[Jeremy Harris]

I know a lot of BS is spouted about the apparent "problem" in fitting an earth electrode and connecting a charge point up as a TT installation, but the reality is that there aren't that many installations where it's impossible to fit one. For years every house had an earth electrode for the protective earth, it was the normal way houses here were wired. It's still the normal way that houses are wired in many other countries, too.

The only installations where fitting an earth electrode can be a problem is where there either isn't space to put one far enough away from incoming services (rare, but can happen) or where the soil is of such poor conductivity that it's not practical to get Ra low enough (very permeable sand and gravel soils for example). Even then it's usually possible to fit one, by going deep enough and using something like bentonite around the electrode (or the new conductive concrete that's just come out). There are other concerns, like making sure there's not something conductive that's still connected to the PME PE within touching distance of the car parking area, but again these aren't that common. Driving an earth electrode used to be a bit of a workout in some soils, but the advent of SDS drill adapters that fit the nut driver on a rod makes it pretty easy to get even a long rod in in most soils.

Interestingly, conductive concrete may mean that it's simple to just fit a good earth electrode in new builds, and we may even see a switch back to using TT, rather than PME if conductive foundations become a reality in the domestic sector (they already are in some commercial installations, where TT is the normal earthing system used). Conductive concrete may also mean that shallow earth pits can be used, rather than rods driven deeply into the soil.

 

[Jeremy Harris]

The issue of open PEN fault protection is interesting, as, in terms of safety, nothing is as good as a properly installed earth electrode and suitable RCD. All of the built-in, or add-on, open PEN fault protection devices are less safe, although they do comply with the changed regulations. The bottom line is that if you want to be certain that the touch voltage of an exposed conductive part, relative to the local ground potential, is always within the safe limit you really have to have a local earth reference. Using secondary forms of supply sensing to estimate whether the touch voltage might be too high is never as safe as having the charge point PE directly connected to local earth potential.