Insulation resistance test on a ring final circuit

[mak]

Might be trivial question. My understanding is that we test on either leg of the ring since both legs make up a radial, but some say they test both legs at once, i.e. LL to NN, it would make sense if the other leg is not insulated since this is a live test, but I don't see why not if the other leg is "wago-ed".

 

[ipf]

I don't believe it has ever been the correct terminology for the ring final circuit.
Ring mains exist in gas, water, HV distribution and LV distribution but I don't think it has ever been used for LV final circuits.

It seems it was just an accepted term.