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Buying a house supplied by OVO - what is TT supply to TNCS?

  • 13 September 2019
  • 3 replies
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Hi
The house we are buying is supplied by OVO, there is an electrical report saying it needs converting from TT supply to TNCS (PME) due to high reading and need to contact OVO for this. I don't really understand what these means but something to do with earth loop impedance and I am guessing safety cut outs? Are there options for us, does it need a full rewire, I've tried to google it and seems suppliers are often unable to help? Is there some way to check if OVO can upgrade the old tt supply?
Thanks for any advice
Hannah
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Best answer by Transparent 13 September 2019, 21:28

Hi @hannah9590 - good question; and welcome to the Forum!

Firstly you're not expected to understand this. But there are several of us here who have enough knowledge and experience to advise 🙂

Secondly, it would help enormously if you would fill out your Forum Profile. The answer depends somewhat on where you are in the country. We don't need a street address, but the first part of the post-code or your nearest main town with a population over 15,000 would do.

Thirdly, as you have yet to purchase this house, could you confirm at what stage you are in the process?
  • made an offer
  • offer accepted and solicitors in contact
  • in receipt of vendor's disclosure forms (TA6 & TA10)
  • contracts exchanged, & moving date agreed
  • completion
The fitting of an earth-stake isn't difficult, but is unlikely to involve your Energy Supplier (OVO). It is normally done by a local qualified electrician who liaises with your Distribution Network Operator as required. The local knowledge is important because you're best using an electrician who knows the characteristics of the soil in your area.

I have seen this handled incorrectly, resulting in a house that had earthing provided both from a newly-installed earth stake (incorrectly fitted) and via the neutral from the sub-station. That's what we need to avoid happening in your new home!

It is unusual that it's left to a purchaser to make such arrangements unless you've already obtained legal title of the property.

More commonly your solicitor states to the vendor that such work must be completed before you are prepared to exchange contracts, and that you must be supplied with a copy of the signed certification. This will show the results of the earth loop test, and the speed at which the rcd(s) tripped in the house when a leakage test was undertaken.

There is no reason to suggest that the house needs a rewire based on the information you've provided here. But there may be other reasons as to why you think this is so, in which case please say what those are.

You can copy this Topic to your solicitor if you wish. It might help clarify things.


Feel free to re-post here and ask for any further information you require.

You should not try to use technical terms if you're not sure what they mean. Just keep to ordinary English and be as clear as you can.

I hope that helps.
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Userlevel 7
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Hi @hannah9590 - good question; and welcome to the Forum!

Firstly you're not expected to understand this. But there are several of us here who have enough knowledge and experience to advise 🙂

Secondly, it would help enormously if you would fill out your Forum Profile. The answer depends somewhat on where you are in the country. We don't need a street address, but the first part of the post-code or your nearest main town with a population over 15,000 would do.

Thirdly, as you have yet to purchase this house, could you confirm at what stage you are in the process?
  • made an offer
  • offer accepted and solicitors in contact
  • in receipt of vendor's disclosure forms (TA6 & TA10)
  • contracts exchanged, & moving date agreed
  • completion
The fitting of an earth-stake isn't difficult, but is unlikely to involve your Energy Supplier (OVO). It is normally done by a local qualified electrician who liaises with your Distribution Network Operator as required. The local knowledge is important because you're best using an electrician who knows the characteristics of the soil in your area.

I have seen this handled incorrectly, resulting in a house that had earthing provided both from a newly-installed earth stake (incorrectly fitted) and via the neutral from the sub-station. That's what we need to avoid happening in your new home!

It is unusual that it's left to a purchaser to make such arrangements unless you've already obtained legal title of the property.

More commonly your solicitor states to the vendor that such work must be completed before you are prepared to exchange contracts, and that you must be supplied with a copy of the signed certification. This will show the results of the earth loop test, and the speed at which the rcd(s) tripped in the house when a leakage test was undertaken.

There is no reason to suggest that the house needs a rewire based on the information you've provided here. But there may be other reasons as to why you think this is so, in which case please say what those are.

You can copy this Topic to your solicitor if you wish. It might help clarify things.


Feel free to re-post here and ask for any further information you require.

You should not try to use technical terms if you're not sure what they mean. Just keep to ordinary English and be as clear as you can.

I hope that helps.
Wow, thanks so much for your detailed response.

The postcode is LE67 2FA (UK)

We are almost at exchange change of contracts stage (we have mortgage offer, home buyer survey, most of solicitor work is done), we anticipate 2-3 weeks until completion.

I contacted Western Power who said a high ELI needed them to carry out an inspection (I think it is 24, but was last tested 2 years ago)

I will fill out the forum profile.

You are right I don’t understand the language! I’m not sure if RCD units overcome the high impedance?

Thanks for taking the time to try and help
Userlevel 7
Badge +3
Hi @hannah9590. Well that's heaps more detail than I'd needed, but it does mean that I can bring up Western Power's map on the screen in front of me and look at the detail.

Firstly I'm not surprised there are earthing issues near your new home. The supply is from overhead wires and Western Power have already installed four additional earthing points on the 440v (3-phase) Feed running along Richmond Road from the sub-station in Manor Brook Close (Reference 93/7855).

For the sake of others reading this, the ELI which Hannah refers to is Earth Loop Impedance, and is a measure of how much resistance there is to electricity trying to flow to ground in the event of a fault within the home. It needs to be low enough to ensure that a safety trip will function.

There's more detail about the range of acceptable values over here on the website of Professional Electrician. A reading of 24Ω is high for a TT system, but I'm not sure on what basis there has been a recommendation to use PME (Protective Multiple Earth) instead.

My house is TT and, when I bought it, had an earthing system dating from 1960's and was clearly "non-compliant". However I worked alongside a local electrician to solve the problem, and we fitted two new earth rods about 3m apart adjacent to a position where the soil was permanently wet.

Safety within the house will be provided by an RCD (Residual Current Device). This trips out when there is too great an imbalance between the current leaving the live connection and returning via the neutral. So it would operate even if the earth connection was iffy.

Hannah - you mention RCD unit(s). But you haven't confirmed whether you know if any are fitted. Since you don't yet own the property I'm assuming you can't post a photo of the consumer-unit here yet.

I'm still surprised that your solicitor hasn't requested that this be resolved by the vendor as a condition of your purchase. Perhaps you've already haggled all you can out of them!


If you want to talk to Western Power themselves about changing the connection to your new house, telephone their Contact Centre on 0800 096 3080 (Mon-Fri 08:30-17:00). They would normally start by asking for the Meter Number (MPAN) which I guess you don't yet know.

If you already know anyone in the area of Ibstock/Coalville, I suggest you start asking for recommendations of a good local electrician. Ideally you want a tradesman who relies on his reputation to provide ongoing business.

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