Overhead PME

[chloebear]

Hi I have recently come accross a couple of instances where the feed to the house is via Overhead cable, but is labled up at the service head as PME. In these instances should the supply be treated as a standard TNCS system - even though the supply is fed from overhead?

 

[ajelec10]

Yes that is correct if there is an eatrh termial provided then you can use it and asume the system is TN-C-S
Regards
AJ

 

[scotsparky]

TN-C-S and PME are the same thing Regs call it TN-C-S Supply authority call it PME 0.35 ohms max Zs

 

[Gravid]

Thats Ze isn't it Scot ? external. Or have i got the two mixed up. What would happen if you couldn't get that reading ?

 

[Mac]

Thats Ze isn't it Scot ? external. Or have i got the two mixed up. What would happen if you couldn't get that reading ?

I came across one of these,where the DNO had replaced all the cabling to a workshop in a back garden.The bloke had his fuse board replaced previous and it was connected up as PME,but the ZE reading was way over 0.35.In the end i just spiked it where the original one was before

 

[scotsparky]

yes Ze good that some people are paying attention besiders on my qwerty keyboard the letters are very close.

If it is a TN-C-S system and your ZE was above .35 ohms contact the supply authority and tell them. Its there earth they have to maintain it.

 

[tomasi]

Seem to remember a problem with pme supplies that are underground and then rise up a pole and then travel a distance to
the point of use.
I think it was concerning true earth potential (the ground external) and the earth potential of the pme supply
because it also doubles as a neutral and therefore possible neutral currents,therefore any lets outside metal object
say a water pipe bonded to the building could have a potential voltage across it to the external ground.
Heard about this a while back,think further guidance is needed when dealing with such supplies?

 

[Spudnik]

Well, as an update to PME supplies, i have heard that SSE are now looking to do away with PME entirely and convert existing supplies to TN-S.

Not sure when and how tho.

 

[scotsparky]

That will be interesting Jason what about the old 2 cores to houses they going round them all to sort them?

 

[Spudnik]

They arent going to visit each property, but when a meter relocation is required, which involves the underground cable, instead of converting from TNS (if it is) to PME, it will stay as TNS.

Sorry, didnt make it very clear

 

[Mac]

That will be interesting Jason what about the old 2 cores to houses they going round them all to sort them?

Still got an old 2 core in my house.They would have to dig up half the ground floor to replace it

Well, as an update to PME supplies, i have heard that SSE are now looking to do away with PME entirely and convert existing supplies to TN-S.

Not sure when and how tho.

Sorry mate,don't want to sound picky,maybe i'm wrong,but didn't you post something a few months ago that all TT systems were being upgraded to PME/TNCS by the DNO.All to be completed by 2013.

 

[Spudnik]

Sorry mate,don't want to sound picky,maybe i'm wrong,but didn't you post something a few months ago that all TT systems were being upgraded to PME/TNCS by the DNO.All to be completed by 2013.

Yep, indeed i did and i was just as surprised when i was told.

Dont know what to believe anymore.

Trouble is, DNO's have their own rules and can change them whenever they see fit, especially if it suits them better.

I think TT systems still have to be changed, but im not entirely sure what to.

 

[scotsparky]

put that down as an ooops jason????

 

[Spudnik]

Not at all.

Just relaying the information as i get it.

 

[8181piv]

I have just had an internal meter moved outside fed from overhead cable, no signage to state PME infact earthing via rod. New meter now installed and labeled as PME same cable used. If i came across this again how can i verify earthing arrangement.