Identifying a PME system

Ken77 · Nov 11, 2013

This may seem like a daft question but when looking to establish whether or not a supply is a TNC-S supply (PME) can you assume that where you have a new service head which has the link to for earthing conductor by incoming neutral that this is a PME supply?

Can you get a case where although you have new cable feeding the new service head it is still a TNS system with no earth supplied by the network?

I have asked the DNO to confirm what the supply is however they claim they do not keep any records of this, and need to send an engineer around to look at it. How would one tell?

telectrix · Nov 11, 2013

measure your PSCC and PEFC. if they are the same, chances are you've got PME.

Tiny Spark · Nov 11, 2013

Ime a little confused,
TNCS and TNS both have a supply earth.

TNS has a Swetted pot with the earth connection where a TNCS has a linked N&E which goes down the PEN conductor.

guest119 · Nov 11, 2013

Can you get a case where although you have new cable feeding the new service head it is still a TNS system with no earth supplied by the network?

That'll be a TT then?

Boydy

Darkwood · Nov 11, 2013

This question has been asked several times last few days .... is this homework?

delko · Nov 11, 2013

As Telectrix said above testing would confirm TNS or TNCS.

Guest55 · Nov 11, 2013

telectrix said:
measure your PSCC and PEFC. if they are the same, chances are you've got PME.

if you know what youre looking at theres no need to get the testers out ;-)

and the chances of the dno providing tns without an earth connection is slim to none tbh.

Guest55 · Nov 11, 2013

Tiny Spark said:
Ime a little confused,
TNCS and TNS both have a supply earth.

TNS has a Swetted pot with the earth connection where a TNCS has a linked N&E which goes down the PEN conductor.

unless the supply cable is pvc con / split con , then you need to look a bit closer.

Tiny Spark · Nov 11, 2013

biff55 said:
unless the supply cable is pvc con / split con , then you need to look a bit closer.

Never actually seen one but I have heard of such things LOL
Dont see many service heads in the factory LOL

HandySparks · Nov 11, 2013

Tiny Spark said:
Never actually seen one but I have heard of such things LOL
Dont see many service heads in the factory LOL

Here's one. You can see the black insulated outer strands running to the neutral terminal and the uninsulated strands to the earth.

[ElectriciansForums.net] Identifying a PME system

ackbarthestar · Nov 12, 2013

That pic looks more like a TT than a TNS fed from a split con cable. A little bit more at the bottom would clarify it I suspect.

HandySparks · Nov 12, 2013

ackbarthestar said:
That pic looks more like a TT than a TNS fed from a split con cable. A little bit more at the bottom would clarify it I suspect.

No. Definitely TN-S. The green and yellow running downwards is just the bond to a water pipe.

guest119 · Nov 12, 2013

Bare earths from the split con cable are going to the earth connection which is solid linked to the external earth block.............TNS

Boydy

Geoffsd · Nov 12, 2013

The question was "How do you tell if PME?" - not TNC-S or TNS.

Look for label ?

Engineer54 · Nov 12, 2013

Geoffsd said:
The question was "How do you tell if PME?" - not TNC-S or TNS.

Look for label ?

I didn't know that the DNO's had different labels for PME and TNC-S?? They would i believe post a PME sticker for both PME and TNC-S earthing arrangements. And YES, there is a difference of definitions between TNC-S and PME....