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Old 02-18-2011, 02:32 PM   #1
green.bubbly
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Default Questions on grounding the foundation rebar

The inspector told my wife that I need to ground my rebar to a 10 foot ground rod using #4 copper wire. I understood everything that needed to be done except a couple of things. Do I drive the rod into the ground IN the footing or on the outside of the slab?

The way I understood it was that the rod should be sunk in the footing near my main breaker panel with enough rod sticking out above the concrete to run another ground wire to my panel.

Do this sound correct?


Thanks
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Old 02-18-2011, 03:03 PM   #2
mrb
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Default Re: Questions on grounding the foundation rebar

that does not sound correct at all. you have to bond the rebar to the panel ground, not its own rod. look up ufer ground
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Old 02-18-2011, 03:09 PM   #3
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Default Re: Questions on grounding the foundation rebar

Ya - I didn't get ufer grounds until I read up. Basically, the deal is that concrete is very conductive and tying into the rebar basically lets the whole slab become the "ground".

http://www.psihq.com/iread/ufergrnd.htm

Maybe is required
http://www.sonoma-county.org/prmd/do...letin/e-8x.pdf
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Last edited by Falcon67; 02-18-2011 at 03:29 PM.
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Old 02-18-2011, 04:02 PM   #4
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Default Re: Questions on grounding the foundation rebar

ufer ground is required in nec 2008
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Old 02-18-2011, 05:14 PM   #5
green.bubbly
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Default Re: Questions on grounding the foundation rebar

Sorry folks, when I saw the word ufer, I remembered that there was a recent thread on that subject.

Thanks for the info and the links.
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Old 02-18-2011, 08:17 PM   #6
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Default Re: Questions on grounding the foundation rebar

Just one thing I'll mention about ufer grounds that may help someone out. Here in Oregon, whoever does the rebar for the concrete, stubs a short piece of bar up for the ufer ground. The building inspector, when doing the rebar/concrete inspection then tags this stubup as suitable for a ufer ground connection. Often times this stubup gets forgotten or the building inspector forgets to tag it as suitable for a grounding electrode.

What you can do at this point, which is also perfectly acceptable, is to take at least 20 feet of #4 bare copper wire and ziptie/tie wire it to the rebar so it's embedded in the concrete by at least 2" of concrete on all sides. Just leave yourself a tail long enough out of the concrete to reach the ground buss in the panel. You do not want to have any splices in this wire. Then have the electrical inspector verify this as the ufer ground before pouring.

One example, I'm wiring a large concrete tilt-up warehouse right now where the ufer ground was forgotten for both the electrical services this building has. What I had to do was dig a trench about shovel width, the depth of the footing. Then I layed #4 copper 20+ feet long across some 2-3 inch dobies. I then had the contractor cover it with concrete. Just another idea that may save someone some trouble if the ufer is forgotten. Always run these things by your inspector first though. This was his solution for my problem.

Kinda wrote a book here....sorry guys.
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Old 02-18-2011, 09:22 PM   #7
green.bubbly
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Default Re: Questions on grounding the foundation rebar

OK, I am trying to figure out the best or proper method of doing this. I have seen where a piece of rebar is simply bent 90 degrees and protruding up from the slab. That rebar is attached to another piece of rebar at least 20 feet long. Then the ground wire is clamped to the end of the rebar when the panel is wired.

Then as Aceman mentioned, you can just take a 20+ foot piece of #4 copper wire and attach it the the rebar in the footing and have it come out of the concrete at the panel.

Which is better or proper and do I need to encase either option in a shield where it comes out of the concrete. I kind of like the 20 plus feet of #4 copper as there is no need to worry about the rebar losing it's electrical connection. But what i do not like about just the copper wire is that it would be fairly easy to break it where it exits th concrete.

And this is why I do not sleep at night...
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Old 02-18-2011, 11:21 PM   #8
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Default Re: Questions on grounding the foundation rebar

I would call the electrical inspector back and ask for a clarification if you are in doubt. You don't want the hold ups if you have to re-do this again, don't need the added cost, the inspector will at least know you are trying to do this right. Lots of good answers here and lots of help, but remember, the only guy you have to make happy is the Electrical Inspector.....no one else counts.
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Old 02-19-2011, 07:58 PM   #9
green.bubbly
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Default Re: Questions on grounding the foundation rebar

Thanks for all the input. I called John the inspector this morning and asked him what was needed. Basically all he wanted was a #4 copper wire clamped to the bottom piece of rebar. The wire then needed to come out of the bottom of the slab on the outside where it will be connected to a ground rod and the meter base.

I told him that I think I understood and then had this reply which you gotta love. He told me that it it was wrong, he would fix it for me.

Yes, I love my inspectors. They have already been so helpful and accommodating. In fact, John will be stopping by Sunday afternoon to inspect my foundation so we can start pouring concrete early Monday morning.



Below are a couple of pics...








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Old 02-20-2011, 06:37 PM   #10
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Default Re: Questions on grounding the foundation rebar

That clamp to the rebar should have noalox grease between all the connections on it.
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Old 02-20-2011, 07:14 PM   #11
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Default Re: Questions on grounding the foundation rebar

Why is the ground wire tailed outside the building?

Quote:
Originally Posted by contactme_11 View Post
That clamp to the rebar should have noalox grease between all the connections on it.
I've never seen a rebar clamp Noaloxed.....
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Old 02-20-2011, 07:48 PM   #12
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Default Re: Questions on grounding the foundation rebar

Quote:
Originally Posted by contactme_11 View Post
That clamp to the rebar should have noalox grease between all the connections on it.
why?
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Old 02-20-2011, 07:49 PM   #13
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Default Re: Questions on grounding the foundation rebar

is that ground clamp listed for concrete encasement? (and is it for rebar?) it looks different than what im used to seeing. is this in canada?
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Old 02-20-2011, 08:31 PM   #14
green.bubbly
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Default Re: Questions on grounding the foundation rebar

Quote:
Originally Posted by Aceman View Post
Why is the ground wire tailed outside the building?


From what I understand, there will also need to be a copper rod driven into the ground. That ground wire will attach to the ground rod and up to the meter base. I thought it would go inside and attach to the main panel ground bar but I had the inspector repeat what he said and he told me to run under the foundation board and lay it on the ground outside the foundation.

He was going to be around my property today to do the inspection but he called me right after lunch and said he was not coming around today so he would be there first thing in the morning to inspect. He told me if it was wrong, he would fix it for me. If it does go inside, it will be easy to do.
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Old 02-20-2011, 08:39 PM   #15
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Default Re: Questions on grounding the foundation rebar

Run a copper ground cable (sheathed at exposed to outside end to avoid corrosion) thru forms then to a ground stake in damp corner. Note; ground works best in dampness, in dry terrain use 2 stakes @ 500 millimeter apart.

If your really cautious? U can install 2 lots of grounding at opposite corners or at each end.
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Old 02-20-2011, 08:54 PM   #16
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Default Re: Questions on grounding the foundation rebar

Quote:
Originally Posted by mrb View Post
is that ground clamp listed for concrete encasement? (and is it for rebar?) it looks different than what im used to seeing. is this in canada?

Hmmmm?

It is for rebar and direct burial but no mention of concrete encasement.


Quote:
Application: Indoors or Outdoors. Use to secure bare copper ground wire to 3/8" rebar through 1" pipe. Wire Size: #10-#2 AWG. Materials: Bronze with Stainless Steel Screws. Features This new JRD is extremely versatile - fits 3/8" - 1" Rebar, 1/2" - 1" pipe, 1/4" - 1" ground rods. Can be used for mechanically connecting 2 #8 sol wires. Use on water pipes or for direct burial - no need to stock two clamps. Lay-In Lug feature is a tremendous labor saver - no threading through holes - just lay-in ground wire and tighten screw.

Although the one I used seems to have bronze screws instead of SS. He did say that the screws had to be bronze as well.

He did tell me that the store right by my property had the bronze clamps and I have a section of 20' 5/8 rebar on standby if needed.


Don't make me lose sleep tonight. I already tossed and turned last night trying to think of anything I missed before the concrete goes in.

Last edited by green.bubbly; 02-20-2011 at 09:05 PM.
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Old 02-20-2011, 09:12 PM   #17
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Default Re: Questions on grounding the foundation rebar

Quote:
Originally Posted by contactme_11 View Post
That clamp to the rebar should have noalox grease between all the connections on it.
Unless you have manufacturers instructions stating to do so, it is not necessary.
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Old 02-20-2011, 09:22 PM   #18
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Default Re: Questions on grounding the foundation rebar

Quote:
Originally Posted by green.bubbly View Post
From what I understand, there will also need to be a copper rod driven into the ground. That ground wire will attach to the ground rod and up to the meter base. I thought it would go inside and attach to the main panel ground bar but I had the inspector repeat what he said and he told me to run under the foundation board and lay it on the ground outside the foundation.

He was going to be around my property today to do the inspection but he called me right after lunch and said he was not coming around today so he would be there first thing in the morning to inspect. He told me if it was wrong, he would fix it for me. If it does go inside, it will be easy to do.
If you have a concrete incased electrode (Ufer) you do NOT need a ground rod. If you have a metallic underground water pipe, that must be used as a grounding electrode, & the Ufer will become the required supplemental electrode...
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Old 02-21-2011, 07:58 AM   #19
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Default Re: Questions on grounding the foundation rebar

Since we are on the topic I have a question about ufer ground,
because I am in the process of fixing up a barn.
The existing foundation is a single for doors interrupted row of cinder blocks
and the electric is not working and is going to be removed/replaced.
The plan is the remove the cider blocks and replace it with concrete and 2 rows of cider blocks
which is also going to be interrupted by openings for 2 doors, dividing the foundation into two parts.
I do not plan to use re-bars but maybe put one in for ground if that is up to code.
There will be no slap, besides maybe in one of the rooms and I am under NEC2008 ruling
and the plan is to add a small sup panel for like 40~60amp.
Water pipe is going to be pex if that matters.

Thank you
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Old 02-21-2011, 09:47 AM   #20
green.bubbly
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Default Re: Questions on grounding the foundation rebar

Alright, inspector John just left and the foundation and UFER ground is good to go. He did say that we will need to attach that #4 ground wire from the rebar to a ground rod at the service entrance. Sounds like double grounding but I guess it is better than a poor ground. Plus, I am not going to argue with the inspector.
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