Grounding new building.

[Astross89]

I'm about to have my new slab poured. The inspector came for the pre-inspection. He said I should go and get some copper wire and clamp it to the rebar before the poor for a ground. For future electrical install. He said just buried in the dirt. And it'll be there waiting. Does that sound about right.

 

[Stuart in MN]

It's called an Ufer ground: https://en.wikipedia.org/wiki/Ufer_ground The concept was developed in WWII, but it didn't really catch on for general construction until more recently. So this is just a slab for now, but you're going to add a building on it sometime in the future?

 

[Astross89]

It's called an Ufer ground: https://en.wikipedia.org/wiki/Ufer_ground The concept was developed in WWII, but it didn't really catch on for general construction until more recently. So this is just a slab for now, but you're going to add a building on it sometime in the future?

Metal building will be installed probably in a month. I attach the ground to the rebar. Brought the ground wire on the outside of the form board and buried it. So I can access it at a later date.

 

[Bad Habit]

WA State inspector made a buddy of mine chip out the concrete to attach a ground to the rebar, wouldn't accept just ground rods any more.

 

[n20junkie]

I had no idea abour Ufer until I had my garage foundation poured and the guys left rebar sticking out of the wall. Little did I know what a time saver that was.

Many places require Ufer on new builds.

 

[Astross89]

Well with the responses, I'm glad the inspector said something. It's already done. And it gets poured this afternoon

 

[readhead]

When we do our metal building foundations we install a full length of rebar with a 90 degree bend in it and roll it up next to a column. When the electrician comes he bonds the building to the rebar thus grounding the entire building.

 

[larry_g]

In my county the electrical inspector has to check the ufer and tag it before the concrete is poured. Make the call and see if this applies to you. At the very least take a lot of pictures before to prove that your ufer meets code before you cover it up. There are minimums of length it has to be.

Good luck on your project.

lg
no neat sig line

 

[Falcon67]

Well with the responses, I'm glad the inspector said something. It's already done. And it gets poured this afternoon

Has to be fully encased in the concrete - NOT in the dirt. Minimum of 20' of copper #4 as I recall.

WA State inspector made a buddy of mine chip out the concrete to attach a ground to the rebar, wouldn't accept just ground rods any more.

Abilene here requires both UFER and ground rods AFAIK.

 

[Richard Cranium]

Wow, had never heard of ufer grounding. Thanks for the info.

 

[richtersrodz]

Wow.. I should have done that when I had my slab poured inside my old 1920's garage. I just used the grounding rod method, but actually had to pull up the old one (previously installed) and move it over a few feet. It was probably done wrong, but better than nothing at all, like many other things I have found wrong with my house.

 

[My Old Tools]

All three of my metal buildings had metal rebar and plate cages installed before the pour, tied to the slab rebar. The building I-beams were then welded or bolted to those plates. Pretty well grounds the whole thing. I always add a copper rod anyway.

 

[ard]

I prefer having the rebar come up out of the slab @ a wall or column. That way you can always see the ground connection. (Not a single wire disappearing onto the concrete.) just me

 

[RVDan]

Wow I would think concrete would be an insulator and insufficient as a ground.

 

[1/2 Cup]

We have had to ground our rebars for some years now.

 

[larry4406]

New residential construction guy here.

We use 20' of continuous 4 copper wire tied to the footing rebar and then turned up thru the stem well (stem wall is a separate pour using concrete forms). The 20' of copper is fully encased by the footing concrete pour. It is left long enough so that runs up to the electric panel without a splice. Without a splice, no inspection access is required.

Lots of folks turn up the rebar then use an acrorn nut to connect the panel ground and provide inspection access for this splice. The rebar lengths we see here on the job are 20' maximum. So its not possible to have a continuous 20' of concrete encased rebar in the footing plus the necessary continuous turn up (for example thru a stem wall) to attach a wire tie to without welding the rebar. None of our inspectors will agree that simply wire tying rebars together constitutes a "continuous" ground. Thus the #4 copper wire approach we use. Our wire typically ends up being about 25-28' total length with the turn up to the panel. YMMV.

 

[redneckcharlie]

We have been using 20’ UFER’s for years, along with the mud ring to inspect the bonding. Your post is a great example of one of the biggest headaches of contractors dealing with inspectors. It’s assanine that different inspectors within the same department will enforce code differently, but it happens constantly. Electrical inspectors are by far the worse for us to deal with here. We are constantly going over the local inspector to the head for the state to get them to drop their incorrect interpretation of code and demands.

New residential construction guy here.

We use 20' of continuous 4 copper wire tied to the footing rebar and then turned up thru the stem well (stem wall is a separate pour using concrete forms). The 20' of copper is fully encased by the footing concrete pour. It is left long enough so that runs up to the electric panel without a splice. Without a splice, no inspection access is required.

Lots of folks turn up the rebar then use an acrorn nut to connect the panel ground and provide inspection access for this splice. The rebar lengths we see here on the job are 20' maximum. So its not possible to have a continuous 20' of concrete encased rebar in the footing plus the necessary continuous turn up (for example thru a stem wall) to attach a wire tie to without welding the rebar. None of our inspectors will agree that simply wire tying rebars together constitutes a "continuous" ground. Thus the #4 copper wire approach we use. Our wire typically ends up being about 25-28' total length with the turn up to the panel. YMMV.

 

[lakeroadster]

I'm about to have my new slab poured. The inspector came for the pre-inspection. He said I should go and get some copper wire and clamp it to the rebar before the poor for a ground. For future electrical install. He said just buried in the dirt. And it'll be there waiting. Does that sound about right.

Stick To The Code.

There are requirements for the type and sizing of the connections to the rebar. And local codes vary. Find the actual written code requirements (regardless of what the inspector says).

Well with the responses, I'm glad the inspector said something. It's already done. And it gets poured this afternoon

Did they inspect the attachment and the length and diameter of the re-bar? Normally if an ufer is indeed a code requirement they will require this as an inspection hold point.

Ufer grounding is often misapplied and misused. In most cases the standard dual ground rods are more than adequate.

Ufer was developed during WWII for use in areas that are arid. That's because in such areas there isn't enough moisture in the ground for the standard ground rod to work correctly.

Ufer is not without it's problems... Lightning Damage to Concrete Encased Electrodes

When we built our pole barn in 2016 the local inspector who signed off on the column hole depths started talking about an ufer ground. Upon further investigation ufer wasn't required by the county jurisdictional authority. The inspector didn't know what he was talking about.

Again, that's why you need to stick to the written code specifications.

__________________________________________

.... Your post is a great example of one of the biggest headaches of contractors dealing with inspectors. It’s assanine that different inspectors within the same department will enforce code differently, but it happens constantly. Electrical inspectors are by far the worse for us to deal with here. We are constantly going over the local inspector to the head for the state to get them to drop their incorrect interpretation of code and demands.

Amen to that

 

[Norcal]

New residential construction guy here.

We use 20' of continuous 4 copper wire tied to the footing rebar and then turned up thru the stem well (stem wall is a separate pour using concrete forms). The 20' of copper is fully encased by the footing concrete pour. It is left long enough so that runs up to the electric panel without a splice. Without a splice, no inspection access is required.

Lots of folks turn up the rebar then use an acrorn nut to connect the panel ground and provide inspection access for this splice. The rebar lengths we see here on the job are 20' maximum. So its not possible to have a continuous 20' of concrete encased rebar in the footing plus the necessary continuous turn up (for example thru a stem wall) to attach a wire tie to without welding the rebar. None of our inspectors will agree that simply wire tying rebars together constitutes a "continuous" ground. Thus the #4 copper wire approach we use. Our wire typically ends up being about 25-28' total length with the turn up to the panel. YMMV.

NEC article 250.52(A)(3)(1) says tie wires are acceptable.

 

[FTG-05]

NEC article 250.52(A)(3)(1) says tie wires are acceptable.

As does NFPA 780, Standard for the Installation of Lightning Protection Systems, 2004 edition (emphasis mine):

"4.13.3 Concrete-Encased Electrodes.

[snip]

4.13.3.2 The encased electrode shall consist of one of the
following:
(1) Not less than 6m(20 ft) of bare copper main-size conductor
(2) At least 6 m (20 ft) of one or more steel reinforcing bars
or rods not less than 12.7 mm (1⁄2 in.) in diameter that
have been effectively bonded together by either welding
or overlapping 20 diameters and wire-tying"

 

[ard]

Never saw this here:

During World War II, the U.S. Army required a grounding system for bomb storage vaults near Tucson and Flagstaff, Arizona. Conventional grounding systems did not work well in this location since the desert terrain had no water table and very little rainfall. The extremely dry soil conditions would have required hundreds of feet of rods to be driven into the earth to create a low impedance ground to protect the buildings from lightning strikes.

In 1942, Herbert G. Ufer was a consultant working for the U.S. Army. Ufer was given the task of finding a lower cost and more practical alternative to traditional copper rod grounds for these dry locations. Ufer discovered that concrete had better conductivity than most types of soil. Ufer then developed a grounding scheme based on encasing the grounding conductors in concrete. This method proved to be very effective, and was implemented throughout the Arizona test site.

https://en.wikipedia.org/wiki/Ufer_ground

 

[madmaxnj]

Thankfully I talked to the building inspector about my future electrical plans before building. He required this and looked for it when he came to inspect the footing dig. What I forgot to ask was, should the copper wire come up outside the building, or inside through the floor? It is laid up to come up outside, but I'm thinking it should be inside to go to the sub-panel. Thoughts?

 

[larry4406]

Thanks for the wire tie rebar info!

We turn up our wire thru the stem wall. If you are slab on grade then turn up in what will be your framed wall.

 

[m32825]

When slabs are poured in central Florida they are required to have a vapor barrier under them. Does a vapor barrier reduce Ufer capability? Those of you in areas that require Ufers, is a vapor barrier required under the slab?

-- Carl

 

[Norcal]

When slabs are poured in central Florida they are required to have a vapor barrier under them. Does a vapor barrier reduce Ufer capability? Those of you in areas that require Ufers, is a vapor barrier required under the slab?

-- Carl

The Ufer is required to be at the bottom of the footing encased in at least 2" of concrete, vapor barriers, or the like means the concrete is not in "direct contact" with the earth, the slab is not the required footing for the Ufer.

 

[ard]

IMO if there is a vapor barrier then the 'concrete encased electrode' (CEE) is then NOT 'in electrical contact with the ground. Hence you cannot use a Ufer for a ground

Is this a 'thickened edge slab on grade'? With VB wrapping all the way down the bottom of the foundation party (ie that thickened edge) and up the outside?

Usually the Ufer (CEE) is in the foundation. Slab you pour later inside the foundation stem walls. Well, at least that is a common way to do it.

Edit: I was typing when norcal was posting!

 

[m32825]

The Ufer is required to be at the bottom of the footing encased in at least 2" of concrete, vapor barriers, or the like means the concrete is not in "direct contact" with the earth, the slab is not the required footing for the Ufer.

Ok, I see. Vapor barrier goes under everything here to prevent rain dilution of the termite treatment until the pour takes place. Seems like that requirement rules out use of an Ufer in central Florida.

-- Carl

 

[m32825]

Is this a 'thickened edge slab on grade'? With VB wrapping all the way down the bottom of the foundation party (ie that thickened edge) and up the outside?

Exactly. We have a couple garage slabs with 24" thickened edges and there is vapor barrier under all of it. The only place with concrete to earth contact is where you back fill around the sides after the forms come off.

This caught my eye because if any place could use more grounding options it's "lightning alley" here in Florida. I had never heard about Ufers, and yet I see that they are required for new construction in other regions. Just trying to figure out why...

-- Carl

 

[ard]

If the VB is only to avoid dilution, then pull it back from the edge on day of pour. Your inspector might not like that approach.

Although I am also guessing the VB keeps the termite treatment from permeating the slab (and the living space) via cracks and whatnot....

 

[lakeroadster]

"A new informational note has been added to 250.52(A)(3) to clarify how a concrete-encased electrode is impacted by the use of insulation, vapor barriers, films, or similar items that separate the concrete from the earth. This note explains that when such materials are encountered that insulate the concrete from the earth, the "direct contact" with the earth required for the use of a concrete encased electrode has been lost. In such a case, the concrete-encased electrode is not present, and another suitable electrode must be used. This is an important consideration in view of some of the modern building methods in use."

http://www.ecmweb.com/code-basics/grounding-and-bonding-part-3-3

_____________________________________________________________________

"Note: Concrete installed with insulation, vapor barriers, films or similar items separating the concrete from the earth is not considered to be in �direct contact� with the earth."

http://forums.mikeholt.com/showthread.php?t=156423

 

[madmaxnj]

Thankfully I talked to the building inspector about my future electrical plans before building. He required this and looked for it when he came to inspect the footing dig. What I forgot to ask was, should the copper wire come up outside the building, or inside through the floor? It is laid up to come up outside, but I'm thinking it should be inside to go to the sub-panel. Thoughts?

Thanks for the wire tie rebar info!

We turn up our wire thru the stem wall. If you are slab on grade then turn up in what will be your framed wall.

So after they pour the footer, I should have them run the copper wire up through the middle of the cinder block wall? The block is going to run 2' above grade and that's where the framing will start.

Thanks

 

[m32825]

Thanks for the references, lakeroadster. I guess in central Florida this is an area of building code where goals conflict, and you have to weigh the probabilities and costs of each. While lightning might test the grounding of your structure at some point in its life, termites are definitely going to take a crack at it.

 

[wyliesdiesels]

Wow I would think concrete would be an insulator and insufficient as a ground.

Quite then opposite.

Concrete carries electricity pretty wrll.

Ive been shocked through concrete before.

 

[lakeroadster]

Thanks for the references, lakeroadster. I guess in central Florida this is an area of building code where goals conflict, and you have to weigh the probabilities and costs of each. While lightning might test the grounding of your structure at some point in its life, termites are definitely going to take a crack at it.

I don't get your correlation. You bring termites into a discussion about grounding?

Will an ufer ground prevent termites better than the standard 2 ground rod method?

You lost me...

 

[wyliesdiesels]

Yeah i was confused by that as well.

 

[FTG-05]

I don't get your correlation. You bring termites into a discussion about grounding?

Will an ufer ground prevent termites better than the standard 2 ground rod method?

You lost me...

I think it's because he has to have a physical termite barrier. I'm guessing that an effective termite barrier just happens to also be a good insulator - negating the usefullness of an Ufer ground.

But I don't live in FL, so who knows.

 

[m32825]

I don't get your correlation. You bring termites into a discussion about grounding?

Following this thread I learned that Ufer grounds seem like a great idea, and some places even require them for new construction. I haven't seen any discussion of them in central Florida and I was wondering why; this is the lightning capital of the US so it seems like we'd be all over another grounding method.

Termite treatment is required here before a pour, and a vapor barrier is required on top of it (keeps the treatment from being diluted if it rains before the concrete is placed). Vapor barrier gets in the way of a good ground path, so it seems like our termite-related building code eliminates Ufers in this area.

I know that was convoluted, and not where the OP was headed, sorry for the distraction...

-- Carl

 

[larry4406]

So after they pour the footer, I should have them run the copper wire up through the middle of the cinder block wall? The block is going to run 2' above grade and that's where the framing will start.

Thanks

That is what I would do. We use concrete forms to pour our walls and run the wire up thru the forms tied to the rebar in the wall forms to protect it. When you frame, drill a hole thru the sill plate and then up to your panel location. Obviously, turn up the wire where you want your panel to be.

Now is also the time to be deciding on any conduits you want to turn up as well - incoming power, communications, etc.

 

[Fixin'Stuff]

Following this thread I learned that Ufer grounds seem like a great idea, and some places even require them for new construction. I haven't seen any discussion of them in central Florida and I was wondering why; this is the lightning capital of the US so it seems like we'd be all over another grounding method.

Perhaps because overly dry soil isn't much of a problem in Florida? Ufer invented his solution for buildings in the Arizona desert that made the use of ground rods less effective since there was no moisture in the soil to provide a solid ground path.

 

[lakeroadster]

Thanks for the clarification Carl (m32825)

In Florida a couple of ground rods will work just fine. One thing FLA isn't... is "arid". As stated earlier...

Ufer grounding is often misapplied and misused. In most cases the standard dual ground rods are more than adequate.

Ufer was developed during WWII for use in areas that are arid. That's because in such areas there isn't enough moisture in the ground for the standard ground rod to work correctly.