I knew about your weird (to us) electrical wiring but in never occurred to me that anyone would consider having two 'phases' in the same domestic premises.

Industrial yes, but mixing phases is risky. I blew up a mass spectrometer by plugging it into one phase and then ran an extension cable a long wy to plug in its output printer. (In the UK phases must be separated by distance or if in the same area marked up, I have never even seen that it must be rare) The 440V difference did a world of damage to the electronics.

I have just built a house and had it T-T (Terra-Terra) wired especially. Live at 230V, Neutral and my own Earth (Terra in the jargon). No room for error and I am not dependent on anybody elses safety provisions.