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Carrying out an EICR on a property in london, the supply is a TN-S supply with an incorrect tenby earth clamped around the PILC Sub mains cable.
Long lead tested all the main bonds and i am very surprised to still get such a high reading with these parallel paths in place.
3.25ohms
With the bonding disconnected 3.25 which remains relatively the same with the bonding connected again

Would i be correct in saying the DNO will need to be notified and called out?
 
Last edited:
OK now this is getting confusing can someone explain to me when doing a Ze what has bonding to do with the price of eggs.
forget the bonding mate i was saying it out of interest can we just get back to the point, the Ze is high with the main bonding disconnected, i assume the DNO will need to be notified and if so are they obliged to repair the Poor earth
 
OK now this is getting confusing can someone explain to me when doing a Ze what has bonding to do with the price of eggs.
You are required to disconnect the Earthing conductor or all main protective bonding conductors from the MET to eradicate parallel paths when conducting a Ze test. This way you are only testing the Earthing conductor through to the means of Earthing and not including main bonding.
 
I don't see that eradicating parallel paths just disconnecting the bonding to services. If the main earth is connected to the earth bus-bar in the DB then it is connected to all the earths for each final circuit which in turn will connect for instance through the boiler earth to water and or gas. Or the Electric shower through the earth on that to water again to earth and so on. The only way I can see to definitely remove the chance of parallel paths is to disconnect the main earth from the DB bus-bar. Please tell me if I am wrong, although I hardly need say that!
 
Ideally ALL installations should have some thing like this....
[ElectriciansForums.net] Rather High Ze with all the bonding in place

....to make testing easier.
 
It’s not particularly difficult to disconnect the earthing conductor in a domestic installation unless you have say 3 x 10mm conductors not identifying their function and not obvious to o what they supply/connect to, as is often the case in older installations where the tails are 16mm and the earthing conductor is 10mm.
 
Sounds like the DNO lead sheath is not providing a good earth path, and if the readings stay the same regardless of protective bonding connected or not, then the gas/water supply pipes are probably plastic and therefore not providing any earth.
Contact the DNO to sort their cable

If there was an issue with the earth coming from the DNO lead sheath, what would the DNO do, convert the supply to TN-C-S or is it more complex for them than that?
 

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