i seriously doubt he has 3 phase, more likely 3 wires coming in. unless
he lives in a commercial area.

yeah phase failure imbalance can cause all sorts of troubles, with wild
voltage swings. company I used to work for had that trouble, the
company copiers didnt like 30 volt changes We sold copiers and I was
one of the techs, it was a ongoing trouble finally sloved when the
company went out of business....