Neutral earth links in feeder pillars

if there is a load part way along, between links, as that makes use of the '-s' nature of things.

But not a problem if all the tap off points have their own N-PE links? (as the OP seems to suggest might be the case?) Even if a few don't and a "presented as TN-S" supply is tapped off mid way between links... I'm not entirely seeing what the problem is (at least any problems that wouldn't already be present in a conventional TN-C-S system with a single conductor PEN). I'll have a think... 

especially if exposed-conductive-parts, or extraneous-conductive-parts, connected to different bits of the TN-C-S-c-...-s,

Is that any more of a problem that adjacent installation tapped off from different positions along a conventional PME main? (I think I might have a different picture in my mind's eye, so might well be overlooking something significant...).

  - Andy.

AJJewsbury said:

gnoring any colour coding, I guess you could deem it to be simply TN-C-S with the PEN consisting of two (or more) conductors in parallel for part(s) of the route.

Not really ... especially if exposed-conductive-parts, or extraneous-conductive-parts, connected to different bits of the TN-C-S-c-...-s, are simultaneously-accessible (in any combination). It's back effectively to 411.3.1.1 2nd para.

cannot do that, if there is a load part way along, between links, as that makes use of the '-s' nature of things.
Its all splitting hairs, it may or may not be illegal, its not a good approach technically, and as a country we don't like it.

M.

TN-C-S-c-...-s

Ignoring any colour coding, I guess you could deem it to be simply TN-C-S with the PEN consisting of two (or more) conductors in parallel for part(s) of the route. As long as they're not designated as separate N and PE conductors, but rather as PENs, BS 7671 wouldn't object I think. (As Mike suggests, common practice in DNO land where old 4-core + armour cables are converted to PME with "N"-armour links scattered here there any everywhere).

   - Andy.

mapj1 said:

"building networks" of some older blocks of flats that used to be maintained by the area boards, neither of which fell/fall under the wiring regs / '7671

Although, BS 7671 is often specified for new/upgrade works on these systems ... BS 7671 does cover TN-C systems, so can be used, but TN-C-S-c-...-s isn't permitted.

'reconnection' of N and PE is not permitted 

quite. But it is very common on the network operator side of the intake fuse, and in what we would now call the "building networks" of some older blocks of flats that used to be maintained by the area boards, neither of which fell/fall under the wiring regs / '7671.

Quite sensibly, since the rule changes that turned some unsuspecting freeholders of flats into unskilled owners and operators of building networks, the distro in new blocks of flats,  is now designed and tested  to '7671, and normally with SWA or trunked cables with no additional NE bonding. 
But, there is a lot of older stuff out there and we don't know who put this in, or when, or who they were working for and private networks can be a bit odd, to say the least.

Mike.

if everything on site is under common ownership, then it's a consumer's installation. you've described a private network, so I assume that you're providing a service to somebody. I think that makes them consumers and you a distributor and possibly a supplier

ESQCR prohibits PME only on consumers' installations, not on distribution networks whether public/licensed or private/unlicensed

this doesn't affect the engineering discussion, because you've got MEN not PME

mapj1 said:

I think what you have could perhaps be described as TN-S-C-s, as NE is first both common then separated then connected then separated again, which is not really a recognized combination in the UK unless you are operating your own distribution network ;-)

'reconnection' of N and PE is not permitted by BS 7671, and I don't think it has been at least as far back as prior to 15th Ed of the Wiring Regulations.

Well distribution cables only supply boxes doing the  ADS and perhaps metering, that in turn  supply final circuits that may have loads directly connected,. If it has a directly connected load at any point  its not "distro".

I think what you have could perhaps be described as TN-S-C-s, as NE is first both common then separated then connected then separated again, which is not really a recognized combination in the UK unless you are operating your own distribution network ;-)

I'm assuming you are in the UK. In much of Europe, or in AU/NZ this sort of thing would, or at least if done rightl could, be fine.

Mike.

Thanks - it's certainly not PME as each feeder pillar has its own earth cable, so regulation 9 coming out of 8(4) is not true - plus I don't believe we would meet the definition of a "distributor" or that our buildings are classed as "consumers".