Quick quiz question: when might a voltage-operated earth leakage circuit breaker be *required*?

Just found it reading 17th edition Site Notes.

Owain

On 07/05/2019 14:50, wrote:
Quick quiz question: when might a voltage-operated earth leakage circuit breaker be *required*?

Just found it reading 17th edition Site Notes.

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?


--
Cheers,

John.

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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.

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.

Owain

In article ,
scribeth thus
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.

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.

Owain




Umm?, can someone explain quite what that means or how its laid out in
the err, interests of science; please?..

--
Tony Sayer


Man is least himself when he talks in his own person.

Give him a keyboard, and he will reveal himself.

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.

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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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.

--

Roger Hayter

Outdoor supply maybe? However better solutions these days. Secondary
question is anything really fail safe?
Brian

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...
Quick quiz question: when might a voltage-operated earth leakage circuit
breaker be *required*?

Just found it reading 17th edition Site Notes.

Owain

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.

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.

In article , Alan
scribeth thus
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.

So we have a house and out in the driveway there is a charging point
thats off the typical main house 100 amp incomer?.

Which if its going to be a rapid charger won't be enough capacity
assuming the house is pulling its likely max load. _If_ used in the day
time.

So then we either have to provide another "House" worth of supply
presumably another phase or we beef up the main incomer to say 200 amps
now which is going to be a massive undertaking?. Lots of road digging
and new big 'eff off size substations?

Well OK this is a new ball game and may not be the best option it will
be a very expensive one for the local power supply co.

But lets assume that we are now going the use a "trickle" overnight
charger system which I think will be the option to use and unless we
have a house with that useless night storage heating that may be
pulling more amps and not enough for the vehicle charger??

So assume that we now do this overnight and we have and option to take
this off the main distribution board and that will make some demand I
suppose what 30 to 50 amps? Whatever?

Well in practice would there not be a MCB rated at say 40 or 50 amps and
a separate RCD. So if the earth conductor comes undone the leakage of
any capacitors used in the charger may be transferred to the car body?

So the whole car may now assuming the power carrying cable to the car
has a protective earth that carried in the connecting cable from the
charger.

So are we saying that under this scenario the leakage voltage WRT earth
of the car must not rise to above say 70 volts then?

Is that what's meant??

--
Tony Sayer


Man is least himself when he talks in his own person.

Give him a keyboard, and he will reveal himself.

tony sayer Wrote in message:
In article , Alan
scribeth thus
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.

So we have a house and out in the driveway there is a charging point
thats off the typical main house 100 amp incomer?.

Which if its going to be a rapid charger won't be enough capacity
assuming the house is pulling its likely max load. _If_ used in the day
time.

So then we either have to provide another "House" worth of supply
presumably another phase or we beef up the main incomer to say 200 amps
now which is going to be a massive undertaking?. Lots of road digging
and new big 'eff off size substations?

Well OK this is a new ball game and may not be the best option it will
be a very expensive one for the local power supply co.

But lets assume that we are now going the use a "trickle" overnight
charger system which I think will be the option to use and unless we
have a house with that useless night storage heating that may be
pulling more amps and not enough for the vehicle charger??

So assume that we now do this overnight and we have and option to take
this off the main distribution board and that will make some demand I
suppose what 30 to 50 amps? Whatever?

Well in practice would there not be a MCB rated at say 40 or 50 amps and
a separate RCD. So if the earth conductor comes undone the leakage of
any capacitors used in the charger may be transferred to the car body?

So the whole car may now assuming the power carrying cable to the car
has a protective earth that carried in the connecting cable from the
charger.

So are we saying that under this scenario the leakage voltage WRT earth
of the car must not rise to above say 70 volts then?

Is that what's meant??


Dunno but in your well reasoned scenario pretty much all the power
to charge these things overnight won't be coming from solar,
maybe some from wind IF it's working, the rest from....? nukes
(if built) or good old gas?

Er... won't we sposed to be free of all that by 2025 according
to assorted hand wringers & vested interests?

--
Jim K


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