Earthing Spike

[ban-all-sheds]

He really ought to search out Mr Cockburn's œuvre...

 

[JohnW2]

... That's surely earthing, not bonding?

It is, which is why it should not be done - the bath is not an exposed-conductive-part.

I'm glad that you agree with me, but I'm not sure that the general situation is as quite as simple as you seem to imply.

In a functional sense, if one puts a hairdryer (or whatever) inside a metal bath, that bath does become an exposed-c-p. My reason for not earthing the bath is that I believe the 'bernard scenario' is far less probable than other scenarios in which earthing the bath would increase hazards. However, in different circumstances, I might think that the balance of probabilities worked in the other direction, and therefore probably would want to earth (or maybe bond) the metal object (bath or whatever).

I say "earth (or maybe bond)" because this, too, is not straightforward. In the absence of a guaranteed RCD in the supply to whatever were dropped into the bath, one cannot be sure that any protective device would operate, so the 'earthing' function would not have achieved it's aim. However, by connecting the bath to earthed things in the room, one would considerably reduce the perceived hazard when one was stepping out of the bath - but that improvement would be have been achieved by 'bonding functionality', rather than earthing, wouldn't it?

The reality underlying the confusion which many see between bonding and earthing is that one cannot bond (previously unearthed) item A to earthed item B without also earthing A, and that one cannot earth both A and B without them being, to at least a reasonable extent, 'bonded' to one another.

Kind Regards, John

 

[ban-all-sheds]

In a functional sense, if one puts a hairdryer (or whatever) inside a metal bath, that bath does become an exposed-c-p.

No it doesn't. Read the definition.

 

[EFLImpudence]

Wrongly applied bonding (when NOT required) is indeed earthing.

Not necessarily - if you had two metal baths and you connected them together you would have bonded them, but not earthed them.

Yes, you can bond two things together without earth being involved in any way.

You physically can but you should not and it will achieve nothing.
If they are not already earthed in any way then they will not require bonding.

 

[ban-all-sheds]

If they are not already earthed in any way then they will not require bonding.

I know.

Which is why if you did it it would be wrongly applied but it would not be earthing.

 

[JohnW2]

If you are correct, then they would not be told "It's not earthing, it's bonding", would they?

Indeed - and I, too, didn't understand why anyone would say that - although you probably perpetuated the confusion by replying that the purpose was "to equalise potentials".

Whenever, I see/hear the 'bath earthing debate', I think of Bernard and his viewpoint, and his reason for wanting to 'connect the bath to something' is, as I understand it, in the name of earthing (to facilitate operation of a protective device). Of course, a 'side effect' of that 'earthing' would be to minimise pds between the bath and other earthed items in the room ('bonding') if a protective device did not operate (or until it operated) - but, if I understand correctly (which maybe I don't), that is not Bernard's primary reason for wanting to connect the bath to earth.

Kind Regards, John

 

[EFLImpudence]

If they are not already earthed in any way then they will not require bonding.

I know.
Which is why if you did it it would be wrongly applied but it would not be earthing.

Fair enough.

 

[bernardgreen]

It is, which is why it should not be done - the bath is not an exposed-conductive-part.

It IS an exposed-conductive-part when the bath's waste pipe is metal and the other end of the waste pipe is connected to a metal stack pipe that goes under ground.

And if it is not connected the stack pipe but discharges into a hopper that is connected to a metal stack pipe then dampness can create a conductive path between hopper and the metal waste pipe from the bath taht is low enough impedance to pass enough current to provide a tingle if not a severe shock to a person who is touching the bath and something that is not at ground potential. That something could be the CPC of a PME installation where the loading on the phases in the local area is not balanced.

Each installation / upgrade / repair has to treated as individual and while the "rules" will probably apply to 90% of properties one has to consider that some installations do not fit the rules due to matters that are NOT electrical in nature.

 

[JohnW2]

In a functional sense, if one puts a hairdryer (or whatever) inside a metal bath, that bath does become an exposed-c-p.

No it doesn't. Read the definition.

I wouldn't really know where to find a definition of "exposed-c-p in a functional sense" .

However, in any event, even as regards the BS7671 definition, I think you're probably quibbling about what constitutes a "part of equipment". If I buy some item of electrical equipment and myself put it inside a metal enclosure (even one which is partially open, like a bath) I would say that that enclosure constituted a "...part which can be touched and which is not normally live, but which can become live under fault conditions", wouldn't you? I see nothing in the BS7671 definition which requires that 'the part' has to have been put in place by the manufacturer.

Kind Regards, John

 

[JohnW2]

It IS an exposed-conductive-part when the bath's waste pipe is metal and the other end of the waste pipe is connected to a metal stack pipe that goes under ground.

That would make it an extraneous-c-p, which would require bonding, not earthing.

Kind Regards, John

 

[EFLImpudence]

If you are correct, then they would not be told "It's not earthing, it's bonding", would they?

Indeed - and I, too, didn't understand why anyone would say that - although you probably perpetuated the confusion by replying that the purpose was "to equalise potentials".

If it was bonding, that would be the purpose and reason.

Whenever, I see/hear the 'bath earthing debate', I think of Bernard and his viewpoint, and his reason for wanting to 'connect the bath to something' is, as I understand it, in the name of earthing (to facilitate operation of a protective device). Of course, a 'side effect' of that 'earthing' would be to minimise pds between the bath and other earthed items in the room ('bonding') if a protective device did not operate (or until it operated) - but, if I understand correctly (which maybe I don't), that is not Bernard's primary reason for wanting to connect the bath to earth.

It surely is more prudent, sensible and easy to ensure a hair-drier is NOT dropped into a bath while you or someone else is sat in it.

 

[JohnW2]

It surely is more prudent, sensible and easy to ensure a hair-drier is NOT dropped into a bath while you or someone else is sat in it.

Of course, but given the existence of extension leads, I'm not sure how you would go about "ensuring" that. What is this "easy" to which you refer?

Whatever, as I've said, I personally consider the risk of anything live being dropped into a bath full of water/people as being an appreciably lower hazard that which would be created by 'unnecessarily' earthing a bath - which is why I personally would not earth (or bond!) it.

Kind Regards, John

 

[EFLImpudence]

It's easy because people don't have to do it when the bath is full of water and people.
People must be responsible for their actions when the correctly installed electrical installation does not cater for their stupidity.

I have never dropped a hammer-drill in a bath when it was full of water and people.

 

[JohnW2]

It's easy because people don't have to do it when the bath is full of water and people. People must be responsible for their actions when the correctly installed electrical installation does not cater for their stupidity.

Yes, but that's Utopia. If people could be guaranteed never to do stupid things, a good few of the things we do in electrical installations in the name of 'safety' probably wouldn't be necessary. Turn the clock back 50-60 years and we didn't bother about many of those 'safety issues', and hence relied a lot more on people not being stupid ... but times (and attitudes to risk) change!

... and it happens. Although I obviously rapidly put a stop to it, I remember discovering that one of my daughters, when a teenager, was using (and 'operating') a mains-powered radio (or CD/cassette player or somesuch), connected via an extension lead from her bedroom, whilst in the bath!

Whatever, it's a decision/judgement that the designer has to make and, as I've said, if I were the designer my judgement would be that these risks are less than the risks of unnecessarily earthing the bath, so I wouldn't earth (or bond) it. If Bernard were the designer, I imagine that he would probably decide differently.

Kind Regards, John

 

[EFLImpudence]

That's not Utopia.

Utopia would be if we had intelligent electrical installations which varied depending on the kind of faults encountered.