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Bust this myth


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The local AHJs have long insisted that grounds rods are not permitted to make contact with surface slabs if one is installed where the rod comes through.

Now I'm looking for chapter/verse on it for a report in progress and can't find anything. Another myth hits the dust?

Or do I have to check the manufacturer's listing?

Marc

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Have any of them offered a reason for that one?

Ground rods are copper-clad to prevent corrosion from contact with soil. Concrete, on the other hand, can be slightly corrosive to copper. Perhaps there is some concern about the soils down there creating a more aggressive chemical action.

The original Ufer grounds were copper wires laid into foundation footings, and even today the NEC allows a concrete-encased electrode to consist of 20 feet of 4 AWG copper in the footings.

They aren't going to show you a C&V on this from a national code.

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They hesitate to give reasons for anything. Want us to take it for granted.

I skipped this write-up on this report. Unless I find a listing against it (and I've tried) this myth is busted.

Thanks.

Marc

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Marc, in the picture shown there is a code violation. The rod is not in contact with the soil for 8', unless it is a 10' rod. The problem with the 10' rod would be that the top of the rod is supposed to be flush or below the surface.

Even if the top of an 8' rod were flush with the slab, it does not have the contact length with the soil for whatever the thickness of the slab would be.

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From 250.53

(G) Rod and Pipe Electrodes. The electrode shall be installed

such that at least 2.44 m (8 ft) of length is in contact

with the soil. It shall be driven to a depth of not less than

2.44 m (8 ft) except that, where rock bottom is encountered,

the electrode shall be driven at an oblique angle not

to exceed 45 degrees from the vertical or, where rock bottom

is encountered at an angle up to 45 degrees, the electrode shall

be permitted to be buried in a trench that is at least 750 mm

(30 in.) deep. The upper end of the electrode shall be flush

with or below ground level unless the aboveground end and

the grounding electrode conductor attachment are protected

against physical damage as specified in 250.10.

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