I'm interested in this thread. Many years ago, in London, I was working in a lab building equipment from ex-military 24vDC relays and steppers (back in the days when Tottenham Court Road was full of such stuff -- shows my age). Arrived in one morning to a very nasty smell and found all my equipment blown, exploded, etc. Very expensive, very depressing. The lab had a 3-phase 230vAC supply for some massive heaters, and the electrician told me that the neutral had blown and I would have been getting around 460vAC on the outlets. I've always wondered if this was right, and why 460 vAC (a root-mean-square thing?). Thanks for any technical person who can explain this for me.
When the neutral fails in a 3 phase system. You in effect get the equivalent of a series /parallel circuit involving the loads on each phase.
Imagine 2 of the phases have those big heaters connected to them. And your equipment was connected to the 3rd phase. When the neutral failed, you had your equipment connected in series with those heaters. And the phase to phase voltage across both. Since the heaters have a much lower resistance, most of the voltage would have appeared across your equipment.
Although normally your fault scenario would produce 400V instead of 460V.
And the above is why I said to the OP earlier to also unplug their appliances.