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.