Hi,
I figure the Subject of this message will make a few people scratch their head!
If I place two ground rods 6 feet apart but hit bedrock with the second rod and it is in a 2 foot deep trench which way can i bend the rod? Towards the first or away from the first.

I got it down about 4 feet and it would not go any further.

thanks for any replies or comments..

-regards

Greg

If you're hitting solid rock, I would think you are screwed either way. I would be willing to bet that the parralleling efficiency would be better if they were angled away from each other, but I would also be willing to bet that you would not get 25 Ohms, even if you drove a half dozen of them!

Hi,
The firts rod drove in all the way, the second rod located 6 feet away went down 4' the stopped the trench was 2' deep.

Once it is backfilled isnt this in compliance?

-regards

Greg

I had a similar situation, however I could get neither rod to go more tham 3 feet anywhere on the property. I was using a Bosch demolition hammer with grd rod attachment. I finally pulled them both out (by twisting them with a pipe wrench) and drove them at a 45 degree angle. They went to the bedrock then slid along on top of it. The inspector didn't even question it.

Mustang,

I don't believe that you are permitted to bend the rod, but I believe that you are fine if you bury the _entire_ rod horizontally at a depth of 2 feet.

Where does this trench extend? Have you considered using a ground ring instead of rods?

-Jon

Winnie,
Could you explain further? Why would a rod have to be straight?

mustang's right. Now I'm scratching my head

Bend the rod away from the first.
The NEC only requires 8 feet of rod in contact with the earth, six feet apart.
If you are concerned with the rod's length, then add a third rod in a triangular pattern.

The trench would have to be at least 2.5 ft deep. The section only talks about driving the rod to a depth of 8 ft, or where bedrock is encountered, buried in a trench. can't see where they talk about bending it, other than having 8 ft in contact with the soil.

See 250.53(G)

If you hit bedrock you are allowed to drive at up to a 45 degree angle. If you still hit bedrock at a 45 degree angle you then can bury it in a trench that is at least 30" deep.

You may not bend the rod unless its more than 8' long. You must use connectors that are rated for direct burrial.

You need to make sure that at any point the 2 ground rods are at least 6' away.

I was bored and wanted to try out my MSPaint skills

my electrical inspector allows us, if there is a trench already dug to just lay the rods down in the trench, not even driving them in the dirt..makes it nice and easy that way.. trench gets filled and taa daa your done

and are you driving these straight in?? I try to drive them in on a steep angle makes it alot easier. using a hammer drill

Have you tried a 50lbs demo hammer? Just because you hit rock doesn't mean you cant drive through it.

If you are going to bury the grounding electrode, you have to make sure that the dirt being back filled is compacted. Otherwise it is not making a good contact with the earth.
When a rod is driven it is going in with some resistance, which means the earth is hugging the rod snugley, in turn good contact with the earth.

Hi,
Thanks for all the replies.

So then there is a boundry between the two ground clamps? I never realized that you could NOT bend a ground rod less than 10 feet long.

The entire rod has to be between 0-45 degrees vertical or at a right angle to the trench ONLY?

I think I have case 2 but the rod is aiming towards the first.

One ground rod is down 8 feet, the second is six feet away and down 4 feet and then bent on a 45 (or so) in a 24 inch trench.

It sounds like I need to drive another in a different location to see if I can get it down 8 feet.

I was hoping to be able to just keep what I have but if it's not right it's not right.

The distance can be greater than 6 feet can't it?

How would I make a ground ring work?

-regards

Greg

[This message has been edited by mustangelectric (edited 12-12-2004).]

Mustang,

I just re-read the code section on grounding electrodes. I strongly recommend that you do so rather than depend upon 'second hand' information.

While I am sure that I remember seeing that you cannot bend the electrode, I see nothing that says you can't bend the electrode. 250.53(G) describes 1) 2) and 3) of the pictures above, and requires 8ft of length in contact with the soil, but nothing about bending. I found a _Canadian_ code reference where they required driving the rod vertically and then bending, rather than driving at an angle. Go figure , different laws, different code bodies.

The _electrodes_ (not just the clamps) need to be at least 6 feet apart. They can be farther apart.

A ground ring is a loop of bare copper wire, at least 2ga, and at least 20 feet long, which circles the entire structure, buried at a depth of 30 inches or greater.

-Jon

I misunderstood what you originally said Greg. I thought you meant you had the ground rod laying horizontally in the trench at 24" and were bending it up to make connection above ground. Which would mean you only had 5 1/2'ish feet horizontal.

What you actually have is a cross between 1 and 2 in my diagram right? I don't see anywhere that specifically prohibits that.

The optimal distance between electrodes is the length of the buried electrode. That is, if you are using 8' ground rods, they should be buried 8' apart. You can think of a ground rod as being surrounded by shells of earth, the more earth around the ground rod - the less resistance seen. When you have two ground rods, you want to keep these shells from overlapping and research has shown that the effective area of the shell is proportional to the length of the ground rod. As to why the code book allows us to go as close as 6', I don't know. BTW, I have never seen anything that would allow us to bend a ground rod. It seems that that would create a high resistance spot on the electode.

Laura J

To add some more info to Laura's post, check out this link.
http://www.leminstruments.com/grounding_tutorial/html/

Scroll down through the tutorial.

Roger

Hi,
Thanks for the replies. Where is it in the code that says a ground rod can not be bent?

I have seen a lot that were bent.

Whats the difference in bending one and laying it horizontal in a trench?

I do not see the difference electrically what position the rod is in when in contact with the earth at a prescribed depth.

They make ground rods up to 20 feet I think.

What is the largest size ground rod?

-regards

Greg

They make threaded ground rod segments that can be screwed together, pretty much as long as you can drive them. 40' rods are not unusual here in "sand" country.