Copper grounding conductors & reinforcing steel

[BubbaJ]

I have a project where it is proposed that copper grounding conductors will be compression crimped to a continuous loop of reinforcing steel in the building foundation. While the electrician seems very comfortable with the idea of the connection of the dissimilar metals, the communications engineering firm is not familiar with the system and has raised a red flag regarding possible corrosion of the reinforcing steel.

I am not familiar with the process either and would appreciate a little education on the matter or websites where I may conduct my own research or gather information on the compression clamps.

Thanks.

 

[VEBill]

Tidbit: Instead of crimps, I've seen mention of kits where the joint between grounding cable and grounding rod (or rebar in this example) is welded using a sort-of self-welding flare thingy. You put it together, trigger it off, stand back, wait till it settles down, stamp-out the burning bits, and it makes a welded connection. I'm sure someone here will know the proper trade-name.

 

[TheBlacksmith]

Sounds like a themite weld from the description.

 

[BubbaJ]

That option was discussed. The electrician wants to use the compression clamps.

 

[BJC]

These work fine and are a listed item.

http://www.erico.com/products/ERITECH_RC70_RC100.asp

 

[dpc]

The NEC has actually required this type of grounding, referred to as a "Ufer" ground for many years.

There are some corrosion issues, but in generally, copper in reinforced concrete is fairly benign and not terribly reactive with the rebar. Bigger concern may be blowing off a piece of foundation in the event of a direct lightning strike. But it is very, very common, makes a very good (low frequency) ground and is required by NEC for new construction.

 

[waross]

The thermite or exothermic system is called Cadwelding or Cadwelds.
The active material is a mixture of powdered aluminum and powdered copper oxide. Some tin is added so that the finished product is a type of bronze.
Aluminum has such an afinity for oxegen that once the reaction is started, at about 900 deg., the aluminum will react with the oxegen in the copper oxide, yielding aluminum oxide and molten copper. The reaction is contained in a split graphite mold.
See

http://www.erico.com/products/Cadweld.asp

I know of one major utility who required cadwelds for substation grounding grids for decades. They now accept heavy copper compression connections. Another utility in the same area still requires thermite or Cadwelds for substation ground grids.

respectfully

 

[SteveWag]

I have used concrete encased steel, with encased and/or exposed steel-copper connections for grounding for 35 years with no failures that I know of. I have also used copper to steel connections in constructing grounding arrays for AM broadcasting stations with no problems. For antennas, if near a building, I always incorporate the footer steel into both the antenna and power system grounding.

BUT, now this -

http://www.nfpa.org/itemDetail.asp?...azine/necdigest® archives/April 2007/Features

- shows up.

Steve Wagner

 

[BubbaJ]

Thanks, that was a very interesting article.

We recently received info on the clamp to be used, Burndy Hyground. These clamps say they come precoated with Penetrox, an oxide-inhibiting compound with homogenously suspended metal particles.

It is my feeling then that the potential for corrosion is very limited since the dissimilar metals are not in contact with each other.

 

[waross]

Although the Canadian Electric Code and the National Electric Code are well harmonized in many areas, ufer grounding is one area where they diverge.
In Canada a ufer ground consists of 6 meters (sized according to service size) buried either in the bottom 2' of a concrete foundation or buried in the soil below the concrete.
respectfully

 

[BubbaJ]

Bear with me here, this is not my area, but in addition to grounding the foundation, the master ground bar is connected to an exterior buried ground rod field.

I think the grounding issues are being well handled, it was the issue of the connector that was of concern.

 

[peebee]

It seems to me that either the IEEE Green Book or Emerald Book state that the dissimilar metals corrosion issue is either reduced or eliminated when the metals are embedded in concrete.

Don't take my word for it though, it's been a while since I read that....