I'm sure electrically something could be fashioned to measure this and do
something at a threshold level but it seems to me that if such conditions
occur then there is probably a far worse issue somewhere in the wiring which
should be caught by other means well before it became an issue.
Brian

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"Alan" wrote in message
o.uk...
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.