Bathroom supplementary earth bonding - do I need more?

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My hot and cold pipes are rubber, so no possibility of applying supplementary earth bonding to the taps. I have a towel rail piped with central heating water which is plated with some low conductivity alloy (looks like chrome). There is no RCD on the lighting ring.

I've connected an extension lead to the ring main and used the earth from that to determine that the copper pipes to the towel rail have 2.9Ω between them and earth. The towel rail coating appears to be around 40-100KΩ for 5cm.

As the copper pipes to the towel rail are only 2.9Ω from earth and there is already supplementary earth bonding in the airing cupboard to all the water pipes, do I need further supplementary earth bonding in the bathroom itself?
 
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I've connected an extension lead to the ring main and used the earth from that to determine that the copper pipes to the towel rail have 2.9Ω between them and earth.
You need to measure between them and any other similar (extraneous) parts and any (exposed) parts such as metal light fittings.
Is the light the only electrical circuit in the bathroom?

The towel rail coating appears to be around 40-100KΩ for 5cm.
Irrelevant.


As the copper pipes to the towel rail are only 2.9Ω from earth and there is already supplementary earth bonding in the airing cupboard to all the water pipes, do I need further supplementary earth bonding in the bathroom itself?
Probably not.
You say ONLY 2.9Ω but that is quite high.
Have you deducted the resistance of the leads?
 
You need to measure between them and any other similar (extraneous) parts and any (exposed) parts such as metal light fittings.
Is the light the only electrical circuit in the bathroom?

Probably not.
You say ONLY 2.9Ω but that is quite high.
Have you deducted the resistance of the leads?

I managed to balance the DMM on a box of wall tiles and measure from the light switch to the central heating pipes. The new reading is 0.2Ω.
Yes, the lighting circuit is the only circuit in the bathroom (and above 2.25m)
 
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It would appear that the bonding in the airing cupboard IS the supplementary bonding and sufficient.
... assuming that it really is proper supplementary bonding (i.e. connected to a CPC somewhere) and not just a plumber's 'cross-bonding'.

Kind Regards, John
 
It would appear that the bonding in the airing cupboard IS the supplementary bonding and sufficient.
... assuming that it really is proper supplementary bonding (i.e. connected to a CPC somewhere) and not just a plumber's 'cross-bonding'.
It doesn't itself actually have to be connected to a cpc(earth wire) as long as the pipe is somewhere but I presume that's what you meant.

Banjo has said the taps are supplied in plastic (rubber) so there is only the radiator.
There is only 0.2Ω between the light circuit and central heating pipe(s). (I am assuming (again) this figure includes the leads.)

This is well within the limit for required supplementary bonding.
 
... assuming that it really is proper supplementary bonding (i.e. connected to a CPC somewhere) and not just a plumber's 'cross-bonding'.
It doesn't itself actually have to be connected to a cpc(earth wire) as long as the pipe is somewhere but I presume that's what you meant.
Again, you speak common sense (with which I wouldn't disagree), but 701.415.2 appears to require that the supplementary bonding connects extraneous-c-ps to "the terminals of the protective conductor of each circuit ...". Do you have a way of interpreting that which does not require a supplementary bonding cable to be directly connected to the CPC(s)?

Kind Regards, John
 
Yes, the water pipes themselves can be used as supplementary bonding.

So, as long as, the circuit is connected to a pipe (somewhere) and this pipe is connected to other pipes such that the required resistance is met then all is well.

Apart from that, there is only a lighting circuit and the radiator pipe(s) in the bathroom which require bonding and the resistance between them is only 0.2Ω (including meter leads ? (and the switch drop if a plastic switch)).
 
Yes, the water pipes themselves can be used as supplementary bonding. ... So, as long as, the circuit is connected to a pipe (somewhere) and this pipe is connected to other pipes such that the required resistance is met then all is well.
Again, I can't argue with your common sense, but I'm not convinced that many people would think that complied with the word of the regs.

The same sort of common sense would probably say that only one of the pipes would usually need to have supplementary bonding, wouldn't it?

Kind Regards, John
 
Yes, the water pipes themselves can be used as supplementary bonding. ... So, as long as, the circuit is connected to a pipe (somewhere) and this pipe is connected to other pipes such that the required resistance is met then all is well.
Again, I can't argue with your common sense,
It's not only common sense - 543.2.1 (ii) and (vii)

but I'm not convinced that many people would think that complied with the word of the regs.
Nevertheless, it does.

Hence the number of posts (elsewhere) from people who 'can't see' any supplementary bonding without realising that their meter can.

The same sort of common sense would probably say that only one of the pipes would usually need to have supplementary bonding, wouldn't it?
Not sure exactly what you mean.
Only one would need to be connected to the lighting circuit but that one may need to be connected to others in the location depending on the resistance between it and the others.
 
Yes, the water pipes themselves can be used as supplementary bonding. ... So, as long as, the circuit is connected to a pipe (somewhere) and this pipe is connected to other pipes such that the required resistance is met then all is well.
Again, I can't argue with your common sense,
It's not only common sense - 543.2.1 (ii) and (vii)
True, and I suppose you might also have cited 544.2.4. One question is how direct/close (or otherwise) do you feel that "the connection from the circuit to a pipe (somewhere)..." has to be - given that some sort of 'incidental' connection will probably already exist 'somewhere'?
The same sort of common sense would probably say that only one of the pipes would usually need to have supplementary bonding, wouldn't it?
Not sure exactly what you mean. Only one would need to be connected to the lighting circuit but that one may need to be connected to others in the location depending on the resistance between it and the others.
I meant essentially what you say. When you say "...may need to be connected to the others...", you are presumably also implying "... or may not need to be connected ...", aren't you?

Is not the usual reality that, in copper-plumbed premises, there will (by virtue of the plumbing) be a very low resistances between all pipes, and (by virtue of the plumbing and MPB, plus CPCs of plumbing-related equipment) a pretty low resistance between any of the pipes and the CPCs of all circuits in the bathroom? Under those circumstances (say, if there is no RCD) what, if any, supplementary bonding would you feel was required?

Kind Regards, John
 
Yes, the water pipes themselves can be used as supplementary bonding.

So, as long as, the circuit is connected to a pipe (somewhere) and this pipe is connected to other pipes such that the required resistance is met then all is well.

Apart from that, there is only a lighting circuit and the radiator pipe(s) in the bathroom which require bonding and the resistance between them is only 0.2Ω (including meter leads ? (and the switch drop if a plastic switch)).

I think it may be difficult to meet parts (iii) and (iv) of 543.2.6

Cheers
Chris
 
One question is how direct/close (or otherwise) do you feel that "the connection from the circuit to a pipe (somewhere)..." has to be - given that some sort of 'incidental' connection will probably already exist 'somewhere'?
701.415.2 says 'preferably near to the point of entry' but it will depend on the situation wouldn't it?
It would seem silly to run a 4mm² conductor a distance to the point of entry if there were a pipe nearby with a resistance nine-ish times lower.

I meant essentially what you say. When you say "...may need to be connected to the others...", you are presumably also implying "... or may not need to be connected ...", aren't you?
Yes.

Is not the usual reality that, in copper-plumbed premises, there will (by virtue of the plumbing) be a very low resistances between all pipes, and (by virtue of the plumbing and MPB, plus CPCs of plumbing-related equipment) a pretty low resistance between any of the pipes and the CPCs of all circuits in the bathroom? Under those circumstances (say, if there is no RCD) what, if any, supplementary bonding would you feel was required?
If the required resistances are achieved, none is required?

I am slightly puzzled that you ask.
 
One question is how direct/close (or otherwise) do you feel that "the connection from the circuit to a pipe (somewhere)..." has to be - given that some sort of 'incidental' connection will probably already exist 'somewhere'?
701.415.2 says 'preferably near to the point of entry' but it will depend on the situation wouldn't it? It would seem silly to run a 4mm² conductor a distance to the point of entry if there were a pipe nearby with a resistance nine-ish times lower.
Silly, yes, but I'm still not convinced that it would be compliant with the word of the regs not to do so.
Is not the usual reality that, in copper-plumbed premises, there will (by virtue of the plumbing) be a very low resistances between all pipes, and (by virtue of the plumbing and MPB, plus CPCs of plumbing-related equipment) a pretty low resistance between any of the pipes and the CPCs of all circuits in the bathroom? Under those circumstances (say, if there is no RCD) what, if any, supplementary bonding would you feel was required?
If the required resistances are achieved, none is required? I am slightly puzzled that you ask.
If you agree that what I said is an extremely common situation, is it your belief that supplementary bonding is very rarely required, even when there is no RCD protection (assuming satisfactory MPB etc)? I know that you are a great believer in basing your decisions about supplementary bonding on resistance measurements alone, but does not that sometimes leave ('the word of') some of the regs unsatisfied?

Kind Regards, John
 

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