Shed Installation.

[batty]

But that is simply why you can't use a water/ gas pipe as your main earth and you need to ensure your earth rod has a low enough reading to cover future changes.

 

[steptoe]

for me it is a case of,

measure Ze [or Ra] , measure Zs, measure R1 R2, Ze +R1+R2 = Zs, or if my measured Zs is higher (very doubtful) then its the highest reading I put down on my sheet,

BTW, I dont generally have an issue (in certain conditions) working Zs out using R1+R2 + Ze if a live test in not possible, [limitations box folks] ,

but I do find it unacceptable to reverse engineer this to R1 R2 being Zs-Ze , parrallell paths and all that [as pointed out]