Concrete Encased Electrode

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George Stolz

George Stolz

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What is the minimum size grounding electrode conductor that can be connected to a concrete-encased electrode?

For this example, imagine a dwelling unit with a 100-amp service fed by #2 AL conductors.
 
Re: Concrete Encased Electrode

George,
The minimum permitted is that shown in Table 250.66. The maximum required is #4 per 250.66(C).
Don
 
Re: Concrete Encased Electrode

George look at NEC 250.52 (3), now I was instructed by one inspector to dig a 10' trench and do the 20' #4 application, which was ok with him :confused: .
 
Re: Concrete Encased Electrode

Yes to the concrete, but now you see why I put the :confused: symbol in, and I agree with you,something is missing, looking at the NEC the way I read 250.52 A (3) I think where the problem is the #4 should have been bonded to the reinforcing steel, would that be the correct way. But the foundation was existing so what do you do in this case. by the way no cold water ground was present, wood frame building. So that is the reason we went ground rod and concrete encased electrode
 
Re: Concrete Encased Electrode

Used as a Grounding Electrode

250.52 Grounding Electrodes.
(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.


Used as a Grounding Electrode Conductor

"250.66 Size of Alternating-Current Grounding Electrode Conductor.
(B) Connections to Concrete-Encased Electrodes.
Where the grounding electrode conductor is connected to a concrete-encased electrode as permitted in 250.52(A)(3), that portion of the conductor that is the sole connection to the grounding electrode shall not be required to be larger than 4 AWG copper wire.
 
Re: Concrete Encased Electrode

Originally posted by pierre:
Used as a Grounding Electrode

250.52 Grounding Electrodes.
(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.
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pierre

that's if you're building your own.

'...or...'
 
Re: Concrete Encased Electrode

I am curious about something.

Say you have a small building on a slab, but no real foundation or even a footing.

Is there no requirement to bond to the rebar in the slab in that case?

As I read it, it is not even acceptable as a GE. Why would that be the case? It would seem to be an even better choice than a foundation, being as it would have more surface area exposed to the earth.
 
Re: Concrete Encased Electrode

So is NEC 250.52 (A) (3) and 250.66 (B) saying, a concrete encased electrode would only be effective before the building slab is poured, then you could bond to the reinforcing steel which would be accessible, and if you are using the 1/2" coated steel reinforcing bars or rods you would need a piece of #4 wire from the ground bar to the electrode or if you go with the 20' of #4 wire, this would go directly to the ground bar, which takes me back to, what if the slab is existing, do you chip out some concrete and expose the reinforcing steel, so as to bond to it?
 
Re: Concrete Encased Electrode

In existing buildings you do not have to chip out concrete, see '05 NEC 250.50 exception. However, I'm not sure what happens on a new building if the ufer ground was not installed at time of pour. My office is just now starting to discuss some of the code changes.
 
Re: Concrete Encased Electrode

I don't have a 2005 so I can't look it up. I keep getting the impression reading posts on the subject that the new code is being interpreted as a requirement to provide an encased electrode. I thought it was only a requirement to use one if it's there.
 
Re: Concrete Encased Electrode

250.50 says "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." I work in a seismic zone D1 and all footings are required to have 2 #4 rebar ran continuous through the footing. This seems to be a concrete encased electrode, so now I really need to use it according to the 2005 NEC.


Chris
 
Re: Concrete Encased Electrode

There is no code requirement to install concrete encased electrode, just to use it if it is there. The wording requires the use of the concrete encased electrode if it exists in a new building. This rule applies even if the rebar is already concrete encased when the electrician gets on the job. This is going to present some problems as in many fast track installations the footings are poured before the electrical contract is even let. Note, there was some mention of "coated" rebar. Rebar that has a nonconductive coating is not suitable for use as a grounding electrode.

You are permitted to install a minimum of #4 bare copper 20' long to create your own grounding electrode in the concrete. If you install this #4 in a concrete footing that also has rebar, the #4 must be bonded to the rebar.

The rebar in a slab is not a grounding electrode per the NEC. I'm not sure of the reason, but expect it has to do with the moisture content of the earth which is normally higher with a greater depth.
Don
 
Re: Concrete Encased Electrode

I'm thinking a footing with coated rebar wouldn't meet the definition for encased electrode and therefore wouldn't have to included in the GES. Are you saying You'd have to add the copper to make it an electrode Don?
 
Re: Concrete Encased Electrode

Sam, you can add a bare copper in the footing if you want to instead of driving a ground rod, it is not required. :D
 
Re: Concrete Encased Electrode

Ok, then.

I just want to make sure I wont have to order a cement truck to get a service grounded in 2018 when California adopts the 2005. :D
 
Re: Concrete Encased Electrode

Originally posted by rcarroll:
However, I'm not sure what happens on a new building if the ufer ground was not installed at time of pour. My office is just now starting to discuss some of the code changes.
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In Cheyenne, they leave a rebar stubbed up into the garage, inside of the exterior garage wall behind where the service will sit.. At foundation inspection, the inspector verifies that the Ufer is present. Without it present, the foundation isn't signed off to pour. This seems to work well for them.

The connection is made out of the concrete, making it accessible (if a little bit of a trip hazard. :)
 
Re: Concrete Encased Electrode

Or have I lost my marbles? :)
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That's the way I remember it.

That #4 can stop above the concrete where a #6 or #4 can be attached to it using normal (non-exothermic hoo-haa) means: just like attaching to a water pipe, ground rod, etc. Does that sound weird and new to anyone else?
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Do I have to say anything? Cause I will if you want me to. :D

I just remember Allen griping about his ufer's getting cut off--if that happened after the pour, he still has 20' of #4 in the concrete, he still has his ufer. He just needs to pull his GEC to it.
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I thought that was solved for Allen four or six monthes ago. Did he forget. :cool:
 
Re: Concrete Encased Electrode

George,
I made the statement because when you install #4 bare in a footing with 20' or more of 1/2" or larger rebar, the rebar is still there and it is a required grounding electrode. Also if the electrical system was struck by lighting, this bonding will help reduce potential structural damage to the foundation.
Don
 
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