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While buying parts for Ufer ground for

2011-10-24 21:26:12.817538+00 by Dan Lyke 5 comments

While buying parts for Ufer ground for my shed, was told by guy at Maltby that the city would require a driven rod, too. Learning things...

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comments in ascending chronological order (reverse):

#Comment Re: made: 2011-10-25 16:05:15.332729+00 by: Larry Burton [edit history]

The 2008 NEC – Section 250.52(A)(3), reads as follows:
Electrodes permitted for grounding. Concrete Encased Electrode. An electrode encased by at least 50 mm, (2 inches) of concrete, located horizontally near the bottom or vertically, and within that portion of a concrete foundation or footing that is in direct contact with the earth, consisting of at last 6.0 m (20 ft.) of one or more bare or zinc galvanized or other electrically conductive coated steel reinforcing bars of not less than 13mm (1/2 in) in diameter, or consisting of at least 6.0 m (20ft.) of bare copper conductor not smaller than 4 AWG. Reinforcing bars shall be permitted to be bonded together by the usual steel tie wires or other effective means. Where multiple concrete encased electrodes are present at a building or structure, it shall be permissible to bond only one into the grounding electrode system
I would think this would allow the Ufer ground to replace the driven rod.

#Comment Re: made: 2011-10-25 17:47:07.340509+00 by: Dan Lyke

Here's the Sonoma County note on Ufer grounds. The part which I think applies to me is:

  1. Grade beams intended to retain a minimum earth contact of 2" or more can be treated as a standard T foundation system and ground accordingly.

It looks like there are multiple definitions out there for "Grade beam", because what I thought a grade beam was definitively had 2" or more of earth contact.

#Comment Re: made: 2011-10-25 18:31:27.358241+00 by: Larry Burton

Those pictures make it look like you are pouring a footing rather than a grade beam. Granted, though, I'm not the most knowledgeable person on foundations you have met.

So are you going to drive a traditional ground rod down through the form for your footing and bond it to your Ufer ground?

#Comment Re: made: 2011-10-25 18:57:22.547804+00 by: Dan Lyke

My impression on footing vs grade beam is that footing is the bottom half of an inverted T foundation, so you pour the footings, then the walls. I believe that a "grade beam" is when you pour the walls thick so that the footing and the walls are the same thickness, or at least that there's no step between the footing and the walls (Google searching on "grade beam" has images of structures that are sloped, narrower on the top than the bottom).

From reading that description, it looks like Sonoma County's notion of "grade beam" is a beam roughly on grade between two or more piers.

#Comment Re: made: 2011-10-25 19:01:04.103766+00 by: Dan Lyke

The inspector looked at it, said "oh, you're doing a Ufer ground, that looks good", but... if the city asks for it, I'm going to drive the traditional ground rod outside the form, probably in the service trench.

It sounds like the city wants me to run gas to the building as well, and both the buried gas lines and the electrical conduit should be solidly tied to a ground, adding an 8' post in the trench seems like a reasonable $20 (+a shload of effort).