I had to connect up a consumer unit's earth terminal to a new D.N.O. provided P.M.E. earth terminal today. The previous earthing arrangement was TT. As an experiment I did a loop test on the earth electrode. I was interested in its resistance after many weeks of no rain here and the well draining sandy soil. The reading was about 100 Ohms.
Then as I was connecting the new 16.00mm2 green and yellow earthing conductor I saw arcing across from the cable to the new earthing terminal before I tightened the terminal screws. At first I was concerned. I then measured the Voltage across the earthing conductor from the consumer unit to the new P.M.E. earthing terminal with a D.M.M. It read about 3 Volts A.C. So I had a Voltage rise of about 3 Volts from the C.N.E. and true Earth. Despite that the sparks were impressive.
The property has solar panels and the local D.N.O. had written 249 Volts 0.36 Ohms on the main cut out.