Equipotential bonding of boiler pipes

[tilla tech]

Hi
Had a look thru previous threads but couldnt find anything.

I have noticed that plumbers/heating eng cross bond all the metal pipes on a combi boiler except the copper overflow pipe which runs to an outside gully.
From what I understand I would have thought that this over flow pipe would be the last thing that you would leave out when cross bonding, since it could introduce potential from outside.

Any thoughts on this.

Thanks

 

[Spark123]

There isn't an electrical regulation which requires the cross bonding of the pipes at a boiler, however if the manufacturers instruction states it then it needs to be done.
As for the overflow pipe - if it is not in contact with the general mass of earth then it is unlikely that it poses a risk of introducing a dangerous potential into the equipotential zone. If it does then it requires main bonding which is a connection directly back to the Main Earthing Terminal as opposed to supplementary bonding.

 

[nozspark]

In a modern boiler they are all connected together by the manifold anyway!!

 

[Taylortwocities]

Correct! Its one of those carry-over, I've always done it this way, things.

Unless the MI specifies it, of course - but they aren't always kept up to date.

 

[ColJack]

how would an overflow pipe introduce an earth potential unless the end of it was burried in the ground?
if it just goes outside then ends above a drain it's not connected to earth..

 

[Click-Sure]

I think the OP is refering to the blow-off (installed for safety reasons in unvented systems). It typically goes straight out the wall and then back on itself with a couple of elbows or some fancy pipe-bending skills.

The condensate pipe is always plastic and therefore would be pointless to bond, even if you could.

 

[gas4you]

I have asked about the earthing of the prv discharge pipe many times, to many electricians.

It seems 50/50 as to whether it needs earthing (or should I say did, as I haven't asked since 17th came out).

Those against said it shouldn't as it terminated outside the equipotential zone.

To this day I am still totally confused, but as the regs (as pointed out on here) do not seem to include these boiler pipes I no longer worry.

Over to you learned lot

 

[RF Lighting]

That seems about right, as I'd say 50% of electricians don't actually fully understand the purpose of earthing, and what does or does not need earthing or bonding.