On 07/05/2019 16:39, wrote:

On Tuesday, 7 May 2019 15:55:42 UTC+1, John Rumm wrote:
I can't immediately think of one... more to the point I am not even
sure you could buy a new VO RCD these days anyway?


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

I get the impression they are expecting the protective device will be
included into the design of the charger / cable rather than the
electrical installation itself.

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

722.411.4.1(iii)

#### start OCR

"722.411.4 TN system
722.411.4.1 A PME earthing facility shall not be used as the means of
earthing for the protective conductor contact of a charging point
located outdoors or that might reasonably be expected to be used to
charge a vehicle located outdoors unless one of the following methods is
used:

(i) The charging point forms part of a three-phase installation that
also supplies loads other than for electric vehicle charging and,
because of the characteristics of the load of the installation, the
maximum voltage between the main earthing terminal of the installation
and Earth in the event of an open-circuit fault in the PEN conductor of
the low voltage network supplying the installation does not exceed 70 V rms.

NOTE 1: Annex 722, item A722.2 gives some information relating to (i).

NOTE 2: See also Regulation 641.5 when undertaking alterations and
additions.

(ii) The main earthing terminal of the installation is connected to an
installation earth electrode by a protective conductor complying with
Regulation 544.1.1. The resistance of the earth electrode to Earth shall
be such that the maximum voltage between the main earthing terminal of
the installation and Earth in the event of an open-circuit fault in the
PEN conductor of the low voltage network supplying the installation does
not exceed 70 V rms.

NOTE: Annex 722, item A722.3 gives guidance on maximum resistance
required for the earth electrode in (ii).

(iii) Protection against electric shock is provided by a device which
disconnects the charging point from the live conductors of the supply
and from protective earth in accordance with Regulation 543.3.3.101(ii)
within 5 s in the event of the voltage between the circuit protective
conductor and Earth exceeding 70 V rms. The device shall not operate if
the voltage exceeds 70V rms for less than 4 s. The device shall provide
isolation."

### End OCR

My reading of that is "Don't use PME single phase supplies for EV
charging if possible", and "make sure whatever protection you are using
it keeps the touch voltage under 70V!"

There are some notes in the 18th edition on this section.
722.4 is a list of notes on the section 722.3, and that is about earth
electrode resistance:

"A722.3 Earth electrode resistance

For the purposes of condition (ii) of Regulation 722.411.4.1, the sum of
the resistances of the earth electrode and the protective conductor
connecting it to the main earthing terminal must meet the following
condition, as applicable"

There is then the equation:

Ra = = 70 x U / I x (U - 70)

Where Ra is the sum of all resistances. U the nominal line voltage wrt
Earth, and I the RMS max demand of the whole installation included EV
charging loads.

So for example with a install max load of 100A you get

Ra = 70 x 230 / 100 (230 - 70)

So Ra must be = 1.01 Ohms.


With respect to RCDs, type B devices[1] are commonly specced for vehicle
charging stations.



[1]
http://wiki.diyfaq.org.uk/index.php/...haracteristics


--
Cheers,

John.

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