Obviously, you have a 230v domestic mains supply, but others are around, plus some safety devices:
'RCDs and ELCDs'
Safety devices both of which must act within 1/30th of a second when more than 30mA of current goes "missing", RCDs detect imbalances in current drawn through each pin, Earth Leakage Current Devices detect current flowing to earth.
Power is fed into Primary Coil, Drawn from the Secondary. Pr/Sc is called step-down ratio.
Works at 50Hz, like 3 'pairs' of supply, each with the AC sine wave of each 120 degrees out-of phase to each other. In theory, the sum at any instance of all three supplies will be zero, but this relies on the voltage and current being the same on each phase.
The advantage is clear, in that the "runs" of 3-phase have negligible magnetic fielding, compared with a single-phase run of the same length. ALSO, because the fields cancel, 3-phase cables heat up far less, UNLESS THE PHASES AREN'T BALANCED. Overheating is the key reason for balancing phases, as 3-phase supplies are often quite high current(!).
Don't even attempt to use 3-phase if you're not completely aware of everything, there is much more to it than this, like neutral return-currents, phase mixing and inter-phase voltages (upto 600v peak!).
Rubbish yellow connectors used by muddy builders and scissor lift battery chargers. Oh, and it's used by Americans.