Earthing arrangement TNCS or TNS and the DNO

[AndySummers]

Hi, I wish to establish what the earthing arrangement is, the cut-out has a label above it that says "PME System" and the earth cable disappears into the bottom of the cutout and then comes back out the bottom and connects onto the supply cable sheath. Reading some other forums people suggest this is TNCS (it may have been TNS and then converted or the extra connection to the supply cable to lower Ze) - do people agree? Secondly I have tried phoning the DNO (WPD) but they say although they are the DNO they are not responsible for the earthing and therefore do not hold records of supply earthing arrangements... I thought the DNO were required to hold these records? [I have a picture of the cut-out but I can't post pictures to this forum yet] Thanks.

 

[i=p/u]

It sounds like both add a rod and have all 3 ..

 

[Engineer54]

Hi, I wish to establish what the earthing arrangement is, the cut-out has a label above it that says "PME System" and the earth cable disappears into the bottom of the cutout and then comes back out the bottom and connects onto the supply cable sheath. Reading some other forums people suggest this is TNCS (it may have been TNS and then converted or the extra connection to the supply cable to lower Ze) - do people agree? Secondly I have tried phoning the DNO (WPD) but they say although they are the DNO they are not responsible for the earthing and therefore do not hold records of supply earthing arrangements... I thought the DNO were required to hold these records? [I have a picture of the cut-out but I can't post pictures to this forum yet] Thanks.

They are fobbing you off, if they have provided an earthing point, they are the only ones responsible for that earthing DNO earthing point and have a duty to maintain that earthing provision.... Sounds as if they have made a complete hash of a PME connection too, if they are incorporating the sheath that has probably failed, and why they have converted the earthing to PME!!


Always ask, or should i say insist on talking to the ''Area Duty Engineer'' when contacting the DNO, otherwise you'll be only speaking to a dumb telephone enquires girl that has been taught to deny any responsibility for just about everything!! lol!!

 

[Darkwood]

Hi, I wish to establish what the earthing arrangement is, the cut-out has a label above it that says "PME System" and the earth cable disappears into the bottom of the cutout and then comes back out the bottom and connects onto the supply cable sheath.Reading some other forums people suggest this is TNCS (it may have been TNS and then converted or the extra connection to the supply cable to lower Ze) - do people agree?

How very dare you get advice from other forums

Yes it sounds like the old TNS has been converted either a local earth issue or further upstream.... It is now classed as a TNCS and not a TNS and if you think about it the armour sheath on the supply cable now would you thnk it needs earthing ???? If you think about it you know why their is a link from the N/E and no its not to bring down Ze but may benefit this way from doing so.

 

[SPARTYKUS]

Maybe the TNS failed so was 'upgraded', as the laws of physics changed recently, coincidentally around the time they realised that it was cheaper to run two cores to properties instead of three...

 

[Engineer54]

How very dare you get advice from other forums

Yes it sounds like the old TNS has been converted either a local earth issue or further upstream.... It is now classed as a TNCS and not a TNS and if you think about it the armour sheath on the supply cable now would you thnk it needs earthing ???? If you think about it you know why their is a link from the N/E and no its not to bring down Ze but may benefit this way from doing so.

The link to the TN-S cable sheathing should be discontinued and any exposed lead sheath insulated with amalgamating tape!! It won't be an exposed conductive part then!!!

 

[Darkwood]

The link to the TN-S cable sheathing should be discontinued and any exposed lead sheath insulated with amalgamating tape!! It won't be an exposed conductive part then!!!

Regardless its still provides mechanical protection so if the lead sheath was corroded hence the reason to convert Mr digger that digs the road up nicks the cable would rather the L short down than make his cab live..... wouldn't you agree?
Not my field the DNO but i assume the sheath is grounded normally at the supply side when converted but where you have a breakdown of the sheath i would assume they leave it grounded both ends.

I may be wrong and stand corrected but you must agree i bring up a good point to the safety of the utility company's

 

[Engineer54]

Regardless its still provides mechanical protection so if the lead sheath was corroded hence the reason to convert Mr digger that digs the road up nicks the cable would rather the L short down than make his cab live..... wouldn't you agree?
Not my field the DNO but i assume the sheath is grounded normally at the supply side when converted but where you have a breakdown of the sheath i would assume they leave it grounded both ends.

I may be wrong and stand corrected but you must agree i bring up a good point to the safety of the utility company's

The lead sheath will rarely if ever break down completely, far more common is that the lead sheath is slowly corroding away at various points along it's route usually in sections of soils that have a higher than normal corrosive make-up. As the connection to each house (or whatever) is via a joint and a short length of a much smaller CSA cable off the main network distribution cable, depending where the corrosion is occurring along the network cable, it could be at a value of a couple of ohms to several ohms or more, but the sheath will still be holding a degree of earthing. Most Converted TN-S network cables will still be supplying both TN-S and TNC-S, so not totally a PME installation. I would rather isolate the sheath MET connection, and insulate the exposed lead sheath with amalgamating tape...

Note, when the DNO PME a network cable joint, those that i have seen, will not incorporate the cables lead sheath TN-S earth. It's been a direct connection off the local rod to the neutral conductor...

 

[trev]

Andy, if you need a new bass guitarist, since you hate Sting so much now, I'm your man

 

[Geordie Spark]

Andy, if you need a new bass guitarist, since you hate Sting so much now, I'm your man

How will you manage to get time off from your day job to go on the road??

 

[trev]

I'll sub it out to yarreck

 

[Rampantchilli]

So you are willing to cut off the earth connection from cutout to lead sheath, my immediate thoughts were some what insulting.
you don't know why it's there, and there must be a reason, and you could be removing next doors means of earthing by doing that. If next doors hasn't been converted to TNCS and relies on the 'converted' TNCS in this property providing an earth to the sheath, then your tampering with DNO equipment could be putting others at risk.
leave it as is, the supply cable is not your problem, and doesn't come under BS7671, so shouldn't be messed with by someone who hasn't got all the facts or relevant training

 

[Engineer54]

So you are willing to cut off the earth connection from cutout to lead sheath, my immediate thoughts were some what insulting.
you don't know why it's there, and there must be a reason, and you could be removing next doors means of earthing by doing that. If next doors hasn't been converted to TNCS and relies on the 'converted' TNCS in this property providing an earth to the sheath, then your tampering with DNO equipment could be putting others at risk.
leave it as is, the supply cable is not your problem, and doesn't come under BS7671, so shouldn't be messed with by someone who hasn't got all the facts or relevant training

What the hell are you talking about??
Have you any clue here on what you are saying?? Now what was you saying about initial thoughts??

BTW, i didn't at any time say, that i or any other person other than a DNO operative should remove the sheath connection at a PME conversion!!

 

[Rampantchilli]

the earth cable disappears into the bottom of the cutout and then comes back out the bottom and connects onto the supply cable sheath..

The link to the TN-S cable sheathing should be discontinued and any exposed lead sheath insulated with amalgamating tape!! It won't be an exposed conductive part then!!!

sorry that's how I read your reply

 

[Engineer54]

sorry that's how I read your reply

Read what?? still don't know exactly what youre saying?? Or in the rest of your post #12, ....afraid none of that post makes much sense to me, including what you find insulting!! lol!!:teeth_smile: