On Wed, 04 Jan 2017 23:31:13 -0000, "James Wilkinson Sword"
wrote:

On Wed, 04 Jan 2017 22:56:57 -0000, FromTheRafters wrote:

James Wilkinson Sword pretended :
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?

https://engineering.purdue.edu/~conc...hapter%203.pdf

So as I said before, it's the water conducting. But your floor really really shouldn't be damp.

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.