Can i make a over head supply tncs

[James Sparks]

I have private two wire overhead supply from a tncs pole and meter remote 8th mile away can make this tncs at house

 

[timhoward]

I'm curious - is the "private 2 wire overhead supply" fused down from the TNCS metered supply on the pole?
I'm wondering if conceptually this is a distribution circuit that happens to be seriously long and (presumably) not use ADS as a means of protection.
I'm sure the advice in previous responses is correct but I'm intrigued how this design navigates the regs.

 

[snowhead]

The 2 wire overheads are just extended Tails between the Meter and C.U.
8th of a mile is around 200mtrs, that's some distance for tails.

What size are the overheads and are they singles?
And just for interest what's the voltage at the property and at the pole?

So imagine this, if it's PME at the house and the Neutral overhead fails, but not the Live..

 

[pc1966]

I guess the point here is who is responsible for the feed, and what rules does it come under:

• If it is part of the installation then is it under BS 7671 so 5% drop max and ADS required, also no TN-C.
• However, if DNO rules apply I'm not sure. As far as I know they don't have to meet 5% drop limit, just maintain the ESQCR voltage range at the entry to the installation, and the fusing, etc, it just to protect their network, not to provide shock protection via ADS. They often do TN-C but I don't know how they decide when that is appropriate/safe or not.

 

[pc1966]

So imagine this, if it's PME at the house and the Neutral overhead fails, but not the Live..

That is a real risk, as often the N/E is lowest and most likely to get clipped by something! I think that is one of the advantaged of the Aerial Bundle Cable type you see more often now on rural feeds, if it gets clipped it probably disconnects everything, or at least shorts out and disconnects eventually that way.

 

[Julie.]

As has been said above, it's somewhat complicated!

Basically the principle of the regulation is that once the supply is made to the customer, the functions of cpc/earth and neutral must not be recombined.

A combined cpc - neutral is actually possible within an installation (though we don't think of it that way) for example a PELV has one side of the secondary operating as both earth/cpc and the neutral.

The point is what exactly is the connection at the PCC? (Point of common coupling)

If it is line(s) - neutral then you must maintain this, and provide your own earth. (TT)

If If is line(s) - neutral - CPC/earth then you must maintain this separation of n & earth (TN-S or TN-C-S which may also be PME)

IF (big IF) it is line(s) - CNE then the separation of CNE into neutral and earth would be down to you - but as far as I understand it, this is never supplied like this from the DNO, (although may exist historically - in which case the DNO would sort out if they became aware).

If you have a private supply i.e. from your own transformer, you are able to use a CNE through your system, but once again once it has been separated into neutral and earth, it cannot be recombined.

I doubt very much that the supply is lines(s) - CNE though.