External lighting fault

[Bradley6969]

Fault on external lighting roughly 12 lights around a building, RCBO tripping, my tester only goes to 200 Megger Ohms
L-N is 0 Megger
N-E is greater than 200 Megger
L-E is greater than 200 Megger
LN-E is 150 Megger

Now tested insulation from board and roughly found the middle light with 1 cable so must be joint boxes somewhere I can’t find, went to a light further and found a joint box and tested each leg and was getting near to no Megger Ohms on each side, any further ideas?

 

[Bradley6969]

I ap

i first do a continuity test L-N to see if there are any loads connected. sometimes there may be a neon switch will read something like 23K ohms. ( or is it 2.3 K, i forget, bloody dementia)

all loads are still connected they all have emergency back up too, so L-N I’m getting 0, have done LN-E and getting over range, all I can do is take the rest of fitting apart and bypass all circuitry or go to one in middle and re test there but will possibly give me same readings

 

[telectrix]

if you can't diss. all loads then a L-N test is pointless. as in: