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?
Quick quiz question: when might a voltage-operated earth leakage circuit breaker be *required*?
Just found it reading 17th edition Site Notes.
Owain
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?..
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.
In the early 1970's, the electrician responsible for the labs where I worked earthed a new electron microscope we had installed via an ELCB to it's own earth rod, rather than through the normal building ring-main earth because that earth was noisy and caused the electron beam to wobble. Unfortunately every time the microscope was switched on, the pulse to earth was such that it promptly tripped the ELCB and turned the microscope back off again (it had a substantial power supply delivering 100kV to the electron gun). The ELCB was quietly taken out of circuit by its operator (guess who!), and all was well thereafter!
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.
#### 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]
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.
Outdoor supply maybe? However better solutions these days. Secondary question is anything really fail safe? Brian
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
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.
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??
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