Discuss TT systems parallel earth paths in the Periodic Inspection Reporting & Certification area at ElectriciansForums.net

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M

maddfridge

Good Morning Gentleman

i have recently been testing house all of which are overhead supplies fed and the bog standard earth rod installation

however we had some serious earth path issues with a39 ohm earth rod when combined with the bonding taking it down to 0.27 ohms almost tncs then the next house all sort sorts of odd readings ???

we found that an outside lighting circuit had been run over a caternary wire and had been bonded at the isolators to each of the individual consumer unit earths

even with these disconnected parallel earths vis the gas and water pipes bought the readings down

any of you learned folks out there came across parallel earth other than bonding before ???

oh by the way the 30s style twisted copper wire earthing was still there but had been disconnected eons ago

cheers

p.maaddison
 
Check to see if the DNO overhead supply has been PME'd. Easy to check, there should a N-E down conductor visible at every 3rd to 4th pole that should also have some form of label stating the PME connection. Maybe some of the other local houses have been converted to PME whereas the house your working on hasn't.

Not too sure what you mean by ''outside lighting'', are you talking about council street lighting, supplied by the overhead DNO supply??
 
Check to see if the DNO overhead supply has been PME'd. Easy to check, there should a N-E down conductor visible at every 3rd to 4th pole that should also have some form of label stating the PME connection. Maybe some of the other local houses have been converted to PME whereas the house your working on hasn't.

Not too sure what you mean by ''outside lighting'', are you talking about council street lighting, supplied by the overhead DNO supply??

there are 70 sons on the side fo the houses run in a armoured cable fed from the first house in the road private estate by the way henceno street lighting hope that cleared things up:}
 
...however we had some serious earth path issues with a39 ohm earth rod when combined with the bonding taking it down to 0.27 ohms...

...any of you learned folks out there came across parallel earth other than bonding before ???


Any sort of boiler/water heater/immersion heater will provide a connection between the circuit cpc and the water or gas pipework. If it's all metallic, with metallic underground supply, it'll bring your Zs readings right down.

I can't really see a problem here.
 
Are you testing from the live side of the double pole isolator with it switched off? This will rule out any N-E faults which could be giving you a low reading.

Otherwise, the posts above have covered all the likely reasons.
 
there are 70 sons on the side fo the houses run in a armoured cable fed from the first house in the road private estate by the way henceno street lighting hope that cleared things up:}

So we have 70 No of SONS attached to these private houses fed from a s single point at the first house. I take it that the supply to these fittings is a separately metered DNO supply?? What's the consumers OCPD and the method of controlling this lighting circuit?? Do each of these SON fittings have an OCPD or isolator and is it these devices, that your saying is directly connected to each of the properties MET??

Oh and you haven't said anything yet about checking if this DNO overhead system has been PME'd or not??
 

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