Ufer (Concrete encased electrode) Ground
In another thread there was a discussion about the proper way to do a Ufer ground electrode. Since I saw it too late I thought that I would post this as a separate thread.
Here is how the 2005 NEC describes it.
“250.52(A)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/ 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.”
As I gather what is it saying is that if you are building a new structure with footing with rebar then it must be used as ground electrode and to plan on it.
But if you have an existing building you don’t have tear it up to install a ufer electrode.
You can use multiple piecs of rebar that is spliced togehter. Just needs to be a total of 20 ft.
Or you can use 20 of copper wire.
If you make the connection of the copper ground wire to the rebar you must use a connector approved to encasement in concrete.
The picture is from the NEC handbook and is illustrative on one way to do it. But that is only comment and not code.
Personally I don’t like the idea of having the copper come out of the footing. It might not be too bad for a slab like they illustrate. But with a deep footing and foundation walls you have to install that copper long before it is used and keep it protected and out of the way all that time.
I like the idea of of placing a box in the found pour and have a piece of rebar that passes through that box and the spliced to the uprights that is spliced to rebar in the footings. The the connection can be made at later date.
I don’t see anything in the code that would prohibit doing that. But I would to talk to the inspector before committing to that method.
I won’t copy the whole section, but with a ufer ground electrode ground rods are not needed, period.
However, there might be local amendments that do require ground rods. And sometimes the POCO have their own rules. But for things like ground rods it has become SOP and probably a lot of people requirement without even realizing what the code says.
And here is the requiring for having a Ufer. This is from the Handbook and is not code, but explains the code.
“This section was revised for the 2005 Code to clearly require the inclusion of a
concrete-encased electrode, described in 250.52(A)(3), in the grounding electrode
system for buildings or structures having a concrete footing or foundation with not less
than 20 ft of surface area in direct contact with the earth. This requirement applies to
all buildings and structures with a foundation and/or footing having 20 ft or more of 1/
2 in. or greater electrically conductive reinforcing steel or 20 ft or more of bare copper
not smaller than 4 AWG. However, an exception does exempt existing buildings and
structures where access to the concrete-encased electrode would involve some type of
demolition or similar activity that would disturb the existing construction. Because the
installation of the footings and foundation is one of the first elements of a construction
project and in most cases has long been completed by the time the electric service is
installed, this revised text necessitates an awareness and coordinated effort on the part
of designers and the construction trades in making sure that the concrete-encased
electrode is incorporated into the grounding electrode system.”
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A-holes. Hey every group has to have one. And I have been elected to be the one. I should make that my tagline.
Replies
Thanks Bill. I like the box idea also. Survival rate on the wire might not be good.
Jim
Never underestimate the value of a sharp pencil or good light.
Here the actual UFER bar is spliced to another "L" shaped bar and the copper/ bar connection is made above the foundation. This bar usually come up out a garage foundation wall and a "mud ring" and cover plate is used so that the copper/bar connection can be checked after the house is finished."Poor is not the person who has too little, but the person who craves more."...Seneca
Hey Bill,
I have the copper wire just leaning against the cribbing pile. Glad you posted this, I'll wind it up and put it in a small box at base of foundation wall while mover pulls his steel out. Thanks again.
Kevin
I thing that I have done to keep the wire "safe" is to enclose it in a piece of pvc conduit stubbed up out of the foundation and supported by the re-bar there. I use a full stick and let it come out of the top of the foundation wall.
It looks like just another empty pipe coming up out of the foundation wall. The pipe can be cut off in the wall or cut off[from around the wire] and terminated in the panel.
Of course this method requires planning so that the wire is stubbed up close to the final panel location.
Edited 7/14/2007 8:26 pm by IBEWChuck
Bill, my local Homerbox doesn't carry galvanized rebar, does the NEC have a list of suppliers for this I've never seen it stuff?
The idea that just a tie wire connection is sufficient for a ground path sounds bogus. 2 rusty pieces of rebar tied with also rusty wire are a conductor?
I've never been impressed with this, but I'm sure better minds than mine think it's adequate. Just seems bogus.
Joe H
They don't permit the tie wire here, you need a 20 foot stick of rebar and even the concrete guys know it.
It says "bare or zinc galvanized". So ordinary rebar can be used. What they don't want is the epoxy coated or similar that is non-conductive."The idea that just a tie wire connection is sufficient for a ground path sounds bogus."I have not studied this and don't know if there are any studies.But SOP is to have a large overlap between the two sections. And it is all surrounded with "conductive" concrete. My guess is that the for both mechanical and electrical purposes the wire is just to hold the 2 piece near each other. Both the mechanical and electrical connections are formed by the concrete.With that much overlap and the relatively large contact area between then it does not take much conductivity to have a good connection..
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A-holes. Hey every group has to have one. And I have been elected to be the one. I should make that my tagline.