Ahh, it's making more sense now. I wasn't aware of the distance between breakers.
Question 1:
How can a healthy monofase circuit fall from 230V to 0V (between phase and N) only when the Neutral of a load is connected (after that phase is already connected) and without tripping a 63A breaker?
Can a major fault be enough to bring down the voltage to 0v and not enough to trip the breaker?
A very high resistance contact on the neutral
somewhere between the PoCo breaker and the point you're measuring the voltage would do it. Voltage looks normal with no load, but then goes to 230 on the neutral when you put a load on
How can a neutral have a 230V reading between neutral and earth only when connecting the Neutral (of the load)?
I am still not 100% clear on the wiring, but it sounds like it's being affected by the same fault.
Is there any possibility that the wiring has been damaged between the floors, such that only the one apartment would be experiencing the fault? Small holes in the insulation of the cable + damp or condensation have been known to do things like this.
