# ground rod



## Speedy Petey (Jan 10, 2007)

I'd have to say none. All you are changing is the amount is GEC that is in the soil.


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## KayJay (Jan 20, 2008)

antonio said:


> if i double the depth of a ground rod how much difference will it make in terms of total earth resistance


When a ground rod is driven down deeper into the earth the resistance is greatly reduced.
Generally, a doubling of the rod length would reduce resistance around 40%.
On the other hand, increasing the rods diameter would not significantly reduce its resistance, as a doubling of the diameter would reduce resistance less than 10%.

Similar statements can be found in most earth/ground resistance test equipment manuals and in the Soares book on grounding.


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## Speedy Petey (Jan 10, 2007)

KayJay said:


> When a ground rod is driven down deeper into the earth the resistance is greatly reduced.
> Generally, a doubling of the rod length would reduce resistance around 40%.


Doubling it's depth, and doubling it's length are two vastly different things.

What are we talking about here?


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## 480sparky (Sep 20, 2007)

Why would you want ot bury any deeper? That would gain absolutely nothing except more work on your part. If the top is below grade, that's as good as it gets.


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## brian john (Mar 11, 2007)

480sparky said:


> Why would you want ot bury any deeper? That would gain absolutely nothing except more work on your part. If the top is below grade, that's as good as it gets.


It depends on soil conditions, specs that may call for a lower ground resistance with limited space for a ground grid therefore the best option is drive deeper.

As noted driving deeper can in some conditions get you into better soil more constant moisture. Then again you can hit rock.


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## 480sparky (Sep 20, 2007)

brian john said:


> .....Then again you can hit rock.


Isn't hitting a rock (one the size of a microwave or larger) pretty much a given? :icon_wink:


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## Speedy Petey (Jan 10, 2007)

480sparky said:


> Isn't hitting a rock (one the size of a microwave or larger) pretty much a given? :icon_wink:


'Round here it is.


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## 480sparky (Sep 20, 2007)

Speedy Petey said:


> 'Round here it is.


I hit one every time. I'm trying to find the requirement for it in Art. 250, but just can't seem to find it.

Maybe I should write a proposal for the '14.:jester:


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## brian john (Mar 11, 2007)

Hitting a rock is one thing hitting one the size of a Volkswagon is another.

When we dug the basement for my house we were suppose to go down 6 feet at 6 feet we hit solid granite. MY neighbor hit granite at 2 feet and had to blast. Needless to say driving ground rods is a hassle.​


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## 480sparky (Sep 20, 2007)

brian john said:


> Hitting a rock is one thing hitting one the size of a Volkswagon is another.​
> 
> 
> When we dug the basement for my house we were suppose to go down 6 feet at 6 feet we hit solid granite. MY neighbor hit granite at 2 feet and had to blast. Needless to say driving ground rods is a hassle.​


If you hit one square, it doesn't matter what size it is. The rod stops.

I installed one last spring that hit a rock and curved the rod so much it started to come back up out of the ground 3 feet away.:blink:


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## Speedy Petey (Jan 10, 2007)

480sparky said:


> I installed one last spring that hit a rock and curved the rod so much it started to come back up out of the ground 3 feet away.:blink:


I've seen that happen! This is the only other time I have heard of it.


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## jrclen (Oct 23, 2007)

I'm lucky. In my location I can usually get the rod down 6 feet just by raising and then pushing it down. Light tapping will take care of the other two feet. One out of 20 will hit a rock and force me to pull it out and move it over a foot. Our ground is like a beach, pure sand.


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## acrwc10 (Jan 28, 2007)

480sparky said:


> If you hit one square, it doesn't matter what size it is. The rod stops.
> 
> I installed one last spring that hit a rock and curved the rod so much it started to come back up out of the ground 3 feet away.:blink:


As long as you already had 5' of it in the ground before it started to come out 3' away you should have been good :whistling2: Or maybe not. 
You can get a coal miners bit for the roto hammer that is 8' or more long. Just up one size on the rod 1/2" bit 5/8" rod :laughing:


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## RePhase277 (Feb 5, 2008)

acrwc10 said:


> As long as you already had 5' of it in the ground before it started to come out 3' away you should have been good :whistling2: Or maybe not.
> You can get a coal miners bit for the roto hammer that is 8' or more long. Just up one size on the rod 1/2" bit 5/8" rod :laughing:


I have often thought it would be nice if the rods all came with a tip and a couple inches of twist. That way, it could be chucked into a hammer drill.


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## leland (Dec 28, 2007)

480sparky said:


> I hit one every time. I'm trying to find the requirement for it in Art. 250, but just can't seem to find it.
> 
> Maybe I should write a proposal for the '14.:jester:


Go for it!:thumbsup::laughing:


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## nick (Feb 14, 2008)

*one rod two rods*



antonio said:


> if i double the depth of a ground rod how much difference will it make in terms of total earth resistance


 Well what they are saying is ground rods do come with threaded tops and can be screwed together one to the other with a ground rod coupling ,and they make a ground rod driver to drive them down increasing the length of the rod and this lowers the resistance to earth . I drive lots of rods and by putting one rod in say its tested at 10 ohms resistance and then screw on another it can cut resistance greatly meaning more than half the resistance not all soil will do that . in florida there is no rocks but on the coast there is this coral stone stuff which is like rock we drive at a angle and in the code you can lay a ground plate in the soil flat if you need too. check it out ? best to yas


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## olduser55 (Jan 16, 2009)

We don't have to much trouble with rocks here. But in Tech school we were doing a service change, had to drive a new ground rod. Drove the 5/8'' rod right through the 1" water main feeding the house. 1 in a billion shot.


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## volty (Jan 14, 2009)

jsnbyrn said:


> We don't have to much trouble with rocks here. But in Tech school we were doing a service change, had to drive a new ground rod. Drove the 5/8'' rod right through the 1" water main feeding the house. 1 in a billion shot.


Bummer! I call before I dig, keep meaning to call before I pound. 

Sometimes dig down to find the gas line if it is close to be sure we miss it. 
811 is the new national Utility Protection Service / call before you dig number.



InPhase277 said:


> I have often thought it would be nice if the rods all came with a tip and a couple inches of twist. That way, it could be chucked into a hammer drill.


I always use a 3/4" spline rotory hammer, much easier than a sledge.


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## 76nemo (Aug 13, 2008)

Speedy Petey said:


> I'd have to say none. All you are changing is the amount is GEC that is in the soil.


 
I thought I remember Mike Holt having two 50' rods driven at his own home and proved it didn't make a darn bit of difference.

That was just one location, obviously better soil would make a difference, but we ARE talking about 8' down here. Wouldn't think doubling it would make any difference in most locations.


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## electricista (Jan 11, 2009)

Just install a few of these at $600 or so apiece. Chemical ground rods. Personal I am a big fan of a CEE.


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## heel600 (Oct 31, 2007)

volty said:


> Bummer! I call before I dig, keep meaning to call before I pound.
> 
> Sometimes dig down to find the gas line if it is close to be sure we miss it.
> 811 is the new national Utility Protection Service / call before you dig number.
> ...


In NJ, they only mark out what they own. It's your water line from the curb box to the house, and your sewer line from the house to the curb.

Only the phone, cable, power and gas


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## Bkessler (Feb 14, 2007)

They 811 numbers are worthless for pounding in a ground rod, If your gas meter is on your left and the street on the right or vice versa, what is a spray paint line in the dirt gonna do for you? Nothing, we all know where the gas line is just be freakin' careful. hand dig if you have to.....don't where nylon cloths that day....... and remember S.D.R......!


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## a-bulb (Feb 13, 2008)

nick said:


> Well what they are saying is ground rods do come with threaded tops and can be screwed together one to the other with a ground rod coupling ,and they make a ground rod driver to drive them down increasing the length of the rod and this lowers the resistance to earth . I drive lots of rods and by putting one rod in say its tested at 10 ohms resistance and then screw on another it can cut resistance greatly meaning more than half the resistance not all soil will do that . in florida there is no rocks but on the coast there is this coral stone stuff which is like rock we drive at a angle and in the code you can lay a ground plate in the soil flat if you need too. check it out ? best to yas


This coral stone ...is it called packed shell also? This crap was hard as a rock but you go inland a little bit the soil gets real sandy and you can almost push the damn thing in by hand. We did have a trick for the packed shell though..take a piece of 1/2" conduit with a fitting to attach it to a water hose-Turn the water on-push the pipe into the ground and watch it eat through the packed shell. done in 10 seconds, it's amazing! then you just drop the rod in the hole and after the next rain fall the hole closes around the pipe. When I first moved to florida one of the other guys saw me busting my ass in that florida sun and said I have something to show you. Best trick of the trade ever. Now I'm back in CT hitting rocks again. The ground rod attachment for the Hilti works great though.


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## shunt trip (Jan 15, 2009)

*ground rods*

It depends on the soil conditions. Ask your local inspector.


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## brian john (Mar 11, 2007)

shunt trip said:


> It depends on the soil conditions. Ask your local inspector.


 
I am serious and not being sarcastic WHY would you ask an inspector.


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## MF Dagger (Dec 24, 2007)

Shunt trip... Did you make that reamer that you have a link for?


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## shunt trip (Jan 15, 2009)

Bryon john 
i'm guessing there is a soil issue. Most inspectors will kick you down some knowledge if special conditions exist,(Local codes) after all it usually comes down to "The local authority having jurisdiction. Nec is the miminum requirement Washington state has its own set of different requirements. Some because of special conditions. I have seen special conditions and worked well with local inspectors just by asking for a definition.

MF DAGGER, yup.


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## jwelectric (Sep 28, 2008)

brian john said:


> I am serious and not being sarcastic WHY would you ask an inspector.


 
Maybe because I am to sorry to find out the answer for myself :001_huh:


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## hardworkingstiff (Jan 22, 2007)

jwelectric said:


> Maybe because I am to sorry to find out the answer for myself :001_huh:


Kind of reminds me of a pitbull. lol


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## brian john (Mar 11, 2007)

I seldom to NEVER look to inspectors for answers, ESPICALLY regarding grounding.


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## Effectively Grounded (Dec 15, 2008)

First, if it was new construction, then a CEE is much easier and a better option. As long as you work things out ahead of time with the GC which many don't do. Plan ahead.

The original question was about resistance and the truth is that it is reduced as you increase depth. The amount of reduction greatly varies due to soil conditions.

You can always drive the 8'rods at a 45 deg angle.

You can always bury the rods horizontally 30" below grade.


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## nicholas (Aug 5, 2010)

*ground rods*



480sparky said:


> I hit one every time. I'm trying to find the requirement for it in Art. 250, but just can't seem to find it.
> 
> Maybe I should write a proposal for the '14.:jester:


drive them at a angle sometimes works


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## 480sparky (Sep 20, 2007)

nicholas said:


> drive them at a angle sometimes works



You'll just hit_ another_ rock.


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## drsparky (Nov 13, 2008)

Old worn out thread alert.


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## McClary’s Electrical (Feb 21, 2009)

nicholas said:


> drive them at a angle sometimes works


 
You "revived" a 2 year old thread for that


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## Loose Neutral (Jun 3, 2009)

Now that it's on. I dont usually carry a drill in my pouch running 3/4 emt. Way easier to carry my screw driver and reamer.


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## Speedy Petey (Jan 10, 2007)

Unless there is a really valid reason for it please let old threads sleep.


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