New Consumer Unit

[Simonslimline]

These really blur the lines, because you only have one origin (the incoming supply) usually with one CNE link at the origin and separate earths at each flat, but then according to BS7671 each dwelling is classed as a separate installation, however the gas and water services are distributed and shared as well.
So we end up with a hybrid system, and the DNO make the rules, their supply, their rules.

If you search for the UKPN documents on line they are free to download, but they can be a bit boring to read lol.

Something i was wondering regarding Ze/Zdb. i have a service head in my flat which is fed from the TP head in the basement. Is it technically Zdb from my service head and not Ze?

 

[spark 68]

Something i was wondering regarding Ze/Zdb. i have a service head in my flat which is fed from the TP head in the basement. Is it technically Zdb from my service head and not Ze?

According to B7671 with each flat being a separate installation it would be Ze, however as already said with this being a hybrid system then technically it would be a Zs.

About as clear as mud lol, if I was filling in an EIC sheet for say a CU change I would put it down as Ze for your flat.

The DNO class it as TNC-S/PME for bonding purposes as this is still the most onerous situation in the event of a broken suppliers N to the TNC-S/PME head at the origin, so I can see why they class it as such.

 

[telectrix]

Something i was wondering regarding Ze/Zdb. i have a service head in my flat which is fed from the TP head in the basement. Is it technically Zdb from my service head and not Ze?

i suppose it's what you define as the source of the installation. the TP head or your 1P head. as the TP head is technically outside your home, then you could say that the source of your installation is your head.

 

[uksparks]

You are all saying that I have not carried out and pre tests, true I haven't but what makes you think I am not going to? I always very time test it to death, read all my previous posts regarding board changes over that last two years on here and you will see I always pre test.

I actually said earlier in this thread I am going next week to do all the pre tests before I change it.

You are suggesting you cannot even quote before doing this, I always give a ball park figure subject to various things, noses they agree to that why on earth would I waste my time pre testing it to then quote.

So just to set the record straight..

I always pre test every time!

 

[uksparks]

Yes agree HS, sometimes it is not clear, but then again I always carry out a few essential pre-tests before I give a price, which the OP clearly hasn't , one day he will regret not doing a few preliminary tests and checks before quoting and this will end up biting him on the arse one day, can you guess why I always pre-test now ?

I always pre test a board every single time thanks, but no, not once have I pre tested it before quoting ad that's just stupid in my opinion, at least get them to agree to a price subject to conditions that you explain to them first.

 

[telectrix]

test the 6mm bond. if it's securely connected, undamaged, and gives an acceptable value of resistance. leave it alone, just note it down on the cert. ( advice from uncle tel...... do not say can't be arsed)

 

[uksparks]

test the 6mm bond. if it's securely connected, undamaged, and gives an acceptable value of resistance. leave it alone, just note it down on the cert. ( advice from uncle tel...... do not say can't be arsed)

I generally as a rule of thumb note down the resistance of the bonds as it kind of proves to a degree that I checked them.

 

[uksparks]

Right I'm off to sleep.

 

[telectrix]

me too if i can find my bloody painkillers.

 

[spark 68]

You are all saying that I have not carried out and pre tests, true I haven't but what makes you think I am not going to? I always very time test it to death, read all my previous posts regarding board changes over that last two years on here and you will see I always pre test.

I actually said earlier in this thread I am going next week to do all the pre tests before I change it.

You are suggesting you cannot even quote before doing this, I always give a ball park figure subject to various things, noses they agree to that why on earth would I waste my time pre testing it to then quote.

So just to set the record straight..

I always pre test every time!

Not having a go UK , I still would have determined what I was dealing with before quoting, for instance what is the actual Earthing system, and is it actually present and correct ?, what size is the DNO fuse, all of these have a bearing on what additional work you may need to carry out, or not as the case may be, and therefore the price.
This is without looking for potential tripping RCD problems.

I have only dropped myself in the s*it once, and it will never happen again.

To your original question, if the 6mm bonding is easy enough to replace then do it, if it isn't then I would leave it in place with a note, even if it is TNC-S/PME, so long as it is not showing signs of distress/overheating etc. as other posters have already said, have a look at the best practice guides issued by the ESC or whatever they are calling themselves this week

 

[Engineer54]

According to B7671 with each flat being a separate installation it would be Ze, however as already said with this being a hybrid system then technically it would be a Zs.

About as clear as mud lol, if I was filling in an EIC sheet for say a CU change I would put it down as Ze for your flat.

The DNO class it as TNC-S/PME for bonding purposes as this is still the most onerous situation in the event of a broken suppliers N to the TNC-S/PME head at the origin, so I can see why they class it as such.

How is a PME TP&N supply into a block of flats with several sub distribution supplies that are individually metered at each flat a ''Hybrid'' system?? Each of those sub-main CU'S/DB's will still be derived from a PME supply, so PME conditions apply throughout the building. Each flats supply will have a Zdb/Zs value not a Ze value. the Ze can only be measured at the MET at the incoming TP&N supply position.

Main bonding of service pipes etc within each flat, will still need to be taken to the flats EMT.

 

[Engineer54]

Your average 1930's built house is going to have suspended floors downstairs and T&G floorboards both up and downstairs, so spring a few floorboards and run a 10mm bond to where you need it.

Never seen a 1930's built house with T&G floorboards, T&G floorboards came in much later like 25 years or so later. In the 30's they would have been pretty thick standard butt floorboards, built to last rather than the much thinner early T&G floorboards, that are even thinner these day's. That's if you get to have floorboards it's now all sheet boarding...

 

[ipf]

Never seen a 1930's built house with T&G floorboards, T&G floorboards came in much later like 25 years or so later. In the 30's they would have been pretty thick standard butt floorboards, built to last rather than the much thinner early T&G floorboards, that are even thinner these day's. That's if you get to have floorboards it's now all sheet boarding...

And it is sheeeet, too!

 

[spark 68]

Originally Posted by Engineer54 How is a PME TP&N supply into a block of flats with several sub distribution supplies that are individually metered at each flat a ''Hybrid'' system?? Each of those sub-main CU'S/DB's will still be derived from a PME supply, so PME conditions apply throughout the building. Each flats supply will have a Zdb/Zs value not a Ze value. the Ze can only be measured at the MET at the incoming TP&N supply position.

Main bonding of service pipes etc within each flat, will still need to be taken to the flats EMT

.



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.

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 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.

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.




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.

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

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.

 

[davesparks]

Never seen a 1930's built house with T&G floorboards, T&G floorboards came in much later like 25 years or so later. In the 30's they would have been pretty thick standard butt floorboards, built to last rather than the much thinner early T&G floorboards, that are even thinner these day's. That's if you get to have floorboards it's now all sheet boarding...

From experience I'd say T&G boards have been around a lot longer than that. But maybe it varies depending on where in the country you are.

 

[telectrix]

Never seen a 1930's built house with T&G floorboards, T&G floorboards came in much later like 25 years or so later. In the 30's they would have been pretty thick standard butt floorboards, built to last rather than the much thinner early T&G floorboards, that are even thinner these day's. That's if you get to have floorboards it's now all sheet boarding...

eng. i have to disagree with you on this one. my parents house was T.G. floorboards, original from 1926. block parquet in hall and 1 living room.

 

[pennychew]

From experience I'd say T&G boards have been around a lot longer than that. But maybe it varies depending on where in the country you are.

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

 

[pennychew]

eng. i have to disagree with you on this one. my parents house was T.G. floorboards, original from 1926. block parquet in hall and 1 living room.

Posh git!

 

[shanky887614]

Never seen a 1930's built house with T&G floorboards, T&G floorboards came in much later like 25 years or so later. In the 30's they would have been pretty thick standard butt floorboards, built to last rather than the much thinner early T&G floorboards, that are even thinner these day's. That's if you get to have floorboards it's now all sheet boarding...

or bloody laminate.

you cant get under the floor without replacing it or the ceiling below

 

[Tidy Max]

Ours was built in 1890 and theres no t n g here!