# EV Car Chargers - Earth Rod

Discussion in 'Electricians' Talk' started by Jimbo, May 18, 2019.

1. ### JimboWell-Known Member

Have the opportunity to run a cable for car charger today as part of some other works that have exposed a nice neat run from the board of approx. 15m.

Will a car charger point accept 10mm cables? Anything wrong with standard 6242 in this situation? Target is 7kW.

Note - I won't be connecting either end, just running the cable since this can be done in the exposed fabric for future use.

2. ### JimboWell-Known Member

Ignore found a manual answered first point.

Manual states

If it can be proven that the existing installation complies with regulation 544.14.1 (the earth of the home charger and main earth electrode cannot exceed 70VRMS if the PEN conductor becomes open circuit) a separate earth electrode may not be required.

How would this be proven?

3. ### Lucky13Member

there is no 544.14.1 in BS7671, There is a formula to do the calculation, but from memory you still need an electrode connected to the PME earth in case you loose the PEN. you then need to know the full capacity of the charger and the installation combined. Since you can never know the loading of the installation at any particular time it makes the calculation pretty much useless and even if you did the rod effectively replaces the PEN conductor so you need a rod certainly less then 5ohms and in most cases sub 1 ohm. On the domestic side with newer properties and refurbishments more are having to have 30ma RCD protection across all circuits so its far easier to just do away with the PME and convert the whole installation to TT then you don't have to worry about all the other problems with installing EV points on domestic properties with PME earthing.

4. ### Bob RathboneWell-Known Member

You can prove it but you will need a dedicated earth electrode tester. The basic premise of the reg is to limit the maximum touch voltage to earth during either an earth fault or failure or the PME CNE conductor. Do as Lucky 13 suggests, drop the earth and fit a RCD with a local electrode by the charging unit, that way you have a 'clean earth'. But only on the circuit for the charger, leave the existing installation as it is.

5. ### ComlecWell-Known Member

Given that there is a grant of £700 available for EV charging point. Why not just get an installer to do it.

6. ### JimboWell-Known Member

Thanks for the replies.

Re the grant - I don’t yet have a vehicle and I’ve just run in the 10mm feed as building works have exposed a simple route.

My installation has an oil tank with a long line of copper pipe in the ground and attached to the main bonding, I wonder if that would be enough already.

7. ### JimboWell-Known Member

Would you mind expanding on these problems?

8. ### Lucky13Member

mainly ensuring that there are no class 1 items of equipment (wall lights ect) or any earthed pipe work that can be simultaneously touched, Gas / oil pipes running along the wall near the charger / car. Its recommended to be 10 meters away form anything but that all depends on the charging location / size of drive ect ect

Jimbo likes this.
9. ### JimboWell-Known Member

Thanks Lucky.

Seems to be some room for interpretation as to whether an exported PME is ok in a domestic environment, particularly since some cars seem to need a lower impedance fault path than TT can always provide.

And now you’ve given me the class 1 proximity to consider as well! Is there a guide to all this somewhere with some diagrams, my google skills are failing me.

11. ### JimboWell-Known Member

Thanks - appreciate it.

Found this run through of section 722 too:

I think by the time I need to get the charge point itself, the products themselves will have caught up to the 3-pole breaker bit, given the popularity of the TNCS supply, in which case it all becomes nice and simple with the wiring pulled in ready... hopefully.