How to get a TT system upgraded to TNC-S

[Paul P]

Hi

I have just rewired a mate’s house with his help and the existing earthling is TT on overheads. We have tried to get it changed to PME (TNC-S) but who do you contact now a days. Back when I did nothing but house bashing in was a piece of cake, now its been split up they keep sending bods who check the Ze and say no I don’t connect tails into a meter.

Bonding etc is to current PME requirements, I just need the earth connection done.

 

[mattmoo1974]

National Grid: Distribution Network Operator (DNO) Companies
Hope this helps

 

[Short Circuit]

Paul,
Not sure where you are, but in the North East the DNO will not change the system to TNC-S anymore as they say the grid wont take it! I have tried a couple of times lately and they just keep refusing. Probably just as well of sticking to the TT and making sure the readings are good

 

[malcolmsanford]

That is interesting, have that said why the grid won't take it as a PME earth system is just relevant on sticking spike points along the neutral ...................seems a strange comment.

 

[Short Circuit]

No, didnt give any reason other than it wont take it! I'll see if i can find out more. Its more than likely an excuse not to be coming out, although they are missing out on what seems like good money for nothing when they do change the eathing arrangement

 

[Paul P]

No, didnt give any reason other than it wont take it! I'll see if i can find out more. Its more than likely an excuse not to be coming out, although they are missing out on what seems like good money for nothing when they do change the eathing arrangement

You mean they charge now. Boy am iabehind the times. Sounds cheeper to get a time delayed RCD main switch

 

[malcolmsanford]

You mean they charge now. Boy am iabehind the times. Sounds cheeper to get a time delayed RCD main switch

Lol Paul your well behind the times. If your fitting a normal dual or high integrity board then you don't need the 100mA S type upfront switch either, unless your going to run a supply out to an outside building and you want to protect the sub main.

 

[BertUK]

this is a strange 1 but ill tell you all anyway,i was changing a c/u in a house and it was a TT system,i checked Ze and it came out at 297 ohms so i rang YEDL and reported it,they told me someone would be out within the hour,in the meantime i did some investigation and found out that the guy next door had block paved all the front of his property and up the jennel between the 2 houses,the main earth of the house i was doing came out in the jennel and went down the wall under the block pavers,i gave it a short tug and out it popped ,clean cut,the guy who did the blockwork must have cut it off.so i thought ok.....no way of getting a new cable to the rod without taking all the blockwork up i,ll PME it,so i got it all ready,16mm earth into the meter box made the end off ready to connect into the cut out.......then waited............and waited..................and waited........for 4 hours.YEDL turns up and guy walks over to me and says "hi...whats the problem".....I told him it was a TT system and it was 297 ohms....he says "whats a TT sytem" im like haha are u joking....he said no mate im a cable jointer not an electrician....so i explained the problem and what i proposed to do and he said ok lets do it....he literally connected the earth into the neutral cut out and said ok do your test....tested the Ze and got 0.17 ohms and he said is that ok...i said yes its ok so he said right i,ll go and do something a bit more interesting and walked off.i couldnt belive it i was like...ive waited 4 hours for this and could have just done it anyway.

so my advise would be dont ring them up...just do it.

bearing in mind my mate works for YEDL and he told me our village was all set up for PME anyway.

 

[Paul P]

Lol Paul your well behind the times. If your fitting a normal dual or high integrity board then you don't need the 100mA S type upfront switch either, unless your going to run a supply out to an outside building and you want to protect the sub main.

Thanks you have a good point, i went to the trouble of fitting a fridge/freezer socket on a 20 A radial with the cable run in steel conduit to the socket so it did not have to be protected by a 30Ma RCD. I have a C/T 3X5X5 duel rcd board with RCBO on the smoke detectors, i could put another on the fridge and give up on the PME thing.

Unfortunatly the cutout is sealed so cant get the earth into it.

 

[malcolmsanford]

I'm not sure what the calibre of guys now work for the DNO, but that is truely frightening .......................what happens if he never made a good connection, what happens under a fault condition and the termination is poor it will blow, is the neutral termination man enough for a fault situation .......................

 

[malcolmsanford]

Thanks you have a good point, i went to the trouble of fitting a fridge/freezer socket on a 20 A radial with the cable run in steel conduit to the socket so it did not have to be protected by a 30Ma RCD. I have a C/T 3X5X5 duel rcd board with RCBO on the smoke detectors, i could put another on the fridge and give up on the PME thing.

Unfortunatly the cutout is sealed so cant get the earth into it.

That is exactly what I would do Paul, put the Fridge/freezer on it's own RCBO. If the system remains a TT there is very little chance you'll get a low enough Zs to activate the MCB on fault.

 

[Paul P]

That is exactly what I would do Paul, put the Fridge/freezer on it's own RCBO. If the system remains a TT there is very little chance you'll get a low enough Zs to activate the MCB on fault.

Thanks I do have a 30mA RCD on the tails at present because of the fridge socket I will put a Henley Block in its place so I don’t have to hassle the Electricity Board or what ever they call them selves now. I will also tidy up the earth stake as it is old and temporary looking.​

 

[Engineer54]

Thanks I do have a 30mA RCD on the tails at present because of the fridge socket I will put a Henley Block in its place so I don’t have to hassle the Electricity Board or what ever they call them selves now. I will also tidy up the earth stake as it is old and temporary looking.​

Just curious, ... but what do you mean by ''tidy up'' the earth stake??

 

[Paul P]

Put it in a propper box and conduit it down the wall. It is the original one that is just poked in the ground and not protected at all

 

[Engineer54]

No thoughts about actually improving the system then??...