Yes, sorry.[assuming you mean 701.415.2(vi)]
Yes, sorry.[assuming you mean 701.415.2(vi)]
It doesn't - but if it's only electrical contunity is a poor connection to something which is already bonded, how on earth can it introduce any potential other than that of the equipotential zone (which wouldn't qualify it as an extraneous-c-p).It doesn't have to be earth potential.A bath is not an extraneous conductive part, and cannot introduce a potential into the bathroom.
As I've just written, if the bath is not an extraneous-c-p (which I don't think it would be in the circumstances you describe), then those considerations do not apply.What is the difference between an (external) extraneous-c-p with a resistance of <23kΩ (or >1666Ω) to the MET and a bath with a similar resistance to a bonded pipe with regard to R<50/Ia and/or RCD omission?
Well, yes I see your point but you could say a metal bath is not an extraneous-c-p unless it touches the ground.... But, by answering 'Yes', you've created a circular argument - 701.415.2(vi) only applies to extraneous-c-ps, so you can't use it to define whether or not something is an extraneous-c-p, can you?!
But it's not earth potential that is the problem here.A (metal) bath can surely only be an extraneous-c-p ("liable to introduce a potential....") if it is in electrical continuity with something which enters the property from outside
So, if it has a resistance of >1667Ω (or <50/Ia) to an exposed-c-p, what would you do?and that 'something' is not itself already bonded. A poor connection to something bonded does not make it an extraneous-c-p.
Nothing is an extraneous-c-p unless it is connected to something outside of the equipotential zone (such as 'true earth').Well, yes I see your point but you could say a metal bath is not an extraneous-c-p unless it touches the ground.... But, by answering 'Yes', you've created a circular argument - 701.415.2(vi) only applies to extraneous-c-ps, so you can't use it to define whether or not something is an extraneous-c-p, can you?!
I don't really understand what you are saying here. If all the pipes are "correctly bonded" (to the MET) how can there be significant pds between them?It's the same as testing for supplementary bonding. All the pipes may be correctly bonded but sill have a potential between themselves.
It doesn't matter what potential is "the problem" (and I'm not too sure what you mean by that, anyway). If it doesn't have electrical continuity with something outside of the equipotential zone which isn't already bonded, then it surely can't be an extraneous-c-p (cannot be liable to introduce any potential), can it?But it's not earth potential that is the problem here.A (metal) bath can surely only be an extraneous-c-p ("liable to introduce a potential....") if it is in electrical continuity with something which enters the property from outside
If it were not an extraneous-c-p, I probably wouldn't do anything. This is why I've never been too happy about your 'tests'.So, if it has a resistance of >1667Ω (or <50/Ia) to an exposed-c-p, what would you do?and that 'something' is not itself already bonded. A poor connection to something bonded does not make it an extraneous-c-p.
If someone drops a double insulated appliance ( i.e. with no earth connection ) that is switched on into a plastic bath of water then the potential of the water will be about mid way between Neutral and Live ( circa 120 volts ). No protective device will be operated. The same lack of operation of protective devices would happen if the bath was metal but not earthed and had no conenction to metal pipes.
The risk of someone dropping a live double insulated appliance into a bath of water is a small but not insignificant risk.
With teh water at 120 volts any touching the water in the bath and and earthed ( or bonded ) pipe ( or nay other earhted or bonded item ) will get a shock. An RCD if fitted might operate quickly enough to reduce the duration of the shock to one that is short enough to not cause non reversible damage to the person.
My preference would be to earth or bond the bath so that the RCD operates when the appliance drops into the bath water.
We've been through this umpteen times before. I agree that it is a 'swings and roundabouts' situation but I personally think that the risks (such as you describe) associated with not earthing a metal bath are probably less than the risks of 'unnecessarily' creating a large amount of earthed metal within the room (which greatly increases the risk to, say, someone using a vacuum cleaner with a damaged lead in the room). Both risks are extremely small, but your and my views as to which is the greater appear to differ.If someone drops a double insulated appliance ( i.e. with no earth connection ) that is switched on into a plastic bath of water then the potential of the water will be about mid way between Neutral and Live ( circa 120 volts ). No protective device will be operated. The same lack of operation of protective devices would happen if the bath was metal but not earthed and had no conenction to metal pipes. ... The risk of someone dropping a live double insulated appliance into a bath of water is a small but not insignificant risk.
Ditto. There is no way you want to risk the possibility of a significant potential difference between the bathtub and the taps or other plumbing fixtures within reach, and the tub is of such a size and installed in such a way that to complete isolate it (along with everything else) from earth is impractical. Therefore it needs to be bonded.My preference would be to earth or bond the bath so that the RCD operates when the appliance drops into the bath water.
D.14 The exposed metalwork of all apparatus which is required by these Regulations to be earthed, which might otherwise come into fortuitous contact with extraneous fixed metalwork shall be either effectually segregated therefrom or effectually bonded thereto so as to prevent appreciable voltage differences at such possible points of contact (see also Regulation B.53).
NOTE 1. - The extraneous fixed metalwork required to be bonded and earthed in these circumstances includes the following:
(i) Baths and exposed metal pipes, radiators, sinks and tanks, in the absence of metal-to-metal joints of negligible electrical resistance.
(ii) Where practicable, accessible structural metalwork.
(iii) Framework of mobile equipment on which electrical apparatus is mounted, such as cranes and lifts.
NOTE 2. - There are special requirements for bonding to metalwork of other services in P.M.E. installations (see Regulation D.34(iii) and Item 4(2) of Appendix 5).
Here's what the 14th edition had to say about it:
OTE 1. - The extraneous fixed metalwork required to be bonded and earthed in these circumstances includes the following:
(i) Baths and exposed metal pipes, radiators, sinks and tanks, in the absence of metal-to-metal joints of negligible electrical resistance
As I've just written to bernard, it really is 'swings and roundabouts' - and, as I said, FWIW my personal view is that the risks you and bernard want to address by earthing a bath are probably less than those created by 'unnecessarily' creating a lot of earthed metal within the room. Opinions will undoubtedly always differ!Ditto. There is no way you want to risk the possibility of a significant potential difference between the bathtub and the taps or other plumbing fixtures within reach, and the tub is of such a size and installed in such a way that to complete isolate it (along with everything else) from earth is impractical. Therefore it needs to be bonded.My preference would be to earth or bond the bath so that the RCD operates when the appliance drops into the bath water.
In the OP's question, the equipotential zone is only the bathroom.Nothing is an extraneous-c-p unless it is connected to something outside of the equipotential zone (such as 'true earth').Well, yes I see your point but you could say a metal bath is not an extraneous-c-p unless it touches the ground.... But, by answering 'Yes', you've created a circular argument - 701.415.2(vi) only applies to extraneous-c-ps, so you can't use it to define whether or not something is an extraneous-c-p, can you?!
Poor wording - between themselves and exposed-c-ps.I don't really understand what you are saying here. If all the pipes are "correctly bonded" (to the MET) how can there be significant pds between them?It's the same as testing for supplementary bonding. All the pipes may be correctly bonded but sill have a potential between themselves.
Yes, it does.It doesn't matter what potential is "the problem" (and I'm not too sure what you mean by that, anyway)But it's not earth potential that is the problem here.A (metal) bath can surely only be an extraneous-c-p ("liable to introduce a potential....") if it is in electrical continuity with something which enters the property from outside
We are talking about parts with relatively high impedance to other parts so - yes.If it doesn't have electrical continuity with something outside of the equipotential zone which isn't already bonded, then it surely can't be an extraneous-c-p (cannot be liable to introduce any potential), can it?
If it were not an extraneous-c-p, I probably wouldn't do anything. This is why I've never been too happy about your 'tests'.So, if it has a resistance of >1667Ω (or <50/Ia) to an exposed-c-p, what would you do?and that 'something' is not itself already bonded. A poor connection to something bonded does not make it an extraneous-c-p.
It is not if the above conditions (quoted by Taylor) are met.I also thought that supplementary bonding wasn't necessary due to having that lovely RCD,
Not in the bathroom generally, but you may have to supplementary bond the bath to the pipe if it is not "effectively connected to the PEB" (main bonding).it seems you are saying that I must sup bond in the bathroom too?
What is the difference between an (external) extraneous-c-p with a resistance of <23kΩ (or >1666Ω) to the MET and a bath with a similar resistance to a bonded pipe with regard to R<50/Ia and/or RCD omission?
If one takes that view, it's surely even more clear that the bath can't be an extraneous-c-p - since it is entirely contained within the bathroom?In the OP's question, the equipotential zone is only the bathroom.
As I said before, 701.415.2(v) only applies IF the bath is a extraneous-c-p. As I also said before, you create a circular argument if you attempt to turn that on its head and say that if it is not "effectively connected to the PEB", then in must be an extraneous-c-p.Then in respect of 701.415.2(vi) what does "effectively connected to the PEB" mean and how do you determine this?
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