The most common high voltage lines are 10kV, 11kV, 14kV. They are indeed stepped down to 415 + neutral for your street, alternating houses are usually on different phases. EBOB you are incorrect. That pic of the socket has 4 pins which = 3 phase and earth. NO NEUTRAL. There are plenty of machines that run on 415VAC and do not require the neutral. The earth connection is required on all GPO sockets regardless of the number of phases. EBOB you are correct. There are more machines that use 415VAC and 240VAC (hence requiring the neutral) and thus use 5 pin connectors.