Ground rod

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cordial98

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I was just asked by a GC about burying a ground rod under a concrete slab, is there ever a time when you could do that and if so what connection type would be needed?
 
Re: Ground rod

(3) Concrete-Encased Electrode. An electrode encased by at least 50 mm (2 in.) of concrete, located within and near the bottom of a concrete foundation or footing that is in direct contact with the earth, consisting of at least 6.0 m (20 ft) of one or more bare or zinc galvanized or other electrically conductive coated steel reinforcing bars or rods of not less than 13 mm (? in.) in diameter, or consisting of at least 6.0 m (20 ft) 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.
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To bury the 8 foot rod does not comply to the concrete encased electrode.

250.53(G) the electrode shall be permitted to be buried in a trench that is at least 750 mm (30 in.) deep
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As long as the rod is 30 inches deep I don't see anything wrong with it being under the pad.

:)
 
Re: Ground rod

Mike,
That method of installing a ground rod is only permitted where you can't drive it vertical or at a 45.
I think the original question is about a driven rod under a slab. I see no code rule that says you can't do that. I also don't see anything that would prohibit the use of a driven rod under an interior slab.
don
 
Re: Ground rod

Nothing says that you can't drive the rod flush with the finished grade where the pad will be and then pour the pad over the top of it. In that instance, you'd only need a clamp suitable for direct burial. The allowance for burying a ground rod is only valid if rock bottom is encountered. Myself, rather than mess around driving a rod that will be covered by the pad, I'd use a Ufer ground. Less messing around, and a better ground anyway. Just my opinion.
 
Re: Ground rod

I had a question come to me about a month ago where the electrical contractor has installed a 20 foot piece of #5 rebar in the driveway for the grounding electrode.

When I read this question that situation came to mind.

When the ?new? inspector called me about this rebar I gave him the answer that the driveway was not a footer as outlined in 250,50(A)(3) and the rebar would not work as the grounding electrode. This inspector had just finished my Level I Inspector?s class.

The electrician had tried driving the rod at several places and could not get it to sink so the final call was to allow him to bury the rod under the driveway 30 inches down.

This is what had come to my mind when I read this post. Please forgive my assuming this was the same situation. Next time I promise to do better.

Side note; the location of the house on the lot had been moved due to hitting of rock while installing the footer. Several loads of dirt were hauled in to get the right water wash away form the house when doing the yard. The lot was a wedding present from Grandpa to his grand daughter.
 
Re: Ground rod

I think I have the answer I was looking for but this is what it's about,

An existing generator room with the ground rod driven outside about 8 inches from the wall, everything was fine. Now they came in and poured a 36 inch sidewalk leading into our computer room, they poured the slab leaving the rod untouched but now we have a rod and wire sticking 4 inches above the slab.

But from what I looked up and asked here I believe they can go ahead with what the Architect told them to do, and that is cut the slab, drive the rod and repour.
 
Re: Ground rod

Having the rod exposed like that is an actual violation. Driving it down and pouring concrete over it is not.
 
Re: Ground rod

Scott and Don

It would depend on how long the rod is.

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.

If the rod is 10 foot long then 2 foot can be left above ground if:

250.53 (G) 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.
250.10 Protection of Ground Clamps and Fittings.
Ground clamps or other fittings shall be approved for general use without protection or shall be protected from physical damage as indicated in (1) or (2) as follows:
(1) In installations where they are not likely to be damaged
(2) Where enclosed in metal, wood, or equivalent protective covering


I was way off base with my assumption that the rod was going to be laid down on the ground with concrete poured over it wasn?t I? :)
 
Re: Ground rod

jw,
That is the point I was trying to make with my question to Scott. The rule is that you must have 8' in contact with the earth...it doesn't say you can't leave part of a 10' rod exposed.
Don
 
Re: Ground rod

I'm not sure I'm convinced that burying an 8' rod 30" below a driveway would be a better ground than that 20' of #5 bar encased in concrete would be. Even if that concrete was on grade like the driveway. I'm actually not sure that a concrete slab on grade wouldn't meet the intent of 250.52(A)(3). You'd have to look at the definitions of footing and foundation (the ones in the dictionary, of course). Seems like I remember an illustration from one of Mike Holt's books showing a Ufer ground in a slab on grade. That slab is going to draw moisture whether it's on grade or below, and that's the key to it's effectiveness. I'm thinking I'd have accepted the Ufer in place of the buried ground rod. Just my opinion.
 
Re: Ground rod

Don, I was thinking about the 8' rod in full contact with the ground but I know that the rod length was not given so that would only be speculation. I know that is not usually allowed here so I put that out of my mind. :D

I was thinking about the rod being exposed to physical damage. In the situation described I would say that it would certainly be a likely hood.
 
Re: Ground rod

About half the rods I see stick up about an inch. One guy told me to do it like that so the inspector could see it. :roll:

You know what happens when they mow the lawn. :mad:
 
Re: Ground rod

Originally posted by jes25:
About half the rods I see stick up about an inch. One guy told me to do it like that so the inspector could see it. :roll:

You know what happens when they mow the lawn. :mad:
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I had an inspector that insisted that the connection to the rod had to be available for maintenance. I drove it even further down and placed a four inch plastic pipe over it with a female connector and a threaded plug. He was not a happy camper but I asked him to write it up so I could get the money for the extra work and he backed off. I then learned that the home owner was going to run a business involving computer servers and T1 line out of the home. So I installed rod couplers and stacked on two more rod sections until I got down to less than five ohms. I told the owner that what he did with that ugly piece of pipe was his business. I suspect he removed it but since he could do that without disturbing the GEC I can't see that it would do any harm.
--
Tom Horne
 
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