High EFLI on TN-S, DNO won't fix

[Sloaneranger37]

Hi all

Firstly, I'm not an electrician but have found these forums extremely helpful reading over the last couple of weeks due to a running battle I've been having with UK Power Networks. Hoping some of the experts on here might be able to shed some light on the below...

I recently arranged for British Gas to come and replace my old boiler. As part of the pre installation process they did some electrical testing and found an EFLI reading of approx 20. BG won't go ahead with the installation until this is resolved and advised me to contact my DNO (UK Power Networks - am based in London) and get them to take a look.

UKPN came out last week and did some tests. They confirmed the EFLI reading as fluctuating between 6 and 11.5. The main earth in my house is clamped to an incoming pipe and the UKPN guy confirmed my setup was TN-S (can post a couple of photos if helpful). His advice was that as UKPN didn't install my set up (not sure how he worked that one out) it isn't UKPN's problem and I needed to get an electrician out to either install an earth spike or to potentially have my system converted to PME. I have an electrician coming tomorrow.

Been on the phone to UKPN again today, who told me there are 2 types of TN-S system, one which they've installed and will maintain, and one where the main earth has been clamped onto the incoming supply where they won't maintain it (sounded like BS but there you go). Lady on the phone said I'd need to get my own electrician to either "have a go at installing his own version of TN-S" or stick an earth spike in. She also said that to convert me to PME, they'd need to book it in as a new connection which would cost £1000s since there wasn't a satisfactory earth present. Seems others in similar situations on here have been able to get the DNO to convert to PME for £100-200.

Just interested in folks' views on whether UKPN are talking BS re: them not being responsible for maintaining a TN-S earth and what best way to get EFLI reading to 0.8 would be.

Property is a first floor flat in an end of terrace house in SW London.

Cheers all

 

[Midwest]

A DNO does not have to provide an earthing facility, if they have provided one, aka PME, they have to maintain it.

Think the quotation of £1000's to convert to PME, is just a wild arse guess. Most I've heard of is £200, but it does depend on the locality if it's available, but bear in mind when a DNO repairs cables, they normally change to PME.

PME conversion would be better than having an earth stake installed (TT). See what your electrician advises, and get a proper written quotation for PME from your DNO. I was once advised by a DNO to convert a TN-S to TN-C-S myself

 

[Andy78]

I agree with all said above. Get a quote from the DNO for a supply cable earth connection. They will usually come out and do a free survey to enable this. This is superior to a TT earth rod system in that

• The EFLI values will be lower allowing proper functionality of the protective devices in your electrical system.
• The EFLI values will be more stable
• The supplied earth will be under the maintenance of the DNO rather than yourself with an earth rod.

Lady on the phone gave some dubious advice regarding a DIY TN-S connection. This should not be attempted by an electrician due to legal and safety concerns.

 

[The Ghost]

Yes pics would be helpful. Do you have an RCD installed? I think what the DNO means regards the earth is not theirs is some electrician thought it would be a good idea to put a BS951 earth clamp on the incoming sheath and use that as an earth. The DNO solder their earth point on so he saw it was not theirs. Hence not obliged to maintain it. It is bad practice for an electrician to put a clamp on their sheath as well as fraught with danger and illegality. I recently attended a clients house with the same scenario, BG said the EFLI was too high and could not install the boiler however they had a 30ma RCD which technically makes it safe up to 1667 ohms but I thought I am not going to get into that conversation with a BG man equipped with a socketandsee device. We got the DNO in to supply PME earthing and everything was fine. It is not a new install its just a change to earthing arrangements. Normally I just ring and ask the DNO for a PME supply at around £250 and job done, where they can supply it.

 

[PEG]

Hi,how long has it been a flat,and is the incomer original?

 

[Sloaneranger37]

Thanks for all the responses. No RCD installed currently - going to have that done as part of sorting the earth out. Have only lived in the property a few months so having fun uncovering the mess the last people left behind...

@Vortigern sounds right about someone else having put a clamp on the incoming sheath. Photos attached. First 3 photos are of the incoming supply by main front door (showing earth clamp on incoming sheath, with downstairs flat's CU on the left and my side of the supply going up into the roof). Last 2 photos are my CU.

@PEG No idea how long it has been a flat, at least since 2005 - probably older. Whole house dates back to about 1920s. I believe the incomer is original but you might disagree from the photos...

Electrician is coming out tomorrow morning but sounds like getting DNO to put PME in is the best option - although they were a bit clueless about whether this could be done on the phone earlier. Will post back with progress - thanks for everyone's input.

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[Richard Burns]

If you are getting EFLI of 6 ohms and the connections to the sheath and to your MET are sound then it would appear the sheath of the cable is no longer continuous back to the substation. This would cause problems for the DNO in providing a PME earth as they would have to replace the cable from the point of disconnection of the sheath.
However it is also possible that the connection at the sheath is not good.
It is possible that the local area is not a PME earthed network, though this is increasing unlikely as the DNOs all change to PME at each opportunity.
PME earthing from the DNO would be the best option if they are not silly about the cost.

The service head looks old but probably more modern than 1920 but not greater than 1950ish.
The earth connection could have a been a DIY effort or could have been the DNO.
It is unlikely (but possible) that the DNO did not originally (or at a later date) supply an earth to a flat in London, so I would expect that they should maintain it, having said that, if the engineer has been out and denied it is their connection I doubt they will change their minds.

The lack of earthing is a significant problem and should be addressed to minimise risk as soon as possible (the other flat is also at risk without RCD protection.)
It might be an idea to ask the electrician if an upfront RCD could be fitted to replace the main switch on a temporary basis, this is not an ideal solution as it could cause loss of power to the flat on a minor fault which is against the wiring regulations but it would be safer than not having RCD protection.

 

[PEG]

Is this a first floor or a ground floor flat? Who does the second meter belong to? It is fed from above,and does not look to have been in,long,in that position,anyway

 

[crawf]

Oh British gas the people that know everything Had to go meet the lovely man onsite to explain to him that yes the reading is to high for your little check list but do you know what earthing arrangement we have here the reply is "what is that"? That tells you all you need to know about the lovely "engineers" at British gas