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Grounding rebar in a foundation???


DonTx
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Another inspector called today and asked me about groudning rebar in a foundation.

He was asking if there was more than 20 feet of rebar in a foundation, that it had to be grounded. Supposedly it's in the 2005 NEC, which I don't have.

Is this true? Can someone shed some light on this?

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only mention of steel reinforcing bars in the 2005 NEC. Article 250.53

(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 (1#8260;2 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.

Exception: Concrete-encased electrodes of existing buildings

or structures shall not be required to be part of the

grounding electrode system where the steel reinforcing bars

or rods are not accessible for use without disturbing the

concrete.

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During my last semester of ICC certification, here in NJ it will be the responibility of the building inspector to ensure the rebar is accessible after the footings are poured.

Not all footings require rebar and those that don't have them installed obviously will not be subject to this requirement.

That was the latest info as of 12/05.

I start a sub code class tomorrow night and I believe the instructor is an electrical inspector. I'll try to confirm this with him.

Darren

www.aboutthehouseinspections.com

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Originally posted by Scottpat

I would think that grounding would be region or area specific. In sandy soils the Ufer grounds are the way to go. In clay soils like my area driven ground rods are used.

We have mostly clay soil and still do ufers. They do the job and are more production building friendly- Easy to install and verify.

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Originally posted by Scottpat

I guess I should have said Ufers are used more in Arid locations.

Scott,

Not looking to bust stones, just get educated. Why would a driven rod be better in a "wetter" area with clay type soil? I would think difficulty in driving the rod into the clay and high water tables eating the driven rod would make ufers even more desirable, no?

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Why would a driven rod be better in a "wetter" area with clay type soil? I would think difficulty in driving the rod into the clay and high water tables eating the driven rod would make Ufer even more desirable, no?

I really can't give you an educated answer other than this is what I have been told by a couple of electrical contractors in my area and an municipal inspector.

From what I understand it has to do with the impedance of the soil. Sand or arid clay soil has a low impedance and this is why the Ufer system works best. Damp clay like in my area can use the driven rod(s) for grounding as the soil has a high impedance.

The Ufer would work in any location, and I agree that it is superior to the driven rod. As for the cost of a Ufer verses the driven rod, I would think that it would be comparable.

Now this begs the question of how install a Ufer system on a conventional foundation? Would you place it in the concrete footings? I have only seen a Ufer in a slab setting.

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Originally posted by Donald Lawson

Another inspector called today and asked me about groudning rebar in a foundation.

He was asking if there was more than 20 feet of rebar in a foundation, that it had to be grounded. Supposedly it's in the 2005 NEC, which I don't have.

Is this true? Can someone shed some light on this?

Yes. It's true. Under the 2005 NEC, in new construction, if there's rebar in the footing or foundation it's required to be connected to the grounding system.

Section 250.52 lists seven types of grounding electrodes -- the Ufer ground is one. Just before that section, 250.50 tells us that all of the electrodes that are present at each building are supposed to be bonded together to form the grounding electrode system.

As for impedance, Scott, you'll be interested to know that up here even with our heavy clay soils and constant drippy rain, driven rods have lousy impedance. The explanation I've heard (strictly rumor, mind you) is that the constant rain leaches minerals from the soil and make it a poor conductor. (Remember that pure water doesn't conduct electricity, it's the minerals in the water that do it.) This explanation doesn't sound right to me, but I haven't heard a better one.

- Jim Katen, Oregon

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Originally posted by Scottpat

[quote

Now this begs the question of how install a Ufer system on a conventional foundation? Would you place it in the concrete footings? I have only seen a Ufer in a slab setting.

If we lived in a perfect world, the foundation contractor would be informed of the location of the service entrance equipment, would then extend a specific segment of the rebar out of the footing @ that location, and tag it w/an orange indestructible plastic marker indicating it as the Ufer connection. The tag would read "Electrical System Grounding Connection: Do Not Tamper w/or Destroy".

IOW, build it into the process of home building; simple, cheap, effective.

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Here's what Douglas Hansen has to say about Ufer systems. From Electrical Inspection of Existing Dwellings - 2001 Edition:

Grounding electrodes are the metal placed in the earth to connect the electrical system to earth. The typical grounding electrodes in residential systems are water piping, ground rods, and steel reinforcement inside the foundation. If present, they must all be bonded together to form the grounding electrode system. Other grounding electrodes recognized by the NEC® include effectively grounded building steel, ground plates (rare), ground rings, and other buried metal, such as well casings.

(snip)

The concrete itself acts as the electrode; the steel inside the foundation does not directly touch the soils. While concrete at first might not seem to be a conductive material, moisture and salts readily migrate through concrete, and the soils beneath the footing are more likely to be moist than below areas outside the footing. The act of pouring the concrete can also "dope" the soils with chemicals that increase its conductivity. The steel inside the foundation is used as the conductor to reach the concrete.

The NEC® calls for the electrode to include at least 20 feet of reinforcing steel near the botto of the footing. Of course after the concrete is poured, the placement of steel can no longer be visually determined. A steel bar can be brought up out of the foundation for the connection to the grounding electrode conductor, or the conductor could actually connect inside the foundation, in which case the inspector would only see a wire emerging from the concrete.

In some areas, it is commonplace to see two steel bars emerging from the foundation. The reason for two instead of one stems from a common misunderstanding. While the code calls for a minimum of 20 feet of reinforcing steel, there is no requirement that the grounding electrode conductor connect directly to those 20 feet of steel. Many jurisdictions fail to appreciate this distinction, and mistakenly assume that the 20 feet of steel is a separate electrode than the reinforcing steel that is already present in the foundation. If a piece of 20-foot rebar is bent to bring a piece up out of the foundation, then less than 20 feet remains encased. To solve this "problem", inspectors require 2 pieces. Many jurisdictions require this steel to be in addition to the steel that is already present, despite the fact that the code does not intend for it to be anything other than the original steel. Because of this widespread misunderstanding, the NEC® added language to the 1999 edition stating that the ordinary tie wires between pieces of reinforcing steel are considered sufficient for bonding the sections of steel to each other.

In areas with corrosive soils, the reinforcing steel is sometimes coated to prevent it from rusting. In such cases, the rebar is no longer an effective conductor for connecting the system to the foundation. The code allows a #4 copper wire to be laid into the foundation for a minimum of 20 feet. All an inspector would see is a wire emerging from the concrete.

Another problem arises from bringing two pieces of steel outside the foundation; suitable clamps are not available for more than on piece of rebar.

OT - OF!!!

M.

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Originally posted by kurt

Originally posted by Scottpat

[quote

Now this begs the question of how install a Ufer system on a conventional foundation? Would you place it in the concrete footings? I have only seen a Ufer in a slab setting.

If we lived in a perfect world, the foundation contractor would be informed of the location of the service entrance equipment, would then extend a specific segment of the rebar out of the footing @ that location, and tag it w/an orange indestructible plastic marker indicating it as the Ufer connection. The tag would read "Electrical System Grounding Connection: Do Not Tamper w/or Destroy".

IOW, build it into the process of home building; simple, cheap, effective.

That's pretty much how it's done here. During the pre-pour inspection, the building inspector makes sure that a stub of rebar is extended up above the top of the foundation for the Ufer ground.

It usually isn't labeled. Everyone knows what it is.

- Jim Katen, Oregon

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Here is the "official" NJDCA position on the subject. There was no link avaiable so I had to type it; excuse any typos.

Bulletin 02-2

January 2002

Subject: Availability of concrete-encased electrodes

Reference: N.J.A.C. 5:23-3.4 NEC 1999 Section 250-50©

There appears to be some confusion over the intent of the term “if availableâ€

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Yeah, What kurt said!

Let's get that perfect world thing going.....Can we unite to actually drive the performance guidelines of builders and developers. Is that an unreasonable dream? I think not. Fireman drive codes, Builders and Achitects drive codes, the government drives codes. Why can't drive a couple of codes of our own for inspection purposes and continuity (no pun intended)?

Ok, I need to go to bed and stop ranting.........

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