Electric vehicle charge point manufacturers are adding intelligent electronics to remove the need for earth rods
Now that the 18th edition wiring regulations have bedded into our minds, we've quickly establish some rules of thumb that apply to typical installations. For electric vehicle (EV) charge points, in residential projects, we would expect to be fitting an earth rod next to the charge point
"Why earth rods?"
Fitting an earth rod is the most cost-effective and quickest way to comply with regulation 722.411.4.1. This regulation seeks to avoid a shock hazard which could occur if the fault develops within the supply network of TNCS (PME) earthing systems, i.e. most domestic supplies in the UK. Isolating the EV charger earth from the TNCS system and creating a localised TT earthing arrangement is relatively straightforward.
However, earth rods aren't without their challenges. It can be physically challenging to get the rod in the ground, especially on rocky terrain or close to building foundations. Driving the rod through other services such as drains, gas or water pipes is always a risk. Achieving a low enough resistance to trigger the RCD is not guaranteed, and resistance can change with ground conditions or corrosion of the rod over time. Plus ,aesthetically, it's another ugly pipe on the wall which won't go down well with many clients.
Earth rods and TT supplies are fine if you're the first to install, but what if the neighbouring property already has a charge point. You then need to think about the separation distance between earthing systems. This is a grey area which was flagged up in the recent Western Power Distribution EV strategy document.
"What's the alternative?"
Another option included within 722.411.4.1 (iii) is just starting to be exploited
In other words, a piece of intelligent electronics which monitors the incoming supply and disconnects the charger including the earth path if a fault condition is detected.
"Necessity drives demand"
Manufacturers are responding to the challenges of earth rods and utilising this clause to introducing new charge points with PEN fault monitoring which mitigate the need for earth rods.