TT to PME conversion

Gavin John Hyde · Jun 16, 2021

At a house today fitting yet another car charger.
Straightforward install apart from fuse holder having a crack in it.
Called SSEN who sent an engineer out, he pulled fuse and replaced holder.
Install was overhead TT to old cottage. live fused neutral comes in via a henley block before going through meter.
I had an Ra of 86 Mohms so reasonably happy given ground conditions
We got talking about things as you do he then said I will convert it to PME for you if you want,
Okay,, expecting him to change cut out etc. he then runs a piece of 16mm earth from MET to the Neutral terminal/henley block!
Just like that, I asked him about what he just did and he said all the cables outside are basically PME now and its no problem.
Weird thing is if i had requested PME SSEN would have wanted ~£200 for it.
Anybody else had DNO just connect Neutral and Earth together and say here's your PME?
I recognize a lot of the cables out there before entering the house are PME'd and very little is still TNS.
I thought they might want to carry out checks further along the supply before doing it.
That said have seen plenty of DIY PME conversions when out and about. can never be sure if it was a dno job or DIY job...
A part of me thinks this is all good and well until one of them gets it wrong.

On the positive side now have a Ze of 0.19!

mattg4321 · Jun 16, 2021

That’s all UKPN ever do.

It’s usually free too.

But it’s a short piece of 16mm earth from the neutral block in cutout to an earth terminal adjacent to the cutout. Bang a sticker next to it saying PME. Job done for them.

bill01803 · Jun 16, 2021

I always leave everything TT

pc1966 · Jun 16, 2021

I'm impressed to see an overhead feed to a cottage being as low a Ze as 0.19 ohms!

Gavin John Hyde · Jun 16, 2021

pc1966 said:
I'm impressed to see an overhead feed to a cottage being as low a Ze as 0.19 ohms!

So was I - that why i figured it was still TT and hadnt been converted until now..

As rural as it is, I expect there has been a lot of work to the network. Funny thing is the houses down the road - around 100m are PME with proper PME heads. they were converted from old barns/stables with new supplies around 2 years ago.

marcuswareham · Jun 17, 2021

If installing a car charger would it not have been easier to keep it TT, and then not have to worry about PEN fault protection, etc etc

I guess getting it converted to PME means you dont need to worry about the possibility of the TT system being connected to the PME earth via water pipes and the like to the other houses, although if those houses are new conversion probably plastic pipe

Gavin John Hyde · Jun 17, 2021

marcuswareham said:
If installing a car charger would it not have been easier to keep it TT, and then not have to worry about PEN fault protection, etc etc

I guess getting it converted to PME means you dont need to worry about the possibility of the TT system being connected to the PME earth via water pipes and the like to the other houses, although if those houses are new conversion probably plastic pipe

Charger can use PME as per Manufacturers specs. With exception of Ohme chargers I only fit ones that can use PME now. makes life so much easier.

FatAlan · Jun 17, 2021

SSE are really good. I've had them swap to PME a few times with no charge. I think all they do is quick Ze check to see if suitable. You have to make sure bonding is upgraded to 10mm which could add to the work.