notice the


What is the 'zone of influence'?

Marti has corrected me. Even have that book, guess I need to read it again.

 

[tom baker]

Paralleling efficency of ground rods is best when they are twice the length apart or 16 ft for 8 ft rods. When driven electrodes are closer than 6ft together, the concentric shells of the earth overlap, and the two rods function as one.

 

[petersonra]

Paralleling efficency of ground rods is best when they are twice the length apart or 16 ft for 8 ft rods. When driven electrodes are closer than 6ft together, the concentric shells of the earth overlap, and the two rods function as one.

And this matters why?

Has anyone ever shown there is any special benefit in general from having a lower earth resistance?

 

[iwire]

Has anyone ever shown there is any special benefit in general from having a lower earth resistance?

I am sure the people who sell grounding electrodes and grounding components could come up with something.:roll:

 

[steve66]

Thus, two-rod installations are common, but are they necessarily correct?

Maybe not the lowest possible ground resistance, but as long as there are 2 rods at least 6' apart, the NEC is satisfied.

IMO, that makes it correct.

Steve