Service head

[Andy™]

The presentation to the installation has to be TN-C-S it can't be anything else as there is no earth connection prior to the cut out.Regardless of test results, thus by law it must be PME, thus the DNO has broken ESQCR by not fitting PME label.

Think about it...

not quite.... if its wired in split con it can easily be TNS

 

[Sidewinder]

No mate it can't.

To be correctly TN-S the installation earthing connection MUST be before the head, end of.

 

[Andy™]

henley series 6 service heads are designed for TNS use with split con.

henley link

and if you still dont agree, show me some proof that the earth must be before the service head.

 

[Barx]

I agree with those that say it could be either. TNS or TNC-S. Seen loads of exact same heads done both ways. And you can't rely on it being TNS if no PME sticker. You can either do test as described above. If L-E and L-N tests are pretty much same reading then you can assume TNC-S. Only other way to prove is to remove the cover. (Which I'm not saying you should do)

 

[Manator]

I am afraid Sidewinder is correct Andy, split con is almost never used for TNS supplies because there is a problem stripping any sleeving, split con used for TNC-S is earthed at each jointing, hence PME throughout the line. TNS cable from supply is almost always in constant contact with earth. The joint for earth is made before entry into the service fuse, new models allow for this braided link to be taken inside to the earth terminal, with the neutral link removed. The presentation has to be established by set methods, which is why almost all TNS earthing will be visible outside the carrier.

 

[Sidewinder]

Andy,

All your post is is that of a manufacturer of a service fuse carrier.

This does not prove anything.

The separation point for TN-S/TN-C-S is at the service head.

IF the earth is prior to the head this is TN-S, if it is in or after the head then it is TN-C-S, check the diagrams in the brb.

Barx,

Regardless of the status of the "PME sticker" if the supply is TN-C-S then it MUST be PME, check ESQCR, especially on new installs, there is a time frame for retrofitting, but I thought that this had expired.

We are now discussing STATUTE LAW, forget 7671 that is just peanuts in comparison.

Guys, please check up the brb and more importantly the statutory regs, these cannot be ignored, in the same way that to tamper with DNO kit is a criminal offence.

i.e. it is a criminal offence to pull service fuses, cut seals on fuses and meters, change meter tails DNO side of the meter, fit or remove 951 clamps to DNO cables (apart from that 951 bit being just plain damn stupid).

This is all to do with how the supply is PRESENTED to the installation, not on what your take on this is regardless of measurements it is NOT your decision it is that of the DNO, this is their realm, if we all stuck more to our bit & got the DNO to do their bit then it may be that they would realise the issues out there, but it seems that we (well some of us are) are doing their bit illegally, thus letting them make more profit and hiding the real issues by being criminals.

 

[Manator]

PME retrofit is 2012 Sidewinder, so they still have some time left to bring all TNC-S supplies in line. If more people report any problems to the respective DNO,s then we may be able to get on with our bit like you say.

 

[Sidewinder]

OK, thought it was all done by now, however, surely there was a point at which all new supplies if TN-C-S must have been PME on install, just like our regs, though I'd have to check!

If you get what I mean?

 

[Andy™]

This is all to do with how the supply is PRESENTED to the installation,

if its presented with 3x conductors, one for line, for for neutral, one for earth, then its TNS.

kinda in the same way you can have a PILC with a (DNO fitted) link from neutral to MET/clamp and it now being a TNCS supply

 

[Barx]

he he, this is all getting a bit irate for me. Staying out of it....

 

[chrishaworth]

Fairly common up here as TN-C-S. Also the neutrals in the centre terminals of the meter with the lives on the outside is not uncommon (neutrals directly connected, lives via the gubbins of the meter).

Cheers. Chris

 

[Manator]

he he, this is all getting a bit irate for me. Staying out of it....

This is healthy debate, Andy, Sidewinder and I are forum buddies, and enjoy a good debate, which is what makes each contribution better for the understanding. It is often very easy to get set in your ways, and then another side presents itself, which makes you re think again.

 

[Sidewinder]

[quote name='Andy

 

[Andy™]

still doesnt automatically make it TNCS. like i said, service heads are available designed specifically for TNS (& TNCS).

and the earth isnt 'generated' from a PEN. it runs all the way back to star. it may be connected to neutral at some point (i.e joins), but the fact is, its still presented as 3 conductors and TNS

 

[steptoe]

Fairly common up here as TN-C-S. Also the neutrals in the centre terminals of the meter with the lives on the outside is not uncommon (neutrals directly connected, lives via the gubbins of the meter). Cheers. Chris

I dont get where you are with the meter terminals,

most meters are as follows,

LINE in

NEUTRAL in

NEUTRAL out

LINE out

so yes, neutral SHOULD be in the centre 2 terminals AFAIAA .

ps, they are ALL LIVE cables

 

[Andy™]

seen some meters with live through meter as usual, but only a small (1.5) neutral to termianl 2, and the neutral to installation into neutral temrinal on head. no idea why it was done that way, but it works

 

[steptoe]

the Neutral is only need to drive the meter, so only a few amps(milli?) needed.

E7 is commonly that way.

EDIT - AGAIN,

sorry to be pedantic, but when an Electrician doesnt know what a LIVE cable is then we really are in the deep stuff,

and people wonder why we are the lost trade.....

please use the term LIVE and LINE in the appropriate places folks,

I thank you,

 

[Andy™]

usually is on off peak where ive seen it like that, but have seen the odd normal supply like that

 

[Sidewinder]

Andy,

Yes obviously DNO head assemblies are designed for different situations as are many bits of kit, however, if you check it out you will find that unless the earth is derived prior to the cut out / head then the supply is TN-C-S, thus PME or at least it will be by 2012, and I would guess that any connected within a certain previous time frame must be.

This is due to the presentation, if there is no earth prior to the cut out then it is a CNE conductor thus TN-C-S it can't be anything else by definition of the supply types can it.

 

[gselectrical]

I once contacted the DNO to report a high Ze on a TN-C-S supply. 0.72ohms the reading was. Supply was from an overhead line. 3 cables on overhead (L,N,E) but supply from overhead into property was single concentric so I assumed TN-C-S. DNO came out, checked joints, said they could not lower the Ze because the pole was so far from the trannie. So they replaced the single concentric with a split concentric and said "There you go, thats TNS now, which gives you a max reading of 0.80ohms". Took a reading again. 0.72ohms.

Anyway as the earth was not derived prior to the cutout, does that mean it was still TN-C-S?

I think that cable in the pic looks like Split con, looks too big to be single con.

GS