Here are the three phase voltages recorded after we had a 4 hour round of load shedding (South African term for rotational blackout).
The transformer is set at 240/415 volts but it's likely there is some drop on the medium volt (6,600 volt) side as well as drop on the low voltage cable due to my feed being 300 meters away from the transformer. You can see the red phase is lowest and that is partly due to there being two single phase houses on that one where white and blue phases each have only one single phase house each.
All other houses have three phase power.
