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Historical question, TNC.

broadgage
I recall reading in a DIY magazine about a proposal to adopt what we would now call TNC wiring, in order to save copper.

Neutral and earth combined up to the fixed light or the socket outlet, though still 3 core flex to appliances.

The risks of a broken combined neutral/earth conductor were noted. To alleviate such risks it was proposed that at the distant end of each radial circuit, that this conductor be connected to any of the following.

1) The CNE of another circuit.

2) A metallic water pipe

3) Structural metalwork.

4) An earth wire installed for the purpose.


Sounds all a bit dodgy, and obviously was never adopted, but was this ever a serious proposal, or was it a rather involved April fools day prank ?


Late 1970s IIRC.

I am aware of concentric wiring* which was what we now call TNC, being used on private supplies, and sometimes misused on public supplies, and I am aware of the practice of "earthing" to the neutral in some places, but neither of these is the same as the proposal that I recall.


*I took out a load of concentric wiring in about 1978, Formerly a 110 volt DC private supply, but later connected to public mains.
  • Former Community Member
    0 Former Community Member
    I did an inspection probably 25 years ago on what was described then as "a naughty boys' school" which was wired in single core MICC. I remember looking at the MICC supplying 13 A socket-outlets and it appeared to be no larger that a thermocouple to a gas boiler. Also, 100 A cast iron switchfuses with MICC outgoing no larger than a pencil.


    No idea what they did with the place but it was Government run, hence:

    I recall that there was a Regulation that before using TN-C, you had to get approval from the Secretary of State or similar title but can't remember the Reg number.


    If still in use, RCD protection would be problematic!


    Regards


    BOD
  • 0
    I'm told that TN-C to the socket etc was practiced in the former East Germany and possibly other parts of the Bloc.


    I've a feeling that a well known high-street chain in the UK also adopted it across their shops - as in Bod's case in MICC.


    Older editions of the regs did talk about concentric wiring which appeared to be used with the metal sheath as what we'd now call a PEN - but that's going back a lot earlier.


       - Andy.

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