Earthing a bath

[JohnW2]

Internal pipes and taps obviously cannot actually be extraneous conductive parts, as defined in BS7671, since they cannot in themselves be "liable to introduce a potential into the building" (since they are entirely contained within the building).

If that is the case then they do not require bonding.

I'm sure you understand all this at least as well as I do, so I don't quite understand why you're making such a meal of it. The water (and gas, if they exist) supply pipes are e-c-p's and therefore require Main (Equipotential/Protective) Bonding (MPB) close to where they enter the building. The internal pipework and taps within the building (which may or may not be in electrical continuity with the supply pipes at entry) never require MPB and, under current regs, rarely are required to have any bonding at all (i.e. not Supplementary boding either).

The OP's pipes are bonded, so we have to assume that they are e-c-ps.

IIRC, all the op told us was that pipes in the bathroom 'were earthed'. That obviously is not going to be Main Protective Bonding (unless the water supply enters the building in the bathroom). Even if it were, the requirement would be to connect the pipes via a Main Bonding coductor to the MET, not to other pipes or the bath, or even a local CPC! I therefore don't really understand what you are going on about!

Then if there is no other way for the pipes and taps to introduce a potential they are not e-c-ps and BS 7671 does not require them to be bonded.

As I said, pipes and taps within a building can never be e-c-ps as defined by the regs (provided that proper MPB is present). Again, you appear to be talking about Main Protective Bonding (since that's the only context in which e-c-p is relevant) to pipework distant from the entry point into the building, which is not a concept of BS7671 under any circumstances.

If not, why do you regard it as 'crazy' to have the bath so connected, whilst accepting that the regs usually result in that being the case with the taps, pipes and radiators?

The regulations only result in pipes being connected to the cpcs if the pipes are e-c-ps.
If they are not e-c-ps then they do not require bonding, and therefore do not end up connected to the cpcs.

See above. You seem to be fixated on extraneous-conductive-parts within a building, which really cannot exist (per BS7671 definition) if MPB is in place. There is no requirement in the regs for multiple MPBs, just in case the primary one fails and thereby renders other pipework liable to introduce a potential.

Kid Regards, John.

 

[ban-all-sheds]

I'm sure you understand all this at least as well as I do, so I don't quite understand why you're making such a meal of it.

I'm not.

I have been trying to get you to understand what extraneous-conductive-parts are, and what the requirements are for bonding them, and that is proving to be a difficult task, which is why it may seem to you that I'm making a meal of it.

The internal pipework and taps within the building (which may or may not be in electrical continuity with the supply pipes at entry) never require MPB and, under current regs, rarely are required to have any bonding at all (i.e. not Supplementary boding either).

One of the requirements for omitting supplementary equipotential bonding is that the extraneous-conductive-parts are effectively in electrical continuity with the supply pipes at entry.

IIRC, all the op told us was that pipes in the bathroom 'were earthed'.

He has.

Which is what 99.9999999999999999999999999999% (approximately) of lay people would describe supplementary equipotential bonding as.

That obviously is not going to be Main Protective Bonding (unless the water supply enters the building in the bathroom).

Indeed not.

But it might be supplementary equipotential bonding.

Even if it were, the requirement would be to connect the pipes via a Main Bonding coductor to the MET, not to other pipes or the bath, or even a local CPC! I therefore don't really understand what you are going on about!

I'm going on about the fact that the pipes have had supplementary equipotential bonding applied to them.

As I said, pipes and taps within a building can never be e-c-ps as defined by the regs (provided that proper MPB is present).

Really?

So a CH pipe which is in metal-metal contact with a boiler manifold which is in metal-metal contact with a cold water pipe which is connected to the MET cannot introduce an earth potential to the bathroom?

A hot water pipe which is in metal-metal contact with a hot water cylinder which is earthed via the immersion heater cannot introduce an earth potential to the bathroom?

Interesting.

Again, you appear to be talking about Main Protective Bonding (since that's the only context in which e-c-p is relevant) to pipework distant from the entry point into the building, which is not a concept of BS7671 under any circumstances.

No - I'm talking about the supplementary bonding of e-c-ps within the bathroom, i.e. the pipes.

See above. You seem to be fixated on extraneous-conductive-parts within a building, which really cannot exist (per BS7671 definition) if MPB is in place.

See above.

1) If the cold water taps in the bathroom are supplied by copper pipes teed off the incoming supply pipe, which is connected to the MET, why are those pipes not introducing an earth potential to the bathroom?

2) If they cannot exist, why does 701.415.2 say what it does?


Is the OP's bath an extraneous-conductive-part?

 

[holmslaw]

..

 

[ban-all-sheds]

Such as? (Bearing in mind that there's been nothing to suggest that the bath is an e-c-p.)

 

[securespark]

Clearly this thread will now degenerate into a useless squabble between people who bothered to look inside a copy of BS7671, and those who read Mr Cockburn's book instead.

That is unfair. I have not read Mr Cockburn's book. My views may not agree with the standards that BS7671 set as the minimum to be achieved. But my views are based on 40 years experience and almost as many years of working in "What If" mode and analysis of faults accidents.

The regs may be a minimum, but with supplementary, it is possible to create a hazard where there was not one to begin with.

Think about why supplementary in kitchens was done away with when the 16th came in.

 

[bernardgreen]

Think about why supplementary in kitchens was done away with when the 16th came in.

I have and can think of no sensible reason it was done away with.

I can recall one reason that was quoted about that time. That was that

earthing the sink created a hazard to a person who came in contact with a live conductor while touching the sink. If the sink was not earthed then it would not provide a return path to earth thus preventing the person receiving an electrical shock

Is that the reason bonding in kitchens was "done away with".

Common sense tells one that most sinks have a connection to "earth" ( or neutral in a PME ) via the water pipes to the taps so the perceived shock hazard mentioned as the reason for not bonding is there whether or not there is supplimentary bonding to the sink.

Then consider an electric cooker or oven, these are "earthed" by their supply lead, so if supplimentary bonding of a sink is considered to create a hazard then by the same logic the ovens, cookers and all other metal cased equipment in the kitchen should NOT be earthed.

The get out clause for "electricians" faced with this contradiction is to say that supplimentary bonding of items is not earthing the items. In description it may be different in the words used but in physical terms it is in fact earthing all the items bonded if one or more ot the bonded items is connected to the CPC or "earth" of the electrical installation.

If bonding of sink to pipe work was expressly banned then there would need to be electrical insulation between the sink and all taps fitted to the sink as the contact would be electrically the same as a bonding wire.

Personally I think supplimentary bonding was not "done away with" as an outright ban but was considered as "un-necessary" where the sink was in electrical contact with the pipe work that would be in electrical contact with items ( boiler manifold plate, immersion heater ) that were directly connected to the CPC ( earth or neutral ) of the electrical installation.

 

[dingbat]

You may have your opinion and you are welcome to have it.

Others may dis-agree, please accept that.

Often those 'others' are quite correct.

But, why should opinion come into it?

 

[dingbat]

Internal pipes and taps obviously cannot actually be extraneous conductive parts, as defined in BS7671, since they cannot in themselves be "liable to introduce a potential into the building" (since they are entirely contained within the building).

One of the common failings of students is the inability to read and understand the regulations. If you are going to quote regulations you'd be better off quoting what the regulation actually says, rather than adding your own words to make it say something different.

 

[JohnW2]

I have been trying to get you to understand what extraneous-conductive-parts are, and what the requirements are for bonding them, and that is proving to be a difficult task, which is why it may seem to you that I'm making a meal of it.

Fair enough. I'm not going to reply to your post point-by-point, since that would get very tedious and repetitive. There seems to really be only one major point of disagreement/confusion, and that's about the definition of 'extraneous conductive part' (e-c-p), or interpretation thereof.

As we all know, the regs define an e-c-p as "A conductive part liable to introduce a potential, generally Earth potential, and not forming part of the electrical installation". The meaning of the latter part is clear enough, so the imprtant part is "A conductive part liable to introduce a potential, generally Earth potential".

I think we probably all understand (at least in relation to TN systems) the reason for defining an e-c-p and requiring it to be main bonded to the MET, so we know the 'spirit' in which the definition should be interpreted. Within that spirit, I would suggest that "introduce" is intended to mean 'introduce into the building, or parts of the building' and that "potential, generally Earth potential" means 'a potential which may be different from that of the MET of the installation'.

I think it's probably sensible if I stop there for the time being, to see if you disagree (and, if so, why) with that interpretation - since everything else I have said, and would go on to say, is essentially dependent on that interpretation.

Kind Regards, John.

 

[JohnW2]

One of the common failings of students is the inability to read and understand the regulations. If you are going to quote regulations you'd be better off quoting what the regulation actually says, rather than adding your own words to make it say something different.

I agree totally, but there is often a need for interpretation (which is obviously not the same as 'making it say something different') - and I am having exchanges with people whom I know are as conversant with the actual wording of BS7671 as I am. Please see my latest response to BAS (and whatever may develop from it!).

Kind Regards, John.

 

[ricicle]

FFS

The problem with a forum is that only one person in this thread has seen the set -up.

The regulations are there in black and white. It is up to the designer/installer to decide how/if to apply them to the particular situation.

 

[JohnW2]

The regs may be a minimum, but with supplementary, it is possible to create a hazard where there was not one to begin with.
Think about why supplementary in kitchens was done away with when the 16th came in.

Bernard has already responded to this, but I will add a few comments, essentially in support of what he has said.
Like Bernard, I do not think that supplementary bonding in kitchens was 'done away with' by the 16th edition of the regs, any more than was most supplementary bonding in bathrooms 'done away with' by the 17th edition. What did go was a requirement for such bonding in many circumstances. Had the IET believed that such bonding actually represented an appreciable potential hazard, then the would presumably have 'banned it', not just stopped requiring it - and, as both Bernard and I have said, that would,in practice, require installation of plastic inserts in the plumbing system.

In practice, it's also obviously the case that the majority of supplementary bonding is/was between things which are already actually electrically connected via plumbing. Installation of the bonding therefore rarely changes anything - and, again, if you felt that meant a hazard was being created by the plumbing, that would need to be changed.

I think one of the confusions in my exchanges with BAS and others is that I was supporting the common sense (to me) of 'bonding together' metal objects (taps, pipes, baths, metal baths) which could be touched simultaneously, but not (as in Supplementary bonding) making any explicit connection to any part of the electrical installation (i.e. a CPC). I really don't see how this could possibly create any hazard, particularly given that the electrical connections concerned will very commonly already exist via plumbing.

Kind Regards, John.

 

[JohnW2]

The regulations are there in black and white. It is up to the designer/installer to decide how/if to apply them to the particular situation.

Indeed - and it was very rapidly established that the regulations don't require any bonding of the bath mentioned in the op.

Most of the the rest of the thread has consisted of a legitimate discussion about the feeling of some that it makes sense to ensure that metal objects that can be simultaneously touched are electrically connected together, even when that is is no way required (but not forbidden) by the regulations.

Kind Regards, John.

 

[echoes]

Is the rationale simply that supplementary bonding is unnecessary if the e-c-p's in the bathroom (pipes etc) are already effectively (and verifiably) connected together, and to the main bonding?

 

[JohnW2]

Is the rationale simply that supplementary bonding is unnecessary if the e-c-p's in the bathroom (pipes etc) are already effectively (and verifiably) connected together, and to the main bonding?

Yes, that's part of the requirements (per 701.415.2 of the regs) for supplementary bonding not being required in bathrooms. In addition, it is necessary (a) that automatic disconnection times are compliant with 411.3.2 AND (b) that satisfactory RCD protection is in place.

(a) requires a sufficiently low earth impedance, and I'm not sure how easy that is to achieve with TT systems.

Kind Regards, John.