Your home devices operate with a form of electricity where polarity between two wires alternates 50 times per second (50Hz). If you draw a time diagram of the voltage you will see a sinusoidal curve which oscillates 50 times per second (see (4) in the diagram: 20 msec = 1/50 second) between +308V (1) and -308V (2). So why do we call it AC 220? Well, what really counts is the average energy you get! And that is proportional to the area between the x axis and the sine curve. If you draw a rectangle with a height of 220 (3) for the duration of one period(4) its area will be exactly the same as the sum of the two half waves. So, the “effective” voltage is 220.
A pair of wires which delivers AC 220 is called a “phase“. The public grid has three such phases with one side of all three phases being connected to a “central” wire (blue color, common wire, COM). The other ends (HOT ends, usually black and gray color) are spread over the various electric circuits (rooms) of your facilities.
The three phases are not in sync – they have a phase difference of 120° which means that you can get more power if you connect a device between two HOT ends (380V). Normal devices will not tolerate this, but strong motors, ovens or climatization systems are constructed in a way that makes us of this extra power.
