On Wed, 04 Jan 2017 22:22:46 -0000, "James Wilkinson Sword"
wrote:

On Wed, 04 Jan 2017 22:16:19 -0000, wrote:

On Wed, 04 Jan 2017 21:22:56 -0000, "James Wilkinson Sword"
wrote:

On Wed, 04 Jan 2017 21:11:26 -0000, wrote:

On Wed, 04 Jan 2017 20:00:22 -0000, "James Wilkinson Sword"
wrote:

On Wed, 04 Jan 2017 19:13:21 -0000, mike wrote:

On 1/4/2017 10:48 AM, burfordTjustice wrote:
On Wed, 04 Jan 2017 10:42:34 -0800
mike wrote:

On 1/4/2017 9:58 AM, James Wilkinson Sword wrote:
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.

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.


"James Wilkinson Sword" is in the UK...different rules
Question wasn't about rules.
Was about concrete as a ground. Unlikely it's much different in the
UK.

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)

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.

1cm from electrode to electrode = 20MOhms. That's an INSULATOR. No electricity worth considering is passing at all.

Then it should be safe, pull up your kilt, plop down on a concrete
floor and grab that wire.

What part of 20MOhms didn't you understand?

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.

Don't tell me you are one of those scotsmen who wear panties.

I go commando.

Cool, especially when the wind is blowing in off the North Sea in
January. ;-)