Earthing Rods for EV Homecharging

[Stavieg70]

HI all. I am not an electrician and know only but a few things about it so I want to ask a question .
So Chargemaster is supposed to install a home charging unit on my property. Their technician came and said I needed additional electrical work (either an double pole isolation switch or run a 6mm cable from my board next to the main distribution and change a breaker from 16 to 32. I went for the 2nd option as it was cheaper.
The other thing he asked was to call my DNO to lower my earthing as my Ze was 0.44 on a TCNS system and they need it 0.35 and lower.
UK Power Networks does not offer appointments and they deal as if and when they are available on last minute notice so it can take forever.
When the electrician came to run the cable I asked him to measure the Ze and he found it at 0.24

1) Can the Ze change from day to day or time to time or did someone get it wrong (I think the Chargemaster one because he didnt very keen to work that day)
2) Could the whole Ze thing be bypassed if they install an earthing rod with the charging unit (I know Chargemaster does that but their technician did not even mention it)

Thank you all for the help in advance

 

[Wilko]

Hi - the values for Ze you have posted would not have stopped me proceeding as they are both ok, in my humble opinion. For what it’s worth I noticed the Ze at my house dropped a similar amount last year, no doubt due to improvement works by DNO upstream from me.

If a rod is used as the means of earthing for an installation then the earth fault disconnect is managed by your RCD and rod. So the installation becomes independent of the DNO for final circuit fault management.

 

[Stavieg70]

Hi - the values for Ze you have posted would not have stopped me proceeding as they are both ok, in my humble opinion. For what it’s worth I noticed the Ze at my house dropped a similar amount last year, no doubt due to improvement works by DNO upstream from me.

If a rod is used as the means of earthing for an installation then the earth fault disconnect is managed by your RCD and rod. So the installation becomes independent of the DNO for final circuit fault management.

Sorry so I can understand it. If they install an earthing rod on their charging unit then it doesnt matter what the DNO Ze number is?

 

[Wilko]

The short answer - for your purpose - yes.
Ze is the impedance looking back into the supply from Line (230V say) to E. If a rod is installed and utilised to provide the E then you can be independent of their E at your installation. However, there are safety concerns about 2 earthing systems in proximity (TNCS house and TT charge point) and a risk assessment is required to be done and satisfied. This may be why they didn’t mention the TT rod option to you perhaps(?).