Does concrete make for a good ground?

[wfopete]

I bought a place that has a tired, old utility pole at which my circuit box is attached too. The pole was leaning badly and loose in the ground. Beneath ground level the pole is a bit rotten but not too bad ;-).

Now I know the right thing to do would be to replace the pole but that would set me back $500 and this is Arkansas and doing that would violate the character of the community.

So my solution is to straighten the pole, which I've done. Next I dug down and out around the base (I've got the pole stabilized and braced) about a foot deep and wide around the pole. I set a concrete forum around the pole which will end up with a concrete base a foot deep, a foot wide and about a foot above ground level surrounding the pole. I figure even if with a rotten base, having the concrete a foot above the pole will keep things in check.

My concern is the top 18"-24" of the grounding rod will get encased in concrete as opposed to soil. I do not know how deep the grounding rod is. So I'm wondering if I am compromising my ground by doing this?

 

[golfnut]

On most new construction here everything is grounded to a piece of rebar stubbed out of the concrete. They claim it is better than a single rod through the concrete and into the soil.

 

[Falcon67]

Google "ufer ground"

 

[NormBourne]

Believe me, a ground/earthing rod is an absolute essential.

Where one sees a connection to concrete re-bars, it is simply a bond, in other words we are earthing the reinforcing mat, within the concrete to the general mass of earth. (CONCRETE IS NOT A GOOD ELECTRICAL CONDUCTOR)

Similarly we always bond gas pipes and water pipes to the electrical earthing system.

Remember that what we are looking for is an electrical connection to the general mass of earth, that is why earthing rods are plated in copper or of stainless steel construction.

I have reservations regarding the support concrete to your pole, it would be an advantage to increase the depth of the concrete, around the base of the pole.

It would be advisable to install a new earth rod clear of the concrete base.

I speak here from experience having been an electrician in excess of 50 years, 35 of those as the director of a mid size electrical contracting business.

 

[wfopete]

I have reservations regarding the support concrete to your pole, it would be an advantage to increase the depth of the concrete, around the base of the pole.

It would be advisable to install a new earth rod clear of the concrete base.

The concrete will be about a foot deep around the pole (beneath ground level). Once I dig beyond a foot in depth I start seeing water coming up. I guess that helps the grounding issue though. Plus I've sunk three eight foot T post along the sides of the utility pole which will be secured to the pole and be anchored with the concrete at the base of the pole. Kind of a poor man's splint I suppose. If the pole needs more help than this it will just have to wait for it's replacement to come along.

As far as a new earth rod; I can do that!

 

[AndyA]

My NEC 2005 book says "An electrode encased by at least 2 inches of concrete, located within and near the bottom of a concrete foundation or footing that is in direct contact with the earth, consisting of at least 20 ft of one or more bare or zinc galvanized or other electrically conductive coated steel reinforcing bars or rods of not less than 1/2 inch in diameter"

Looks like you need 20ft of #4 or bigger rebar to meet code.

The normal 8ft copper coated steel rod is probably the easiest way to go.

 

[Flivver250]

No it doesn't

 

[Kevin C]

The bar is copper plated for corrosion protection. Corroded rods may increase resistance, but the coating is self does not have a signification effect on conductivity (in soil, clean bare steel vs copper would have the same resistance).

The term ufer was mentioned as an example of a design that takes advantage of the conductivity of concrete. Concrete has lower resistance than most soils.

concrete absorbs and retains moisture quickly, but loses it slowly over time. In addition, the composition and pH of concrete is such that it allows ionic transfer, which means that it has available ions to conduct electric currents. Furthermore, the soil around the concrete becomes “doped” by the presence of the concrete. As a result, the pH of the soil rises and consequently reduces what would normally be high-Ohm resistance conditions.

http://www.ashireporter.org/HomeInspection/Articles/New-Life-for-the-Ufer-Ground/1676

Based on that.... The concrete around the upper foot or so of the bar, should reduce the resistance of the bar compared to one that is just driven into the earth.

A second rod that is six feet away from the first would be a good addition. Copper coated ground rods have a life expectancy of about 40 years, soil conditions may reduce that.