Discuss High Zs On TNS in the Periodic Inspection Reporting & Certification area at ElectriciansForums.net

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Nathy boy

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Was looking at someones consumer unit today as a favor and took a ze reading of 10 ohm on what i assume to be a TNS - 6mm earth from terminal to metal casing on the DNO fuse carrier (no link from neutral to earth)

It is only about 500mm long so upgrading to 16mm wont improve much i don't think.

As i don't get involved with domestic just after advice - do i tell them to speak with the DNO and tell them their ze reading is high and sort the earthing & if so do they typically charge (i have heard story's of them demanding a fee)? Or would it be cheaper to make the system a TT as the consumer unit already had a 30mA RCD backing up all the circuits.

Trying to find the cheapest possible option for her!!!

Thanks in advance.
 
1

1shortcircuit

In my opinion this definitely requires a call to the DNO.

It's THEIR earth and they have a duty to maintain that earth. I would imagine a call to their emergency team would receive a pretty rapid response.

Please post back to let us know how you get on:thumbsup

1SC
 

Richard Burns

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Agrree with above and also so long as the earth is actually fitted by the DNO and not a DIY install then they should not charge for repairing it.
 

oldtimer

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Report it to DNO who will as if there is RCD protection if so they will look at it when they are good and ready if not they will be out the next day plus as they are not responsable for supplying an earth so there will be a charge also if they cannot get a good earth the will TNCS it then tell her to upgrade the main earth from 6mm to 16mm. So upgrade her earth for her and leave a bit extra on it
 

telectrix

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i hear alarm bells here. earthing conductor connected to metal casing of cut-out. not a usual DNO method of providing an earth. sounds like a DIY job. my advice would be to request PME or bang a decent rod in.
 

Des 56

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It could be the suppliers earth
Is the "£arth terminal to metal casing on the carrier" a metal enclosure with supply cable from underground, which houses the cut out, then earth lug is bolted to that casing, or some other set up ?

They have a duty to maintain their earth,but otherwise "kerching"
 
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Nathy boy

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Des you hit the nail on the head. "a metal enclosure with supply cable from underground, which houses the cut out, then earth lug is bolted to that casing"

Had a chat with a colleague and apparently if you report to the DNO that the existing tails are not adequate (they are in old VIR i believe) they will upgrade the tails and the earth along with it free of charge (he had it recently in Leeds - so take note cause apparently they charge for an earthing upgrade).

Going to nip back tonight hopefully and put them some 16mm in for their earth and leave it loose. Need to bond her gas and water too as its non existent.

Thanks for the help chaps will keep you posted.
 
E

Engineer54

i hear alarm bells here. earthing conductor connected to metal casing of cut-out. not a usual DNO method of providing an earth. sounds like a DIY job. my advice would be to request PME or bang a decent rod in.
Standard practice Tel where an old cast iron service cut-out was supplied. Off the cable, onto the casing off the casing, to the Installations MET....
 

telectrix

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yeah. if it's coming off the cable sheath. OK. but my thinking is that it might be a DIY jobby, and the cast head is not a true earth.
 
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trebor

Its extremely unlikely that the 6.00mm is a dno connection, the metal cut out is probably i gues a green or black ISCO where the metal casings commonly were not earthed and often have a wooden bush where the cable enters the cut out, you should ask the DNO to make a connection to the cable sheath, as a point of interest have a good look round the back of the service cable immediately below the cut out, you will sometimes find a bare earth coonductor tucked up behind the meter board which has never been used, at the times of these cut outs there was no automatic connection by the inspector
 
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Engineer54

Its extremely unlikely that the 6.00mm is a dno connection, the metal cut out is probably i gues a green or black ISCO where the metal casings commonly were not earthed and often have a wooden bush where the cable enters the cut out, you should ask the DNO to make a connection to the cable sheath, as a point of interest have a good look round the back of the service cable immediately below the cut out, you will sometimes find a bare earth coonductor tucked up behind the meter board which has never been used, at the times of these cut outs there was no automatic connection by the inspector
It will probably be an old 7/044 or7/036 rather than a 6 mm, and was the old electricity boards favourite sizes for domestic service cut out earthing cable. Those metal casings were generally earthed, the wooden bung where the cable entered them, was a pitch seal not an isolating bush....
 
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