In the USA: electrical code requires the hot(120-130V/60hz/usually black) wire from the home's breaker to connect to the brass colored screw on an outlet(the right slot from the front), and the neutral wire(no voltage/usually white), to the nickle colored screw(left slot from the front). I believe in Russia the standard voltage is 220/50hz. Here in the USA 240-260V circuits(single phase) have two hot terminals(120-130V each) and no neutral(there is a ground terminal though). That's probably how your home AC is provided as well. With our 120V system: If the phase is reversed between two components, it usually results it audible hum(60hz). If your phase is reversed with 220V, between two components in your system, YES: it should be audible. If you run into that: reverse the hot wires of one powercord plug, and try the listening test again.