Earthing steel bath

[bernardgreen]

I think it has been shown before that Bernard is someone who would protect from the minutest (blue moon) risk

Rather I do not ignore the effect of the blue moon events.

to the detriment of greater more likely risks and does not distinguish between earthing and bonding.

I do distinguish between earthing and bonding as in the terminology used and the methods used but if item [1] is connected to the MET ( main earth terminal ) by bonding and item [2] is connected to the same MET by the CPC ( earth wire in the cables ) then both items are connected together via the MET. Is the connection a bonding o or an earthing. You and I and a few electricians may be able to "understand" this apparent contradiction but the average lay man cannot.

 

[JohnW2]

Each case needs to be risk accessed and appropriate action taken.

Precisely.

At one extreme set of circumstances it is safer to leave the bath neither earthed nor bonded.... At the other extreme it is probably safer to earth the bath.

We are not talking extremes.

Whilst, as I hope you will understand, I am totally in agreement with you about the concepts, ‘spirit’ and bottom line, I think that is unnecessary quibbling. There is a risk assessment required for each situation, and the bottom line of that assessment has to be one of those two alternatives – whether one calls them ‘extremes’ or simply ‘a dichotomous decision’.

The bath may require bonding.
Unless it is part of the electrical installation (how?) it should NEVER be earthed.

In attempting to be fair to him, I try to put myself into the same mindset as Bernard. If (as he sometimes has suggested) he genuinely feels that there is a significant risk of the bath becoming live as a result of a ‘fault’ (flying hair-dryers) then I suppose that would be (perceptually/functionally) so close to the concept of an exposed-c-p that he could argue that it ought to be earthed.

Earthing (applying a cpc) is to operate the opd in the event of a fault making the part live. ... Bonding (main and supplementary) is to equalise potential between parts in the event of a fault (until an opd disconnects the supply).

That’s obviously a correct statement of the concepts and ‘intents’ [as a matter of detail, 411.3.2.6 refers to the use of supplementary bonding when ADS via an OPD cannot be achieved]. However, as Bernard often points out, the distinction has minimal practical relevance (apart, perhaps, from reg-required cable CSAs) in the sort of situations we are talking about – since one cannot ‘earth’ a bath without ‘bonding’ it to exposed-c-ps, and one cannot bond a bath without connecting it to CPCs (i.e. ‘earthing it’).

Earthing (and bonding) is a necessary evil and not something to be done for its own sake. It is done because we cannot isolate everything. It would be better if we could.

Agreed, and it’s by no means impossible that the day could come (probably not in our lifetimes) when ‘isolating everything’ becomes the standard (and preferable) option for indoor installations.

Kind Regards, John

 

[JohnW2]

I think it has been shown before that Bernard is someone who would protect from the minutest (blue moon) risk

Rather I do not ignore the effect of the blue moon events.

Given that attitudes to risk vary widely, no-one can criticise you for that, per se. However, as I'm sure you understand, those who disagree with you (about baths etc.) feel that you may have got the risk-balance assessment wrong - i.e. that by taking steps to address those 'blue moon events' you would be increasing the risk resulting from less rare (albeit still rare) events - hence, on balance, maybe decreasing the overall level of 'safety'.

Kind Regards, John

 

[EFLImpudence]

You're doing it again.

Each case needs to be risk accessed and appropriate action taken.

Precisely.

At one extreme set of circumstances it is safer to leave the bath neither earthed nor bonded.... At the other extreme it is probably safer to earth the bath.

We are not talking extremes.

Whilst, as I hope you will understand, I am totally in agreement with you about the concepts, ‘spirit’ and bottom line, I think that is unnecessary quibbling. There is a risk assessment required for each situation, and the bottom line of that assessment has to be one of those two alternatives – whether one calls them ‘extremes’ or simply ‘a dichotomous decision’.

That's why I wrote 'precisely'.
It is not dichotomous.
It is guarding against an all but impossible occurrence by introducing an always present hazard.

The bath may require bonding.
Unless it is part of the electrical installation (how?) it should NEVER be earthed.

In attempting to be fair to him, I try to put myself into the same mindset as Bernard. If (as he sometimes has suggested) he genuinely feels that there is a significant risk of the bath becoming live as a result of a ‘fault’ (flying hair-dryers) then I suppose that would be (perceptually/functionally) so close to the concept of an exposed-c-p that he could argue that it ought to be earthed.

No.

Entering the mindset of the mistaken is a foolish exercise.

Earthing (applying a cpc) is to operate the opd in the event of a fault making the part live. ... Bonding (main and supplementary) is to equalise potential between parts in the event of a fault (until an opd disconnects the supply).

That’s obviously a correct statement of the concepts and ‘intents’ [as a matter of detail, 411.3.2.6 refers to the use of supplementary bonding when ADS via an OPD cannot be achieved]. However, as Bernard often points out, the distinction has minimal practical relevance (apart, perhaps, from reg-required cable CSAs) in the sort of situations we are talking about – since one cannot ‘earth’ a bath without ‘bonding’ it to exposed-c-ps, and one cannot bond a bath without connecting it to CPCs (i.e. ‘earthing it’).

You can earth a bath without satisfactorily bonding it and you cannot bond an isolated bath - it would be undesirable earthing.


I refer the honourable gentleman to Bernard's reply to vindicate my original points.

 

[EFLImpudence]

I think it has been shown before that Bernard is someone who would protect from the minutest (blue moon) risk to the detriment of greater more likely risks .

Rather I do not ignore the effect of the blue moon events.

Given that attitudes to risk vary widely, no-one can criticise you for that, per se. However, as I'm sure you understand, those who disagree with you (about baths etc.) feel that you may have got the risk-balance assessment wrong - i.e. that by taking steps to address those 'blue moon events' you would be increasing the risk resulting from less rare (albeit still rare) events - hence, on balance, maybe decreasing the overall level of 'safety'.

Q.E.D.?

Red text included to restore context.

 

[JohnW2]

Q.E.D.?

Indeed so.

Red text included to restore context.

Fair enough. I chose not to modify Bernard's (truncated) quote but, instead, re-iterated your point. Whatever, I think that we are agreed

Kind Regards, John

 

[bernardgreen]

You can earth a bath without satisfactorily bonding it and you cannot bond an isolated bath - it would be undesirable earthing.

Do you mean earthing by connecting to true ground instead of the MET via the CPC. Or do you mean via a small cross section wire that can carry enough current to earth the bath but would melt if made to carry bonding current and hence not be a satisfactory bond. Think about the minimum cross section required to bond the incoming services even though the supply pipe is plastic and non conductive. The amount of current that can flow along a plastic pipe could be easily carried by a 1 mm ² wire but regs require 4, 6 or even 10 mm ² Maybe for the blue moon event that plastic becomes conductive.

As to to the detriment of greater more likely risks likely hood of a risk being more likely depends on the environment of each individual situation.

Can an portable electrical fall into the bath ? Bath water comes to approx 150 volts with low impedence from 230 volt source.. Isolated bath and nothing trips to cut the supply. Earthed or bonded bath and the supply is likely to be cut.

While the 150 volt bath water is relatively harmless to some one in the water ( very little voltage gradient in the water ) it would be lethal to anyone touching the bath and any other bonded or earthed metal work.

So you original answer of "must not be earthed" is only applicable to some situations.

 

[JohnW2]

It is not dichotomous. ... It is guarding against an all but impossible occurrence by introducing an always present hazard.

Words, again The decision ('to earth or not not earth') clearly is dichotomous. Your point (with which I agree) about the consequences of one of those two possible courses does not alter the fact that it is a dichotomous decision ('yes/no'), no matter what the consequences.

Entering the mindset of the mistaken is a foolish exercise.

I have to disagree with that. It is often the only way of aquiring an understanding of someone else's viewpoint. I'm obvioulsy not suggesting that one should adopt someone else's mindset, but that one should 'put oneself in their place' in order to try to understand them.

You can earth a bath without satisfactorily bonding it and you cannot bond an isolated bath - it would be undesirable earthing.

You've slipped the word 'satisfactorily' into that! You cannot possibly earth a bath without bonding it to something, whether that bonding be 'satisfactory' or not. When you say that "you cannot bond an isolated bath", I presume you really mean that one does not need to - because bonding is only needed if something already has some path to earth. 'Bonding' is the connection of two things via a conductor in order to make them as close to equipotential as possible - one could (but clearly wouldn't need to) 'bond' two spoons together if one really wanted to. You seem to feel that if one uses a conductor to connect two things that don't both have at least some path to earth that cannot be called 'bonding', since bonding is not needed in that situation, but I think that's probably a fairly narrow view - as far as I am concerned, bonding is bonding, whether 'required' or not. When (as must be the case) you come across supplementary bonding which is not required by current regs, do you stop calling it 'bonding'? (genuine, not rhetorical, question!)

I refer the honourable gentleman to Bernard's reply to vindicate my original points.

I don't think that we have ever disagreed about our respective disagreements with Bernard's views/approached!

Kind Regards, John

 

[EFLImpudence]

Do you mean earthing by connecting to true ground instead of the MET via the CPC. Or do you mean via a small cross section wire that can carry enough current to earth the bath but would melt if made to carry bonding current and hence not be a satisfactory bond. Think about the minimum cross section required to bond the incoming services even though the supply pipe is plastic and non conductive. The amount of current that can flow along a plastic pipe could be easily carried by a 1 mm ² wire but regs require 4, 6 or even 10 mm ² Maybe for the blue moon event that plastic becomes conductive.

Without going into that much detail earthing something, which you consider an exposed- c-p, (by definition) with a cpc of a circuit may not be of low enough resistance to satisfy the bonding requirements.
So, after your earthing the bath may then require bonding.

Can an portable electrical fall into the bath ? Bath water comes to approx 150 volts with low impedence from 230 volt source.. Isolated bath and nothing trips to cut the supply. Earthed or bonded bath and the supply is likely to be cut.

Is it?
Well, that really is taking the purpose of earthing to an extreme.
I cannot argue with such thinking.

So you original answer of "must not be earthed" is only applicable to some situations.

As I originally said "That is your decision if you think that is the more likely scenario".

 

[EFLImpudence]

It is not dichotomous. ... It is guarding against an all but impossible occurrence by introducing an always present hazard.

Words, again The decision ('to earth or not not earth') clearly is dichotomous. Your point (with which I agree) about the consequences of one of those two possible courses does not alter the fact that it is a dichotomous decision ('yes/no'), no matter what the consequences.

Isn't that the point? It's not 'yes/no' if you think like some people do.

You've slipped the word 'satisfactorily' into that! You cannot possibly earth a bath without bonding it to something, whether that bonding be 'satisfactory' or not.

I had to because obviously it could bond it unsatisfactorily meaning it would the have to be bonded satisfactorily.

When you say that "you cannot bond an isolated bath", I presume you really mean that one does not need to - because bonding is only needed if something already has some path to earth. 'Bonding' is the connection of two things via a conductor in order to make them as close to equipotential as possible - one could (but clearly wouldn't need to) 'bond' two spoons together if one really wanted to. You seem to feel that if one uses a conductor to connect two things that don't both have at least some path to earth that cannot be called 'bonding', since bonding is not needed in that situation, but I think that's probably a fairly narrow view - as far as I am concerned, bonding is bonding, whether 'required' or not. When (as must be the case) you come across supplementary bonding which is not required by current regs, do you stop calling it 'bonding'? (genuine, not rhetorical, question!)

You cannot bond an isolated part. It would be undesirable earthing which may then cause the part to require bonding.

 

[JohnW2]

Isn't that the point? It's not 'yes/no' if you think like some people do.

Sorry, I don't understand. Other than "yes, earth the bath" and "no, don't earth the bath", what other decisions could be taken about the earthing of the bath (by anyone)?

You cannot bond an isolated part. It would be undesirable earthing which may then cause the part to require bonding.

That seems to be another manifestation of your seemingly restricted definition of 'bonding'. Do I take it that you do not accept that any situation in which one joins two conductive parts with a cable (to ensure equalisation of potential, whether 'needed' or not) is 'bonding'?

Kind Regards, John

 

[EFLImpudence]

Isn't that the point? It's not 'yes/no' if you think like some people do.

Sorry, I don't understand. Other than "yes, earth the bath" and "no, don't earth the bath", what other decisions could be taken about the earthing of the bath (by anyone)?

But Bernard's point is that even if the part is isolated he can think of a situation, however infinitely remote, where earthing would be better so he will earth it.
Therefore not a dichotomous yes or no but yes and yes.

You cannot bond an isolated part. It would be undesirable earthing which may then cause the part to require bonding.

That seems to be another manifestation of your seemingly restricted definition of 'bonding'. Do I take it that you do not accept that any situation in which one joins two conductive parts with a cable (to ensure equalisation of potential, whether 'needed' or not) is 'bonding'?

But the situation is not about equalising potential.
It is about earthing isolated baths - by definition with a cpc of a nearby circuit.
Therefore this cpc will introduce a formerly non-existent potential which will necessitate bonding of the associated parts.


It seems previously I may have missed the relevance of the word extreme.
Take for example the building of a new house.
You diligently design it so that all of the internal metal pipework is isolated by the use of plastic inserts at all relevant positions - the entry points and at the boiler where they contact the gas pipe.
However, someone buys the house and because they are stupidly careless and like using the hair drier while they or another family member is in the bath they decide to earth the metal bath with the cpc of the electric shower - there is nothing else nearby (except the light) so they don't want to run a cable to the MET (not that that would make any difference), thus introducing a potential to all the water pipes.
So, the situation now is that, in the bathroom, the shower, light and pipes require bonding to an Ia of, say, 250A and the same may be necessary now in any other bathrooms.
Why not, just in case, do the same in the kitchen?

 

[JohnW2]

Sorry, I don't understand. Other than "yes, earth the bath" and "no, don't earth the bath", what other decisions could be taken about the earthing of the bath (by anyone)?

But Bernard's point is that even if the part is isolated he can think of a situation, however infinitely remote, where earthing would be better so he will earth it. Therefore not a dichotomous yes or no but yes and yes.

As so often, this is getting very semantic! The decision is clearly between 'yes' and 'no' (which I would have said was undeniably a dichotomous decision). You may be right that Bernard will always decide 'yes', but that doesn't mean that there wasn't a dichotomy of choice, even if he never uses one of them!

Thinking back to how the 'aside' arose, I think it may be semantic again, particularly in view what you now go on to say about 'extreme'. I think you may have read too much into that word - or, rather, misuderstood the sense in which it was being used. I suspect that you were thinking of 'extreme' as implying 'exceptional', 'remarkable' or something like that. However, the word can also be used (and I think this was what Bernard intended) merely to indicate the end of a range of possibilities - whether two or more. If, say, backboxes were available in a range of depths from 15mm to 47mm, I would say that the 'extremes' of that range were 15mm and 47mm - but I would not be implying that there was anything special, 'exceptional' ore even uncommon/rare about either 15mm or 47mm ones. Given that there are no 'shades if grey in between, I agree that it's a bit superfluous to talk about 'extremes' when there are only two possibilities, but I reall do think that's all that Bernard meant - I don't think (can't really believe) that he intended to imply that either of the courses was in any way 'exceptional'.

Kind Regards, John

 

[PompeySparks]

As others have said, never bond anything unless it is classed as an extraneous part (22kohms or less when tested to the MET)

Consider especially PME systems and potential (although unlikely) loss of neutral!

Or put another way... ‘would you take a bath on your neutral bar???’

 

[JohnW2]

As others have said, never bond anything unless it is classed as an extraneous part (22kohms or less when tested to the MET)

I think that the great majority of us agree that something should not be bonded unless it presents some route to earth. I'm not sure that the 22k&#937; criterion is necessarily the ideal (I don't particularly want a 10mA shock - and it could, of course, kill some people) - but, as EFLI is always saying, 'middle ground' resistances to the MET are almost never going to be encountered (it's going to either be <10&#937; or >1M&#937. [FYI, note that, per EFLIs use of words, it is not possible to 'bond' something which has a resistance >22/23k&#937; to MET, since he then calls it (unnecessary) 'earthing']

Consider especially PME systems and potential (although unlikely) loss of neutral! Or put another way... ‘would you take a bath on your neutral bar???’

I don't think that's the main issue - after all, if adequate main bonding (and any required sipplementary bonding) is in place, then it should be perfectly OK to 'take a bath on the neutral bar' (or anything connected to it), even in the face of a supply neutral fault! I think the much more important reason for not unnecessarily connecting things (like isolated baths) to earth is that it increases the risk of shock should someone be in contact with something live (the frayed lead of a vacuum cleaner is often cited!) when they touch the 'unnecessarily earthed' bath (or whatever).

Kind FRegards, John