Bonding question

[saucyjack]

Hi chaps. I'll admit to being a bit confused about a bonding situation. A client of mine's incoming water supply is via plastic pipe. Now, an IR test between said plastic pipe and the subsequent metalwork (where the the copper pipe-work joins) gives a reading of >500M ohms, so confirming it's effectively insulated from earth (the metalwork that is). However, an IR test between the cold-water pipe-work and a known earth (actually the bonding clamp on the consumer's side of the gas supply) reads 0M ohms, thus implying that (at some point) the pipe-work of the water supply is bonded. Now, I can't verify where this may be; whether it's via the combi-boiler internal connection(s), or from a bonding cable I haven't managed to find. Net question being, as I can't currently (no pun intended!) assess the reliability of the water pipeworks bonding (i.e. I can't determine where it is!), do you guys think I should fit a new bonding cable and clamp regardless, to be on the (ultra) safe side? Or, as it's already at the same potential as the the gas metal-work etc., do I need to actually do so? (Sorry if this is a bit long-winded, just trying to be as descriptive as poss about the situation).
Thanks in advance for any advice!

 

[Deleted member 26818]

No.
Bonding is required to eliminate any difference in potential, which may be introduced from outside the installation.
You have established that the water supply does not introduce a difference, so there is no point in bonding it.

 

[Richard Burns]

I agree with the above, there are almost always a series of interconnections of metal water pipes and the electrical installation inside a property, this is not the issue.

To bond a piece of metal work that is not extraneous will only mean that there is another piece of metal that may be above earth potential during a fault and increase the danger not reduce it. In your case it would make little difference since there is already an interconnection but bonding for the sake of it is not safe.
If whilst doing a Ze measurement and had the main earth disconnected you were to measure resistance to the pipework from the disconnected main incoming earth this would give you more of an idea if the metal work were actually extraneous.

 

[IzzyS]

Now, an IR test between said plastic pipe and the subsequent metalwork (where the the copper pipe-work joins) gives a reading of >500M ohms, so confirming it's effectively insulated from earth (the metalwork that is).

Don't take this the wrong way, but are you connecting one probe to the plastic pipe and one to the metal?

 

[saucyjack]

That was my initially my goal, to to check that the plastic incomer was just that, i.e. a plastic pipe, and thus not introducing earth potential. And I wouldn't take any advice the wrong way fella, no worries

 

[saucyjack]

just realised that my last post wasn't my most literate! (At least the point remains the same :smile5.

 

[Corbs]

there will be a metal jig on the combi boiler so the water is earthed via that, as the gas is connected to said jig

 

[davesparks]

0M ohms could be a very high number, after getting that result you should move down to a lower range until you get a reading.

 

[saucyjack]

Thanks to all you guys for the advice, it's very much appreciated! (At least now I won't have to crawl around running 10M of 10mm Y&G behind some (very) old and somewhat manky kitchen cupboards!)