Protective bonding

[studentspark]

Would like a bit of guidance on protective bonding

An installations gas service has main protective bonding connected to the MET (3 flats looped on one 10mm G/Y conductor)

The water enters in plastic, in a communal hallway, it then runs in copper from the hallway into the flat.


The water service enters in plastic, changes in to copper, and runs up the wall to the flat
(It does not go back into the ground)
There is no bonding connection visible on this pipe. (The incoming water was changed from lead to plastic a couple of years ago) I suspect water was never bonded.

This water pipe now does not required MPB, as it not an extraneous conductive part?

But in my mind it is now an exposed conductive part as it is connected to a boiler, which has a connection to a 230v source?

They will be a ‘Earth' connection to the water pipe via the boiler manifold to the boilers CPC connection, and the gas pipe which is bonded.

But would it be advisable to add supplementary protection to the water pipe.


The towel rail in the bathroom tests at 4.69kΩ to the MET which suggests it does need bonding.

Testing gas and water in the kitchen to the MET (Disconnected gas bond), I get 0.08Ω (Boiler manifold probably providing then low ohm reading on the water pipe work)

Plastic push fit connectors on plumbing evident

Testing the towel rail in the bathroom to MET I get 4.69kΩ which has left me a bit unsure what to do.

Testing between the towel rail and the bath taps, I get a similar reading 4.56kΩ, which is quite a high reading, I would expect a reading in the low ohms.
All circuits have RCD protection.

It suggests that supplementary bonding is required?

Hope that make some sense

 

[EFLImpudence]

An installations gas service has main protective bonding connected to the MET (3 flats looped on one 10mm G/Y conductor)

Ok.

The water enters in plastic, in a communal hallway, it then runs in copper from the hallway into the flat.
The water service enters in plastic, changes in to copper, and runs up the wall to the flat
(It does not go back into the ground)
There is no bonding connection visible on this pipe. (The incoming water was changed from lead to plastic a couple of years ago) I suspect water was never bonded.

If it is a plastic supply, then there is nothing to bond.

This water pipe now does not required MPB, as it not an extraneous conductive part?

Correct.

But in my mind it is now an exposed conductive part as it is connected to a boiler, which has a connection to a 230v source?

It will be connected to earth by the boiler connections and CPC anyway.

They will be a ‘Earth' connection to the water pipe via the boiler manifold to the boilers CPC connection, and the gas pipe which is bonded.

Exactly.

But would it be advisable to add supplementary protection to the water pipe.

No.
The loops you often see under boilers are not required nor necessary.

The towel rail in the bathroom tests at 4.69kΩ to the MET which suggests it does need bonding.

It says it is an extraneous-c-p to the bathroom.
Whether it needs bonding depends on the normal bonding rules.

Testing gas and water in the kitchen to the MET (Disconnected gas bond), I get 0.08Ω (Boiler manifold probably providing then low ohm reading on the water pipe work)

Yes.

Plastic push fit connectors on plumbing evident

Testing the towel rail in the bathroom to MET I get 4.69kΩ which has left me a bit unsure what to do.
Testing between the towel rail and the bath taps, I get a similar reading 4.56kΩ, which is quite a high reading, I would expect a reading in the low ohms.

Well, it is strange but doesn't really make any difference to anything, does it?
As said, it suggests it is an extraneous-c-p to the bathroom.

All circuits have RCD protection.

So - are the other two conditions met which would allow the 'omission' of supplementary bonding?

It suggests that supplementary bonding is required?

Well, the 4.56kΩ suggests it is an extraneous-c-p.

Other things determine whether supplementary bonding is required.

 

[studentspark]

Other things determine whether supplementary bonding is required.

1. Well it has an RCD
2. It has MPB to gas
Water is not considered an Extraneous CP !

3. All extraneous-conductive parts within the location are effectively connected to the protective equipotential bonding.

Well with that reading they are not. It too high, to be low enough, and its two low to not be considered a ECP . Its in the middle. Thats my doubt, and why Im thinking Supplementary PB might be needed

 

[EFLImpudence]

3. All extraneous-conductive parts within the location are effectively connected to the protective equipotential bonding.

Well with that reading they are not. It too high, to be low enough, and its two low to not be considered a ECP . Its in the middle. Thats my doubt, and why Im thinking Supplementary PB might be needed

Yes, but not necessarily all the supplementary bonding that would be needed without RCDs.

You could try to find why the reading is so high or, if not, just bond the towel rail pipe(s) to something else so that it is effectively connected.

 

[JohnW2]

The towel rail in the bathroom tests at 4.69kΩ to the MET which suggests it does need bonding.

Do I take it that this a 'wet' towel rail (plumbed into the CH system, like a radiator), rather than an electrically-heated one?

Kind Regards, John

 

[studentspark]

Do I take it that this a 'wet' towel rail (plumbed into the CH system, like a radiator), rather than an electrically-heated one?

Yes, Wet towel rail, no electric element

 

[JohnW2]

Yes, Wet towel rail, no electric element

Thanks for confirming - I thought I ought to check. As you wrote ...

1. Well it has an RCD It too high, to be low enough, and its two low to not be considered a ECP . Its in the middle. Thats my doubt, and why Im thinking Supplementary PB might be needed

As I'm sure you realise, it's a very odd resistance to be seeing - one would normally expect it to be either 'very low' (if there is copper continuity all the way back to the MET) or 'extremely high' (if there are plastic fittings or bits of plastic pipe in the path), which makes it difficult to imagine what the cause could be. Someone might suggest that there is, say, a plastic coupling (you mention 'push fit') but with the eater bridging across that, but I thing that 4.69kΩ is probably far too low for water.

What about nearby radiators - do they have low resistance to the MET?

If it were me, my curiosity would probably like to find an answer but, as you suggest, to install SB would at least regularise the meassurements.

However, if you do that, I would suggest that you consider EITHER bonding the towel rail only to some other extraneous-c-p (which doesn't really qualify as 'proper SB') OR 'do it properly' (per regs) and bond together all exposed-c-ps AND exposed-c-ps in the room. Per what I've been saying in discussions with EFLI, I think that if you bonded just one extraneous-c-p to one or more exposed-c-p(s), you might create a situation that could possibly be dangerous in the face of a fault.

Kind Regards, John

 

[JohnW2]

Well with that reading they are not. It too high, to be low enough, and its two low to not be considered a ECP . Its in the middle. Thats my doubt, and why Im thinking Supplementary PB might be needed

Yes, but not necessarily all the supplementary bonding that would be needed without RCDs.

As I've just written to studentpark, if the reason cannot be found (and rectified) one could at least 'regularise the measurements' by just bonding the towel rail to some other extraneous-c-p (although that, in itself, would not be 'proper SB').

However, as I've said to him, if he wanted 'proper SB' (per regs), which requires connection to exposed- as well as extraneous-c-ps, then I think that (contrary to what you suggest above), he probably should install "all" the SB in the room - since, as I wrote to you last night, if one bonds some, but not all, of the extraneous-c-ps in a room to one or more exposed-c-ps, in the case of a fault dangerous PDs could possibly be present between the bonded and not-bonded extraneous-c-ps.

Kind Regards, John

 

[EFLImpudence]

Is it a question of having 'proper SB' - or rather to meet the conditions of 701.415.2(vi) for omitting SB with RCDs this one item has to be effectively connected to the PEB (which, according to the note can be determined by the application of 415.2.2).

 

[EFLImpudence]

Student:

You say the towel rail has that high measurement.

Are you measuring the towel rail itself or the pipes to it?

 

[EFLImpudence]

...and are there any exposed-c-ps in the bathroom?

 

[JohnW2]

Is it a question of having 'proper SB' - or rather to meet the conditions of 701.415.2(vi) for omitting SB with RCDs ....

As I said, one could 'tick the boxes', and thereby satisfy the requirements for omission of SB, by electrically connecting the towel rail to some other extraneous-c-p. However, studentspark suggested that he could address the problem with "Supplementary PB" - so I was point out that to simply (electrically) connecting two extraneous-c-ps would not qualify as ('proper') Supplementary Bonding in the eyes of the regs.

... this one item has to be effectively connected to the PEB (which, according to the note can be determined by the application of 415.2.2).

That is, of course, the bit I do not really understand, and which has caused so much of the confusion, in our other current discussion. The 'test' of 415.2.2 concerns "The resistance R between simultaneously accessible exposed-conductive-parts and extraneous-conductive-parts" - which is not (at least not directly) a measure of how effectively anything "is connected to the PEB"

As I've said, all that test ensures is that if the maximum possible current (before a device operated) flowed through the entire path from an exposed-c-p to an extraneous-c-p, then the potential difference between those two parts would not exceed 50V - but, as I've said, I find it all-but-impossible to envisage a situation in which such a current would flow through such a path!

Kind Regards, John.

 

[JohnW2]

Is it a question of having 'proper SB' - or rather to meet the conditions of 701.415.2(vi) for omitting SB with RCDs this one item has to be effectively connected to the PEB (which, according to the note can be determined by the application of 415.2.2).

I should perhaps have added that I've always found those conditions for omitting SB to be pretty strange, since all but one of them can only be failed by an installation which is already non-compliant with BS7671 (by virtue of other regulations)...

Where the location containing a bath or shower is in a building with a protective equipotential bonding system in
accordance with Regulation 411.3.1.2, supplementary protective equipotential bonding may be omitted where all of the following conditions are met:
(iv) All final circuits of the location comply with the requirements for automatic disconnection according to Regulation 411.3.2
(v) All final circuits of the location have additional protection by means of an RCD in accordance with Regulation 415.1.1
(vi) All extraneous-conductive-parts of the location are effectively connected to the protective equipotential bonding according to Regulation 411.3.1.2.
NOTE: The effectiveness of the connection of extraneous-conductive-parts in the location to the main earthing terminal may be assessed, where necessary, by the application of Regulation 415.2.2.

If main bonding is required but not present, if any of the final circuits fail to satisfy the requirements for ADS or if any circuits supplying (or even 'passing through') the bathroom are not RCD-protected, then the installation is non-compliant, leaving only the one condition you mention [ (vi) ] that needs to be satisfied in an otherwise compliant installation.

As I've also said (in relation to the 'Note' above), I really cannot see how "application of Regulation 415.2.2" can meaningfully confirm the "effectiveness of connection of the extraneous-c-p to the PEB" [as required to satisfy 701.415.2(vi) ]. Even if one modifies the 'test' of 415.2.2 to measure the resistance between extraneous-c-p to MET (rather than to exposed-c-ps, which is what it says), I am personally doubtful that 'passing that test' would give much confidence of an "effective connection". Given that one would only be interested in satisfying 701.415.2(vi) if RCD protection were present, 415.2.2 only requires that the measured resistance be less than about 1,666Ω - would you really consider two things to be 'effectively connected' if you measured, say, 1,500Ω between them?

Kind Regards, John

 

[EFLImpudence]

Wrong thread

 

[JohnW2]

[ ... reply to message which was posted 'in wrong thread' moved to the right thread ]