i have a few questions about the grounding system in a house. ok here goes. can anyone tell me about ground rods and where they need to be set and where they come from .basically im asking some one to explain the whole grounding system to me any help would be appreciated. thanks

Jayson - this topic is FAR too complex for anyone to give you an 'in-a-nutshell' explanation on this topic. There are many of us who have studied this subject for years and are still learning everyday. I strongly recommend you buy Mike Holt's "Grounding & Bonding" book on this subject - it is color illustrated, takes you through Art. 250 and is as clearly written as possible for this subject. I think most people come away feeling it is a very understandable and 'user-friendly' text on the subject....$30

Check out and scroll down through this topic, (and art. 250 in a code book) there is some banter in there that gives a fairly straight forward quicky answers. https://www.electrical-contractor.net/ubb/Forum2/HTML/001636.html

Jayson if you really want to understand the grounding electrode system I think you should follow Dana1028s advice.

I participated in that thread that e57 linked to and if you do not have the basics down it may only confuse and discourage you.

We where batting around our own ideas of grounding and bonding and did not necessarily stay within the NEC rules.

Mike Holt's Books are great from what I have seen and it is available here.

https://www.electrical-contractor.net/The_Store/Electrical_Theory1.htm

The Soares Book on Grounding is also excellent you can get it on-line, but it should be available at a local large bookstore.

http://www.iaei.org/products/books_02soares.htm

Another option is to look at part III of article 250 and ask us specific questions about the grounding electrode system.

We will all be glad to help but you need to focus the question a little more.

Bob

well i guess what i meant to ask was how many ground rods do u need .like u take a ground wire from the ground bar to a rod in the earth right ? can any one help me with this?
thanks for your help

Jayson,

You need two ground rods set at least 6 feet apart. You could get by with one, but you would have to perform a test that takes time and a fairly expensive piece of equipment. Trouble is, there are very few places in this country where one ground rod would pass the test, so you'll likely end up pounding in the second rod anyhow.

Jayson, go to the link below and progress through the tutorial for a good explanation.
http://www.leminstruments.com/grounding_tutorial/html/

Roger

I understand NEC says 6 feet minimum between ground rods. I attended a grounding seminar where we were told that rods should be 2X rod length apart. Right now I don't remember the term for why 2X is best but it had to do with dissipation.

They call it "the well of influence" and it is a circle the size of the rod depth as a radius. If you have 2 sharing the same well they are only getting the benefit of one rod. Someone decided that a 2 foot overlap on an 8' radius was the point where you were losing enough grounding ability that you should stop the bleeding and they made that the minimum.
The reason we get the pitch in seminars is for those times when we are not trying to do the "minimum" and we are driving deeper rods. At that point you also want to spread out accordingly. Using the same logic the minimum distance should be 75% of rod length, up to 200% when the wells don't touch.
When you are really serious about grounding you will be running several of these rods in a circle with a ground ring between them and long "radials" back to the center of your grounding system, usually a radio tower with a Ufer ground in the radio shack. The radials will also extend out from the ring quite a ways to make your ground plane bigger.
The only other thing I have worked with that gets grounded like that is a toll plaza.

[This message has been edited by gfretwell (edited 09-16-2004).]

gfretwell,

Thanks for clarifying the 'well of influence'.

thanks for all the help

The only other thing I have worked with that gets grounded like that is a toll plaza.

Why on earth would a toll plaza require a ground system??

-Hal

On a flat road, in a flat area, it might be the tallest thing around. (I would assume)

That is exactly it. Toll plazas tend to be lightning magnets since they are usually the only structure for miles around. These days they are also stuffed with electronics so grounding and surge protection is very important.
I was also surprised at how bad the traffic pounds the roadway. Ductbanks are 4x4 foot solid reinforced concrete and 5 or 6 feet below the roadbed. I did MM99 on Fla I-75 and it was an education.
Ever notice the blast of cold air at a toll booth? They use 100% fresh air makeup in the booth, sucking fresh air from the other side of the plaza buildings.