"Stefek Zaba" wrote in message
...
Dave Jones wrote:


12 of the 16 black cores are used as neutral, and four of the black cores
have had their insulation stripped and they have been directed to an
earth
terminal.

Although at face value this means that my neutral line is being used to
provide an earth, the 4 earth cores are not connected to neutral in my
house, possibly they are only connected back at the substation - which
would happen to an earthed cable sheath anyway.

I've no experience of supply cables to speak of; but it sounds more PME
(TN-C-S) than TN-S, simply because - going on your description - there'd
be no way for the installer to distinguish between the 12 cores used to
provide N and the 4 used for E. For all we know the cores you describe are
bound together where the final supply to your place tees off the feeder in
the road...

But Dave has it most right when he says,

If you're not sure phone the supplier up, they should tell you
The "should" here refers to the fact that they have a legal obligation to
tell you what earthing arrangement you have, what the maximum earth loop
impedance of the supply is, and what the maximum prospective short-circuit
fault current is. (Don't expect those last two figures to be consistent
with a 240 (or 230)V supply and Mr Ohm's most excellent Law, btw: they're
both worst-case figures from opposite ends of the same spectrum, and
suppliers allegedly most often say "0.35ohm" (for TN-C-S) or "0.8ohm" (for
TN-S) (which would imply L-to-E fault currents - admittedly not exactly
the same as a PSC, but damn close for PME at least - of about 690A and
300A respectively), while simultaneously quoting PSCs of 10kA or 16kA (the
Conventional Maximum figures).

Of course, getting through to anyone in "engineering" at an electricity
supply company in these days of micro-privatised
sub-sub-outsource-contracted Competitive Electricity Supply is a
patience-stretching experience...

Stefek

The cable sounds as if it is a split concentric cable. This is generally
used to provide a TN-S supply. This is not PME. The only way to be certain
is to contact your local network operator and ask them.