Ground Ring: Ground Rod Distance

[qms006]

Is there a min or max distance between ground rods that should be provided when encircling a building with a ground ring?

If, so is there a code that governs this distance?

 

[ivsenroute]

No, only when 2 rods are being used for the electrodes. If you are using the rods to pin down the ground ring the 6' rule would not apply because the ground ring is the electrode, not the rods.

If you are working from a set of drawings, the specs should be found there, otherwise call the engineer that stamped them.

 

[paul]

Ground rods are not required to connect to a ground ring according to the NEC. However, often times engineers add them to the ring. They go off of soil samples and how many then figure they're going to need to get a certain Ohms to ground resistance. I've done phone company buildings designed by the same engineer and depending on the soil the rods have been anywhere from 4' to 10' apart.

Note that these rings I installed were in addition to the two rods for the service.

 

[dereckbc]

Code requirement is 6 feet minimum spacing, but that is far from optimum.

I do a lot of ground ring design builds for Telco and the best advice is minimum spacing of 2 x rod length or further.

You have to play around a bit with the design, the building demensions will dictate the spacing and depth. Typically I place either a standard rod or chemical rod where the GEC will enter the building, and at least hit the 4 corners of the building is spacing allows. Otherwise for a large building like a data center we use 20 foot rods every 40 to 60 feet spacing.

 

[brian john]

I have read and seen spec that call for the spacing to be twice the length of the rod, for optimum performance.

Two 8" rods would be 16" apart, two 10' rods 20" apart.

 

[supermanhicks]

What codes or best practice texts describe the best method for designing s ground ring system? If I have the soil resistivity, how do I know how long the ground rods should be? I know there is some rules in NEC 250 but those are guidelines, like minimum wire should be a #2. How do I know what size wire is appropriate for the application?

 

[ivsenroute]

I occasionally do plan review on prints that specify a ground resistance of less than 2 ohms so it is up to the EC to determine how they want to attain that requirement.

I am suppose to get plans for another cell tower build with the building and all. I am curious as to how this one will be spec'd out. They are normally very heavily grounded.