New Consumer Unit

[uksparks]

Thats exactly how most of the older terraced houses round my way are as well. How will you test it to confirm it's TNS or TNC-S?

as Dave says in #27. I did get caught out once by the nic bloke, to be fair it said pme on the head, but the readings were different and he insisted it was split concentric.

 

[spark 68]

I meant to add as we need to test Ze and PSSC then it makes sense to do these tests together, before reconnecting the EC and the doing your Zdb and the other PFC measurement.

Plus I would have done a Ze test at the pre-test stage before even quoting a price

 

[HandySparks]

Well I check them at the same time, obviously because I am checking Ze the main switch is off anyway, and in domestic the tails are usually fairly short and I am testing from the live side of the mains switch, and with only a short run for the 16mm EC it makes no practical difference.

Bearing in mind this test (for TNC-S v TNS) is only really necessary on the odd occasion where it could be an either/or situation

Sure, only required if it's not clear by inspection. But a while ago I saw a head that looked like TN-C-S, but when opened up (not by me), was clearly TN-S, supplied using split concentric underground cable.

Just thought that although different values of PEFC and PSCC say 'TN-S', similar values don't necessarily mean 'TN-C-S'. In which case, a direct resistance check may decide the matter.


Edit: And yes, agree, if testing PEFC (and Ze), you'd test PSCC (and Z line) at the same time, anyway.

 

[spark 68]

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 ?

 

[Tidy Max]

I always pre-test, it doesn't take long at all and is worth it.

 

[Simonslimline]

could well still be TNS even though it looks like TNC-S.

Same in the flat i live in. A service head in each flat with the MEC connected in to the side of the cutout. The cutout is fed from a split concentric from a TP service head in the basement which is PME.

 

[R G]

Hmm . not sure about TNCS/PME as already said test the Zs and Zp-n , I wouldn't be quoting until that and the preliminary testing of the circuits is done along with the usual visual checks , or you could get yourself in deep s--t .give them the quotation of all that you find..

 

[spark 68]

Same in the flat i live in. A service head in each flat with the MEC connected in to the side of the cutout. The cutout is fed from a split concentric from a TP service head in the basement which is PME.

It can get awkward on flats such as yours because the incoming supply DB can be TNC-S at the incomer, but each flat is technically TNS as a separate dwelling/installation in it's own right, although for bonding requirements and certification purposes are treat as TNCS/PME

I had some documentation from UKPN which goes into far more detail into these "hybrid systems", for us though they are treat as TNC-S according to UKPN.

 

[Simonslimline]

It can get awkward on flats such as yours because the incoming supply DB can be TNC-S at the incomer, but each flat is technically TNS as a separate dwelling/installation in it's own right, although for bonding requirements and certification purposes are treat as TNCS/PME

I had some documentation from UKPN which goes into far more detail into these "hybrid systems", for us though they are treat as TNC-S according to UKPN.

Yeah i have 10mm bonding in the bathroom to water pipes which are fed from a plastic incomer from the street. Never tested it to see if its actually extraneous though.

 

[spark 68]

Yeah i have 10mm bonding in the bathroom to water pipes which are fed from a plastic incomer from the street. Never tested it to see if its actually extraneous though.

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.

 

[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.