Earthing a steel bath if fusebox has an RCD?

[JohnW2]

It's a metal bath. It is in the room. Unlike the door handle and the spoon it is electrically connected to something which can be at a different potential to exposed conductive parts in the room. Why is it not an extraneous-conductive-part?

If, because it does not have adequate main bonding, 'something' in the room may be at a different potential to the exposed-c-ps in the room, then that 'something' would be an extraneous-c-p, which required attention to its inadequate main bonding. If you are going to suggest that everything in electrical continuity with that something (quite probably every pipe and every protective conductor in the building) had become an extraneous-c-p, which therefore required bonding, it would be both silly and unnecessary.

If, by adequate bonding, the pipe is rendered 'safe to touch' (at the same time as touching an exposed-c-p), how on earth is a metal bath electrically connected (well or badly) to that pipe going to be unsafe to touch?

This is why we have to main bond 'true' extraneous-c-ps close to where they enter the building. Once that has been done adequately, the risk of a potential (other than that of the equipotential zone) being introduced into the building is 'eliminated' (minimised) and one therefore does not have to consider every 'secondary' conductor (those in electrical continuity with the main-bonded true extraneous-c-p) as being an extraneous-c-p.

Kind Regards, John

 

[ban-all-sheds]

You seem to be talking like BAS.

A good start.

If the metal pipes are extraneous-c-ps then they are extraneous-c-ps (which require main bonding).

Not in the bathroom. There they require supplementary bonding.

However, something (like a bath) which happened to be in electrical continuity with that extraneous-c-p would not automatically (in fact, not normally) itself become an extraneous-c-p.

So a metal pipe emerging from a wall/floor/ceiling into the bathroom is an e-c-p, and requires supplementary equipotential bonding to ensure that there won't be a PD between it and exposed-c-ps or other extraneous-c-ps?

But a metal bath supplied by those pipes is not an extraneous-c-p,and it doesn't matter if a PD exists between it and exposed-c-ps or other extraneous-c-ps?

If it did, virtually every pipe and every protective conductor within a building would qualify as an extraneous-c-p

They do, when they enter a bathroom. Well - cpcs are not extraneous-c-ps, but they are bonded to ones which are.

which not only would be silly, but would indicate a lack of understanding of what the concepts of extraneous-c-ps and main equipotential bonding are all about!

That would be the earthed equipotential bonding, will it?

Anyway - this is about supplementary bonding.

 

[ban-all-sheds]

DO NOT TRY THIS...

None of that has anything to do with supplementary equipotential bonding.

 

[bernardgreen]

DO NOT TRY THIS...

None of that has anything to do with supplementary equipotential bonding.

The common sense view ( as apposed to the view that a reader of regulations may have ) is that doing something that ensures the RCD will operate is better than doing nothing just because the regulations say it is not necessary.

 

[ban-all-sheds]

Common sense and making provisions to deal with someone dropping a hair dryer into a bath is a tad oxymoronic.

 

[JohnW2]

So a metal pipe emerging from a wall/floor/ceiling into the bathroom is an e-c-p, and requires supplementary equipotential bonding to ensure that there won't be a PD between it and exposed-c-ps or other extraneous-c-ps?

Yep.

But a metal bath supplied by those pipes is not an extraneous-c-p,and it doesn't matter if a PD exists between it and exposed-c-ps or other extraneous-c-ps?

Not in it's own right. If the pipes are extraneous-c-ps, they need to be bonded. Once they are bonded to exposed-c-p's etc., things electrically connected (be that well or poorly) to those bonded pipes cannot be liable to introduce a potential (different from that of the exposed-c-ps etc.) into the room, and so do not qualify as extraneous-c-ps, and do not need bonding.

You appear to be talking about a situation in which an extraneous-c-p enters the room and is not bonded. In that situation, I agree that anything in electrical contact with that (potentially dangerous) pipe also becomes potentially dangerous - but it is then the actual extraneous-c-p (the pipe) that needs bonding. Somewhat ironically in relation to what you have previously said, if the pipe is not bonded, then the higher the impedance of the electrical connection between between bath and pipe, the less potentially dangerous does the bath become.

Kind Regards, John

 

[JohnW2]

The common sense view ( as apposed to the view that a reader of regulations may have ) is that doing something that ensures the RCD will operate is better than doing nothing just because the regulations say it is not necessary.

As I (and others) are always saying, in the 'floating' metal bath case, that has to be balanced against the increased risk of electric shock, that arises, in other scenarios, as a result of unnecessarily creating a large mass of earthed metal in the room (an otherwise totally floating bath with plastic plumbing).

Kind Regards, John

 

[PBC_1966]

You appear to be talking about a situation in which an extraneous-c-p enters the room and is not bonded. In that situation, I agree that anything in electrical contact with that (potentially dangerous) pipe also becomes potentially dangerous - but it is then the actual extraneous-c-p (the pipe) that needs bonding. Somewhat ironically in relation to what you have previously said, if the pipe is not bonded, then the higher the impedance of the electrical connection between between bath and pipe, the less potentially dangerous does the bath become.

Compared to what - The pipe with its introduced potential or earth?

Assuming an introduced potential by way of that extraneous pipe, obviously the better insulated is the bathtub from the pipe the less chance there is of the bath becoming live with respect to earth. But what about the potential difference between the pipe and the tub, a potentially (no pun intended) much more serious matter for somebody who might be sitting in the bath and who touches the pipe? To eliminate the possibility of shock in that case, the bathtub would need to be pretty well insulated from earth, which is really not practical (and hence why the Wiring Regs. recognized this and indicated that the bath must be bonded way back 60 years ago).

 

[Spark123]

(*Where the only reason for the bath possibly being an ecp is the presence of metal pipes)

You seem to be talking like BAS. If the metal pipes are extraneous-c-ps then they are extraneous-c-ps (which require main bonding). However, something (like a bath) which happened to be in electrical continuity with that extraneous-c-p would not automatically (in fact, not normally) itself become an extraneous-c-p. If it did, virtually every pipe and every protective conductor within a building would qualify as an extraneous-c-p - which not only would be silly, but would indicate a lack of understanding of what the concepts of extraneous-c-ps and main equipotential bonding are all about!

Kind Regards, John

Not entirely, the other reasons I was thinking of were along the lines of the bath being in contact with a metal building structure or the bath being sunk into the ground.
My view remains the same, if the metal bath is only being made extraneous by means of the metal pipes running to it and they are all already supplementary bonded then there's no point in supplementary bonding the bath to the pipes.
Btw, by definition a CPC isn't an extraneous conductive part but I'll leave that one alone!

 

[PBC_1966]

As I (and others) are always saying, in the 'floating' metal bath case, that has to be balanced against the increased risk of electric shock, that arises, in other scenarios, as a result of unnecessarily creating a large mass of earthed metal in the room (an otherwise totally floating bath with plastic plumbing).

Realistically, how would one achieve a truly floating tub - Floating with a high enough resistance to earth so as not to pose a still-significant shock risk to somebody contacting something live at the same time, that is?

About the best you could hope for is a free-standing bath in the middle of a wooden floor, then you might be in with a fighting chance. Put it against a wall and anchor it through masonry, or put it on a concrete floor and the resistance to earth is going to drop considerably, even without allowing for possible water added into the equation. You'd have to take some pretty careful and deliberate steps to adequately insulate from earth, and account for what would happen to those measures in the presence of spilled water etc.

 

[JohnW2]

Compared to what - The pipe with its introduced potential or earth? Assuming an introduced potential by way of that extraneous pipe, obviously the better insulated is the bathtub from the pipe the less chance there is of the bath becoming live with respect to earth.

Exactly. There had previously been talk of "a high, but not high enough" resistance between bath and pipe - but, IF the "potential" is coming from the pipe, then, as you say, the higher the impedance of its connection to the bath, the 'safer' is the bath (with no 'upper limit').

But what about the potential difference between the pipe and the tub, a potentially (no pun intended) much more serious matter for somebody who might be sitting in the bath and who touches the pipe? To eliminate the possibility of shock in that case, the bathtub would need to be pretty well insulated from earth, which is really not practical.

We seem to keep on going over this ground. IF there really is such a concern (and, per another message I'm about to post, I really doubt that it often should be), then the bath itself qualifies as an extraneous-c-p in it's own right, and would require main equipotential bonding, quite apart from considerations of supplementary bonding.

Kind Regards, John

 

[JohnW2]

Realistically, how would one achieve a truly floating tub - Floating with a high enough resistance to earth so as not to pose a still-significant shock risk to somebody contacting something live at the same time, that is?

I personally think that you are over-estimating the problem. I'm not sure what you regard as a 'still-significant shock', but most people won't feel a lot below 1mA (which translates to a 23kΩ path to earth). I strongly suspect that with any 'upstairs bath', and even with wet floors, you'd often find a path resistance to earth less than hundreds of kilohms, probably more. With a dry upstairs floor, you'd probably be 'off the top' of an IR meter.

In any event, per my recent post, if you believe that there is a significant path from the bath to true earth (through tyhe structure of the building) you would need to main bond it.

Whatever, you're now talking about something totally different from the subject of this thread. Indeed, since you're talking about about a shock resulting from simultaneous contact with a bath and 'something live', the more earthing and bonding you do, the greater the severity of such a shock. It's an RCD that could make a difference.

Kind Regards, John

 

[JohnW2]

Not entirely, the other reasons I was thinking of were along the lines of the bath being in contact with a metal building structure or the bath being sunk into the ground.

Sure, but as I seem to be typing repeatedly at the moment, if you believed that to be the case, then there would be a need for main bonding.

My view remains the same, if the metal bath is only being made extraneous by means of the metal pipes running to it and they are all already supplementary bonded then there's no point in supplementary bonding the bath to the pipes.

Quite so. As I've been trying to say to BAS, if one believes that everything electrically connected to a bonded extraneous-c-p also has to be regarded itself as an extraneous-c-p (and thus requiring its own bonding), then the whole thing gets totally silly!

Btw, by definition a CPC isn't an extraneous conductive part but I'll leave that one alone!

Good point - but BAS seems to regard anything in electrical continuity with an extraneous-c-p as also being an extraneous-c-p!

Kind Regards, John

 

[EFLImpudence]

Then don't keep repeating that if it is an extraneous-c-p it will require main bonding.
It is main bonded by the main bonding on the pipe(s)

The problem is with regard to supplementary bonding where an extraneous-c-p to the bathroom is not effectively connected to the PEB.
I agree that it likely is effectively connected to the PEB (<1666Ω) but that is the hypothetical discussion.

If it makes it easier to discuss practically, then forget about the RCD omission part of it, without which the supplementary bonding requirement may be dependent on resistances of 0.25Ω.


If you just rely on "The bath cannot be an extraneous-c-p so that's that" then there is no point.

 

[JohnW2]

Then don't keep repeating that if it is an extraneous-c-p it will require main bonding. It is main bonded by the main bonding on the pipe(s)

But people have started talking about the bath independently being an extraneous-c-p by virtue of paths to true earth through wet floors, structural metalwork, or whatever. If that were the case (or though to be a possibility), then it would be "liable to introduce a potential into the building ", and therefore would require primary bonding in its own right. I presume that you would not say that an incoming underground gas pipe did not need explicit main bonding of its own because it was connected to the (bonded) incoming water pipe at the boiler, would you?

The problem is with regard to supplementary bonding where an extraneous-c-p to the bathroom is not effectively connected to the PEB.

Yes, but as I keep saying (and assuming we are not considering 'wet floors' etc.), if the bath is entirely contained within the bathroom, it cannot possibly introduce a potential into the bathroom, and therefore surely cannot be "an extraneous-c-p to the bathroom", can it? ... and if it's not "an extraneous-c-p to the bathroom", then it would not require supplementary bonding under any circumstances, would it?

I think that bernard, and to some extent PBC, may have introduced some confusion by citing situations in which there might be an argument for earthing the bath - a discussion which is not reliant on whether or not the bath is "an extraneous-c-p to the bathroom".

Kind Regards, John