Plumbers. Bless them.

[JohnW2]

If I had a live CPC in my cottage the shock hazard from touching a damp wall while holding a metal kettle is significant.

It may be literally true that the 'shock hazard' is significant but, unless you live in a cottage which is unheated and with walls constantly covered in mould, I seriously doubt that you'd every get anything like enough current through you by touching the interior surface of a wall to represent a significant threat to your life, even if the potential of your CPCs (hence exposed-c-ps, like your kettle) rose to 230V.

Kind Regards, John

 

[ban-all-sheds]

Why do we never learn that it is pointless trying to reason with bernard over bonding?

As someone once observed, it is not possible to use reason to argue against positions not arrived at by that method in the first place.

 

[JohnW2]

Why do we never learn that it is pointless trying to reason with bernard over bonding?

Maybe because we know, through experience, that his views on bonding and earthing are by no means the most extreme that are around

Bernard is certainly no fool, and his arguments on this subject are always fairly well reasoned - but reasoned on the basis of premises and assumptions about probabilities (i.e. 'risks'), and relative probabilities, which many of us may disagree with.

Kind Regards, John

 

[bernardgreen]

It may be literally true that the 'shock hazard' is significant but, unless you live in a cottage which is unheated and with walls constantly covered in mould

It is a one man DIY project, Seriously the walls have no damp proof so are internally conductive. There was a detectable "tingle" between the chuck of a double insulated drill and the wall before the heating was installed.

Bernard is certainly no fool

Taking on this cottage proves I might be

but reasoned on the basis of premises and assumptions about probabilities (i.e. 'risks'), and relative probabilities, which many of us may disagree with.

That sums it very well. I grew up in the time of change from "earth wires" that really were earth via the water pipe, through "earth wires" that were only a monitoring wire on behalf of a voltage operated isolator which cut the supply when the "earth wire" went above a safe voltage (*) and on to RCDs and PME and its varients. These evolutions of safety systems were compromised by cost contraints. The use of combined "earth" and neutral removed the need and cost to include a true earth wire in the network.

(*) this voltage operated method would be the ideal system had it not been that low impedance alternative paths from the monitoring wire ( so called "earth" wire ) to true ground meant very high fault to "earth" currents could be flowing without the voltage becoming high enough to trip the voltage operated circuit breaker.

There is nothing wrong with PME in the vast majority of domestic properties. With the loss of metallic service pipes as earth rods PME is for most users of electricity the safest method as maintaining an efficient ground rod would not happen n most houses and would be near impossible in flats above the first floor..

I have also experienced three domestic instances of failed neutrals where the CPC has been far from ground potential, One resulted severe tingles from earthed ( or bonded ) items while also in contact with true ground. Turning of the power did not stop the tingles. I have seen the aftemath of an open circuit neutral on a three phase supply to a hill top communications site. The earth bonds in the building were scorched by the current they were sinking to ground. Being a radio site the site had an extensive ground rod and mat system with a very low impedance. I am sure that the very rare instances of fire damage in meter boxes from so called "power surges" is where the MET ( neutral ) is bonded to a metal water supply pipe from a metallic water main network,

I seriously doubt that you'd every get anything like enough current through you by touching the interior surface of a wall to represent a significant threat to your life, even if the potential of your CPCs (hence exposed-c-ps, like your kettle) rose to 230V.

The damp wall is not a serious risk of electrocution but reaction to the tingle might lead to a consequential accident.

 

[SaladFingers]

Taking on this cottage proves I might be

There's a lovely quiet spot near me, where people of the night meet to take on cottages.

 

[EFLImpudence]

quite a lot

Nevertheless there is no justifiable reason to earth an isolated metal part -

be it a bath or the proverbial spoon.

Going back to when no baths were isolated (metal pipes and wastes) is not relevant.

 

[EFLImpudence]

Just thought -

Going back further to the 'tin' bath in front of the fire - no different.

Was there an earth conductor ready to be connected when it was on the flagstones rather than hanging on the wall?

 

[JohnW2]

It may be literally true that the 'shock hazard' is significant but, unless you live in a cottage which is unheated and with walls constantly covered in mould...

... Seriously the walls have no damp proof so are internally conductive. There was a detectable "tingle" between the chuck of a double insulated drill and the wall before the heating was installed.

...I seriously doubt that you'd every get anything like enough current through you by touching the interior surface of a wall to represent a significant threat to your life, even if the potential of your CPCs (hence exposed-c-ps, like your kettle) rose to 230V.

The damp wall is not a serious risk of electrocution but reaction to the tingle might lead to a consequential accident.

Literally true but, as below, this may be one of those situations in which your risk perception and assessment may be different from that of others. Accidentally touching a hot part of the kettle (without touching anything else, and without any electrical issues) might also 'make you jump' and suffer a consequential accident.

Bernard is certainly no fool...

Taking on this cottage proves I might be

25 years ago, I took on a home which, at least in terms of scale, may be even greater proof that I am a fool - and, 25 years on,the 'project' is most certainly still 'ongoing'!

but reasoned on the basis of premises and assumptions about probabilities (i.e. 'risks'), and relative probabilities, which many of us may disagree with.

That sums it very well. ...

Within reason, there's nothing particularly wrong in erring on the side of caution, provided one is careful not to assess relative risks incorrectly (some people may think that the 'metal bath' is an example) - but it can become a bit restrictive, and unnecessarily intrusive on one's life if taken too far. If one travels in cars, crosses roads and uses ladders and power tools, then one has, in some senses, defined a level of risk that one is prepared to 'accept', and perhaps should apply that same 'level of acceptable risk' across all aspects of one's life.

I grew up in the time of change from "earth wires" that really were earth via the water pipe, through "earth wires" that were only a monitoring wire on behalf of a voltage operated isolator which cut the supply when the "earth wire" went above a safe voltage (*) and on to RCDs and PME and its varients. ...(*) this voltage operated method would be the ideal system had it not been that low impedance alternative paths from the monitoring wire ( so called "earth" wire ) to true ground meant very high fault to "earth" currents could be flowing without the voltage becoming high enough to trip the voltage operated circuit breaker.

As I've said before, as I see it, there is no obvious reason why one could not still have the 'best of all worlds' if one wanted. Have all the modern things, but also have a (truly) voltage-operated breaker (and earth electrode) sensing the pd between CPCs and 'true earth', with the breaker (or a separate one) also triggered by excessive current in the 'earthing conductor' (sensed by running it through a current sensing toroid). Provided that it was a truly voltage-operated device (easy with modern electronics), it would not require any impedance to be introduced into the CPC/earthing system, and the threshold could be set such as to reduce the extent to which 'parallel paths to earth' would undermine its functionality. As far as I can see, nothing in the regs would prohibit any of that and, although far from foolproof, would further reduce some of the (already very low) risks that concern you.

Kind Regards, John

 

[doitall]

Where does over sleeving green and yellow wires come into this or have we gone off topic now BAS is proved wrong.

 

[xdave]

I thought we were waiting for you to get a response from the IET and then post the e-mail up for discussion?

 

[JohnW2]

I thought we were waiting for you to get a response from the IET and then post the e-mail up for discussion?

Indeed so - and, in the meantime, are keeping the topic warm by 'talking around it'!

One may also take note of my usual rule of thumb that if a thread extends to more than about 2 pages (and 13 is a lot more than 2!), one can be all but certain that it has 'evolved' in an off-topic fashion!

Kind Regards, John

 

[JohnW2]

duplicate deleted

 

[EFLImpudence]

Where does over sleeving green and yellow wires come into this

I thought it had been resolved.

The situation cannot arise as there must be a cpc so it would seem logical to use the green&yellow.

 

[doitall]

I thought we were waiting for you to get a response from the IET and then post the e-mail up for discussion?

Indeed so - and, in the meantime, are keeping the topic warm by 'talking around it'!

Kind Regards, John

Since you ask so nicely

I am required to preface my remarks by saying that I have no authority to interpret the requirements of BS 7671:2008(2011), Requirements for Electrical Installations, however, within that constraint, I hope you will find my comments helpful.

It is my understanding that multicore cables/flexes, may have their green and yellow conductors sleeved (although I feel it should be avoided wherever possible).

Single green and yellow cables (those used in trunking and conduits etc.), should never be over sleeved.

Twin and earth cables should equally never have the CPC sleeved with any colour other than green and yellow.

Signed and dated, removed by me.

That makes it 4 to the plumbers and 1 that wont discuss it.

 

[JohnW2]

I thought it had been resolved. The situation cannot arise as there must be a cpc so it would seem logical to use the green&yellow.

I think it's been resolved in most of our minds almost since inception! Provided that the OP heeded my advice to make sure that the IET (and others he may ask) understand that he proposes to omit a CPC as well as oversleeve the G/Y core, it would still probably be educational (for some) to see any response which comes from the IET.

Kind Regards, John