I did read somewhere a badly installed earth rod could be dangerous as well, as it is possible to get a false safe reading when installing. Given my electrics has some peculiarities the electrician told me, I put my trust in him as he has done my electrics for the solar. It would not be a regs approved install option if it wasn't deemed safe and with electricity we all want safe as you said. As with anything with electrical installation it is only as safe as the installer and the equipment connected and made harder by the householder who always does the unexpected
but that's why we have the Darwin awards. We are hoping to have a new build in the future and then would be the best time to get a belt and braces safe install, along with 3 phase to power all of this kit.
The main risks associated with installing an earth electrode are obvious ones, like banging the thing through an underground service, failing to keep it and the equipment it's connected to adequately spaced away from any exposed conductive part that's earthed using a different earthing scheme, failure to use the correct type of RCD protection (for an EV charge point this needs to be a Type B RCD, or a Type A RCD/RCBO plus DC tolerant earth leakage detection within the charge point itself), failure to ensure that the PE conductor is properly connected and failure to ensure that the resistance of the earth electrode to ground is adequately low.
The resistance of the earth electrode through the ground should be less than 200Ω, and generally it's not hard to get down to this figure in most UK soils. The exception is mainly very free draining sand, that can be a bit of a problem, especially because the resistance is likely to vary a great deal with the weather, more than for most other soils.
The limiting factor for electrode resistance, Ra, is the trip current of the RCD and the maximum allowable touch voltage of exposed conductive parts in the event of a fault. The max allowable touch voltage is 50 VAC normally (25 VAC by a swimming pool or hot tub, both of which require their pumps, heaters etc to have the same sort of open PEN protection as an EV charge point). RCDs have a maximum trip current of 30 mA, so the maximum electrode resistance that will still ensure that an RCD trips before 50 VAC is reached is way over 200Ω, it's 50 VAC / 30 mA = 1,666Ω, so there is a massive safety margin built in to the 200Ω maximum recommendation for Ra.
As an indication of real world Ra values, I have two earth electrodes, one going through a drilled hole in a concrete detached garage floor, through the sub-base underneath and down into compacted clay. Because of the stuff above, I screwed two 4ft rods together and drove them down until the top rod was just above garage floor level (just enough space to get a box on it). That one measures between 35 and 45Ω all year around. The other one is just a single rod driven directly into hard clay, yet gives a value of Ra that's lower, between 25Ω and 35Ω (which is very much on the low side of normal).
Converting those electrode Ra values into the maximum touch voltage that would appear on any exposed conductive part before the RCDs were to trip, assuming worst case conditions, gives a value of 1.35 VAC for the garage and 1.05 VAC for the one by the stand-alone charge point, voltages that are both less than that from a single AA battery, so plenty safe enough.
Only other thing to watch, and this applies to any RCD protected installation (which will be all UK installations done in the past decade or so, and all outdoor power outlets since 1981), is that the RCDs are regularly tested. There's a mandatory test label that should be on the RCD itself or on its enclosure, stating the test interval, normally not less than every 6 months for the user self-test button, and not less than every 10 years for normal domestic installations, as a part of the required EICR. During the EICR the tests conducted will not only check that RCDs trip, but that they trip within the required maximum time limit and current, and that they trip when subjected to a slowly increasing leakage current, rather than one suddenly imposed (as with the self-test button).
