Broken PEN conductor

[bernardgreen]

Bernard would undoubtedly say that it was possible.

I would undoubtedly say that "that a shock is possible just by touching a live conductor while standing on the floor;

And say that the severity of the shock will vary depending on the type of floor, type of shoes ( if any ) and proximity of Earthed item to the person.

When standing on a dry carpet with bare feet the "shock" would be a mild tingle and may be so weak as to be not noticed. ( do not attempt to try that out )

 

[EFLImpudence]

Yes, but there is a 'path' to earth (through timber, masonry plaster etc. - nothing, other than a vacuum, is a perfect insulator))

You know what I meant.


Do you therefore think it would be better NOT to earth exposed-c-ps as it is less hazardous to touch a possibly live e-c-p with no (significant) earth path - than to touch a live flex with earthed metal all around?

A few lengths of plastic pipe would also remove the pipework from being a hazard too, rather than bits of wire all over the place.

 

[JohnW2]

I would undoubtedly say that "that a shock is possible just by touching a live conductor while standing on the floor;

... and, as I have implied, I would agree that it is possible.

And say that the severity of the shock will vary depending on the type of floor, type of shoes ( if any ) and proximity of Earthed item to the person. When standing on a dry carpet with bare feet the "shock" would be a mild tingle and may be so weak as to be not noticed.

... and I've essentially said all that, too. However, I've also said that (having tried a good few times over the years), I think that I have yet to find a measurable path to earth from a floor (other than in cellars or outhouses) in any house I've lived in, even most ground floor solid floors (certainly the couple I have in my present house). That's why, as I said, I suspect that the path to earth which is responsible for the 'tingles' we often hear about is often/usually capacitive, not resistive through the fabric of the building.

There obviously are exceptions. My daughter's 18th century cottage has a kitchen (a Victorian extension) consisting of un-grouted quarry tiles sitting on sand which, in turn, is sitting on soil - and in wet weather, there is not uncommonly 'standing water' on it. I obviously can measure a path to earth from that, and it theoretically should be 'bonded'.

Kind Regards, John

 

[JohnW2]

You know what I meant.

Well, sort of. As I said, the theoretical 'path to earth' through floorboards and masonry etc is likely to usually be 'unmeasurable', but if those parts of the building were very wet, things would probably be very different.

Do you therefore think it would be better NOT to earth exposed-c-ps as it is less hazardous to touch a possibly live e-c-p with no (significant) earth path - than to touch a live flex with earthed metal all around?

As you know, whether one would regard that as 'better' depends primarily on which of the two scenarios one regards as the more likely - you and bernard seem to be close to representing the two ends of that spectrum of opinions/judgements. However, as you go on to say, it's metal plumbing that causes many/most of the potential problems, since there are millions of installations out there which do have earthed pipes, radiators, taps etc.

A few lengths of plastic pipe would also remove the pipework from being a hazard too, rather than bits of wire all over the place.

Indeed - and compulsory 'insulating segments' in incoming services where they enter the building (possibly outside the building in the case of gas) would make things even better.

Kind Regards, John

 

[ban-all-sheds]

When standing on a dry carpet with bare feet the "shock" would be a mild tingle and may be so weak as to be not noticed. ( do not attempt to try that out )

Has anybody here ever felt that sort of "sticky" feeling, when lightly dragging a fingertip over a metal object whilst shod and stood on a dry carpeted or wooden floor, and thought "Oh - hello - that's not right"?

 

[JohnW2]

Has anybody here ever felt that sort of "sticky" feeling, when lightly dragging a fingertip over a metal object whilst shod and stood on a dry carpeted or wooden floor, and thought "Oh - hello - that's not right"?

Are you perhaps talking about 'static'?

Kind Regards, John

 

[Lectrician]

It should also be pointed out that there is a large risk of fire with an open circuit PEN, as current finds different routes to flow, including through bonding and other parallel paths.

Chicken wire retaining insulation in a building carried the current for a terrace of houses causing them to catch fire. Fires have started in lofts. Cables often burn out. I’ve seen lighting circuit cables melt after taking the entire night storage heater load through a N to E fault, and cables melt where earths in a lighting circuit were common when a building was split into two flats. There have been more instances of fire, or near fire than shocks.

 

[ban-all-sheds]

Are you perhaps talking about 'static'?

No.

 

[bernardgreen]

Has anybody here ever felt that sort of "sticky" feeling, when lightly dragging a fingertip over a metal object whilst shod and stood on a dry carpeted or wooden floor, and thought "Oh - hello - that's not right"?

Are you perhaps talking about 'static'?

The sensation is often the result of the object having a two pin ( no Earth ) power supply module. Capacitive coupling in the power supply creates a potential on the output around the mid point of the mains supply. As it is capacitively connected via ( hopefully ) very small stray capacitance no signbificant current can flow. Hence it is similar to static electricity but much lower voltage and continuous

 

[bernardgreen]

there is not uncommonly 'standing water' on it. I obviously can measure a path to earth from that, and it theoretically should be 'bonded'.

If it were a TT installation then there would already be a bond via the ground from floor to TT rod.

 

[JohnW2]

It should also be pointed out that there is a large risk of fire with an open circuit PEN, as current finds different routes to flow, including through bonding and other parallel paths.

Indeed - but, of course, an additional local earth electrode would/will (unless it is a very exceptional earth electrode) not really make a blind bit of difference to that.

Given that the "different routes" will almost inevitably involve extraneous-c-ps (nearly always utility supply pipes) with very low impedances to true earth, then, if one wanted to address the risk to which you refer, rather than require earth rods (which seems like a useless gesture), as I recently wrote, would it not have been better to require 'insulating segments' in incoming service pipes?

Kind Regards, John

 

[JohnW2]

If it were a TT installation then there would already be a bond via the ground from floor to TT rod.

Well, for a start, her installation is TN-C-S. However, even if it were TT, the impedance from the floor to the TT rod would almost certainly be too high to be effective as 'bonding'.

Kind Regards, John

 

[bernardgreen]

even if it were TT, the impedance from the floor to the TT rod would almost certainly be too high to be effective as 'bonding'.

But the floor and the TT rod ( and hence the CPC and MET ) would be at the same potential (*) so bonding would not need to be substantial to carry high currents

(*) assuming there are no 25kV overhead electrified railways nearby putting traction current returns ( Neutral ) into the ground and thus causing significant voltage gradients under the house.

 

[JohnW2]

But the floor and the TT rod ( and hence the CPC and MET ) would be at the same potential ....

Is that necessarily the case? If there were an uncleared L-CPC fault in the installation, the potential of the earth rod would rise to more-or-less the full supply potential above true earth. I would have thought that a solid floor which was at least a few feet (potentially a fair bit more) from the rod, would have a potential closer to true earth than were the case with the rod. Is that not correct?

[ Although Ohm's law would suggest that (were we talking about a simple conductor), when there were no current flowing through the path between them, there would be no potential difference between the rod and the floor, the things which go on 'in the 3D environment of the earth' are obviously a lot more complex than the situation of a simple conductor - otherwise applying 230V (relative to true earth) to a rod in one place would result in the potential of another rod a mile (or 10 or 1000 miles!) away rising to the same potential! ]

Kind Regards, John