so when you do an electrical test and you have the zs and ze,do you need to physically test for r1+r2 or can you calculate it,say at a lighting point ???
You could calculate it, and hope that you'd done nothing wrong with the wiring. Or you could measure it and be sure.
I've just realised i didn't read your Q at all well - apologies. In your example, how do you "know" Zs and Ze?
Not really - (a) you NOT then testing the continuity. (b) you not testing the polarity (dead). (c) as anyone who has done the C&G 23891 will know one of the popular questions is "when can Zs be LESS than Ze given that Zs = Ze + (R1 + R2)"? hint: No not cryogenics.
IF your an electrician and you have got your 2391 then you should know the answer-your probably a lazy **** who works for a local council
if u have "The Electrician's Guide to Inspection and Testing Based on BS7671:2001 Incorporating Amendments 1 & 2, 2004 16ht Edt" read from page 42 - 47. Ze is the part of the earth fault loop impedance external to the installation (the impedance of the supply) R1 is the resistance of the comsumers phase conductor from the origin of the circuit to the most distant part of the ciruit R2 is the resistance of the comsumers protective conductor from the origin of the circuit to the most distant part of the ciruit taken from page 39 of "The Electricions Guide to good electrcial practice Based on BS7671:2001 Incorporating Amendments 1 & 2, 2004 16ht Edt" so no i dnt know it all