OK,
As a first volley, does everyone agree with the description of traditional TN-C-S & TN-C-S(PME) in BS7671?

Yes I am with you so far.

-------------------------
John Peckham

http://www.astutetechnicalservices.co.uk/

Thanks John, anyone else please?

Yep, go on


Stu

Yep! Proceed

With you so far on TNC-S and PME, but I suspect that I will start disagreeing soon!

Regards,

Alan.

I've popped out, rounded up the loose cattle, two heifers to be more precise, talked to the police by phone twice, chatted to one of the young mum's down the stables, along with a farmer, his wife and son, disturbed a courting couple in a Volvo estate down the picnic area car park, as you do, all in the darkness of night!

Now I'm ready for the next instalment, tomorrow maybe? We don't want all the fun at once, so proceed at a steady pace!

Andy

My youngest daughter attended a family picnic on your beach today.

I digress, back to PME.

Andy

To be pedantic - no.

Page 44 only shows a PME variant of TN-C-S, ie the usual form

It does not show TN-C-S and TN-C-S(PME) - it just shows the latter.

Like Alan, I suspect this won't be the first divergence from popular misconception - and as a further point for the debate, ESQCR prohibits a TN-C system derived from a public network - so perhaps we also need to consider that the drawing on Page 44 is only applicable to simple public networks for "systems" below 1000V AC

Regards

OMS

-------------------------
Failure is always an option

As in Fig 3.9 on page 44?

Yes, with you so far!

- Andy.

Are we heading towards the term 'Multiple' by any chance?

Legh

-------------------------
Why do we need Vernier Calipers when we have container ships?

http://www.leghrichardson.co.uk

"Science has overcome time and space. Well, Harvey has overcome not only time and space - but any objections."

I don't have a copy of 7430, is it the same TNC-S PNB drawing as shown in GN8 4.9, and was this the drawing that was pulled from the DPC.

Regards

So that is 4 recognised authorities that say PNB is TN-C_S, ECA Guide to the Wiring Regulations, ECS Technical Manual, GN8 and BS7430.

-------------------------
John Peckham

http://www.astutetechnicalservices.co.uk/

Is there perhaps a link between each of those documents John, perhaps a connection by the authors via various other organizations - or a bit of sharing of resources going on perhaps - who knows.

For those of you who have never looked inside a distribution transformer, there's a copper strap that connects the winding ends on the LV star windings to the N terminal on the spill box. the big earth stud on the transformer body connects only to the metallic frame, cooling tubes, tank etc - it doesn't extend through to the star point. That conection is made either at the Neutral spill terminal of further downstream (or both)

Is that copper bar inside the transformer tank a PEN conductor perhaps ?

Regards

OMS

-------------------------
Failure is always an option

What always amazes me, is the size of the conductors connecting the windings of the TX to the spill box terminal bars. They are tiny

I still believe that if a installers cables leave the spill box, with a neutral/earth link in the consumers panel, the system is TN-C-S (PNB), as the neutral conductor from the TX is a PEN conductor

Regards

Jobbo

regards

OMS

-------------------------
Failure is always an option

OMS

We always assess the earthing arrangement on site during the initial DSEAR report, as you well know, BS EN 60079 prohibits the use of TN-C-S and the standard doesn't state which type (PNB or PME). We have to ensure a true TN-S system is in place

Regards

Jobbo

So how do you do that then - do you have a single transformer feeding a switchboard (or section of a switchboard) with probably hermetically sealed ONAN Dyn 11 transformers and REF protection scheme acting between the transformer and switchboard including the switchboard bus bar sections. Do you have 4 (or multiples thereof) of say 500mm2 copper conductor AWA unloading tails and a switchboard with an integral earth bar and a neutral earth bond just prior to that switchboard ACB.

I've got a number just like that supplying buildings that are along way from each other and surrounded by lots of soil - and they most certainly fall under DSEAR.

Should I be worried ?

regards

OMS

-------------------------
Failure is always an option

If it helps, here's one I prepared earlier:

TN-S

TN-C-S

(they're deliberately simplified to avoid presumptions about which side of the DNO/consumer boundary things might be, and various points are labelled to try and make it easier to refer to from a text-only forum).

- Andy.

OMS

I personally do not design the HV/LV systems for these sites, nor do I carry out the DSEAR report alone, I am part of a team.

When we were initially assess by the NICEIC hazardous area scheme, the area engineers (forget his name, but he was head of that department) said that providing a PEN conductor did not enter into the consumer main panel, the system would be TN-S. he would except if the neutral/earth link was within the spill box or primary PD if seperate to the panel. I generally cross reference all given data, during the initial detailed inspections of these sites. I don't know detailed information of these TX's, that's down to the HV engineers

I can see where you are coming from, because there are so many TX configurations.

Perhaps someone would care to post a drawing?

Regards

Jobbo