EV & TNCS Food for Thought

[marcuswareham]

Just a little thought here,

With PME / TN-C-S supplies being most common, and the difficulty with EV charging from this earthing arrangement are:

722.411.4.1:
(i) = Very difficult to ensure 3 phase loads are always balanced in the real world

(ii) = Unless in a new build with foundation electrodes or digging up a big garden and driveway and installing an earth mesh, very difficult to achieve an electrode with a low enough resistance, and with enough separation from any metalwork bonded to PME

(iii) = This would require an earth electrode even if its a small one, and then you still have PME separation issues

(iv) = This only works maybe 50% of the time and it is very possible to have an open circuit PEN conductor and the voltage to remain within the range, therefore not providing any protection, and giving a false sense of security

(v) = The only 2 devices I can think of like these are the Matt:e 3 phase o-pen which creates a simulated true earth point via the line conductors, this seems to be a good solution although not for domestic single phase installations. The other is the Zappi 2 charger which monitors the L - N voltage like in (iv) but it also has a current sensing coil around the CPC, so If there is a PEN fault and the voltage remains within the acceptable range if any current is flowing on the CPC (by contact of EV metalwork and true earth) then it will disconnect, the issue I see with the zappi is the current sensing part is not automatic disconnection and requires user intervention (in the case of a person in contact with the EV and true earth, to receive a shock for a very short duration to achieve disconnection)


Last option = Make the EV charge TT, which in some locations can be very hard to achieve due to buried metal work bonded to PME, such as water and gas pipes, and PME cable joints with electrodes. Also if the car charger is located close to anything else such as an outside light bonded to the PME earth there is a touch voltage risk between the EV and the outside light, etc


My thought is surely all of these problems could be avoided by having the charging & related circuitry in the EV double insulated, and therefore the exposed metalwork of the EV would not need to be bonded. Then a PME earth could be used as there is no risk of contact with PME earth and true earth in the event of a PEN failure


I understand EVs might use the chassis as there negative under normal running conditions, but maybe when on charge this could be isolated. Of course this is just a thought and would be a big ask to tell every manufacture to double insulate there charging electronics!! The only way it would happen is if a law was passed to require it.


What are your thoughts on this, I am not looking for answers just interesting to think it through.



Thanks Marcus

 

[BOrg42]

Matt:e also do a unit for single phase domestic installations.