Earthing a water pipe??

[aptsys]

Are you perhaps considering the possibility of a fault to an extraneous-c-p affecting other properties which also have extraneous-c-ps?

Kind Regards, John

Just the mass of earth. Faulty equipment in contact with the ground, pond pump, whatever.

 

[John D v2.0]

Then the ground would be an ecp and it wouldn't be an earth free environment

 

[aptsys]

An "earth" free environment is essentially impossible. I'm not sure I understand your point.

If you have a faulty appliance which comes into contact with anything with anything other than infinite impedance, it is now no longer a floating circuit.

 

[JohnD]

An "earth" free environment is essentially impossible.

Such an environment is often provided in electronics factories.

 

[John D v2.0]

An "earth" free environment is essentially impossible. I'm not sure I understand your point.

If you have a faulty appliance which comes into contact with anything with anything other than infinite impedance, you have removed one of the two levels of isolation.

Earth free is possible with careful design eg suspended timber floor and no other ecps.

My point was that John w said were you considering a fault to a shared ecp and you said you were referring to a fault to the earth, but that in this case would be an ecp.

Regarding the fault losing one level, indeed that was my point previously about having an invisible fault for a long time, so the only solution would be to have a metal free environment as well. That is effectively this whole debate about whether to earth everything in sight or not.

Indeed the live conductors are introducing a potential into the property so they are effectively ecps in their own right.

 

[aptsys]

Earth free is possible with careful design eg suspended timber floor and no other ecps.

You still get a shock stood in the loft if you touch a phase conductor, usually not terribly painful, but timber has a moisture content to it and is still conductive.

Such an environment is often provided in electronics factories.

Why? I've never come across this in my time.

 

[JohnD]

I can't remember why, but I have worked in a company that did it.

 

[John D v2.0]

You still get a shock stood in the loft if you touch a phase conductor, usually not terribly painful, but timber has a moisture content to it and is still conductive.

I've never tried it!but it could be the presence of metal pipes indirectly connected to the neutral?

If someone is getting a shock you're supposed to use a wooden broom to remove the cable if you can so I assumed wood wouldn't conduct significantly at 240v.

What impedence to earth is required for something to be earth free?

 

[John D v2.0]

timber has a moisture content to it and is still conductive.

I did a bit of research as I thought this was an interesting point, according to Wikipedia a 1m long piece of "damp wood" of 200x50 section with no parallel paths would be 100Kohm to 1Mohm.
I seem to remember a guy on YouTube doing some tests passing current between his hands, I think even 10mA was very painful. Even with 100kohm you would get 2.4mA so I can believe it's possible to get a noticeable belt.

 

[bernardgreen]

Such an environment is often provided in electronics factories.

Never seen that......In fact the opposite..... people working on assembly and / or testing of electronic items are often "grounded" to a clean earth using wrist and / or ankle straps. The lead typically has a resistor 1 MegOhm or greater. The reason is to prevent build-up of static charges on the person, never the less it is a veak weak earthing of the person.

http://www.descoeurope.com/Europe-Catalogue/Wrist-Straps-and-Coiled-Cords/

Some assembly benches are supplied via 230 - 230 isolation transformers but that is different matter.

 

[rsgaz]

I seem to remember a guy on YouTube doing some tests passing current between his hands

It was bigclive... Skip to 13:30

 

[JohnW2]

Just the mass of earth. Faulty equipment in contact with the ground, pond pump, whatever.

You mean, say, an "L-ground" fault in one property and an "N-{exposed-c-p}" fault in another property fd from the same transformer, or something like that?

Kind Regards, John

 

[JohnW2]

If someone is getting a shock you're supposed to use a wooden broom to remove the cable if you can so I assumed wood wouldn't conduct significantly at 240v.

Dry wood doesn't - so an 'indoor broom' ought to be pretty safe.

Kind Regards, John

 

[DIYedboy]

Obviously, most of what you lads are saying is all going waaay over my poor little head, but to add a couple of points, perhaps the reason the poor sparkies had to go to prison was a direct result of the poor woman being the wife of....................an MP.
Years ago I remember being told about a window cleaner that was killed whilst cleaning windows due to the metal window frame being earthed, can you shed any light on that?

 

[JohnW2]

Years ago I remember being told about a window cleaner that was killed whilst cleaning windows due to the metal window frame being earthed, can you shed any light on that?

That illustrates the reason why it is inadvisable to earth things 'unnecessarily'.

To get an electric shock, a current has to flow through one's body. If you just touch something "live" (i.e. at 230V or whatever), and absolutely nothing else, (don't try it!) you won't get a shock - but if some part of your body is in contact with something earthed, current will flow through your body from the "live" part to that earth.

Kind Regards, John