New Consumer Unit

[baldsparkies]

Blimey !!
Type of earthing arrangement at the origin vs a trip in H.G.Wells time machine to trace the origin of T&G floorboards.
Very diverse is this one.

 

[Risteard]

the earth on the gas

You sure about that?

 

[Risteard]

I meant to add as we need to test Ze and PSSC then it makes sense to do these tests together

Presuming you mean PEFC then really the earthing conductor should be reconnected before testing this, as with Ze you want the measurement through the earthing conductor alone but for PEFC you want any parallel paths which are likely to increase the prospective earth fault current for the installation.

 

[Engineer54]

Blimey !!
Type of earthing arrangement at the origin vs a trip in H.G.Wells time machine to trace the origin of T&G floorboards.
Very diverse is this one.

Still more interesting than some of the threads on here at the moment ..lol!!

 

[spark 68]

Originally Posted by spark 68
.



I was going off of UKPN documentation,

Yes it is TNC-S at the head or origin, of which there is only one.

Now according to BS7671 each flat is an installation in it's own right, as you rightly say they are bonded locally inside each flat as you would do if it was a separate install like any other.

If you are classing each flat as a separate install as above then technically that flat is a TNS, there is no CNE link at that head, the earthing to that flat is separate, yes it is derived from a TNC-S supply, now either that flat is classed as a separate installation or it isn't.

Well it's not TN-S is it, so can't be classed as such!!
Being a separate installation does not mean the supply suddenly chances from PME to TN-S
Ok poor choice of wording on my account, SNE would be a better description, see my original paragraph justbelow , and I am agreeing with you here in that is why the DNO are treating the whole installation as PME.

This is where the complication is, that flat has technically a SNE (separate Neutral Earth) however the bonding requirements are to be taken as TNC-S, it is where the boundary is actually drawn, either at the flats own service head as per BS7671 with it's own bonding requirement as you
yourself pointed out above, or the whole block of flats classed as one installation.

It's no different than any large PME installation that comprises of multiple sub-main distribution circuits none of those sub-mains can or will be classed as a TN-S installation.
It is only different in so far as that as a dwelling it has a different definition as far as BS7671 is concerned, ie. as a separate installation, in other large installations such as a factory and the like these are not classed as seperate entities, as I said it is only where we are drawing the boundry, and is just semantics.
we are agreeing to a large extent here it is just the demarcation point that differs.

It is all semantics really as the definitions of where each part overlaps, I called it a hybrid in "" as it is not always clear where the demarcation point begins and ends as far as we are concerned, our remit is only to BS7671, it does not extend beyond the suppliers cut out which may (or may not) be present in that flat.

There is no demarcation as far as the type of supply provided by the DNO. If it's a PME supply then it will remain a PME installation throughout the installation derived from that supply. The neutral of that DNO supply still being the source of the only electrical earth throughout the whole installation....
As above, again you are of course correct, but then you are used to larger installations and you will no doubt be familiar with the entire supply network on your large projects, here we were just talking about a simple CU change in a flat, the installer will only certify from the cut-out in that flat, he is not going start chasing through the finer points of the DNOs building supply infrastructure as this is neither necessary nor desired, it would be complete overkill for a simple part p notification

I already said if I was replacing a CU in that flat that even though it would be technically (and correctly) a Zs but would record it as that flats Ze on the EIC, because that is where that particular dwelling/installation according to BS7671 ends (or rather begins ), the chances are we would have no access to the supplier switch gear anyway, in other words treat that flat as a separate entity, which is about all we can do.

It's only a separate entity in the fact that each flat is separately metered installation.
How can you call or record a Zs/Zdb value as Ze when it's clearly NOT? If you can't gain access to the main DNO supply then you record that on any certificate you need to produce
Agreed again, lol, I already said this, I would still certify it as that flats Ze though, because that is the external earth for that particular flats supply, agreed not to the building, this is because of the way the EIC and the definition is given to a domestic dwelling, again I did say further back that flats can be awkward, if we are carrying out work in that flat we would only certify from that flats own single phase cut-out, to go any further would be overkill again.

The UKPN documents go a lot further than a simple block of flats, one example given is a modern industrial estate, now previously each separate unit had it's own CNE link in each (separate) building all bonded to the various services shared between seperate buildings, and was designated as a TNC-S/PME to that building, which is fair enough so far.

That's because they would be separate buildings, and each joint to the network distribution cable supplying each building would or should have the neutral conductor earthed, as stipulated in the PME requirements...
That is true, nothing to disagree with here, this is just a normal set up, I said this was how the usual set-up was usually implemented.

The DNO (UKPN in this case) has/had decided in an effort to reduce circulating N -E currents to put just one CNE link at the supply end (sub-station/switchroom or whatever) and supply each unit with an SNE (TNS) supply, however again for the usual reason where PME is concerned (broken suppliers N etc.) that the bonding requirements for these units will be as per TNC-S.
This is similar to above but on a bigger scale

Then that is NOT a PME system is it, it's a straight TN-S system. Every TN-S system has a single point N-E connection at the TX or main switch board.... If the neutral is not being used as a combined neutral earthing conductor on the system, then PME/TNC-S bonding requirements is not required....
Here you would have to take that up with UKPN lol, they stated the objectives and what was required in their documentation, they called this a hybrid system not me, this was a PME system according to them and not just the usual switchgear link, if I can post up the relevent page I will.
I cannot really argue with them lol, it is way above my payscale.

Ps. I already said in the post of mine you quoted, or in one the others related to that subject that the DNO classed the flats supply as TNC-S/PME as far as bonding was concerned and rightfully so in my opinion, so I am not sure where or if you are disagreeing with me or not lol.

My comments in bold...

My comments in Blue

The TNC-S incommer/flat scenario by the way was purely hypothetical but based on a real system, I haven't seen Simons flat, he could have a TNS or TT incomer for all I know.

I mainly brought this particular scenario up to illustrate a point that not everything is black and white, there are lot's of grey areas, this was partly due to earlier discussions in the thread, and partly to where the OP (UK Sparks) assessor pulled him up saying because that particular service head was supplied from a split-concentric cable that it could not be TNC-S/PME. just looking at the responses here then clearly that is not true, it is possible to have a cut-out with no CNE link and a SNE and yet still be TNC-S/PME.

I myself had a strange one, here was just a normal domestic house, nothing unusual at all, anyway the supply was originally TNS with the usual lead sheath, this had been converted by the DNO to PME with the link fitted but they had also bonded the Lead sheath as well.
This actually made sense thinking about it, but at first glances it looked as though it had both earthing systems at the same time! it was only by opening the head that I could see what had been done, the tests referred to to earlier (PSSC/PEFC) were substantially the same.

The pretty pics in the OSG of various heads and systems are mostly right, but there are a lot of variations out there, assume nothing lol.

 

[ipf]

My house was built in 1926 and it has decent quality t+g throughout. Us geordies have always been one step ahead of the times though

Certainly with the tongues.........:icon12:..............just behind them scousers!!

 

[SirKit Breaker]

Don't forget, the Regs are not the be all and end all. They are guidance and need to be complied with as far as is reasonably practical. It is better to bond where you can, than not to bond at all. I wouldn't be concerned about the 500mm rule, it wont take fault current much longer to travel 20 feet than it does to travel 500mm. Cable has a hell of a lot of redundancy built in, so i can't see your 6mm having any issues unless your PFC is off the scale.


Cheers..............Howard

 

[uksparks]

You sure about that?

What do you mean?

 

[ImpededLoop]

What do you mean?

I think he was hinting that you bond the gas pipework rather than "earthing" it.

 

[uksparks]

I thought that's what he was getting at, there's no need to be so picky!

 

[Anthony S]

I thought that's what he was getting at, there's no need to be so picky!

You have to be very careful with your terminology, because your being watched lol