Ufer (electrical grounding mechanism) not possible with floating raft slab?
It might seem like a no-brainer but I felt I needed to ask (as I’m not an electrician). I’m asking as pertains to US electrical code requirements: I suspect, however, that as this is a pretty primal thing that it would be in international code.
With a floating raft concrete and rebar foundation (on insulation) one would have to go with the old-fashion grounding mechanism of direct rod to earth rather than Ufer (electrical grounding through slab’s perimeter rebar). Would this be correct?
NOTE: I’m just doing some preliminary planning/research.
GBA Detail Library
A collection of one thousand construction details organized by climate and house part
Search and download construction details
Replies
The slab wouldn't meet the "concrete in direct contact with the earth" requirement. But I assume you could lay bare wire under the foam, adding a lot of moist ground contact to what the still-required rod provides.
Yes.
您是否因为在干燥的土壤中获得良好的地位而对UFER感兴趣？还是作为替代方案？在大多数地方，一根杆杆便宜且运行良好，所以这不是问题，但是也许您正在处理它不正常工作的非常干燥的土壤？
As has been mentioned, clarification as to why you're asking would be helpful. The code requires that such a ground be used *if* it is present. In the case described, it is not present, for the reason Jon R stated. The code even has a clarifying remark: "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."
You can't just lay a ground wire under the footing and call it good. You CAN run a length of #2 copper 30" deep and use that though, I believe the minimum length is 20 feet (I'd have to check that, I typically put in rings around buildings where I'm always well over the minimum length). You could do this set a ways out from the foundation, probably in the same excavation, you just need earth ALL The way around the wire.
如果使用杆，请记住，您现在必须达到最小电阻测量。这通常意味着至少需要两个杆。如果将这些设置为地下，我建议通过放热焊缝进行连接（通常意味着“ Cadweld”，这是一个品牌）。我不建议在地下使用机械夹。
仅当混凝土直接接触地球时，UFER地面才能起作用。如前所述，任何绝缘屏障或蒸气屏障都阻止了UFER的工作原理。
BTW, Ufer grounds are somewhat unique to the US in that they were developed here. You don't see them as often internationally.
Bill
Folks, thanks for the replies.
I've done wiring for sub panels and for a garage build that I'd worked with my electrician on. The garage build was spec'd to have a Ufer ground: I installed that prior to the concrete pour. On my other sub panel/branches (pump house and a shed) I used ground rods: the pump house has one rod and the shed has two- I suspect the difference being that I did the pump house earlier on.
No issues here (Pacific Northwest) with grounding to earth as there's a high water table.
我怀疑我正在将分支机构和主体之间的接地机制混合在一起，并且我必须与Rod（S）进行主服务面板，这是我目前拥有的（由于它是一个制造的房屋，因此已超过主服务- 我想做一个新的“常规”构建的主要原因；我厌倦了制造房屋的所有奇怪之处；因此，我的参考有点不合时宜）。
My query here has more to do with literally managing the ins and outs of things through the building envelope. It appears that a ground wire will need to piece the building envelope. I will, for sure, work out the electrical code stuff/requirements with my electrician.