Ufer ground

[bh]

Has anyone had any experience with the connection of a copper cable to steel rebar as outlined in 250.52(3)? I have heard that a steel cable has less reaction with the steel rebar when encased in concrete. I think copper is a better choice (and approved by the NEC) but I am unclear about the copper to steel connection enclosed in concrete.

 

[physis]

Re: Ufer ground

The copper and iron whould make a battery in wet concrete wouldn't it. But wouldn't the electrical connection between the two short the current produced so that there wouldn't be any electrolysis?

I don't know if rust could be just as much of a problem.

 

[allenwayne]

Re: Ufer ground

We are required to make a CU to steel connetion in the footer On the side of the house that is the P.O.E.
The biggest problem is theft,we leave 10 ft of #4 bare and it seems 50% of the time it is cut and scrapped.We found a crimp sleeve that is rated for solid or stranded,but we still charge the builder

 

[volt102]

Re: Ufer ground

Why not just put 20' of copper in the footing. You need to use the concrete encased electrode because you have rebar in the footing. If you put the 20' of copper in the concrete it would satisfy 250.52(A)(3) wouldn't it?

Jim

 

[rattus]

Re: Ufer ground

Originally posted by physis:
The copper and iron whould make a battery in wet concrete wouldn't it. But wouldn't the electrical connection between the two short the current produced so that there wouldn't be any electrolysis?

I don't know if rust could be just as much of a problem.

Sam, you have just shorted the battery and the current will cause the iron to erode. At least is does in earth. I have seen the iron rods used to turn buried brass valves neck down as a result of galvanic action. They are then easily twisted off. Similar thing might happen in concrete.

 

[don_resqcapt19]

Re: Ufer ground

Jim,

If you put the 20' of copper in the concrete it would satisfy 250.52(A)(3) wouldn't it?

I don't think so. The rebar is still in the footing and is still a required grounding electrode. It is my opinion that if you put 20' of #4 copper in the footing, that the rebar must be bonded to the #4.
Don

 

[physis]

Re: Ufer ground

Sam, you have just shorted the battery and the current will cause the iron to erode

I'm not to sure about that Rattus. Will ions migrate through the two metals as would happen through an electrolyte?

 

[volt102]

Re: Ufer ground

Don,

If rebar is used near footing or bottom of foundation, you need to use a concrete encased electrode as one of your required electrodes.

Twenty feet of rebar encased in concrete or twenty feet of copper encased in concrete both are concrete encased grounding electrodes.

The code doesn't state that the different types of concrete electrodes have to be bonded together, only that the reinforcing bars shall be permitted to be bonded together by the usual steel tie wires or other effective means. That's it.

In my opinion, 20' of copper in concrete would be acceptable.

Jim

 

[rattus]

Re: Ufer ground

Sam, I doubt that there would be a problem in cured concrete even if concrete is conductive. I does happen in moist earth over a period of years.

 

[T-Wragg]

Re: Ufer ground

If you don't tie the twenty feet of #4 copper to the rebar it is impossible to protect and control the placement of the #4 copper during the concrete pour.

 

[allenwayne]

Re: Ufer ground

I have always thought that as lomg as the conncetion was to piece of 20 ft of rebar that was exposed to direct earth contact,requirements havs been met If gas added then we go from panel to gas drop to bond that`s on rough in

 

[infinity]

Re: Ufer ground

Twenty feet of rebar encased in concrete or twenty feet of copper encased in concrete both are concrete encased grounding electrodes.

The code doesn't state that the different types of concrete electrodes have to be bonded together, only that the reinforcing bars shall be permitted to be bonded together by the usual steel tie wires or other effective means. That's it.

I think that what Don is saying is that if the 20' of 1/2" rebar is available in the footing than it's required to be used so a bond to the copper electrode would be required. The 20' of copper isn't required to be used but the rebar is required to be used if available.

 

[don_resqcapt19]

Re: Ufer ground

Jim,
Infinity has is exactly correct. If the rebar is there, then it is available and is a required grounding electrode. The addition of the #4 copper does not make the rebar "unavailable".
Don

 

[JohnE]

Re: Ufer ground

Originally posted by don_resqcapt19:
Jim,
Infinity has is exactly correct. If the rebar is there, then it is available and is a required grounding electrode. The addition of the #4 copper does not make the rebar "unavailable".
Don

Don,

So if I have multiple sections of 20' rebar (not bonded together by usual ties, etc.) do I have to use all of them? They are all available.

John

 

[rasmithircgov.com]

Re: Ufer ground

Originally posted by volt102:
Don,

If rebar is used near footing or bottom of foundation, you need to use a concrete encased electrode as one of your required electrodes.

Twenty feet of rebar encased in concrete or twenty feet of copper encased in concrete both are concrete encased grounding electrodes.
rasmith writes:
I agree with you. The code says OR, and or is in definition exclusive. AND in inclusive.

(3) Concrete-Encased Electrode. An electrode encased by at least 50 mm (2 in.) 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 6.0 m (20 ft) of one or more bare or zinc galvanized or other electrically conductive coated steel reinforcing bars or rods of not less than 13 mm (? in.) in diameter, or consisting of at least 6.0 m (20 ft) of bare copper conductor not smaller than 4 AWG. Reinforcing bars shall be permitted to be bonded together by the usual steel tie wires or other effective means.
rasmith

The code doesn't state that the different types of concrete electrodes have to be bonded together, only that the reinforcing bars shall be permitted to be bonded together by the usual steel tie wires or other effective means. That's it.

In my opinion, 20' of copper in concrete would be acceptable.

Jim

[ August 10, 2005, 01:40 PM: Message edited by: rasmithircgov.com ]

 

[roger]

Re: Ufer ground

John,

So if I have multiple sections of 20' rebar (not bonded together by usual ties, etc.) do I have to use all of them? They are all available.

note the first two words in 250.52(A)(3) "An electrode" which is singular.

After you have bonded to one you have satisfied the code.

I would also point out that 250.52(A)(5)and(6)
are plural, and if numerous Concrete-Encased Electrodes were intended to be used if available, (3) should have been written to reflect plural.

Roger

[ August 10, 2005, 02:03 PM: Message edited by: roger ]

 

[JohnE]

Re: Ufer ground

Roger, I agree. I was just trying to make the point that jim just made which is that 20' of copper satisfies the requirement even if 20' of rebar is present. Admittedly, I was not actually looking at the code when I posted.

John

 

[JohnE]

Re: Ufer ground

Originally posted by t-bird:
If you don't tie the twenty feet of #4 copper to the rebar it is impossible to protect and control the placement of the #4 copper during the concrete pour.

For years I have been installing 20' copper in the footing even though not required until recently. We lay the bare wire in right after footing is poured. While concrete is setting up, we just push wire into footing, and then form guy trowels over it. You can place it exactly where you want it and it stays. Obviously it doesn't get inspected, but I have a good working relationship with many inspectors. One said "I don't exactly see you drive ground rods either, so if you say it's there, I believe you". I guess it's much different now that it's a requirement to have the ufer ground, since I was installing it voluntarily. Another note - I only had 2 builders who were on top of things enough to get me there the day footing was poured - so this certainly wasn't foolproof.

John

 

[jwelectric]

Re: Ufer ground

Originally posted by volt102:
Why not just put 20' of copper in the footing. You need to use the concrete encased electrode because you have rebar in the footing. If you put the 20' of copper in the concrete it would satisfy 250.52(A)(3) wouldn't it?

Jim

I think that maybe Jim is on to something here.

If we look closely at 250.50 we see;

All grounding electrodes as described in 250.52(A)(1) through (A)(6) that are present at each building or structure served shall be bonded together to form the grounding electrode system.

Here it tells us that all electrodes in (A) 1 through 6 must be bonded together. Well I now ask what is a concrete encased electrode? In (A) 3 it states;

consisting of at least 6.0 m (20 ft) of one or more bare or zinc galvanized or other electrically conductive coated steel reinforcing bars or rods of not less than 13 mm (? in.) in diameter, OR consisting of at least 6.0 m (20 ft) of bare copper conductor not smaller than 4 AWG.

The way I see this is if there is no rebar present then 20 foot of #4 copper will work as the electrode.
With the same breath I say that if both are present I only have to choose one of them not both.
The word OR is a word that gives choice it does not mean both or AND nor INSTEAD OF.

I see 250.52 (A) (3) as giving a choice between the rebar OR #4 copper. I see nothing that mandates that the rebar has to be used if both are present.
(A) (3) is ?Concrete-Encased Electrode? not concrete encased rebar.

 

[petersonra]

Re: Ufer ground

It seems to me that if you go to the added expense to put in the copper wire that is not required under any cirucmstances, why not bond it to the rebar regardless of whether the bond is required or not?

could such a bond be made inside the concrete?