Voltage looks normal with no load, but then goes to 230 on the neutral when you put a load on
What do you mean "goes to 230 on the Neutral"? Measuring Neutral to earth?
[quote]Is there any possibility that the wiring has been damaged between the floors, such that only the one apartment would be experiencing the fault?[quote]
It's very unlikely that the wiring has been damaged. We are talking here about a cable XVB 3G10 which is 10mm2, so it's also unlikely that there is a high resistance.
