Main water bonding and plastic pipe bends

[Paulbrown95]

Hi guys, sorry if this has been asked before.

I’m currently in a flat where the tenant queried the water bonding. There’s a 6mm green and yellow leaving the DB and goes to the gas meter as it’s clipped direct I can see it isn’t continuos and go to the water. There is also no other bonding conductors leaving the DB. When I carry out a wander lead test I get 0.03 ohms across the Gas bond which leads me to think there is a link somewhere to the water that isn’t visible or it’s just the reading going through the boiler. When I go onto the 16mm when it’s disconnected from the DB I get 0.00 ohms. There is also a plastic bend straight after the incoming stop cock and the copper work after that is getting a resistance of 15.1k ohms. My question is should water pipes after plastic bends and joints therefore be bonded ? And as I’m getting a good reading on the wander lead even though there is no visible cable at the MET is the bonding ok ?
Apologies for the long winded question. TIA

 

[Dartlec]

The idea of Main Bonding is to avoid any different potential being introduced on the pipe as it enters from outside (earth).

Is it a ground floor flat or upper floor? It may be that bonding of pipes is done for the block as a whole on the riser pipe, in which case it's not necessarily needed in each individual flat.

If plastic joint has been installed then that's often enough to remove any external potential, but if the copper pipe then runs through concrete floor again it might still need bonding..

Where is the 15.1k reading on the internal water copper to? The MET? With gas bonding disconnected? From memory that would still make the copper pipe an "extraneous" part.

The boiler may well be 'assisting' the bonding - the only way to really be sure is to disconnect gas bonding, and boiler cpc - and then test MET to water.

 

[Paulbrown95]

The idea of Main Bonding is to avoid any different potential being introduced on the pipe as it enters from outside (earth).

Is it a ground floor flat or upper floor? It may be that bonding of pipes is done for the block as a whole on the riser pipe, in which case it's not necessarily needed in each individual flat.

If plastic joint has been installed then that's often enough to remove any external potential, but if the copper pipe then runs through concrete floor again it might still need bonding..

Where is the 15.1k reading on the internal water copper to? The MET? With gas bonding disconnected? From memory that would still make the copper pipe an "extraneous" part.

The boiler may well be 'assisting' the bonding - the only way to really be sure is to disconnect gas bonding, and boiler cpc - and then test MET to water.

Thanks for the reply. It’s a middle floor flat so my thinking was that as I was getting 0.00 ohms between the main earth (when disconnected) for the flat and the water stop cock that it may have been bonded elsewhere like you say for the whole riser. It’s not the best way to have it as I would always put a separate bond per flat back to that individual DB but at least it’s still bonded.

The 15.1k ohms reading was after a plastic bend installed on the copper piping for the cold water feed at the kitchen sink which as you say as the reading would make it an extraneous conductive part so does that therefore mean that electricians now have to test every copper part of a plumbing install of plastic bends have been used ?

 

[Dartlec]

Thanks for the reply. It’s a middle floor flat so my thinking was that as I was getting 0.00 ohms between the main earth (when disconnected) for the flat and the water stop cock that it may have been bonded elsewhere like you say for the whole riser. It’s not the best way to have it as I would always put a separate bond per flat back to that individual DB but at least it’s still bonded.

The 15.1k ohms reading was after a plastic bend installed on the copper piping for the cold water feed at the kitchen sink which as you say as the reading would make it an extraneous conductive part so does that therefore mean that electricians now have to test every copper part of a plumbing install of plastic bends have been used ?

I'd say that you have followed your responsibility to ensure that adequate main bonding is in place at the stopcock . As an existing installation that's all that would be reasonable I'd say.

If you were doing a full rewire and initial verification then a different level of check would likely be needed.

If it's a middle floor flat then presumably the pipe never leaves the equipotential zone of the flat again, so shouldn't be able to introduce any other potential, which is the point of main bonding.

The fact the pipe after the incomer is extraneous would only be relevant in a situation where supplementary bonding might be required (bathrooms mostly) - and even then if an RCD is fitted all round then it's no longer an issue with 18th.

6mm is still considered adequate for main bonding (if no signs of thermal damage), so I'd say that you have done what you need to before carrying out any new work.

 

[Paulbrown95]

I'd say that you have followed your responsibility to ensure that adequate main bonding is in place at the stopcock . As an existing installation that's all that would be reasonable I'd say.

If you were doing a full rewire and initial verification then a different level of check would likely be needed.

If it's a middle floor flat then presumably the pipe never leaves the equipotential zone of the flat again, so shouldn't be able to introduce any other potential, which is the point of main bonding.

The fact the pipe after the incomer is extraneous would only be relevant in a situation where supplementary bonding might be required (bathrooms mostly) - and even then if an RCD is fitted all round then it's no longer an issue with 18th.

6mm is still considered adequate for main bonding (if no signs of thermal damage), so I'd say that you have done what you need to before carrying out any new work.

Brilliant thanks for the help and reassurance. I’ll stick all the info on the minor works in the comment on existing installation part. Thanks again.