The cable to the meter is  concentric anti-tamper cable. Think like jumbo version of TV antenna coax, but with better terminations. Common in places with history of electricity theft, and some meter installers just like to use it in all cases they do.

It does present as TN-S. 

It may be (who is the DNO) that the DNO advise to treat TN-S as TNC-s as they have a street main replacement policy that means sooner or later it will be. 

UKPN for example advise this.

If you are unsure, tick TNS, but in terms of bond size etc, treat as if it has to be TNC-s ready, then you get the best of all worlds.

Mike.

I would be extremely suspicious of this EICR, as the classification of this installation as TNC-S without further comment is clearly an error of a significant type. There is obviously no N-E link anywhere and there cannot be with the head type and cabling shown. Whilst we often discuss DNO practice here it does not change the apparent installation type that is observed. A further question, what is the Ze stated, it would measure as very close to zero in a TNC-S installation with the N-E link in the correct position, which is in the HEAD? The PSCC is not relevant to this point, only the Earth loop value in Ohms from the neutral to Earth for the installation.

It is also worth bearing in mind, from a BS 7671 perspective, that “PME conditions” are NOT only in cases where the supply is traditional TN-C-S.

There are some supplies that look like TN-S (to a point), but must be treated as PME (including main bonding) - these are termed “PNB”, and in this case, a clue for me is the earth terminal block. This may well have provided connection to an earth electrode at the customer's premises, originally owned by the DNO (may still be), which provides a common earth for the DNO transformer supplying a small number of customers from a pole-mounted transformer (that doesn't always mean the supply arrives from overhead to the premises, but it may well do).

But, it says TN-C-S on the previous EICR.

I've seen that a few times now. My guess was (as Mike suggested) it's just acknowledging DNO advise that any DNO supplied earth terminal should be treated as if it were PME/TN-C-S (which most do these days). There's nothing in the definitions of TN-C-S to say that the N-PE has to be in the consumer's cut-out - there's merely a common convention. The N-PE link could be in the building incomer position (with the consumer's cut-out some distance a way in a flat for instance), or in a DNO feeder pillar outside that then supplies several consumers in the same overall building, or more often, the N-PE link is buried under a pavement somewhere where a joint has been added or a section of damaged cable replaced. Unless N and PE are completely separated all the way back to the substation it can't, by definition, be TN-S and thus it must be TN-C-S (if not TT).

   - Andy.

If the PSCC and PEFC are very similar, it seems reasonable to conclude that there is a N-E link nearby and, therefore, record TN-C-S, but the reasoning ought to be explained on the report.

In any event the EICR should give Ze and PFC. If PFC is significantly greater than 230/Ze, TN-S is more likely.

greater than 230/Ze, TN-S is more likely.

Or it can also be less. Some pre-war lead cable has a lot of lead, and is a bit thin on the copper by modern standards. - was a lights only supply got upgraded that sort of thing. ? 

In the high Zs extreme, also the underground joints can fail or something chews the lead leaving about 3 feet of lead pipe underground acting as an accidental earth electrode and then a gap .  Only a proper Zs test with the plumbing bonds interrupted will actually find that, and it is worth checking for that on older cables - if you get a TT sort of Zs, say  tens of ohms, then just maybe that has happened - then it is call the DNO time.

Mike

Another possible clue is if the neutral earth voltage is only a few hundred millivolt  then chances are that earth and neutral are joined at atleast  a few joints 

Looks like a dog’s dinner! It’s a pity that we have come to expect and indeed accept these low standards. 
What is the CT for?

mapj1: 
 

greater than 230/Ze, TN-S is more likely.

 

Or it can also be less. Some pre-war lead cable has a lot of lead, and is a bit thin on the copper by modern standards. - was a lights only supply got upgraded that sort of thing. ? 

In the high Zs extreme, also the underground joints can fail or something chews the lead leaving about 3 feet of lead pipe underground acting as an accidental earth electrode and then a gap .  Only a proper Zs test with the plumbing bonds interrupted will actually find that, and it is worth checking for that on older cables - if you get a TT sort of Zs, say  tens of ohms, then just maybe that has happened - then it is call the DNO time.

Ah yes, but I was proposing only a one-sided hypothesis. I appreciate that if it is 5 wire overhead, or the lead joints are well made, PEFC and PSSC could be pretty close; but still better to assume TN-C-S.

Is that a typo with “s” where there should be “e”?

Ah but TNC-S should be substantially zero. You are looking at reasons why not but I ask why?