Water bond to earth electrode.

[ste mac]

On a domestic job today and came across an unusual bonding setup. The main house is TNC-S, supply to remote home office via SWA cable. The remote building has an oil fired boiler and the copper pipe work has a 10mm bond cable going out through the external wall to an earth electrode. The electrode is only connected to the bonding, nothing else. Does this or does this not make the bonding cable an extraneous conductive part and therefore require bonding?

 

[Deleted member 26818]

Yes, I'd say so.
Cut it off.

 

[telectrix]

how is the office installation earthed? is it exported TNC-S?

 

[ste mac]

Yes it an exported TNC-S via the SWA armour. I would have difficulty in changing it to TT now since a new solar PV installation is using this cable to feed back to the main house and incoming supply. (see my other thread "Naughty naughty")

 

[Deleted member 26818]

Perhaps someone tried to TT it, and just forgot where to attach the conductor?

 

[SimpleSimon]

So if they've exported it why havent they run the bonding to the local earth bar?!?
I cant even think of the readon what made them think they could do it.

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[Deleted member 26818]

I reckon someone didn't know what they should do, got told they have to use an earth rod, or if they export the PME they have to use 10mm² bonding conductor, so did both.

 

[SimpleSimon]

Of course. Kill 2 birds with one stone saving time and money :/

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[Richard Burns]

Take a 10mm back to the SWA armour from the rod, sorted.

 

[Deleted member 26818]

Take a 10mm back to the SWA armour from the rod, sorted.

The armour won't have the equivelant conductivity of a 10mm² copper conductor, and it's the earth/bonding conductor that's the extraneous-conductive-part.
If it was removed, there wouldn't be anything that required bonding.

 

[Richard Burns]

The armour won't have the equivelant conductivity of a 10mm² copper conductor, and it's the earth/bonding conductor that's the extraneous-conductive-part.
If it was removed, there wouldn't be anything that required bonding.

Depends on the SWA size but if it is the earth for the building it should be OK for bonding, presumably the oil fired boiler and/or copper pipework would need bonding as an incoming service?

 

[Deleted member 26818]

No, you'd have to have a 70mm² 3core SWA cable, before the armour had the same conductivity equivelance as 10mm² copper.
Just noticed, that it's an oil fired boiler, for some reason I thought it was a wood burner.
Appologies.
The oil pipe is most likely an extraneous-conductive-part, so will need bonding, unless it's plastic, same thing for water.
You'll need a 10mm² core in the SWA to use as a bonding conductor, or the office will have to be made TT.
You could technically use a conductor from the office CU to the rod, picking up any pipework on the way.
That would allow you to leave the existing cable in situ, and just crimp a new length of cable on to it.