OP
NickD
Test it properly. R1+R2 then IR, this should show up any faults if you do it properly. If you don't test it methodically, you will spend all day chasing your backside.
Cheers...............Howard
With respect, neither R1+R2 nor IR will pick up a high impedance on the neutral, unless I'm missing something? Which maybe he has here, I'm not clear what is going to 78V though.