Ага,спасибо. Но кое-где попадаются противоположные инструкции:
Line Phase Sensor

Here is a clever device found on the back of every Luxman powered product. You press the button and it will check the phase of the electricity it is receiving. If the AC outlet in the wall is incorrectly wired, meaning the live and neutral are swapped, a red LED will turn on to warn you. You only need to press it once, when you are installing a product to check that everything is in order. Its a simple mistake, that occurs often, and one that can seriously undermine your listening enjoyment.