Is grounding rebar in concrete slab required by NEC?

[hornetd]

Nope. You need to reread what the code actually says, not what you think it says.

Your right of course but I would assert that I wasn't reading the NEC to mean what I want it to say. I simply made a mistake. A good principle to apply here is "Never attribute to malice what incompetence will adequately explain." I wrote an incompetent statement by rushing through a posting I was trying to get done in too much of a hurry. Again I made a mistake. It was not intentional. I'm sorry for the confusion I may have caused.

 

[ptonsparky]

Your right of course but I would assert that I wasn't reading the NEC to mean what I want it to say. I simply made a mistake. A good principle to apply here is "Never attribute to malice what incompetence will adequately explain." I wrote an incompetent statement by rushing through a posting I was trying to get done in too much of a hurry. Again I made a mistake. It was not intentional. I'm sorry for the confusion I may have caused.

That's at least 4000 down on the Forums 'Oops List'.

 

[hornetd]

Sounds like you are describing an Alaskan Slab. The typical installation would require vapor barrier and insulation thus become non usable for a CEE. See Typical installation illustrations:
View attachment 2575176
View attachment 2575178

Your first illustration does not show the vapor barrier extending under the footing. Your second illustration does show it extending under the footing and about well beyond that with foam insulation underneath the footing coming out a full 4 feet.

Question: Does the second illustration show an actual building code requirement or is it just an example of 1 technique?

 

[Fred B]

Your first illustration does not show the vapor barrier extending under the footing. Your second illustration does show it extending under the footing and about well beyond that with foam insulation underneath the footing coming out a full 4 feet.

Question: Does the second illustration show an actual building code requirement or is it just an example of 1 technique?

It is a requirement here but may not be complied with in some cases as there are still a lot of "Don't tell me what to do" mentality out there and no enforcement.

 

[wthomas]

There is a general misunderstanding here: It is not required to ground rebar in a footing or slab or whatever. The requirement is: If there is a rebar present which meets the requirements of a concrete encased electrode ( at least #4, extending at least 20feet horizontally or vertically, encased in at least 2" of concrete in direct contact with the earth) then at least one qualifying rebar must be bonded as a grounding electrode. The 20' length can be made up of shorter pieces of rebar wired together in "the usual fashion". ONLY ONE SUCH BOND is required even if multiple rebar which meet the criteria are present. One is not "grounding the rebar" but using the rebar for a grounding electrode. It does not matter if the qualifying rebar is in a footing or a slab.

 

[don_resqcapt19]

general misunderstanding here: It is not required to ground rebar in a footing or slab or whatever.

It is not required for a slab...it is only required for a footing or foundation.

250.52(A)(3)... shall be located horizontally within that portion of a concrete foundation or footing that is in direct contact with the earth ...

 

[Seven-Delta-FortyOne]

It does no such thing. If the rebar exists, it must be used as a grounding electrode. Nothing in the NEC requires the installation of rebar in concrete. The same with the 4 awg....the code does not require you to install it, but the code does permit you to install it and use it as a grounding electrode.

That is interesting, because that is not the way it is presented here by my local AHJs.

Part of the issue is, like I said, California building code requires rebar in the footings. Therefore it must be used as a CEE, unless it is disqualified because of a vapor barrier or insulation.

When we get a footing/pre-pour inspection, for rebar size and placement, setback, footing size and depth, etc., the inspectigator checks for the presence of a CEE. I’ve built several buildings in the last few years, since that became a requirement, and every single one without an exception, the inspector has looked for a CEE.

But like I said, that is probably because we can’t, don’t, and won’t, build without rebar here in California.

Edit to add: Virtually every set of engineered plans I get has a CEE called out as well, so that makes it a requirement, but even the ones that didn’t it was still checked for by the inspector.

 

[kwired]

That is interesting, because that is not the way it is presented here by my local AHJs.

Part of the issue is, like I said, California building code requires rebar in the footings. Therefore it must be used as a CEE, unless it is disqualified because of a vapor barrier or insulation.

When we get a footing/pre-pour inspection, for rebar size and placement, setback, footing size and depth, etc., the inspectigator checks for the presence of a CEE. I’ve built several buildings in the last few years, since that became a requirement, and every single one without an exception, the inspector has looked for a CEE.

But like I said, that is probably because we can’t, don’t, and won’t, build without rebar here in California.

Edit to add: Virtually every set of engineered plans I get has a CEE called out as well, so that makes it a requirement, but even the ones that didn’t it was still checked for by the inspector.

Most the time rebar is required. should it not qualify because of vapor barrier or coated rebar then NEC doesn't require you to make an electrode. Though you still could possibly just put in 20 feet of #4 bare copper and create one if you so desire, but that is totally optional according to NEC.

 

[tom baker]

The purpose of the ufer ground is as permanent grounding electrode for a service. If there is no service then no need to bond, unless required by other codes

 

[WD40]

That is interesting, because that is not the way it is presented here by my local AHJs.

Part of the issue is, like I said, California building code requires rebar in the footings. Therefore it must be used as a CEE, unless it is disqualified because of a vapor barrier or insulation.

Yeah something changed a few years back in the 'foundation code' or whatever that is, here also its not just in CA.
When concrete reinforcing bars are installed in concrete footings or slab the concrete guys are required by their inspector to make a CEE and get it green tagged.
They call to ask where I want it, then they simply cut out some of the vapor barrier under a 20 foot section of rebar and add a stub up under the panel. Its nice now I dont need ground rods.

 

[Joethemechanic]

Hadrian did not use rebar in the dome of the Parthenon

I guess he could have used wrought iron rebar, but it probably would have rust jacked the concrete apart. Maybe he could have used copper or one of the brass or bronze alloys. Must have done something right,, it stood 1,500 years and only got destroyed because of an explosion

 

[jaggedben]

Yeah something changed a few years back in the 'foundation code' or whatever that is, here also its not just in CA.

I can't recall chapter and verse but I recall that requirements for vapor barriers around foundations are a relatively recent addition to building codes (not the NEC, other code). They may not be in force yet in some places or the AHJs may not really have caught up to it.

When concrete reinforcing bars are installed in concrete footings or slab the concrete guys are required by their inspector to make a CEE and get it green tagged.

This is a process that AHJs use to coordinate the enforcement of two different codes, for rebar and CEE. But if it is strictly required then it's in conflict with the newer vapor barrier requirements.

They call to ask where I want it, then they simply cut out some of the vapor barrier under a 20 foot section of rebar and add a stub up under the panel. Its nice now I dont need ground rods.

This sounds like a kind of informal compromise where the vapor barrier isn't strictly enforced, to allow the previously mentioned process devised for coordinate enforcement of rebar and CEE to still be used. It cuts down on the effectiveness of both the vapor barrier and the CEE. But I suppose the CEE may still be better than alternative electrodes such as two rods, and the mostly complete vapor barrier definitely better than none at all.

Still, to really follow the code they should also give you the option of a complete vapor barrier and alternative electrode(s).

 

[jaggedben]

I guess he could have used wrought iron rebar, but it probably would have rust jacked the concrete apart. Maybe he could have used copper or one of the brass or bronze alloys. Must have done something right,, it stood 1,500 years and only got destroyed because of an explosion

You guys are confusing the Pantheon and the Parthenon, but regardless you may find this interesting.

Riddle solved: Why was Roman concrete so durable?

Researchers have discovered ancient Roman concrete-manufacturing strategies that incorporated self-healing. Applying this knowledge toward modern cement production, they hope to improve the material’s environmental impact.

news.mit.edu

 

[kwired]

The purpose of the ufer ground is as permanent grounding electrode for a service. If there is no service then no need to bond, unless required by other codes

250.32 also requires grounding electrode system for a building supplied by feeder or branch circuit and refers you to part III for how to do so which is same section that applies for how it is done for buildings supplied by a service.

Bottom line is for any situation where a grounding electrode is required 250 part III pretty much applies for how to do it.