Concrete Encased Electrode Ground Sys.
I’ve got new construction sitting on a slab which is connected to solid bed rock a foot or two down. Electrical inspector wants one of two grounding systems, a Modified ground ring NEC 250.52.4 but getting down 30 inches through solid rock in an area where large equipment won’t fit is a problem, the second a concrete encased electrode 250.52.3 unfortunaly the concrete people didn’t ask if I wanted a concrete encased electrode but.. I took hi resolution, close-up photos of every inch of the rebar system around the footing of the slab before the pour and I have in-ground plumbing holes in my slab floor and behold! there on the edge of the hole is rebar passing through. I can see in the photos it’s a 20′ stick of #4, wire tied to all the rest of the rebar, I could easily tie into this bar, the photos prove it meets the code in my mind anyway. The inspector says no, the rebar must have been laid for the sole purpose of being an electrode, code says at least 20′ I have that and and more. In that code section the last sentence says “Reinforcing bars shall be permitted to be bonded together by the usual steel tie wires or other effective means” what does this mean? Earllier another inspecter with expeirence in rocky areas said I could do the Ground Ring system by laying it buried next to the slab for 20′ augmented with 2 8′ bars not at 30″ depth, but they said no to that also. Here in New Mexico you can get inspectors working out of the same office giving you differnt explanation of code and how to do things. I’m a home owner builder need your help.
Replies
You should probably delete one of the duplicate posts. Maybe the one with the attitude responses. (;-)
Thanks I will delete attitude.
Look up Ufer ground. The rebar needs to be close to the bottom of the footer 2" is standard. The #4 wire needs to be bonded to the rebar. There is a clamp for that or another method that heats up copper and bonds the #4 wire to the rebar. Sorry forgot what that's called senior moment. The bonding point must also be incased in concrete. Wire ties are allowed to tie the rebar to another piece of rebar to get your 20' as long as the two pieces of rebar are tied together in 3 places with sufficient overlap. I think 30"
Jay, where does it say encase the bond within the concrete?
My understanding is the concrete tends to eat the copper, bond should be above grade with something like antiseize to protect it from moisture.
it's a mystery he sez.........
Can't think of the name of those little blasting caps either, but there are some special clamps for it.
Joe H
It's a CadWeld or other type exothermic weld connections.
Used it once..it was cool, but expensive. I paid $60.00 for one clamp.
I just completed a warehouse addition and the electrical system was upgraded. The old system was 800 amp 480v service. The new one was 2000amp 480v service. The EE who designed the system specified that the rebar had to be near the bottom of the footer. I mentioned that the code here was that rebar must have 2" of concrete between it and the ground to prevent corrosion and the EE said no more that 2" was acceptable to him. His design and we talked about it required the bond to be inside the concrete. He said that if the rebar stuck out and the bond was made outside the concrete the bond would deteriorate because of the difference on the galvanic scale between copper and steel. Being in the concrete the bond would not deteriorate. Yep CadWeld is the term I was looking for. We had to CadWeld the wire to the rebar and weld special copper plated steel brackets to each columb and Cadweld the brackets to a copper wire that was connected to the grounding system for bonding.
Edited 2/26/2009 6:56 pm ET by Jay20
Seems odd, steel nails and copper roofs are a no no, how's come this works?
Need Junkhound to splain this one.
Joe H
Or how does concrete, which can hold a lot of water for a long time, offer significantly better protection that other locations?
Jon Blakemore RappahannockINC.com Fredericksburg, VA
I think the moisture in the concrete is what makes this whole thing work, hence the prohibition of plastic under the footing.
There was a thread a few months ago about pouring concrete into a woven plastic form that was hung on a 2x4 frame work.
I know there was a mention that product being a no go for Ufer.
Seems like eventually there is going to be corrosion of the joint unless it's done with one of those expensive sparkler thingees.
Joe H
Yeah, you're darned if you have moisture, you're darned if you don't.
Jon Blakemore RappahannockINC.com Fredericksburg, VA
Maybe no oxygen present? = no corrosion?
Joe H
"The rebar needs to be close to the bottom of the footer 2" is standard. The #4 wire needs to be bonded to the rebar. There is a clamp for that or another method that heats up copper and bonds the #4 wire to the rebar. Sorry forgot what that's called senior moment. The bonding point must also be incased in concrete. Wire ties are allowed to tie the rebar to another piece of rebar to get your 20' as long as the two pieces of rebar are tied together in 3 places with sufficient overlap. I think 30""
See, now this illustrates the regional/inspector of the day inconsistency. My inspectors don't care that the ufer bar itself is near the bottom of the footing, but that it is continuous, and connected to the rest of the reinforcement by wire ties. You can't get your 20' out of pieces. Nor does my area require the bonding point to be encased in concrete. We stub the bar up into the wall and bond there with a mechanical clamp, and put a mud ring there so it's accessable.
I know the 'pyrotechnic' method for bonding you are talking about. They don't make us do that here. It's a 'fun' process.
"Reinforcing bars shall be permitted to be bonded together by the usual steel tie wires or other effective means" what does this mean? "
On the 2 recent slabs I had, with Ufer grounds, one just last week, the inspectors told me each time that they wanted more ties on the 20'er where it met the rest of the rebar. Specifically, they wanted at least 4 wire ties (you know, rebar twist ties) within the first 6 feet of the connection btw the 20' stick and it's neighbors.
I guess they just want enough points of contact with the metal--but if you read the description of the "Ufer" ground http://www.psihq.com/iread/ufergrnd.htm it explains that it is the conductivity of the concrete that makes the ground work.
I dunno.
I would arm yourself with as much info as you can, including your photos, and hope for the right inspector for the day!
I agree, inspectors can really vary. I'm always sweating the details I know they COULD call--but they often don't. But, when they do, I'm ready with an arsenal of counterpoints and it usually works (presented respectfully of course.)
good luck.
Pat
RE: Second guessing inspectors.
Boy howdy, are you ever right. I'll never get it.
Project I'm finishing has a 3,000 sg ft second floor deck. I'm in the Seattle area, the client is from California, the guy barbecues 5 nights a week. So, outdoor kitchen, gas heat, and, originally (approved plans), about 500 sq ft of roof. Client decides he needs about 1200 sg ft of covered deck. OK! (It's only money!).
Back to the Archy, then the engineer, redo footings, surprise my lumber guy (Yeah Tom, I need 6/ 25' PT #1 4x6s). Get all my documentation in a file, engineering, lumber grade, pier photos...man I'm so ready to get called on this. I've got about $2,000 worth of Simpson metals, all documented, screw shedules, bolt schedules and nail schedules, photos of every step.
I mean, this is a 1200 sq ft wind sail 25' off the ground, on the side of a mountain. Plus it's a bit unusual, so man, am I ready.
Inspectors never said a word about the structure. Zilch, nada,zip.
I'll never get it.
And you were all ready for it... what a letdown!
The electrician says he knows two inspectors--one's a car guy, and the other, sailing.
He'll start off on cars or sailing when the guys shows up and it's off to the races. An hour later, "Whoa, I gotta go.. where's that card, I gotta sign your card..."