On 19/06/2019 23:50, John Rumm wrote:
On 19/06/2019 23:34, Roger Hayter wrote:
John Rumm wrote:

On 19/06/2019 11:25, Roger Hayter wrote:
Martin Brown wrote:

On 18/06/2019 21:42, ARW wrote:
On 18/06/2019 10:01, Andy Burns wrote:
Robin wrote:

Martin Brown wrote:

So how common is TN-C-S with a single PEN in new build?

I'm sure Adam can add more datapoints than everyone else here
combined.
I am also sure that I am not sure. New builds in Epworth that I have
just worked on (one street). Half are TN-C-S with a 100A supply
and half
are TN-S with a 80A supply.

Thanks. You would think it made more sense to do one or the other.

However I would say that 80% of newbuilds I have worked on in the
last
20 years are supplied with a single core concentric cable.

So the incoming armoured cable has a live core and outer PEN sheath?

I expect it is against the wiring code but is there anything to
prevent
the householder having a stake in the ground bonded to the household
protective earth in addition? It won't make a blind bit of difference
most of the time but if the neutral return ever fails then at least
you
don't suddenly find every household appliance is live to the touch.

A simple earth stake can't do any harm, but it is not necessarily going
to make that much difference to the potential reached during a neutral
fault.Â* Say the active loads on the supply beyond the fault add up to
about 5kW, resistance 12 ohms.Â* And the best likely stake gives 100
ohms
earth resistance.Â*Â* Then it is only going to reduce the final
voltage on
the house earth by about ten percent.

Much will depend on the soil conditions for the stake. Last time I
measured mine[1] it was around 6 - 7 ohms.

[1] Into clay soil, and measured with a high current loop tester rather
than one of the modern "non trip" types.

That's impressive.Â*Â* Does the clay stay wet all year round?

Once you are down a foot or so, yup seems to.

Same here. We have a very high water table and an intermittent spring
part way down the garden. I have to syphon water out of the pit before
using it. There is a capped well only a few metres away.

The top layer can dry out and shrink quite dramatically though. At the
end of the summer can can dump 15,000l of swimming pool water on the
lawn and it does not even leave a puddle!

The clay round here bakes to impermeable in a good summer which can mean
a big thunderstorm runs off the fields towards a couple of unlucky
houses. It doesn't happen very often but when it does the field drains
simply cannot keep up and we get a fountain at the bottom of our drive.

--
Regards,
Martin Brown