Concrete-Encased Electrode

[wilsonv]

Hello, I have a question on using the foundation rebar as one of the grounding electrodes. The code specify the use of a concrete-encased electrode when the concrete foundation is in direct contact with earth and other restrictions which are not in question.

Should this method be suitable when the concrete foundation is not in direct contact with the earth, like when a vapor barrier exist between the foundation and the earth?

Regards

 

[jghrist]

No, the method is not suitable if there is a vapor barrier. A vapor barrier would prevent fault current from flowing into the earth. That is why the code specifies "in direct contact with the earth."

 

[peebee]

In addition, the whole reason that the concrete-encased electrodes work so well is because concrete is hygroscopic -- it loves water, and just sucks it up out of the ground, which makes for a pretty good connection to ground. Dry concrete, on the other hand, is a terrible conductor.

So, not only would your vapor barrier isolate the electrode from the ground you're trying to bond to, it would also dry the concrete out making the concrete a bad conductor.

 

[DonPhillips]

Sorry, I cannot say I have seen anyone place a vapor retarder under a footing, which is where I would expect to see the grounding electrode. In central Ohio, there was a lot of debate about what the NEC meant by foundation and it was determined it was the footing of a typical building. The foundation wall may be waterproofed if the building has a basement but would not be considered as the foundation for the purposes of the grounding electrode requirements of the NEC.


Don Phillips

http://worthingtonengineering.com

 

[peebee]

Regarding "The foundation wall may be waterproofed if the building has a basement but would not be considered as the foundation for the purposes of the grounding electrode requirements of the NEC."

Hmmm.... not sure I agree with that....

 

[DonPhillips]

Just letting you know what the local electrical inspectors and building officials discussed. Frost protected footings were discussed and no one thought a 12" foundation with a vapor retarder and an encased electrode would be as effective as a typical footing, at least 3' deep.

To further clarify, the discussed reinforced block foundation wall sitting on an unreinforced footing, and if this block wall is waterproofed, no one felt this reinforcing was intended to be the electrode since it would not be nearly as effective as a reinforced footing with no vapor retarder.

Just leeting you know what we discussed in Central Ohio.

Don Phillips

http://worthingtonengineering.com

 

[peebee]

I'll buy that.

I had interpreted "waterproofed" in a different way. The manner of waterproofing you describe, though, would probably render a Ufer ground ineffective.