On 07/05/2019 21:59, Roger Hayter wrote:
Alan wrote:

On Tue, 07 May 2019 08:39:55 -0700, spuorgelgoog wrote:

I'm not sure you can either, but the Wiring Regs committee hope that
someone will make them fairly soon.

The answer seems to be electric vehicle charging points in single-phase
PEN installation.

722.411.4.1(iii)

The main earth terminal is connected to a an earth electrode and again
in the event of a break of the incoming PEN conductor the voltage
between the main earth terminal and the earth does not exceed 70 V.


I think that means you need to ensure an earth rod is of a sufficiently
low impedance to earth, to not permit a rise of voltage to 70volts. And
that is in the case of a break in the Suppliers cable.
VOELCB are not currently available, and unlikely to be in the future.

That could be quite a massive undertaking. It is really unlikely to be
done. Assuming a not totally unreasonable 15kw each for two houses that
might be about 120 amps (lower because of the voltage drop but this is
only a rough estimate) requiring an earth impedance of about 0.6 ohms
under worst case soil conditions. This would require excavation and
would dwarf the cost of the rest of the work. In many suburban gardens
it would not be achievable.

So a token TT earth is more likely to be fitted.

Maybe voltage operated circuit breakers will reappear on the market? Or
will the diversion of more than a few tens of milliamps of the current
from the rest of the installation to the TT earth actually trip an
ordinary RCD? I think it should but I'm interested in the
authoritative position. If so, a few hundred ohms of earth impedance
should be quite adequate.


Don't they fit the protection stuff in the charger?
As long as the charger is isolated before the cover is removed nothing
is likely to happen as they are double insulated too IIRC.