Conducting concrete

Somebody in one of these two groups recently said that a concrete based house means you're earthed. Concrete is a bloody good insulator!
Sorry, can't find the post it was mentioned in.
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On Wednesday, January 4, 2017 at 12:58:25 PM UTC-5, James Wilkinson Sword wrote:

Wrong as usual. Concrete that's been cured and then dried out, kept away from moisture, may not be a good conductor. But building concrete, a foundation is such a good conductor, it's the preferred ground for the building electrical service. An electrode is placed inside it before the pour.
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On Wed, 4 Jan 2017 10:31:06 -0800 (PST), trader_4

Ah yes, the old Ufer ground. That protected a lot of ordinance throughout the years.
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Only if the concrete stays wet. Which won't happen unless it rains a lot.
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On Wed, 04 Jan 2017 20:02:30 -0000, "James Wilkinson Sword"

This was originally designed for ammo dumps in the desert so try again. Where you live, it is always wet isn't it? The effectiveness is in the contact area, not any single point.
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First time I've seen ammo dumps mentioned. We're talking about houses, concrete floors, and the dangers of being earthed.

Yes, but not inside the house.

The top surface of the concrete in the house isn't wet. If it is, your carpet would go mouldy.
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On Wed, 04 Jan 2017 22:17:02 -0000, "James Wilkinson Sword"

The danger is not being earthed when you are talking about ammo and this was the most effective way to earth them.

It is wet enough to ionize the stuff in concrete. I didn't make this shit up on the spot, google Ufer.
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Perhaps, if the concrete is guaranteed to be wet, but then the ammo would get damp.
But I wasn't talking about ammo.

It simply isn't true, I tested it.
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On 1/4/2017 9:58 AM, James Wilkinson Sword wrote:

Can't help with a link, but I recently replaced my water main with PEX. That broke the ground to the house and wouldn't pass inspection. Long story short, research indicated that using rebar in concrete was a trend in establishing a safety ground. Apparently, there's enough conductive salt and water in concrete to make it work, as long as the concrete sits on the ground and you're not in the desert. Contact resistance is high, but there's a lot of area.
I followed the code and installed two ground rods. I did some impedance measurements between the rods and the electrical system ground (before connecting) and determined that the "grounding" was insufficient to do anything more than dissipate static electricity, but the inspector liked it. I'd guess that hooking to the rebar is at least as good.
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It was more about getting an electric shock by standing on the floor of your house while touching something live. This was suggested by someone recently as being a danger. I just measured some concrete to make sure I wasn't being ignorant, and it was off the scale (>20MOhms)
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On Wed, 04 Jan 2017 20:00:22 -0000, "James Wilkinson Sword"

Across what surface area? Why don't you sit on the concrete floor barr assed and grab a hot wire. Have your widow get back to us.
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1cm from electrode to electrode = >20MOhms. That's an INSULATOR. No electricity worth considering is passing at all.
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On Wed, 04 Jan 2017 21:22:56 -0000, "James Wilkinson Sword"

Then it should be safe, pull up your kilt, plop down on a concrete floor and grab that wire.
Don't tell me you are one of those scotsmen who wear panties.
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What part of 20MOhms didn't you understand?

I go commando.
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James Wilkinson Sword pretended :

https://engineering.purdue.edu/~concrete/students/farshad/MS-Chapter%203.pdf
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So as I said before, it's the water conducting. But your floor really really shouldn't be damp.
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On Wed, 04 Jan 2017 23:31:13 -0000, "James Wilkinson Sword"

The Ufer ground is not in the floor, it is in the foundation but your concrete floor still has enough conductivity to get you a nasty shock if you have sufficient contact.
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20 MOhms prevents shock.
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On Wed, 04 Jan 2017 22:22:46 -0000, "James Wilkinson Sword"

Try it and get back to me. That is 20meg at one small point. If you can find 2 pieces of rebar with 20' in contact with the concrete, check that to ground or another rebar in the same slab.
"Earth" is a pretty bad conductor in the first place so what you are really trying to create is an equipotential ground grid.

Cool, especially when the wind is blowing in off the North Sea in January. ;-)
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Rebar isn't common here, anyway you have to conduct the electricity down to the metal.

No it isn't. Earth tends to be damp.

Especially then. I run naked along the beach, which causes amusement.
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