Paul, Ever-ready,
Our 4mm and 6mm 2C+E and 3C+E TPS uses the 2.5mm Earth Conductor.
The thing about an Earthing Conductor, is it only carries current under Fault conditions, there-fore, it is Down-sized.
Biggest thing with any sort of Earthing system is your connections.
An effective Earth is only as good as the terminals that Bond it, to the said Earthing Point. [Linked Image]