Alternative to bonding water supply?

[NickD]

Just thinking out loud...how about, as an alternative to bonding (MPBC) an incoming metallic water supply pipe, putting a plastic pushfit immediately downstream from the stopcock before any branches and affixing a big warning notice about why it's there?

(Yes, I know pushfits are (allegedly) not the most reliable things in the world, though having said that my mate who was a fitter at the Royal Ordnance Factories back in the mid 1980s told me they were specified as standard fit on all their pipework.)

 

[123]

No.

Are you on a windup?

 

[davesparks]

That'll be fine as long as you can guarantee the water in that pipe will be 100% pure water and it will never have normal mains water in it or anything like that.

 

[NickD]

That'll be fine as long as you can guarantee the water in that pipe will be 100% pure water and it will never have normal mains water in it or anything like that.

But surely if you follow that logic then you can't have plastic pushfits anywhere? Point of the bond is to bring the extraneous metallic conductor to an equipotential with the main earthing terminal, right?

 

[NickD]

That'll be fine as long as you can guarantee the water in that pipe will be 100% pure water and it will never have normal mains water in it or anything like that.

So why then is there not a requirement for a bond if the supply pipe, with your actual normal mains water in it, is plastic?

 

[davesparks]

But surely if you follow that logic then you can't have plastic pushfits anywhere? Point of the bond is to bring the extraneous metallic conductor to an equipotential with the main earthing terminal, right?

Eh? you can have plastic pushfits anywhere and everywhere you like but it won't necessarily negate the need for main bonding. The point is to maintain all extraneous parts at the same potential, impure water in a plastic fitting will not have a high enough resistance to insulate the installation pipework from a metal incoming service.
A rule of thumb I was told a few years ago was that if a 22mm plastic pipe joining two pieces of copper pipe needs to be over 300mm long before the mass of water in it offers enough resistance to negate the need for bonding of the downstream pipe, I don't know if that work in reality or not though.

 

[davesparks]

So why then is there not a requirement for a bond if the supply pipe, with your actual normal mains water in it, is plastic?

Where did you get that idea from? the requirement is to bond extraneous conductive parts, just because there is a plastic incoming main it does not mean the installation pipework is not an extraneous conductive part.

 

[PEG]

I would guess it would have to be plastics poor conducting ability...:icon12:

 

[NickD]

impure water in a plastic fitting will not have a high enough resistance to insulate the installation pipework from a metal incoming service.

So why then do we not have to bond if the incoming service is a plastic pipe which could, hypothetically, be connected to a metal pipe just underneath the finished floor?

 

[NickD]

just because there is a plastic incoming main it does not mean the installation pipework is not an extraneous conductive part.

You're saying you think a plastic incoming main can be an extraneous conductive part?

(edit: that wasn't meant to sound sarky or whatever, just seeking clarity)

 

[davesparks]

So why then do we not have to bond if the incoming service is a plastic pipe which could, hypothetically, be connected to a metal pipe just underneath the finished floor?

You're saying you think a plastic incoming main can be an extraneous conductive part?

Read what I have written, not what you think I have written!

I never said a plastic main can be an extraneous conductive part, I said the installation pipework could be an extraneous conductive part despite the incoming main being plastic. This is why you test the pipework to establish whether it is an extraneous part or not, you don't just assume that because you can see a few inches of plastic that it is not!

 

[TJ Anderson]

Here's one for you. Cause I have had this myself. The water pipework was not extraneous (>23Kohms to earth). However it had become extraneous via the gas boiler because the gas supply pipework was extraneous. The gas was bonded (10mm (PME)). Would you bond the water separately?

 

[NickD]

I never said a plastic main can be an extraneous conductive part, I said the installation pipework could be an extraneous conductive part despite the incoming main being plastic. This is why you test the pipework to establish whether it is an extraneous part or not, you don't just assume that because you can see a few inches of plastic that it is not!

Ummm...I don't think the installation could constitute an extraneous conductive part...I could see how there could be another extraneous conductive part coming in other than the main and connecting to the installation, but then that second incomer is the extraneous part, not the installation. Not trying to split hairs here but you can't just point at the entire pipework installation and call it an extraneous conducting part.

OK, so say you insert the plastic pushfit immediately downstream of the stopcock, then test the pipework downstream of the pushfit. If the testing rules that it does not test as being extraneous, would you be content not to bond it?

 

[NickD]

Here's one for you. Cause I have had this myself. The water pipework was not extraneous (>23Kohms to earth). However it had become extraneous via the gas boiler because the gas supply pipework was extraneous. The gas was bonded (10mm (PME)). Would you bond the water separately?

Well, it hasn't become extraneous, it's been connected to something that's extraneous (and that is bonded). You don't make something extraneous by connecting it to something that's extraneous...?

 

[frontier219]

Post deleted due to idiocy on my part.

 

[davesparks]

Ummm...I don't think the installation could constitute an extraneous conductive part...I could see how there could be another extraneous conductive part coming in other than the main and connecting to the installation, but then that second incomer is the extraneous part, not the installation. Not trying to split hairs here but you can't just point at the entire pipework installation and call it an extraneous conducting part.

OK, so say you insert the plastic pushfit immediately downstream of the stopcock, then test the pipework downstream of the pushfit. If the testing rules that it does not test as being extraneous, would you be content not to bond it?

You really haven't got a clue have you? If the installation we are considering is say a house or small office etc built maybe 30 years ago with a solid ground floor and an outbuilding with a mains water supply to it, all installation pipework is metallic and an unvented hot water cylinder has been fitted.
The extent of metal pipe in contact with general mass of earth may well be sufficient to make the installation as a whole an ECP. There is no second incomer, yet there is still an extraneous conductive part there, unless of course you are going to treat every pipe which sticks up out of the floor to feed a radiator as a seperate ECP?

 

[Silly Sausage]

Here's one for you. Cause I have had this myself. The water pipework was not extraneous (>23Kohms to earth). However it had become extraneous via the gas boiler because the gas supply pipework was extraneous. The gas was bonded (10mm (PME)). Would you bond the water separately?

In that case, the water pipes would have such a low resistance to the MET they wouldn't require bonding.

However, >23kOhm don't require bonding, but what lower limit would you say the same?

 

[NickD]

Seriously, how are you not getting this? If you don't bond the copper pipe in the installation, and it comes live, what do you think will happen if somebody touches it?

But if you're not careful that line of thinking takes us back to the days of yore of earthing metal window frames again. Anyway, enough of this merriment. Excuse me while I go pore over GN8 Chapter 6....

 

[frontier219]

But if you're not careful that line of thinking takes us back to the days of yore of earthing metal window frames again. Anyway, enough of this merriment. Excuse me while I go pore over GN8 Chapter 6....

Yes, I realised this. However, I'm still not getting how you think the water in the pipe won't negate the use of the plastic fitting.

 

[davesparks]

Seriously, how are you not getting this? If you don't bond the copper pipe in the installation, and it comes live, what do you think will happen if somebody touches it?

He's not the only one not getting it I think!

How exactly is a pipe going to 'come live' if it is not bonded? the whole point of equipotential bonding is to ensure that that the pipework and other extraneous parts does become 'live' if the supply earth connection becomes live through an external fault.

 

[NickD]

The extent of metal pipe in contact with general mass of earth may well be sufficient to make the installation as a whole an ECP. There is no second incomer, yet there is still an extraneous conductive part there, unless of course you are going to treat every pipe which sticks up out of the floor to feed a radiator as a seperate ECP?

Ah, I see what you're trying to say now. At a splitting hairs level yes I do prefer to think of every pipe coming up as an ECP because the idea of the mass of metal being an ECP sticks in my craw, though I accept the guidance is quite happy to look at it that way.

 

[frontier219]

He's not the only one not getting it I think!

How exactly is a pipe going to 'come live' if it is not bonded? the whole point of equipotential bonding is to ensure that that the pipework and other extraneous parts does become 'live' if the supply earth connection becomes live through an external fault.

Re-read what I've written. I'm tired...

 

[TJ Anderson]

In that case, the water pipes would have such a low resistance to the MET they wouldn't require bonding.

However, >23kOhm don't require bonding, but what lower limit would you say the same?

I know it did not require it. It was not extraneous in its own right, and only became same potential as the gas pipe when combi boiler was connected. If the boiler was removed it would go back to non extraneous. I still bonded it though as it was new install and I didn't want another spark in future saying "why did he not bond the water" lol and me not being there to explain it.

 

[Deleted member 26818]

I think some people need to understand the difference between earthing and bonding.
Bonding is intended to equalise differences in potential between extraneous-conductive parts and exposed-conductive parts.
Earthing is intended to provide a return path for current which may become present in exposed-conductive parts under fault conditions.
Neither bonding or earthing are intended to provide a return path for current which may be come present in conductive parts due to poor workmanship.

 

[NickD]

I know it did not require it. It was not extraneous in its own right, and only became same potential as the gas pipe when combi boiler was connected. If the boiler was removed it would go back to non extraneous. I still bonded it though as it was new install and I didn't want another spark in future saying "why did he not bond the water" lol and me not being there to explain it.

I think it's not wise to contemplate too deeply what is truly extraneous or you end up in orange robes with a shaved head sitting on a mountaintop in Tibet going ommmmmmmmmmmmmmmmmmmmm......

 

[Pete999]

That'll be fine as long as you can guarantee the water in that pipe will be 100% pure water and it will never have normal mains water in it or anything like that.

Beat me to it Dave

 

[Engineer54]

There is a very big difference in the rules and the thinking behind those rules, that are applied to ordnance factories and normal buildings, eg domestic houses and flats!!

It doesn't matter if just 100mm of metal gas or water pipe enters a property before being converted to plastic, it will still be bring into that property an extraneous source earth... So officially will need main bonding....

 

[NickD]

There is a very big difference in the rules and the thinking behind those rules, that are applied to ordnance factories and normal buildings, eg domestic houses.

I mentioned the ordnance factory thing purely in reference to reliability of plastic push fit as a connector system, nothing more.

 

[Engineer54]

To be honest, i don't know what you're proposing here?? For electricians to start installing plastic isolation sections to incoming water and gas pipes maybe?? Now that should be interesting!! lol!!

 

[NickD]

To be honest, i don't know what you're proposing here?? For electricians to start installing plastic isolation sections to incoming water and gas pipes maybe?? Now that should be interesting!! lol!!

Mostly it was just like a thought experiment to hear other people's input and take on things, which can be a good way to improve my own understanding/grasp of things. It's been useful.