Earthing at the Origin

[walsall]

Hi All,

All my work is commercial/industrial and I have a question on a domestic. Replaced a cracked socket at a friend's house for them and plugged in tester to do a quick Zs afterwards. 59ohms on a TNS = wrong.

Turned off the board and did a Ze which gave 58.5ohms although couldn’t connect the gas and water bonds. It’s a lead covered ancient cable. The earth bond on the cable which is loose has also had the Main Protective Bonding conductors connected directly to it, probably when the kitchen was installed a few years ago. I guess this was because the MET didn’t have enough ways. Obviously there are no certs for this work as my friend wastold they were only needed for a full rewire…….

Am I correct in thinking that the DNO is responsible for the Earthing Conductor from the sheath on a TNS to the MET?

They’ve gone away for a few days so it’s not a blue light job. I don’t fancy messing about with the clamp on the world’s most ancient cable. I’m proposing getting a proper size MET, reporting a high Ze to the DNO and getting them to sort it. They may make a charge I guess but that’s probably the best way out…..

 

[trev]

If the DNO supplies an earth facility then they are responsible for it's maintenance.

You say you couldn't connect the gas and water bonds while doing your Ze test, what do you mean by that mate?

If you start to fanny about with the DNO's toys they're gonna blame you for the stupidly high measurement. Tell them about it and don't touch,

 

[SPARTYKUS]

OP if you chat nicely to them, get them a cup of tea and a plate of biscuits or similar (tunnock tea cakes are good or coconut macaroons) there will be no charge. Guaranteed

 

[walsall]

Trev - I meant to say disconnect not connect! I didn't want to play with their earth clamp.

Advice taken - thanks, I'll call the DNO.

 

[trev]

Right, wasn't too sure mate

 

[walsall]

By way of a follow up DNO turned up this evening and took a look. Dismantled it and found it was nothing to do with the wobbly clip. There's a street fault, and man with spade in attendance tomorrow.

Cheers all!

 

[Engineer54]

By way of a follow up DNO turned up this evening and took a look. Dismantled it and found it was nothing to do with the wobbly clip. There's a street fault, and man with spade in attendance tomorrow.

Cheers all!

There you go, just goes to show that some of the DNO's are prepared to pull their fingers out and do the job properly!! Just as well you carried out a few checks after replacing the damaged socket faceplate!!

Hope your mate takes you out for a drink. That could of had some serious consequences for someone in the family if had been left unnoticed!!

 

[walsall]

There you go, just goes to show that some of the DNO's are prepared to pull their fingers out and do the job properly!! Just as well you carried out a few checks after replacing the damaged socket faceplate!!

Hope your mate takes you out for a drink. That could of had some serious consequences for someone in the family if had been left unnoticed!!

Normally I would ha probably done an ELI before I touched it. I can't understand why anyone wouldn't do at the very least an ELI after replacing an socket or other accessory every time.

That is unless they (a) don't understand what the tests are, (b) don't have the kit, or (c) both!

Public beware!

 

[walsall]

So eventually DNO digs hole in pavement. Tells customer that they have "PME'd the supply" and it’s all OK now.

Apparently there have been no changes inside the property at all and the earthing conductor still comes off the metal cable sheath. Although they now say it’s a PME supply there is nothing written down and I would assume that if I do any further work there I would put TNS down as the earthing system as would anyone else I suspect!

Hmmmmm

 

[Badged01]

Have they not put one of those nice shiny labels on the service head declaring it a PME supply? If not get back on the phone to them and get something to show its PME ......

 

[walsall]

of course they haven't Badged01!!

I thought though that the last N/E join had to be actually at the head, not somewhere in the road!!

 

[trev]

The N/E link does have to be at the head mate.

 

[Engineer54]

All they have done is earthed the neutral at the road joint, if the lead sheathing is still good, then treat as a TN-S system. If not, then get the buggers back to officially convert the head to a PME supply....

I'd hazard a guess that most of all old TN-S local network distribution cables have had bad sections PME'd., thus leaving these cable carrying both TN-S and TNC-S

 

[walsall]

All they have done is earthed the neutral at the road joint, if the lead sheathing is still good, then treat as a TN-S system. If not, then get the buggers back to officially convert the head to a PME supply....

I'd hazard a guess that most of all old TN-S local network distribution cables have had bad sections PME'd., thus leaving these cable carrying both TN-S and TNC-S

I bet you're right! All this 'investment' that the increasing bills are meant to pay for and we still have ancient cables, some DNOs who won't fit isolators, and the whole issue of safe disconnection...

Another beer vicar?

 

[Delboybully]

All they have done is earthed the neutral at the road joint, if the lead sheathing is still good, then treat as a TN-S system. If not, then get the buggers back to officially convert the head to a PME supply....

I'd hazard a guess that most of all old TN-S local network distribution cables have had bad sections PME'd., thus leaving these cable carrying both TN-S and TNC-S

I was chatting to a DNO bloke a couple months ago. He was there to change an old head for a new one. It was a TNS. He said to me something along the lines of "you have lots of different names for things, we just call them TT or PME. This one we would call a PME"
He told me that everytime they have a fault on a cable that needs to be dug up and fixed, they PME it.

 

[Engineer54]

I was chatting to a DNO bloke a couple months ago. He was there to change an old head for a new one. It was a TNS. He said to me something along the lines of "you have lots of different names for things, we just call them TT or PME. This one we would call a PME"
He told me that everytime they have a fault on a cable that needs to be dug up and fixed, they PME it.

He's not correct though is he, at best that statement is very misleading. There are still thousands of network distribution cables that are still TN-S, and have had no PME/TNC-S connections made to them as yet. There are greater number of older TN-S cables that have had PME connections made to them, but are in no way close to being a true PME supply. There are more network distribution cables out there that are carrying both TN-S and TNC-S, than one or the other TN sytems.

The only distribution supplies that can be guarantee'd to be PME when converted, are overhead distribution supplies, when the DNO's ''must'' earth the neutral at every third or fouth pole on the strings...