Ground rods

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Tom Horne wrote:

IIRC Yfer was consistently under 5 ohms in the desert. Seen any information of concrete encased electrode?
--
bud--

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wrote:

I doubt it really makes that much difference. Concrete is really the conductor. The NFPA determination was that 20' of rebar OR copper will bond to the concrete footer. 250.52(A)(3) On the other hand in a swimming pool they want a 12" x 12" grid to bond that concrete. 680.26(C) I think the truth may actually be somewhere in between.
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snipped-for-privacy@aol.com wrote:

I thought the main contribution of the concrete was leaching alkalinity into the soil, increasing conductivity. I liked your idea, in another thread, of tying the rebar all the way around the foundation.

Although thats for equipotential, not earthing.
------------------- Is there a deteriorating effect of concrete on bare copper grounding conductor and parts like split bolts around the pool.
--
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wrote:

I agree the intent is different but the bonding mechanism to the concrete is the same.

I haven't heard about that but if the pool plaster is really doing it's job the moisture in the concrete should be from the dirt side.
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snipped-for-privacy@aol.com wrote:

Was thinking of the deck, where I believe concrete interior is often 'damp'. And more particularly copper in "concrete encased electrode" by itself. And connecting copper to rebar and floor mesh in concrete do you get galvanic corrosion?
I thought corrosion was a reason for requiring a pool bonding wire to be solid, not stranded (680.26-C). (Not arguing, just trying to put the pieces together.)
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wrote:

They do reqire a listed device to make thgis connection and most AHJs want to see a bronze 2 part clamp so the copper and steel are not in contact. Erico has an acorn listed for rebar but it is a "ground rod" clamp used for Ufers, most say not for pools.

I agree, the "solid" is for better corrosion resistance and less chance of physical damage. Personally I wish they would address the damage issue more. It is not unusual to find the bonding conductors broken on "old work". BTW the #8 to the underwater light from the J box can be stranded but it also has to be potted. This is really somewhat a redundant wire since you also bond the niche to the pool steel with a #8 solid on the concrete side but it is still required
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snipped-for-privacy@aol.com wrote:

How do they get broken/damaged?
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wrote:

There is no burial depth requirement so I imagine the yard man hits them with an edger. Around the pool equipment they are usually just laying on the ground. On my pool I put the ground wire under the pipes going to the pump but that takes coordination between the plumber and electrician. (both me in this case)
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Quite the opposite in my local town. They consider the water supply pipe to be a suitable ground as a standalone. (they also require that supply to be metal all the way to the meter)
s

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wrote:

You have the opportunity to make the best electrode available. I assume you are pouring a new concrete floor? If so, dig a small trench around the perimeter, ring it with 1/2" rebar on chairs and use that for your "Ufer" electrode. Don't put plastic under this part of the pour so the concrete in the ring is in contact with the dirt If you also tie that to the wire in the slab pour you have created a ground plane under your basement. There are two choices in coming up. You can stub up a piece of rebar abnd connect to that (some AHJs will not accept this method) or bring up a #4 copper that was connected to the rebar with a listed acorn or other "rebar" rated connector. It is best to run a piece of RNC (grey PVC) sleeve over this conductor, into the pour so it doesn't get damaged.
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wrote:
BTW if you do want to take your vapor barrier all the way to the wall, lay it out on the floor part, roll it back around the edge and pour your trench up to the base of the floor dirt level, flip the vapor barrier over the wet concrete and pour the floor.
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If you are going to pour a concrete slab with rebar, why just not ground your electrical system to the rebar? Would that not provide a much better ground than a couple of pieces of copper? Just wondering!
Ivan Vegvary
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All the rebar should be inside the concrete. This is to prevent rusting which would cause the rusted rebar to expand and crack the concrete. You would have a very poor electrical ground if this is done.
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Ivan Vegvary wrote:

Yes Ivan it would as long as a non conductive vapor barrier is not installed beneath the concrete. -- Tom Horne
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