I'm going to replace the consumer unit for a customer in rural Oxfordshire. The supply comes in overhead, drops down a telegraph-type pole into the ground, and runs about 2m to a recessed box in the wall (perhaps coming up in the cavity). I can't find the earth rod - probably entirely buried, but am getting Ze of 0.25 ohms, which is encouraging. Because it is hidden, I've put a new rod in, 2.4m deep. I tested it (GN3) and got results of about 95 ohms for the ground resistance, which is 60% of the maximum for a 300mA main switch RCD, and 20% for 100 mA. For discrimination, I'm keen to use the higher rate (delayed) RCD if it is reasonable to do so. The ground was damp ( it hadn't rained that day, but there had been a lot of weather about in the preceding days), and my question is; what order of variation can I expect between damp and dry soil, all other things being equal, and where can I find a quotable source for that information? If it is wildly variable, I may have to wait for a heatwave, so I can retest (which won't suit me or my customer). And question 2 (if I may); can anyone help with a source for information on the dissipation (via the short underground section) of a lightning strike to the incomer which can be expected given the description above. Or should I just include surge protection? Many thanks, Roy