In order to protect against neutral failures, 18th Edition states that the earth impedance between the vehicle charging earth and the true ground (or earth), for chargers fitted outside the home, must be under 200 ohms to minimise any voltage developed between the two and ensure correct operation of an RCD.
It can be possible to achieve this 200 ohms earth impedance by sinking one or more dedicated earth rods for the chargepoint. Pod Point installation guidance recommends 100 ohms as electrodes and ground conditions are subject to wide variations due to both locality and season.
Since 2013 earth rods have been required on PME systems and the flexibility that some installers used to not fit an electrode was removed from the 18th Edition in January 2019, but the difficulty of successfully fitting an earth rod predates both regulations
I am setting up an assessment for a well known accreditation body and I noted that the assessment required an installation earth electrode with a resistance of 20-200 ohms which the paperwork declared was to simulate the supplementary electrode required for TNCS systems supplying EV chargers. I contacted the body in question and a chap confirmed that was indeed the purpose of the thing. Didn't want to argue as I thought it was rubbish. I then read the above in a technical document for the charger being used and I thought have I been drinking too much wine? Did I miss something? I am beginning to wonder. It cant be for holding down touch voltages to 70v because even at 20 ohms that would only allow 3.5A on loss of PEN. It cant be for measurement purposes as the assessment requires the "earthing conductor" to electrode to be green and yellow 16mm2. Please tell me that my daily glass of red hasnt killed so many grey cells that I have missed this?
