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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7 years ago
Conducting concrete
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7 years ago
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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7 years ago
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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7 years ago
Why did you want inspection? When you do work on your house, you don't tell anyone.
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7 years ago
our house while touching something live. This was suggested by someone rec ently as being a danger. I just measured some concrete to make sure I wasn 't being ignorant, and it was off the scale (>20MOhms)
Using what area, at what voltage, and what is the concrete resting on?
NT
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7 years ago
The electrodes were about 1cm apart, and on the ground, in Scotland, which is pretty damp.
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7 years ago
I guess one doesn't test earth grounding with a regular ohm meter. The instructor at one of my code refresher classes asked once if anyone had the correct type of tester. No one did out of at least 50 electricians. Earth grounding is primarily for damage from lightning. He also had a diagram showing how little current would flow through the earth if a well motor had a short to the frame. The resistance was so high that there was no way even a tiny fuse would blow if there was a short. This is from the meter maker Fluke:
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7 years ago
"A good grounding resistance is 5 ohms or less" - well since I got >20 MOhms, I guess that isn't grounded.
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7 years ago
f 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 w asn't being ignorant, and it was off the scale (>20MOhms)
h is pretty damp.
So less than a square millimetre at 1.5-9v
NT
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7 years ago
What's your point?
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7 years ago
Some cut.
So did you use an actual ground tester or a volt/ohm meter? It sure seems odd that your results don't match Mr. Ufer's and bunches of people after him. An article in Electrical Contractor magazine says Ufer's grounding electrodes kept the resistance at 2-5 ohms over a 20 year period.
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7 years ago
Resistance is resistance. Concrete does NOT conduct. WATER conducts. Concrete is a porous material which may or may not contain water. The floor of your house should never contain water, or you have BIG problems, way above a possibility of shock.
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7 years ago
Not that well, it is whatever salts and impurities in it that do.
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7 years ago
My house is on a slab and I get five volt tingle from the taps when I am in the shower. I suspect that when it was built they did not bond the steel mesh to earth, which they are supposed to do now.
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7 years ago
Not really (water that is), pure water is a very poor conductor. It's the impurities in water that make it a reasonable coductor but even tap water isn't that good.
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7 years ago
So is concrete the impurity here ?
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7 years ago
Is there an echo in here?
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7 years ago
r of your house while touching something live. This was suggested by someo ne 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)
hich is pretty damp.
Lol
NT
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7 years ago
salts in it sure can be
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7 years ago
Dry concrete will have a very low conductivity. It's the aqueous phase, and the salts therein, that are responsible for it's conductivity. As concrete sets, the conductivity falls from a high value when first mixed and poured, to a low value after a suitably long setting time. The salts in the aqueous phase will consist mainly of calcium, with some magnesium, potassium and sodium. Over time, these salts get incorporated into the mineral phases in concrete and conductivity falls.
See links here for more details
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