Ground rods

[Tom Horne]

Bud A true Ufer ground is constructed of half inch or larger rebar installed in the entire foundation floor and footing. Each cross point on the rebar is double tied. A piece of rebar is turned up out of the form work at the appropriate place to make it accessible for grounding after the pour. Herbert G. Ufer developed this grounding technique to protect ammunition shelters located in the USA's western deserts from lightning during world war two. A true Ufer ground has a very low resistance to earth when compared with any other electrode other than an extensive underground metallic water system.

It was Ufer's work on the conductivity of rebar encased in concrete that is in direct contact with the soil that led to the development of the "Concrete Encased Electrode (CEE)." The latter can be as little as twenty feet of bare number four copper which is tied to the rebar only to keep it from floating up during the pour. Compared to a true Ufer ground a CEE is just a "patch off the old mans coat."

-- Tom Horne

[bud--]

IIRC Yfer was consistently under 5 ohms in the desert. Seen any information of concrete encased electrode?

[gfretwell]

I doubt it really makes that much difference. Concrete is really the conductor. The NFPA determination was that 20' of rebar OR copper will bond to the concrete footer. 250.52(A)(3) On the other hand in a swimming pool they want a 12" x 12" grid to bond that concrete. 680.26(C) I think the truth may actually be somewhere in between.

[bud--]

I thought the main contribution of the concrete was leaching alkalinity into the soil, increasing conductivity. I liked your idea, in another thread, of tying the rebar all the way around the foundation.

Although thats for equipotential, not earthing.

------------------- Is there a deteriorating effect of concrete on bare copper grounding conductor and parts like split bolts around the pool.

[Ivan Vegvary]

[gfretwell]

I agree the intent is different but the bonding mechanism to the concrete is the same.

I haven't heard about that but if the pool plaster is really doing it's job the moisture in the concrete should be from the dirt side.

[Ralph Mowery]

All the rebar should be inside the concrete. This is to prevent rusting which would cause the rusted rebar to expand and crack the concrete. You would have a very poor electrical ground if this is done.

[Tom Horne]

[John Gilmer]

Meters almost always have a "base" which is permanently connected between the street supply and the home. The tech can turn off the water, remove and replace the meter, and turn the water back on in just a few minutes. The "base" ensures the ground is maintained during the servicing of the meter.

In the "bad old days" the standard electrical ground in cities was the water pipe. These are routienly "grandfathered" in.

But there is nothin against the code in putting as many ground rods as you care to and bond these rods to your service ground. There is also nothing against the "code" in connecting ("bonding") various already grounded objects.

IOW: you can have as good as any "ground" as any modern system but your "official" ground would still be the water pipe.

[bud--]

The "bad old days" are still here. If you read the NEC quoted in Tom Horne's post you will find water pipe (at least 10 ft buried metal) is still *required* to be used as a grounding electrode, just as it has been for a very long time.

"Modern" systems require a "supplemental" electrode because water service pipe may in the future be replaced by plastic. Ground rods were used in the past because they were easiest to install. For new construction a "concrete encased electrode" (commonly called a Ufer ground) is now usually required.

The resistance to earth of a metal municipal water system will be much lower than 1 or 2 ground rods.

[bud--]

Was thinking of the deck, where I believe concrete interior is often 'damp'. And more particularly copper in "concrete encased electrode" by itself. And connecting copper to rebar and floor mesh in concrete do you get galvanic corrosion?

I thought corrosion was a reason for requiring a pool bonding wire to be solid, not stranded (680.26-C). (Not arguing, just trying to put the pieces together.)

[gfretwell]

They do reqire a listed device to make thgis connection and most AHJs want to see a bronze 2 part clamp so the copper and steel are not in contact. Erico has an acorn listed for rebar but it is a "ground rod" clamp used for Ufers, most say not for pools.

I agree, the "solid" is for better corrosion resistance and less chance of physical damage. Personally I wish they would address the damage issue more. It is not unusual to find the bonding conductors broken on "old work". BTW the #8 to the underwater light from the J box can be stranded but it also has to be potted. This is really somewhat a redundant wire since you also bond the niche to the pool steel with a #8 solid on the concrete side but it is still required

[bud--]

How do they get broken/damaged?

[gfretwell]

There is no burial depth requirement so I imagine the yard man hits them with an edger. Around the pool equipment they are usually just laying on the ground. On my pool I put the ground wire under the pipes going to the pump but that takes coordination between the plumber and electrician. (both me in this case)